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A defining characteristic of pulmonary hypertension (PH) is the extensive remodeling of pulmonary arteries (PAs), which results in progressive increases in vascular resistance and stiffness and eventual failure of the right ventricle. There is no cure for PH and identification of novel molecular mechanisms that underlie increased proliferation, reduced apoptosis, and excessive extracellular matrix production in pulmonary artery smooth muscle cells (PASMCs) is a vital objective. Galectin-3 (Gal-3) is a chimeric lectin and potent driver of many aspects of fibrosis, but its role in regulating PASMC behavior in PH remains poorly understood. Herein, we evaluated the importance of increased Gal-3 expression and signaling on PA vascular remodeling and cardiopulmonary function in experimental models of PH. Gal-3 expression was quantified by qRT-PCR, immunoblotting, and immunofluorescence imaging, and its functional role was assessed by specific Gal-3 inhibitors and CRISPR/Cas9-mediated knockout of Gal-3 in the rat. In rat models of PH, we observed increased Gal-3 expression in PASMCs, which stimulated migration and resistance to apoptosis, whereas silencing or genetic deletion reduced cellular migration and PA fibrosis and increased apoptosis. Gal-3 inhibitors attenuated and reversed PA remodeling and fibrosis, as well as hemodynamic indices in monocrotaline (MCT)-treated rats in vivo. These results were supported by genetic deletion of Gal-3 in both MCT and Sugen Hypoxia rat models. In conclusion, our results suggest that elevated Gal-3 levels contribute to inappropriate PA remodeling in PH by enhancing multiple profibrotic mechanisms. Therapeutic strategies targeting Gal-3 may be of benefit in the treatment of PH.

BACKGROUND: Impaired endothelium-dependent vasodilation is a hallmark of obesity-induced hypertension. The recognition that Ca(2+) signaling in endothelial cells promotes vasodilation has led to the hypothesis that endothelial Ca(2+) signaling is compromised during obesity, but the underlying abnormality is unknown. In this regard, TRPV4 ion channels are a major Ca(2+) influx pathway in endothelial cells, and regulatory protein AKAP150 enhances the activity of TRPV4 channels. METHODS: We used endothelium-specific knockout mice and high fat diet-fed mice to assess the role of endothelial AKAP150-TRPV4 signaling in blood pressure regulation under normal and obese conditions. We further determined the role of peroxynitrite, an oxidant molecule generated from the reaction between nitric oxide (NO) and superoxide radicals, in impairing endothelial AKAP150-TRPV4 signaling in obesity, and assessed the effectiveness of peroxynitrite inhibition in rescuing endothelial AKAP150-TRPV4 signaling in obesity. The clinical relevance of our findings was evaluated in arteries from non-obese and obese individuals. RESULTS: We show that Ca(2+) influx through TRPV4 channels at myoendothelial projections (MEPs) to smooth muscle cells decreases resting blood pressure in non-obese mice, a response that is diminished in obese mice. Counterintuitively, release of the vasodilator molecule NO attenuated endothelial TRPV4 channel activity and vasodilation in obese animals. Increased activities of iNOS and NOX1 enzymes at MEPs in obese mice generated higher levels of NO and superoxide radicals, resulting in increased local peroxynitrite formation and subsequent oxidation of the regulatory protein AKAP150 at cysteine 36, to impair AKAP150-TRPV4 channel signaling at MEPs. Strategies that lowered peroxynitrite levels prevented cysteine 36 oxidation of AKAP150, and rescued endothelial AKAP150-TRPV4 signaling, vasodilation, and blood pressure in obesity. Importantly, peroxynitrite-dependent impairment of endothelial TRPV4 channel activity and vasodilation was also observed in the arteries from obese patients. CONCLUSIONS: These data suggest that a spatially restricted impairment of endothelial TRPV4 channels contributes to obesity-induced hypertension, and imply that inhibiting peroxynitrite might represent a strategy for normalizing endothelial TRPV4 channel activity, vasodilation, and blood pressure in obesity.

