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Background— Remodeling of myocardial phospholipids has been reported in various forms of heart failure for decades, but the mechanism and pathophysiological relevance of this phenomenon have remained unclear. We examined the hypothesis that δ-6 desaturase (D6D), the rate-limiting enzyme in long-chain polyunsaturated fatty acid biosynthesis, mediates the signature pattern of fatty acid redistribution observed in myocardial phospholipids after chronic pressure overload and explored plausible links between this process and disease pathogenesis. Methods and Results— Compositional analysis of phospholipids from hearts explanted from patients with dilated cardiomyopathy revealed elevated polyunsaturated fatty acid product/precursor ratios reflective of D6D hyperactivity, manifesting primarily as lower levels of linoleic acid with reciprocally higher levels of arachidonic and docosahexaenoic acids. This pattern of remodeling was attenuated in failing hearts chronically unloaded with a left ventricular assist device. Chronic inhibition of D6D in vivo reversed similar patterns of myocardial polyunsaturated fatty acid redistribution in rat models of pressure overload and hypertensive heart disease and significantly attenuated cardiac hypertrophy, fibrosis, and contractile dysfunction in both models. D6D inhibition also attenuated myocardial elevations in pathogenic eicosanoid species, lipid peroxidation, and extracellular receptor kinase 1/2 activation; normalized cardiolipin composition in mitochondria; reduced circulating levels of inflammatory cytokines; and elicited model-specific effects on cardiac mitochondrial respiratory efficiency, nuclear factor κ B activation, and caspase activities. Conclusions— These studies demonstrate a pivotal role of essential fatty acid metabolism in myocardial phospholipid remodeling induced by hemodynamic stress and reveal novel links between this phenomenon and the propagation of multiple pathogenic systems involved in maladaptive cardiac remodeling and contractile dysfunction.

Life threatening complications from chemotherapy occur frequently in cancer survivors, however little is known about genetic risk factors. We treated male normotensive rats (WKY) and strains with hypertension (SHR) and hypertension with cardiomyopathy (SHHF) with 8 weekly doses of doxorubicin (DOX) followed by 12weeks of observation to test the hypothesis that genetic cardiovascular disease would worsen delayed cardiotoxicity. Compared with WKY, SHR demonstrated weight loss, decreased systolic blood pressure, increased kidney weights, greater cardiac and renal histopathologic lesions and greater mortality. SHHF showed growth restriction, increased kidney weights and renal histopathology but no effect on systolic blood pressure or mortality. SHHF had less severe cardiac lesions than SHR. We evaluated cardiac soluble epoxide hydrolase (sEH) content and arachidonic acid metabolites after acute DOX exposure as potential mediators of genetic risk. Before DOX, SHHF and SHR had significantly greater cardiac sEH and decreased epoxyeicosatrienoic acid (EET) (4 of 4 isomers in SHHF and 2 of 4 isomers in SHR) than WKY. After DOX, sEH was unchanged in all strains, but SHHF and SHR rats increased EETs to a level similar to WKY. Leukotriene D4 increased after treatment in SHR. Genetic predisposition to heart failure superimposed on genetic hypertension failed to generate greater toxicity compared with hypertension alone. The relative resistance of DOX-treated SHHF males to the cardiotoxic effects of DOX in the delayed phase despite progression of genetic disease was unexpected and a key finding. Strain differences in arachidonic acid metabolism may contribute to variation in response to DOX toxicity.

Background Doxorubicin (DOX) is a very effective anticancer medication that is commonly used to treat hematological malignancies and solid tumors. Nevertheless, DOX is known to have cardiotoxic effects that may lead to cardiac dysfunction and failure. In experimental studies, female animals have been shown to be protected against DOX-induced cardiotoxicity; however, the evidence of this sexual dimorphism is inconclusive in clinical studies. Therefore, we sought to investigate whether genetic background could influence the sexual dimorphism of DOX-induced cardiotoxicity. Methods Male and female Wistar Kyoto (WKY) and Spontaneous Hypertensive Heart Failure (SHHF) rats were used. DOX was administered in eight doses of 2 mg/kg/week and the rats were followed for an additional 12 weeks. Cardiac function was assessed by trans-thoracic echocardiography, systolic blood pressure was measured by the tail cuff method, and heart and kidney tissues were collected for histopathology. Results Female sex protected against DOX-induced weight loss and increase in blood pressure in the WKY rats, whereas it protected against DOX-induced cardiac dysfunction and the elevation of cardiac troponin in SHHF rats. In both strains, female sex was protective against DOX-induced nephrotoxicity. There was a strong correlation between DOX-induced renal pathology and DOX-induced cardiac dysfunction. Conclusions This study highlights the importance of studying the interaction between sex and genetic background to determine the risk of DOX-induced cardiotoxicity. In addition, our findings suggest that DOX-induced nephrotoxicity may play a role in DOX-induced cardiac dysfunction in rodent models.

Small molecule histone deacetylase (HDAC) inhibitors block adverse cardiac remodeling in animal models of heart failure. The efficacious compounds target class I, class IIb and, to a lesser extent, class IIa HDACs. It is hypothesized that a selective inhibitor of a specific HDAC class (or an isoform within that class) will provide a favorable therapeutic window for the treatment of heart failure, although the optimal selectivity profile for such a compound remains unknown. Genetic studies have suggested that class I HDACs promote pathological cardiac remodeling, while class IIa HDACs are protective. In contrast, nothing is known about the function or regulation of class IIb HDACs in the heart. We developed assays to quantify catalytic activity of distinct HDAC classes in left and right ventricular cardiac tissue from animal models of hypertensive heart disease. Class I and IIa HDAC activity was elevated in some but not all diseased tissues. In contrast, catalytic activity of the class IIb HDAC, HDAC6, was consistently increased in stressed myocardium, but not in a model of physiologic hypertrophy. HDAC6 catalytic activity was also induced by diverse extracellular stimuli in cultured cardiac myocytes and fibroblasts. These findings suggest an unforeseen role for HDAC6 in the heart, and highlight the need for pre-clinical evaluation of HDAC6-selective inhibitors to determine whether this HDAC isoform is pathological or protective in the setting of cardiovascular disease.

Cardiolipin (CL) is an essential phospholipid component of the inner mitochondrial membrane. In the mammalian heart, the functional form of CL is tetralinoleoyl CL [(18:2)(4)CL]. A decrease in (18:2)(4)CL content, which is believed to negatively impact mitochondrial energetics, occurs in heart failure (HF) and other mitochondrial diseases. Presumably, (18:2)(4)CL is generated by remodeling nascent CL in a series of deacylation-reacylation cycles; however, our overall understanding of CL remodeling is not yet complete. Herein, we present a novel cell culture method for investigating CL remodeling in myocytes isolated from Spontaneously Hypertensive HF rat hearts. Further, we use this method to examine the role of calcium-independent phospholipase A(2) (iPLA(2)) in CL remodeling in both HF and nonHF cardiomyocytes. Our results show that 18:2 incorporation into (18:2)(4)CL is: a) performed singly with respect to each fatty acyl moiety, b) attenuated in HF relative to nonHF, and c) partially sensitive to iPLA(2) inhibition by bromoenol lactone. These results suggest that CL remodeling occurs in a step-wise manner, that compromised 18:2 incorporation contributes to a reduction in (18:2)(4)CL in the failing rat heart, and that mitochondrial iPLA(2) plays a role in the remodeling of CL's acyl composition.

Cardiolipin (CL) is responsible for modulation of activities of various enzymes involved in oxidative phosphorylation. Although energy production decreases in heart failure (HF), regulation of cardiolipin during HF development is unknown. Enzymes involved in cardiac cardiolipin synthesis and remodeling were studied in spontaneously hypertensive HF (SHHF) rats, explanted hearts from human HF patients, and nonfailing Sprague Dawley (SD) rats. The biosynthetic enzymes cytidinediphosphatediacylglycerol synthetase (CDS), phosphatidylglycerolphosphate synthase (PGPS) and cardiolipin synthase (CLS) were investigated. Mitochondrial CDS activity and CDS-1 mRNA increased in HF whereas CDS-2 mRNA in SHHF and humans, not in SD rats, decreased. PGPS activity, but not mRNA, increased in SHHF. CLS activity and mRNA decreased in SHHF, but mRNA was not significantly altered in humans. Cardiolipin remodeling enzymes, monolysocardiolipin acyltransferase (MLCL AT) and tafazzin, showed variable changes during HF. MLCL AT activity increased in SHHF. Tafazzin mRNA decreased in SHHF and human HF, but not in SD rats. The gene expression of acyl-CoA: lysocardiolipin acyltransferase-1, an endoplasmic reticulum MLCL AT, remained unaltered in SHHF rats. The results provide mechanisms whereby both cardiolipin biosynthesis and remodeling are altered during HF. Increases in CDS-1, PGPS, and MLCL AT suggest compensatory mechanisms during the development of HF. Human and SD data imply that similar trends may occur in human HF, but not during nonpathological aging, consistent with previous cardiolipin studies.

Hypertension is a common cause of heart failure, and ventricular arrhythmias are a major cause of death in heart failure. The spontaneous hypertension heart failure (SHHF) rat model was used to study altered ventricular electrophysiology in hypertension and heart failure. We hypothesized that a reduction in the inward rectifier K+ current ( IK1) and expression of pacemaker current ( If) would favor abnormal automaticity in the SHHF ventricle. SHHF ventricular myocytes were isolated at 2 and 8 mo of age and during end-stage heart failure (≥17 mo); myocytes from age-matched rats served as controls. Inward IK1 was significantly reduced at both 8 and ≥17 mo in SHHF rats compared with controls. There was a reduction in inward IK1 due to aging in the controls only at ≥17 mo. We found a significant increase in If at all ages in the SHHF rats, compared with young controls. In controls, there was an age-dependent increase in If. Action potential recordings in the SHHF rats demonstrated abnormal automaticity, which was abolished by the addition of an If blocker (10 μM zatebradine). Increased If during hypertension alone or combined increases in If with reduced IK1 during the progression to hypertensive heart failure contribute to a substrate for arrhythmogenesis.

Data regarding the effectiveness of chronic exercise training in improving survival in patients with congestive heart failure (CHF) are inconclusive. Therefore, we conducted a study to determine the effect of exercise training on survival in a well-defined animal model of heart failure (HF), using the lean male spontaneously hypertensive HF (SHHF) rat. In this model, animals typically present with decompensated, dilated HF between ∼18 and 23 mo of age. SHHF rats were assigned to sedentary or exercise-trained groups at 9 and 16 mo of age. Exercise training consisted of 6 mo of low-intensity treadmill running. Exercise training delayed the onset of overt HF and improved survival ( P < 0.01), independent of any effects on the hypertensive status of the rats. Training delayed the myosin heavy chain (MyHC) isoform shift from α- to β-MyHC that was seen in sedentary animals that developed HF. Exercise was associated with a concurrent increase in cardiomyocyte length (≈6%), width, and area and prevented the increase in the length-to-width ratio seen in sedentary animals in HF. The increases in proteinuria, plasma atrial natriuretic peptide, and serum leptin levels observed in rats with HF were suppressed by low-intensity exercise training. No significant alterations in sarco(endo)plasmic reticulum Ca2+ ATPase, phospholamban, or Na+/Ca2+ exchanger protein expression were found in response to training. Our results indicate that 6 mo of low-intensity exercise training delays the onset of decompensated HF and improves survival in the male SHHF rat. Similarly, exercise intervention prevented or suppressed alterations in several key variables that normally occur with the development of overt CHF. These data support the idea that exercise may be a useful and inexpensive intervention in the treatment of HF.

The research question posed was does marginal copper (MC) intake over a protracted period lead to cardiac pathology in rodents either genetically susceptible or nonsusceptible to heart disease? We used the spontaneously hypertensive heart failure (SHHF) rat strain, a genetic model of hypertrophic cardiomyopathy, and the Long-Evans rat strain that does not develop heart disease genetically. Rats from both strains were fed either a control diet with adequate levels of copper (6.7 mg Cu/kg diet) or marginal in copper (2.8 mg Cu/kg diet) for 3, 6, or 10 months. At each time point, electrocardiographic measures were obtained from leads I and aVF, and hearts were processed for histological evaluation by transmission electron microscopy. There were no differences between strain or treatment in terms of mitochondrial or myofibrillar volume density. However, MC rats, regardless of strain and age, had increased lipid droplets in the myocardium. There were strain differences in electrocardiograms with SHHF rats, demonstrating abnormalities in traces, but they were not made any worse by MC intake. However, overall, the rats fed MC, regardless of strain, did demonstrate increased R-wave amplitude and duration in the QRS complex and some changes in P and T waves, which have been reported for severe copper deficiency. We conclude that MC intake over a protracted period is deleterious to cardiac health but that the genetic susceptibility of the heart to other forms of cardiac disease does not hasten or worsen the copper effect.

Electrospray ionization mass spectrometry has previously been used to probe qualitative changes in the phospholipid cardiolipin (CL), but it has rarely been used in a quantitative manner. We assessed changes in the amount of individual molecular species of cardiac CL present in a model of congestive heart failure using 1,1′,2,2′-tetramyristoyl cardiolipin as an internal standard. There was a linear relationship between the ratio of the negative molecular ion ([M-H]−) current from four different CL reference standards and the [M-H]− from the internal standard, as a function of the concentration of CL molecular species. Therefore, this internal standard can be used to quantitate many naturally occurring CL molecular species over a wide range of CL concentrations. Using this method, changes to individual molecular species of CL in failing hearts from male spontaneously hypertensive heart failure rats were examined. CL isolated from cardiac mitochondria was compared with left ventricular tissue to demonstrate the feasibility of extracting and quantitating CL from either mitochondrial or tissue samples. The acyl chain composition of individual CL molecular species was identified using tandem mass spectrometry. In animals with heart failure, the major cardiac CL species (tetralinoloyl) decreased significantly, whereas other minor CL species were significantly increased.

Background Gestational hypertensive disorders are a leading cause of maternal mortality in the US, accounting for up to 10% of these deaths. During pregnancy, a new rat model (SHHF rat) has been shown to develop spontaneous hypertension with increases of more than 40 mm Hg systolic blood pressure (BP), which resolves after delivery, and which lead us to ask whether the hypertension may be triggered by increased levels of progesterone in these rats. Methods To test this hypothesis, groups of SHHF rats were treated with progesterone (PROG), estrogen (EST), or progesterone and estrogen (PROG+EST) that correspond to levels that occur during pregnancy. Control (CON) rats received saline-filled implants and pseudopregnancy was induced in another group. Wistar-Kyoto rats served as controls for SHHF rats. Results By experimental day 3, progesterone caused a significantly higher systolic BP, similar to pseudopregnancy and to previously reported values during pregnancy in this strain. Blood pressure in SHHF rats given estrogen was not significantly different. RU486 reversibly prevented the increase in BP induced by progesterone. Conclusions These results indicate that an anomalous response to progesterone causes dramatic increases in BP in SHHF rats during a short period of time, in contrast to the decrease in BP in response to progesterone, which has been reported in other rat models of hypertension. An abnormal pressor response to progesterone should be considered a potential mechanism contributing to the development of hypertension during pregnancy.