Traditional aerobic exercise reduces the risk of developing chronic diseases by inducing immune, metabolic, and myokine responses. Following traditional exercise, both the magnitude and time-course of these beneficial responses are different between obese compared to normal weight individuals. Although obesity may affect the ability to engage in traditional exercise, whole body vibration (WBV) has emerged as a more tolerable form of exercise . The impact of WBV on immune, metabolic, and myokine responses as well as differences between normal weight and obese individuals, however, is unknown. Purpose To determine if WBV elicits differential magnitudes and time-courses of immune, metabolic, and myokine responses between obese and normal weight individuals. Methods 21 participants [Obese (OB): n = 11, Age: 33 ± 4 y, percent body fat (%BF): 39.1 ± 2.4% & Normal weight (NW) n = 10, Age: 28 ± 8 y, %BF: 17.4 ± 2.1%] engaged in 10 cycles of WBV exercise [1 cycle = 1 min of vibration followed by 30 s of rest]. Blood samples were collected pre-WBV (PRE), immediately (POST), 3 h (3H), and 24 h (24H) post-WBV and analyzed for leukocytes, insulin, glucose, and myokines (IL-6, decorin, myostatin). Results The peak (3H) percent change in neutrophil counts (OB: 13.9 ± 17.4 vs. NW: 47.2 ± 6.2%Δ; p = 0.007) was different between groups. The percent change in neutrophil percentages was increased in NW (POST: -1.6 ± 2.0 vs. 3H: 13.0 ± 7.2%Δ, p = 0.019) but not OB (p > 0.05). HOMA β-cell function was increased at 24H (PRE: 83.4 ± 5.4 vs. 24H: 131.0 ± 14.1%; p = 0.013) in NW and was not altered in OB (p > 0.05). PRE IL-6 was greater in OB compared to NW (OB: 2.7 ± 0.6 vs. NW: 0.6 ± 0.1 pg/mL; p = 0.011); however, the percent change from PRE to peak (3H) was greater in NW (OB: 148.1 ± 47.9 vs. NW: 1277.9 ± 597.6 %Δ; p = 0.035). Creatine kinase, decorin, and myostatin were not significantly altered in either group (p > 0.05). Conclusion Taken together, these data suggest that acute whole body vibration elicits favorable immune, metabolic, and myokine responses and that these responses differ between obese and normal weight individuals., Highlights • Whole body vibration (WBV) normalizes lymphocytes in obese. • 10 min of WBV facilitates increases in neutrophils in normal weight but not obese. • WBV produces myokine IL-6 in both obese and normal weight. • WBV improves glucose metabolism in obese. • Improvements in glucose metabolism correspond to peak IL-6 concentrations.

Diabetes is the leading cause of kidney failure, accounting for >45% of new cases of dialysis. Diabetic nephropathy is characterized by inflammation, fibrosis, and oxidant stress, pathologic features that are shared by many other chronic inflammatory diseases. The cytokine IL-17A was initially implicated as a mediator of chronic inflammatory diseases, but recent studies dispute these findings and suggest that IL-17A can favorably modulate inflammation. Here, we examined the role of IL-17A in diabetic nephropathy. We observed that IL-17A levels in plasma and urine were reduced in patients with advanced diabetic nephropathy. Type 1 diabetic mice that are genetically deficient in IL-17A developed more severe nephropathy, whereas administration of low-dose IL-17A prevented diabetic nephropathy in models of type 1 and type 2 diabetes. Moreover, IL-17A administration effectively treated, prevented, and reversed established nephropathy in genetic models of diabetes. Protective effects were also observed after administration of IL-17F but not IL-17C or IL-17E. Notably, tubular epithelial cell-specific overexpression of IL-17A was sufficient to suppress diabetic nephropathy. Mechanistically, IL-17A administration suppressed phosphorylation of signal transducer and activator of transcription 3, a central mediator of fibrosis, upregulated anti-inflammatory microglia/macrophage WAP domain protein in an AMP-activated protein kinase-dependent manner and favorably modulated renal oxidative stress and AMP-activated protein kinase activation. Administration of recombinant microglia/macrophage WAP domain protein suppressed diabetes-induced albuminuria and enhanced M2 marker expression. These observations suggest that the beneficial effects of IL-17 are isoform-specific and identify low-dose IL-17A administration as a promising therapeutic approach in diabetic kidney disease.