Objective: Xanthine oxidase (XO) inhibitors enhance myofilament Ca2+ responsiveness of normal rat myocardium. We examined whether this inotropic action is preserved or magnified in failing rat myocardium and whether the magnitude of this effect correlates with tissue xanthine-oxidoreductase (XOR) activity. Methods: Hearts of 18–20 month-old SHHF (spontaneous hypertensive/heart failure) rats with end-stage heart failure, as well as of normal control rats, were perfused with the XO inhibitor oxypurinol. Afterwards, [Ca2+]i and tension were measured simultaneously in fura-2-loaded intact isolated right ventricular trabeculae. XOR activity was determined fluorometrically in myocardial homogenates. Results: In failing myocardium, 100 μM oxypurinol significantly increased systolic twitch tension (by 87 and 92% at 1.0 and 1.5 mM extracellular [Ca2+], respectively), without altering [Ca2+]i transient amplitude. Oxypurinol did not alter the midpoint or cooperativity of the steady-state tension-[Ca2+]i relationship, but significantly enhanced maximum Ca2+-activated tension by 75% in failing myocardium. Oxypurinol also exerted a positive inotropic effect in failing myocardium, which was, however, of significantly smaller relative magnitude. Failing rat myocardium exhibited higher XOR activity than nonfailing myocardium, and this activity was largely suppressed in oxypurinol-treated preparations. Conclusions: The magnitude of functional improvement with XOR inhibitors depends on the initial level of XOR activity. Specifically, the inotropic actions of oxypurinol are more pronounced in failing rat myocardium, a tissue that exhibits enhanced XOR activity. Our findings rationalize how XO inhibitors boost cardiac contractility and improve mechanoenergetic coupling, and why the effects might be relatively ‘selective’ for heart failure.

Sorcin is a penta-EF hand Ca2+-binding protein that associates with both cardiac ryanodine receptors and L-type Ca2+ channels and has been implicated in the regulation of intracellular Ca2+ cycling. To better define the function of sorcin, we characterized transgenic mice in which sorcin was overexpressed in the heart. Transgenic mice developed normally with no evidence of cardiac hypertrophy and no change in expression of other calcium regulatory proteins. In vivo hemodynamics revealed significant reductions in global indices of contraction and relaxation. Contractile abnormalities were also observed in isolated adult transgenic myocytes, along with significant depression of Ca2+ transient amplitudes. Whole cell ICa density and the time course of activation were normal in transgenic myocytes, but the rate of inactivation was significantly accelerated. These effects of sorcin on L-type Ca2+ currents were confirmed in Xenopus oocyte expression studies. Finally, we examined the expression of sorcin in normal and failing hearts from spontaneous hypertensive heart failure rats. In normal myocardium, sorcin extensively co-localized with ryanodine receptors at the Z-lines, whereas in myopathic hearts the degree of co-localization was markedly disrupted. Together, these data indicate that sorcin modulates intracellular Ca2+ cycling and Ca2+ influx pathways in the heart.

The effects of low-dose oral spironolactone (SPIRO) in a rat model of hypertensive heart failure (spontaneously hypertensive heart failure rat) were compared with its effects when combined with captopril (CAP). Twenty-six spontaneously rats with hypertensive heart failure were treated with either placebo (CON), SPIRO (20 mg/kg/d by mouth), CAP (100 mg/kg/d by mouth), or both SPIRO and CAP for 12 weeks. This dose of oral SPIRO did not affect blood pressure, left ventricular end-diastolic diameter, left ventricular ejection fraction, plasma atrial natriuretic peptide concentration, or cardiac fibrosis; however, in combination with CAP, it exerted a significant depressor effect after 12 weeks of treatment that was accompanied by increased urine output and decreased urinary protein excretion. These effects were significantly greater than those with CAP treatment alone. A significant increase in plasma aldosterone level was observed only in CON (174 ± 21%). These data suggest that the addition of low-dose SPIRO to angiotensin I–converting enzyme inhibitor treatment may prevent progression into end-stage congestive heart failure through synergistic effects on diuresis and renoprotection.

We examined mechanical alternans and electromechanical restitution in normal and failing rat hearts. Alternans occurred at 5 Hz in failing versus 9 Hz in control hearts and was reversed by 300 nM isoproterenol, 6 mM extracellular Ca2+, 300 nM −BAY K 8644, or 50 nM ryanodine. Restitution curves comprised phase I, which was completed before relaxation of the steady-state beat, and phase II, which occurred later. Phase I action potential area and developed pressure ratios were significantly reduced in the failing versus control hearts. Phase II was a monoexponential increase in relative developed pressure as the extrasystolic interval was increased. The plateau of phase II was significantly elevated in failing hearts. Thapsigargin (3 μM) plus ryanodine (200 nM) potentiated phase I to a significantly greater extent in control versus failing hearts and abolished phase II in both groups. The results suggest that both regulation of Ca2+ influx across the sarcolemma and Ca2+ release by the sarcoplasmic reticulum may contribute to altered excitation-contraction coupling in the failing spontaneously hypertensive heart failure prone rat heart.

The SHHF/Mcc-fa(cp) (spontaneous hypertension and heart failure) rat is advanced as a novel and suitable non-primate model of pregnancy-associated hypertension and fetal growth restriction because it simultaneously has spontaneous pregnancy-associated hypertension, small for gestational age (SGA) offsprings, and altered placental gene expression. Pregnancy-associated hypertension is a major contributor to maternal and fetal morbidity and mortality with the potential to result in maternal death and the need for iatrogenic preterm delivery. It has been reported to develop spontaneously in humans, but not in animals; consequently, progress in identifying the cause and pathogenesis of this disorder has been hampered. Spontaneous hypertension and heart failure rats develop hypertension spontaneously as they age, therefore we sought to determine whether these rats developed hypertension and SGA offsprings during pregnancy. Our results show that systolic blood pressure (BP) increased40 mm Hg by the end of the first trimester and remained at this elevated level for the remainder of pregnancy, but decreased after parturition. Placenta weights of SHHF rats (0.60 +/- 0.02 g, n = 36) were significantly higher than Wistar-Kyoto (WKY) rats (0.42 +/- 0.01 g, n = 22, P.05), but pup weights were significantly lower (2.68 +/- 0.06 g for SHHF rats compared to 3.24 +/- 0.06 g for WKY controls, P.05). Histologic examination revealed pathologic lesions in neither heart, liver, placenta, nor kidney. L-Arginine administered in drinking water prevented the elevation of BP, particularly during the third trimester. Placentas from SHHF rats displayed altered expression of several genes whose protein products have been implicated in preeclampsia, including serotonin receptor, sodium channel, carbonic anhydrase, estrogen receptor regulator, major histocompatibility complex proteins, superoxide dismutase, and angiotensiogen. In addition, gene expression profiling showed alteration of a number of subcellular putative myristoylproteins not previously associated with preeclampsia, particularly those engaged in post-translational modifications in the placenta. Thus, SHHF rats may be a valuable tool, because it simultaneously has spontaneous pregnancy-associated hypertension, SGA offsprings, and altered placental gene expression.

Acute increases in blood pressure (BP) increase myocardial tumor necrosis factor (TNF)-alpha production, but it is not known whether chronic hypertensive stress elevates myocardial TNF-alpha production, possibly contributing to cardiac remodeling, decreased cardiac function, and faster progression to heart failure. BP, cardiac function, and size were evaluated in normotensive [Sprague-Dawley (SD)], spontaneously hypertensive (SHR), and spontaneously hypertensive heart failure-prone (SHHF) rats at 6, 12, 15, and 18 mo of age and in failing SHHF. Left ventricular tissues were evaluated for secretion of bioactive TNF-alpha and inhibition of TNF-alpha secretion by phosphodiesterase inhibitors. All ventricles secreted bioactive and immunoreactive TNF-alpha, but secretion decreased with age. SHR and SHHF rats secreted more TNF-alpha than SD rats at 6 mo of age, but only failing SHHF rats secreted significantly more TNF-alpha at 18 mo. Amrinone inhibited TNF-alpha secretion in all rats and was less potent but more efficacious than RO-201724 in all strains. TNF-alpha secretion correlated with BP and left ventricular mass in 6-mo-old rats, but this relationship disappeared with age. Results suggest that hypertension and/or cardiac remodeling is associated with elevated myocardial TNF-alpha, and, although hypertension, per se, did not maintain elevated cardiac TNF-alpha levels, SHHF rats increase TNF-alpha production during the end stages of failure.

Calcium channel blockers, verapamil or felodipine, were given to genetically obese 6 and 11-month-old female SHHF/Mcc-facp (SHHF: Spontaneous Hypertension Heart Failure) rats for 8 weeks to investigate their effects on glucose and lipid metabolism and obesity. Both antihypertensive agents significantly decreased systolic blood pressure. In 11-month-old rats, verapamil treatment significantly decreased body weight after 4 weeks whereas with felodipine it was only significantly reduced after 8 weeks. In 6-month-old rats, verapamil significantly curtailed body weight gain. Subcutaneous fat depots were smaller, and abdominal fat depots were larger in verapamil rats compared to felodipine or control rats. Oral glucose tolerance tests in the 6-month-old verapamil and the 11-month-old felodipine groups showed improved glucose tolerance compared to their respective control groups. After 8 weeks of treatment, fasting plasma glucose levels were lower in 6-month-old verapamil rats compared to felodipine and control rats and were decreased by both verapamil and felodipine treatments as compared to control in 11-month-old rats. During the oral glucose tolerance test in 6-month-old rats, both fasting plasma insulin and the area under the insulin curve were increased in verapamil compared to both control and felodipine groups. When compared to controls, plasma cholesterol was increased by verapamil in both age groups, but was significantly decreased by felodipine after 8 weeks of treatment in the 11-month-old group. Plasma triglycerides increased in all control rats compared to initial levels; however, verapamil and felodipine groups showed lower triglycerides in both age groups. In 6-month-old rats, the percentages of plasma HDL significantly increased in both treatment groups as compared to control. This study shows that verapamil and felodipine depressed body weight gain in the young rats, reduced body weight in the old rats, improved lipid parameters and glucose tolerance, but had the opposite effects on body fat distribution and insulin levels in obese female SHHF rats.

Rats with a genetic tendency to develop hypertensive, hypertrophic cardiomyopathy were fed copper-deficient diets and their cardiac responses were investigated.Five male weanling rats of the Long-Evans and SHHF/Mcc-fa(cp) strains were randomly selected to receive diets containing either adequate quantities of copper (94.5 micromol Cu/kg diet) or reduced quantities of copper (15.8 micromol Cu/kg diet) for 6 weeks, (n=5 within each group). Echocardiograms and electrocardiograms were recorded and analyzed at the end of the 6-week interval.Electrocardiograms from copper deficient groups showed longer Q-T intervals and increased QRS amplitudes than controls. Both the copper deficient and control SHHF groups demonstrated significant QRS complex prolongation compared to Long-Evans rats. Echocardiography analysis showed significant increases in left ventricular area, free wall dimension, and myocardial cross-sectional areas in rats fed a copper deficient diet. The frequency of systolic cardiac murmurs increased in copper deficient rats and were related to the presence of valvular regurgitation as determined from echocardiography.However, the data do not suggest that a copper-deficient diet fed to a strain of rats genetically susceptible to heart disease later in life, hastens or worsens the onset of cardiac disease. The genetic predisposition and copper-deficient states exert independent effects upon the heart.

Abstract —Progression to failure in hypertension is associated with ventricular dilation, excessive myocyte lengthening, and an increase in myocyte length/width ratio. The temporal development of these changes in relation to impaired pump performance is unknown. We examined isolated myocytes from 1- to 12-month-old spontaneously hypertensive heart failure (SHHF) rats who develop heart failure at approximately 24 months of age. Left ventricular myocyte cross-sectional area reached a maximum of ≈350 to 400 μm 2 at 3 months of age and did not change significantly thereafter. Nonetheless, LV systolic wall stress, a known stimulus for myocyte transverse growth, increased progressively between 3 and 12 months of age. Unlike the situation in normally aging rats with stable body mass, myocyte length in SHHF rats continued to increase with aging ( P

Ferrara, Cynthia M., W. Michael Sherman, Nicole Leenders, Sylvia A. McCune, and Karla Roehrig. Exercise training and the glucose transport system in obese SHHF/ Mcc-facprats. J. Appl. Physiol. 81(4): 1670–1676, 1996.—The effects of a similar exercise training stimulus on maximal insulin-stimulated (MIS) plasma membrane glucose transporter number and glucose transport were determined in lean and obese SHHF/ Mcc-facprats. Six-week-old lean and obese male rats were randomly divided into four groups: lean sedentary (LSed), obese sedentary (OSed), lean exercise (LEx), and obese exercise (OEx). An 8- to 12-wk treadmill running program equalized daily muscular work for LEx and OEx. Plasma membranes were isolated from control and MIS muscles of mixed fiber types. MIS significantly increased glucose transport (3.4- and 2.8-fold) in LSed and OSed, respectively. MIS significantly increased glucose transporter number (2.5-fold) in LSed, but there was no increase in glucose transporter number in OSed. Peak oxygen uptake and citrate synthase activity were increased a similar amount for LEx and OEx groups, demonstrating a similar training stimulus. MIS significantly and similarly increased glucose transport in LEx and OEx (4.4- and 5.1-fold, respectively). The effects of MIS on plasma membrane glucose transporter number in the exercise-trained rats were similar to the responses observed in the sedentary lean and obese groups. MIS significantly increased glucose transporter number (2.6-fold) in LEx, whereas there was no increase in glucose transporter number in OEx. The reduction in MIS glucose transport in OSed appears to be related to a defect in the processes associated with the translocation of glucose transporters to the plasma membrane. Exercise training of the obese rats apparently did not alter this defect. Similar increases in peak oxygen uptake, citrate synthase, and MIS glucose transport in LEx and OEx groups suggest that insulin resistance does not limit the ability of the glucose transport system to adapt to exercise training in the obese male SHHF/ Mcc-facprats.

This study uses echocardiography to characterize the pattern of left ventricular hypertrophy in a new hypertensive heart failure-prone rat strain designated SHHF/Mcc-cp (SHHF). M-mode echocardiograms of the left ventricle in nine 10- to 12-month old SHHF rats and nine age-matched spontaneously hypertensive rats (SHR) were compared. Wistar-Kyoto and Sprague-Dawley strains served as the normotensive control group. SHHF rats had significantly greater left ventricular mass than did rats in the normotensive control group. Although left ventricular mass was not different between SHHF and SHR, significant differences were seen in the pattern of left ventricular remodeling as determined by relative wall thickness. These differences in left ventricular remodeling may explain the earlier development of heart failure in SHHF. The different patterns of left ventricular hypertrophy in SHHF and SHR suggests that heart failure in SHHF is not mediated by hypertension alone.

We examined contractile performance in perfused ventricles from normal rats and from SHHF/Mccfacp rats with end-stage heart failure. Changes in pacing frequency from 3 to 5 Hz evoked a complex response in normal rat myocardium. The first beat after a switch to 5 Hz was extremely weak, but each successive beat was stronger until force exceeded the 3 Hz steady state value by approximately 30%. Force then gradually declined to a new steady state where developed pressure was depressed but rate-pressure product was slightly greater than that at 3 Hz. By contrast, in failing SHHF/Mcc-facp hearts, an increase in pacing frequency from 3 to 5 Hz did not increase force development. Instead, the isovolumic left ventricles exhibited mechanical alternans. This alternation between weak and strong beats was abolished by 1 mM caffeine but restored by its washout. Inhibition of SR Ca2+ accumulation by 50-500 nM thapsigargin in normal ventricles did not evoke alternans when pacing frequencies were increased. The results indicate that mechanical alternans in failing rat hearts is due to altered reactions of the sarcoplasmic reticulum, but a decreased rate of Ca2+ accumulation is not the primary cause.

Physical activity decreases risk for diabetes and cardiovascular disease morbidity and mortality; however, the specific impact of exercise on the diabetic vasculature is unexamined. We hypothesized that an acute, moderate exercise intervention in diabetic and hypertensive rats would induce mitochondrial biogenesis and mitochondrial antioxidant defence to improve vascular resilience. SHHF/ Mcc-facp lean (hypertensive) and obese (hypertensive, insulin resistant), as well as Sprague Dawley (SD) control rats were run on a treadmill for 8 days. In aortic lysates from SD rats, we observed a significant increase in subunit proteins from oxidative phosphorylation (OxPhos) complexes I–III, with no changes in the lean or obese SHHF rats. Exercise also increased the expression of mitochondrial antioxidant defence uncoupling protein 3 (UCP3) ( p < 0.05) in SHHF lean rats, whereas no changes were observed in the SD or SHHF obese rats with exercise. We evaluated upstream signalling pathways for mitochondrial biogenesis, and only peroxisome proliferators–activated receptor gamma coactivator 1α (PGC-1α) significantly decreased in SHHF lean rats ( p < 0.05) with exercise. In these experiments, we demonstrate absent mitochondrial induction with exercise exposure in models of chronic vascular disease. These findings suggest that chronic vascular stress results in decreased sensitivity of vasculature to the adaptive mitochondrial responses normally induced by exercise.

Aims Cardiolipin (CL) is a tetra-acyl phospholipid that provides structural and functional support to several proteins in the inner mitochondrial membrane. The majority of CL in the healthy mammalian heart contains four linoleic acid acyl chains (L4CL). A selective loss of L4CL is associated with mitochondrial dysfunction and heart failure in humans and animal models. We examined whether supplementing the diet with linoleic acid would preserve cardiac L4CL and attenuate mitochondrial dysfunction and contractile failure in rats with hypertensive heart failure. Methods and results Male spontaneously hypertensive heart failure rats (21 months of age) were administered diets supplemented with high-linoleate safflower oil (HLSO) or lard (10% w/w; 28% kilocalorie fat) or without supplemental fat (control) for 4 weeks. HLSO preserved L4CL and total CL to 90% of non-failing levels (vs. 61–75% in control and lard groups), and attenuated 17–22% decreases in state 3 mitochondrial respiration observed in the control and lard groups ( P < 0.05). Left ventricular fractional shortening was significantly higher in HLSO vs. control (33 ± 2 vs. 29 ± 2%, P < 0.05), while plasma insulin levels were lower (5.4 ± 1.1 vs. 9.1 ± 2.3 ng/mL; P < 0.05), with no significant effect of lard supplementation. HLSO also increased serum concentrations of several eicosanoid species compared with control and lard diets, but had no effect on plasma glucose or blood pressure. Conclusion Moderate consumption of HLSO preserves CL and mitochondrial function in the failing heart and may be a useful adjuvant therapy for this condition.

Interleukin 1 beta (IL-1 β) is a proinflammatory cytokine with potent cardiosuppressive effects. Previous studies have shown that leptin blunts the negative inotropic effects of IL-1 β in isolated adult rat cardiac myocytes. However, the interactions between leptin and IL-1 β in the heart have not been examined on a background of chronic hyperleptinemia. To study this interaction, we have chosen the SHHF rat, a model of spontaneous hypertension that ultimately develops congestive heart failure. SHHF that are heterozygous for a null mutation of the leptin receptor (+/ fa cp, HET) are phenotypically lean but chronically hyperleptinemic and develop heart failure earlier than their normoleptinemic true lean (+/+, LN) littermates. Simultaneous cell shortening and calcium transients were measured in isolated ventricular cardiac myocytes from LN and HET SHHF in response to leptin, IL-1 β or IL-1 β following one hour pretreatment with leptin. Despite evidence of metabolic leptin resistance, HET myocytes were sensitive to the negative inotropic effect of leptin, similar to LN. Contractility returned to control levels in myocytes from HET that were pretreated with leptin prior to IL-1 β, while contractility remained depressed compared with control and similar to leptin alone in LN. Chronic hyperleptinemia resulted in altered JAK/STAT signaling in response to leptin and IL-1 β in isolated perfused hearts from HET compared with LN SHHF. Phosphorylated STAT3 (pSTAT3) and STAT5 (pSTAT5) decreased when HET hearts were treated with leptin followed by IL-1 β. While decreases in pSTAT3 and pSTAT5 may be associated with abrogation of the acute negative inotropic effects of IL-1 β in the presence of leptin in HET, long-term consequences remain to be explored. This study demonstrates that the heart remains sensitive to leptin in a hyperleptinemic state. Crosstalk between leptin and IL-1 β can influence cardiac function and cytokine signaling and these interactions are moderated by the presence of long-term hyperleptinemia.

Little is known about the effects of common antihypertensive drugs in obese, insulin-resistant females. Nine-month-old obese female SHHF/Mcc-fa(cp) rats that received either nifedipine, a calcium channel antagonist, or enalapril, an angiotensin-converting-enzyme inhibitor, for three months were compared with untreated SHHF/Mcc-fa(cp) rats (controls). After one month, nifedipine significantly decreased body weight in obese females compared to either enalapril or controls. After three months of treatment, total, abdominal, and subcutaneous fat masses were decreased in obese females given nifedipine compared to either enalapril or controls. Enalapril treatment was associated with a redistribution of fat mass from abdominal to subcutaneous depots. Nifedipine reduced plasma triglyceride and fasting glucose levels and improved insulin response to an oral glucose load in obese females, whereas enalapril did not appear to affect glycemic control. Systolic pressure was not significantly decreased until after two months of treatment with nifedipine or three months of treatment with enalapril in obese females and may have coincided with improvement in insulin-resistance. Similarly, plasma atrial natriuretic peptide concentrations were significantly lower in obese females given nifedipine. To determine how obese males responded to a calcium channel antagonist, six-month-old obese male SHHF/Mcc-fa(cp) rats were treated for three months with either nifedipine or placebo (controls). Nifedipine-treated obese males showed a mild but significant decrease in weight gain that was due to a decrease in fat deposition in both subcutaneous and abdominal depots and systolic blood pressure was significantly reduced after one month of treatment. Nifedipine did not affect other plasma biochemical parameters in obese males. In conclusion, nifedipine improved systolic pressure and glycemic control in obese female SHHF/Mcc-fa(cp) rats, effects that may be associated with a marked loss in body weight and fat mass and improved lipid metabolism. Nifedipine-treated obese males exhibited only a diminished weight gain that was not associated with changes in diabetic characteristics.

Objective: The aim was to compare β adrenergic receptors, cAMP production, and Ca2+ accumulation by the sarcoplasmic reticulum in ventricular cardiomyocytes from female SHHF/Mcc- cp and JCR:LA- cp rats. Whereas rats from both strains exhibit gross obesity when the animals are homozygous for the recessive “corpulent” gene, the SHHF rats, which are hypertensive, all develop heart failure during their second year of life. The normotensive JCR:LA- cp animals do not. Methods: β Adrenergic receptor number, ligand affinity, isoprenaline and forskolin stimulated cyclic AMP production, and ATP dependent, phosphate supported 45Ca2+ uptake by the sarcoplasmic reticulum were compared in ventricular cardiomyocytes isolated from 6 month old obese female SHHF/Mcc- cp and obese and lean female JCR:LA-cp rats. Results: Bmax and Kd for (–)-[125iodo]-cyanopindolol (l25ICYP) binding were each –50% lower in SHHF/Mcc- cp v JCR:LA- cp myocytes. Cyclic AMP production in response to isoprenaline, isoprenaline plus isobutylmethylxanfhine (IBMX), and forskolin pjus IBMX was also significantly depressed in the SHHF/Mcc- cp cells. In addition, sarcoplasmic reticular 45Ca2+ uptake by SHHF/ Mcc- cp cells was 35% lower than in lean or obese JCR:LA- cp myocytes. Isoprenaline stimulated cAMP production and sarcoplasmic reticular Ca2+ uptake by the lean JCR:LA-cp cells were comparable to that described previously for myocytes from normal Sprague-Dawley rats. By contrast, Bmax and Kd for 125ICYP binding by the JCR myocytes differed substantially from previously described results for normal Sprague-Dawley rats, whereas values for the SHHF cells did not. Conclusions: Declines in Ca sequestration by the sarcoplasmic reticulum of ventricular cardiomyocytes from obese, hypertensive SHHF rats are not related to their obesity. However, obesity may contribute to the decline in cAMP production. This may account, in part, for the exacerbation by obesity of cardiac dysfunction in essential hypertension. Cardiovascular Research 1993; 27 :238-242

Background and aims Vitamin D deficiency has been associated with the etiology and pathogenesis of heart disease including congestive heart failure. We previously observed cardiac hypertrophy in vitamin D deficient rats and vitamin D receptor knockout mice. These studies indicate that the absence of vitamin D-mediated signal transduction and genomic activation results in increased sensitivity of the heart to ionotropic stimuli and cardiomyocyte hypertrophy. This study's aim is to investigate the relationship between vitamin D status and the heart failure phenotype in the rat. Methods and results Vitamin D status was assessed by measuring 25-hydroxyvitamin D levels and related to heart weight in young, middle-aged and aging spontaneously hypertensive, heart failure (SHHF) prone rats. We also measured the effects of the vitamin D hormone,1,25(OH) 2 D 3 , on cardiac function in SHHF rats. Cardiac hypertrophy in this model of the failing heart increased with age and related to decreasing vitamin D status. Vitamin D deficiency presented after cardiac hypertrophy was first observed. Additionally, we found that 1,25(OH) 2 D 3 treatment between 4.0 and 7.0 months of age prevented cardiac hypertrophy and permits decreased workload for the heart while allowing adequate blood perfusion and pressure, resulting in reduced cardiac index. Conclusions Our findings suggest that low vitamin D status is associated with the progression and final terminal phase of the heart failure phenotype and not with initial heart hypertrophy. Also, we report that in the vitamin D sufficient SHHF rat, 1,25(OH) 2 D 3 treatment provided protection against the progression of the heart failure phenotype.

The interaction of salt sensitivity and obesity in development of cardiac hypertrophy is incompletely understood. The SHHF/Mcc-fa(cp) (SHHF) rat model was used to examine the effect of high salt on cardiac hypertrophy and expression of endothelin (ET) and nitric oxide synthase (NOS) isoforms. Homozygous lean (+/+) and obese (fa(cp)/fa(cp)) SHHF were fed a low-salt diet (0.3% NaCl) for seven days followed by a high-salt diet (8.0% NaCl) for seven days. To assess the role of ET in mediating cardiac hypertrophy and gene expression with high salt, additional groups were treated with an ET(A)/ET(B) receptor antagonist (bosentan) while on high salt. Obese SHHF showed an increase in systolic blood pressure and cardiac hypertrophy in response to the high-salt diet. High salt resulted in decreased expression of preproET as well as all three NOS isoforms in the Obese, while cytokine induced NOS (iNOS) and neuronal NOS (nNOS) increased in Leans. Though the salt-sensitive component of the hypertension observed in the Obese was prevented by bosentan, cardiac hypertrophy still occurred and expression of all NOS isoforms remained lower in Obese compared to Lean. Endothelial NOS (eNOS) expression increased in the Lean with bosentan. These studies suggest that cardiac hypertrophy is independent of the level of hypertension and may be mediated by altered production of NOS isoforms in salt-sensitive, obese SHHF.

It is well established that obesity and diabetes contribute to increased cardiovascular complications in humans. Many feel that the increased prevalence of heart disease in obese or diabetic patients can be attributed to increased atherosclerotic lesions caused by hyperglycemia, hyperlipoproteinemia, hypertension, obesity, and hyperinsulinemia. However, more recent data indicate there may be a specific diabetic cardiomyopathy not associated with coronary artery disease that may explain some of the increased mortality and morbidity seen in diabetics (Crepaldi and Nosandini, 1988; Fein and Sonnenblick, 1985). Knowledge of the heart and cardiovascular system in genetic animal models of obesity and diabetes is limited (Chobanian et al., 1982; McCune, 1989). Various combinations of risk factors may cause different heart problems, with obesity and non-insulin-dependent diabetes mellitus (NIDDM) combined with hypertension probably causing the most deleterious effects on the heart. The use of animal models with obesity, diabetes, or both conditions, combined with other risk factors, may clarify what each component contributes to the cardiovascular disease. This report summarizes some of the current information on the cardiovascular and diabetic complications found in the SHHF/Mcc-cp rat model, which exhibits obesity, NIDDM, and congestive heart failure (CHF). rats heterozygous for the cp gene) (Koletsky, 1975) to SHR/N (spontaneously hypertensive) rats. We obtained the rats after the seventh backcross. The only other SHR/ N-cp rats currently available are from the fourteenth backcross (Michaelis et al., 1986) and may have divergence in as many as 20 percent of their genes from our substrain, now designated SHHF/Mcc-cp. This colony exhibits the following traits: hypertension (100 percent), obesity (25 percent), and CHF (100 percent in recent sibships). Obesity is expressed as an autosomal recessive (cp/cp) trait, and hypertension is multifactorial (Yen et al., 1974). The CHF trait has been maintained through at least 15 generations. The colony is closed, but it has not been completely brother x sister mated. The incidence of CHF has increased with inbreeding, and the onset of CHF seems to be occurring at an earlier age. The mode of inheritance of the CHF is probably multifactorial, much like hypertension. The majority of the lean animals that died of CHF were heterozygous for the obesity trait (+/cp). It is possible that the presence of the cp gene on this genetic background is required for the expression of the CHF or at least for the earlier age of onset of CHF. We have been successful in getting our obese male rats to breed (McCune et al., 1989); therefore, all of their lean offspring will carry the cp gene. A homozygote lean (+/+) line is also being bred, and their offspring will be compared for incidence of CHF with the heterozygote lean parents.

Potential regulation of two factors linked to physiological outcomes with left ventricular (LV) hypertrophy, resistance to apoptosis, and matching of metabolic capacity, by the transcription factor cyclic-nucleotide regulatory element binding protein (CREB), was examined in the two models of physiological LV hypertrophy: involuntary treadmill running of female Sprague-Dawley rats and voluntary exercise wheel running in female C57Bl/6 mice. Comparative studies were performed in the models of pathological LV hypertrophy and failure: the spontaneously hypertension heart failure (SHHF) rat and the hypertrophic cardiomyopathy (HCM) transgenic mouse, a model of familial idiopathic cardiomyopathy. Activating CREB serine-133 phosphorylation was decreased early in remodeling in response to both physiological (decreased 50–80%) and pathological (decreased 60–80%) hypertrophic stimuli. Restoration of LV CREB phosphorylation occurred concurrent with completion of physiological hypertrophy (94% of sedentary control), but remained decreased (by 90%) during pathological hypertrophy. In all models of hypertrophy, CREB phosphorylation/activation demonstrated strong positive correlations with 1) expression of the anti-apoptotic protein bcl-2 (a CREB-dependent gene) and subsequent reductions in the activation of caspase 9 and caspase 3; 2) expression of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1; a major regulator of mitochondrial content and respiratory capacity), and 3) LV mitochondrial respiratory rates and mitochondrial protein content. Exercise-induced increases in LV mitochondrial respiratory capacity were commensurate with increases observed in LV mass, as previously reported in the literature. Exercise training of SHHF rats and HCM mice in LV failure improved cardiac phenotype, increased CREB activation (31 and 118%, respectively), increased bcl-2 content, improved apoptotic status, and enhanced PGC-1 content and mitochondrial gene expression. Adenovirus-mediated expression of constitutively active CREB in neonatal rat cardiac recapitulated exercise-induced upregulation of PGC-1 content and mitochondrial oxidative gene expression. These data support a model wherein CREB contributes to physiological hypertrophy by enhancing expression of genes important for efficient oxidative capacity and resistance to apoptosis.

A link between leptin resistance, obesity, and salt sensitivity has been suggested. SHHF/Mcc-fa(cp) rats (SHHF) were used to study the effect of gene dosage of a null mutation of the leptin receptor (cp) on salt sensitivity and response to a combined endothelin A and B receptor antagonist (bosentan). Obese (cp/cp), heterozygous (+/cp), and homozygous lean (+/+) male SHHF were fed a low salt diet (0.3% NaCl) for 7 days, followed by a high salt diet (8.0% NaCl) for 7 days. There were no significant differences in systolic blood pressure between genotypes on low salt. In response to high salt, cp/cp had significantly greater systolic pressure than +/cp and +/+. On high salt diet, cp/cp showed a significant increase in 24 h urinary endothelin excretion and increased renal expression of preproendothelin mRNA. There was no effect of high salt diet on renal excretion of nitric oxide (NOx) or on gene expression of endothelial, neuronal, or cytokine-induced nitric oxide synthase isoforms (eNOS, nNOS, iNOS, respectively). Treatment with bosentan prevented the high salt-induced increment in systolic blood pressure in cp/cp. This was associated with a doubling of renal NOx excretion, but without changes in eNOS, nNOS, or iNOS expression. Endothelin receptor antagonism did not normalize systolic pressure in any of the genotypes. Our studies indicate that obesity secondary to leptin resistance (cp/cp) results in increased salt sensitivity that is mediated by endothelin in the SHHF rat.

The SHHF/Mccfa cp (SHHF) rat is a reliable genetic model of congestive heart failure secondary to essential hypertension. These animals are closely related to the SHR (spontaneously hypertensive rat), but unlike the SHR, all animals, male and female, develop fatal congestive heart failure, most in the second year of life. SHHF rats are now being widely used by the pharmaceutical industry to evaluate potential therapeutic agents for preventing the maladaptive ultrastructural and biochemical remodeling associated with cardiac hypertrophy and the progression to failure. SHHF rats have also proved to be useful for mechanistic studies of the contractile and signaling abnormalities associated with heart failure. The failing SHHF rat heart is hypertrophied, dilated, fibrotic, and exhibits a pronounced decline in fractional shortening in vivo as measured by M-mode echocardiography. The response to s-adrenoceptor stimulation is markedly blunted; there is evidence to suggest a decline in excitation-contraction coupling gain; and there is a decline in maximal Ca2+ activated force per cross sectional area. Isolated perfused failing SHHF hearts exhibit a predisposition to develop mechanical alternans, a negative force-frequency response and altered electromechanical restitution. Comparable abnormalities are seen in human heart failure, making the SHHF rat an ideal small animal model for investigating the natural history of cardiac hypertrophy, the transition to failure, and the unique properties of the failing myocardium.

A link between leptin resistance, obesity, and salt sensitivity has been suggested. SHHF/Mcc-fa cp rats (SHHF) were used to study the effect of gene dosage of a null mutation of the leptin receptor (cp) on salt sensitivity and response to a combined endothelin A and B receptor antagonist (bosentan). Obese (cp/cp), heterozygous (+/cp), and homozygous lean (+/+) male SHHF were fed a low salt diet (0.3% NaCl) for 7 days, followed by a high salt diet (8.0% NaC1) for 7 days. There were no significant differences in systolic blood pressure between genotypes on low salt. In response to high salt, cp/cp had significantly greater systolic pressure than +/cp and +/+. On high salt diet, cp/cp showed a significant increase in 24 h urinary endothelin excretion and increased renal expression of preproendothelin mRNA. There was no effect of high salt diet on renal excretion of nitric oxide (NOx) or on gene expression of endothelial, neuronal, or cytokine-induced nitric oxide synthase isoforms (eNOS, nNOS, iNOS, respectively). Treatment with bosentan prevented the high salt-induced increment in systolic blood pressure in cp/cp. This was associated with a doubling of renal NOx excretion, but without changes in eNOS, nNOS, or iNOS expression. Endothelin receptor antagonism did not normalize systolic pressure in any of the genotypes. Our studies indicate that obesity secondary to leptin resistance (cp/cp) results in increased salt sensitivity that is mediated by endothelin in the SHHF rat. (Mol Cell Biochem 242: 57–63, 2003)

Background: A recent study showed reverse remodeling of left ventricular myocyte shape when the type 1 angiotensin II (AT 1 )-receptor antagonist L-158,809 was administered to spontaneously hypertensive heart failure (SHHF) rats 4 months before the onset of failure. The aim of this study was to characterize temporally early treatment–induced reverse remodeling at the organ and cellular level by echocardiography and morphometry of isolated left ventricular myocytes. Methods and Results: L-158,809 was administered to 9-month-old SHHF rats. Blood pressure normalized shortly after initiation of treatment. Isolated myocytes were collected in terminal experiments to assess cell remodeling. L-158,809 reduced myocyte volume and cross-sectional area significantly after 1 week of treatment with maximal regression of hypertrophy, including reduced cell length, obtained by 4 weeks. Reduced wall thickness was clearly detectable by echocardiography within 4 weeks after initiation of treatment. Conclusions: Regression of left ventricular myocyte hypertrophy occurred rapidly after initiation of AT 1 -blocker therapy in SHHF rats and was completed within 1 month. Regression of myocyte hypertrophy was associated with reduced wall thickness, which was detected consistently by echocardiography within 1 month after initiation of treatment.

Sexual dimorphism may occur during the development of hypertension and congestive heart failure (CHF). Male and female spontaneous hypertension heart failure (SHHF) rats with established hypertension, but before CHF (age 5–8 mo) and during cardiac decompensation leading to CHF (age 18–20 mo in male rats and 22–24 mo in female rats), were studied. At 5–8 mo, male SHHF rats showed early activation of the renin-angiotensin system (RAS), as indicated by increased plasma renin activity (PRA) and higher serum angiotensin-converting enzyme activity compared with female rats. The increase in PRA in female rats was delayed compared with males rats, but it reached comparable levels just before CHF. Urinary endothelin excretion was significantly greater in 5- to 8-mo-old female rats compared with age-matched male rats. Urinary endothelin excretion increased in both male and female rats as CHF developed. Plasma atrial natriuretic peptide (ANP) was comparable at both time points, and both genders showed similar, marked increases as CHF developed. In conclusion, male rats show early activation of the RAS, whereas female rats show early activation of the endothelin vasopressor system. During cardiac decompensation, generalized activation of the RAS, endothelin, and ANP systems occurs and is similar in male and female SHHF rats.

Gender and obesity may influence response to pharmacological modulation of the renin-angiotensin system. We used SHHF/Mcc-fa(cp) rats to study effect of obesity and gender on the ability of an AT1 receptor antagonist to decrease blood pressure. After 2 weeks treatment with irbesartan (50 mg/kg), only lean and obese males showed significant decreases in blood pressure, while obese females were completely resistant. Lean females showed a trend toward lowering of pressure (p=0.06). However, irbesartan similarly shifted angiotensin II dose response curves to the right in all groups. Twelve weeks of irbesartan also failed to decrease blood pressure, but did significantly reduce heart weight in obese females. In untreated rats, obese females had lower plasma renin activity and serum angiotensin converting enzyme activity compared to lean males, while lean and obese females had increased urinary endothelin excretion. Despite an otherwise similar genetic background contributing to hypertension and heart failure, obese females have different patterns of humoral activation compared to lean males, which may contribute to their resistance to the depressor effects of irbesartan.

The importance of endogenous and exogenous estrogen levels to the development of cardiovascular disease in women in controversial. The purpose of our study was to examine the effect of estrogen on the development of hypertension, cardiac hypertrophy, ventricular function, and gene expression for atrial natriuretic peptide (ANP) and components of the renin angiotensin system in spontaneously hypertensive heart failure rats (SHHF/Mcc- facp). Development of hypertension was prevented in 3-month-old ovariectomized rats receiving subcutaneous 17 beta -estradiol implants (EST) compared to ovariectomized (OVX) and controls (CON). EST had the least left ventricular hypertrophy, CON were intermediate, and OVX had the most (P

Angiotensin-converting enzyme (ACE) inhibitors have proven an effective means to control hypertension and manage cardiac hypertrophy. It is presently unknown if newer specific angiotensin II subtype 1 receptor (AT1R) antagonists are as effective or more effective in treating these conditions compared with ACE inhibitors. There is evidence that these classes of drugs may affect cardiac hypertrophy by different mechanisms. This study compared the effect of irbesartan, an AT1R antagonist, with that of captopril, an ACE inhibitor, on expression of early genetic markers of cardiac hypertrophy in lean male SHHF/Mcc-fa(cp) rats. SHHF/Mcc-fa(cp) rats (n = 10/group) were given captopril (100 mg/kg/day), irbesartan (50 mg/kg/day), or placebo for 16 weeks. Irbesartan and captopril significantly reduced systolic pressure and produced similar rightward shifts in the angiotensin I dose-response curve. Renal renin gene expression was increased 8.6-fold by irbesartan and 17.7-fold by captopril. The only effect on echocardiographic findings was a similar decrease in aortic peak velocity, an index of systolic function, by both treatments. Early markers of cardiac hypertrophy were significantly attenuated by both drugs. Both drugs produced marked and equivalent reductions in left ventricular atrial natriuretic peptide (ANP) messenger RNA (mRNA) levels compared with controls. This decrease in ANP gene expression was accompanied by a decrease in plasma ANP concentration in the treatment groups. The shift from V1 to V3 myosin isozymes was similarly decreased in both treatment groups, compared with controls. These data suggest that captopril and irbesartan are similarly effective in controlling expression of genes associated with ventricular hypertrophy in heart failure-prone SHHF/Mcc-fa(cp) rat.

The importance of the loss of ovarian function to the progression of hypertension and heart disease in women is controversial. We investigated whether ovariectomy would accelerate development of hypertension, congestive heart failure, and neurohumoral activation in adult spontaneous hypertension heart failure (SHHF) rats, a genetic model of heart failure. Six months after ovariectomy, no significant differences between control and ovariectomized rats were seen in systolic or diastolic blood pressure, left ventricular fractional shortening by echocardiography, or heart weight. Percent V1 myosin isozyme was significantly lower in ovariectomized rats. Northern blot analysis failed to show significant differences between groups in expression of hepatic angiotensinogen, renal renin, or left ventricular atrial or brain natriuretic peptide mRNA. In a second experiment, serial measures of systolic pressure and left ventricular shortening fractions failed to document a significant difference between control and ovariectomized rats as they developed heart failure, although there was a significant decline in shortening fraction in both groups at the age when regular estrous cycling naturally ceases. Survival time was similar between groups. In summary, ovariectomy of adult SHHF rats does not appear to affect the progression of genetically programmed hypertension and heart failure in this model.

The pathogenesis of diabetic retinopathy has not been fully explained. The earliest histological lesion is the loss of intramural pericytes and thickening of the basement membrane. Increased activity of the polyol pathway is a probable mechanism for these two abnormalities. Investigations have suffered from the lack of an exact animal model simulating the human condition. Examination of the retina in the spontaneously diabetic SHR/N:Mcc-cp rat demonstrated degeneration and loss of intramural pericytes, a progressive increase in basement membrane thickness, and microinfarctions with an area of non-perfusion. Therefore, this model may be used to clarify the biochemical mechanisms linking the metabolic abnormalities of diabetes and retinopathy.

31P-NMR was used to monitor myocardial bioenergetics in compensated and failing SHHF/MCC-fa(cp) (SHF) rat hearts. The SHHF/Mcc-fa(cp) (spontaneous hypertension and heart failure) rat is a relatively new genetic model in which all individuals spontaneously develop congestive heart failure, most during the second year of life. Failing SHF rat hearts displayed a pronounced decrease in resting PCr:ATP ratios (P0.001), which was explained by a significant (P0. 0001) drop in total creatine (47.2+/-3.1 nmol/mg protein) v age matched controls (106+/-3 nmol/mg protein). In end stage failure, NMR determined PCr was 2.9+/-0.1 micro mol/g wet weight under basal conditions. In contrast, 6- and 20-month-old controls and compensated SHFs had PCr values of 5.3+/-0.1, and 5.1+/-0.5 and 5. 1+/-0.2 micro mol/g wet weight. Both compensated and failing SHF hearts were metabolically compromised when the rate pressure product (RPP) was increased, as evidenced by an increase in Pi and a drop in PCr. Compensated SHF hearts, however, were able to increase rate pressure products (RRP, mmHg X beats/min) from 44.5+/-1.4 to 66.6+/-3. 4 K with dobutamine infusion, whereas hearts in end-stage failure were able to increase their RPP from baseline values of 27+/-4 K to only 37+/-7 K. The data indicate that a pronounced decline in PCr and total creatine signals the transition from compensatory hypertrophy to decompensation and failure in the SHF rat model of hypertensive cardiomyopathy.