Background Obesity compromises cardiometabolic function and is associated with hypertension and chronic kidney disease. Exercise ameliorates these conditions, even without weight loss. Although the mechanisms of exercise's benefits remain unclear, augmented lean body mass is a suspected mechanism. Myostatin is a potent negative regulator of skeletal muscle mass that is upregulated in obesity and downregulated with exercise. The current study tested the hypothesis that deletion of myostatin would increase muscle mass and reduce blood pressure and kidney injury in obesity. Methods and Results Myostatin knockout mice were crossed to db/db mice, and metabolic and cardiovascular functions were examined. Deletion of myostatin increased skeletal muscle mass by ≈50% to 60% without concomitant weight loss or reduction in fat mass. Increased blood pressure in obesity was prevented by the deletion of myostatin, but did not confer additional benefit against salt loading. Kidney injury was evident because of increased albuminuria, which was abolished in obese mice lacking myostatin. Glycosuria, total urine volume, and whole kidney NOX‐4 levels were increased in obesity and prevented by myostatin deletion, arguing that increased muscle mass provides a multipronged defense against renal dysfunction in obese mice. Conclusions These experimental observations suggest that loss of muscle mass is a novel risk factor in obesity‐derived cardiovascular dysfunction. Interventions that increase muscle mass, either through exercise or pharmacologically, may help limit cardiovascular disease in obese individuals.

The objective of this study is to test the hypothesis that increased muscle mass has positive effects on cardiovascular function. Specifically, we tested the hypothesis that increases in lean body mass caused by deletion of myostatin improves cardiac performance and vascular function. Echocardiography was used to quantify left ventricular function at baseline and after acute administration of propranolol and isoproterenol to assess β ‐adrenergic reactivity. Additionally, resistance vessels in several beds were removed, cannulated, pressurized to 60 mmHg and reactivity to vasoactive stimuli was assessed. Hemodynamics were measured using in vivo radiotelemetry. Myostatin deletion results in increased fractional shortening at baseline. Additionally, arterioles in the coronary and muscular microcirculations are more sensitive to endothelial‐dependent dilation while nonmuscular beds or the aorta were unaffected. β ‐adrenergic dilation was increased in both coronary and conduit arteries, suggesting a systemic effect of increased muscle mass on vascular function. Overall hemodynamics and physical characteristics (heart weight and size) remained unchanged. Myostatin deletion mimics in part the effects of exercise on cardiovascular function. It significantly increases lean muscle mass and results in muscle‐specific increases in endothelium‐dependent vasodilation. This suggests that increases in muscle mass may serve as a buffer against pathological states that specifically target cardiac function (heart failure), the β ‐adrenergic system (age), and nitric oxide bio‐availability (atherosclerosis). Taken together, pharmacological inhibition of the myostatin pathway could prove an excellent mechanism by which the benefits of exercise can be conferred in patients that are unable to exercise.

Pulmonary Arterial Hypertension (PAH) is characterized by excessive vascular cell proliferation, inward remodeling and increased stiffness and inflammation of the pulmonary blood vessels. We found that galectin-3 (Gal-3) is upregulated in PA from multiple models of PAH including monocrotaline (MCT), MCT + pneumonectomy, and SUGEN/hypoxia rats as well as in human PAH and correlated with severity of disease. Gal-3 is a β-galactoside binding lectin implicated in signaling pathways regulating cell proliferation, inflammation and fibrosis, but its role in PAH is poorly defined. Confocal analysis revealed the majority of Gal-3 expression in the media of PA of both rodent models and humans. Selective inhibitors of Gal-3 attenuated PAH in MCT-treated rats and reduced indices of proliferation, fibrosis and increased apoptosis in PA. Overexpression of Gal-3 in PASMC increased proliferation, migration and expression of profibrotic molecules and protected from apoptosis. Acute exposure of cultured HPASMC with various mitogens and factors important in the development of PAH, failed to increase Gal-3 expression. In contrast, PASMC isolated from rats with PAH exhibited an enduring capacity for increased proliferation and expressed higher levels of Gal-3 suggesting an epigenetic mechanism regulating Gal-3 expression. We found that treatment of PASMC with inhibitors of DNA methylation robustly increased Gal-3 expression in control human and rat PASMC but not in MCT-derived PASMC. Methylation analysis of DNA isolated from PA using MeDIP-qPCR and pyrosequencing revealed hypomethylation of Gal-3 proximal promoter. Analysis of DNA methyltransferase expression in PA revealed a significant loss of only Dnmt3A expression in hypertensive PA. To assess the role of local methylation in the regulation of Gal-3 expression we used CRISPR-dCas9. Targeted Gal-3 promoter methylation using multiple RNA guides and dCas9-Dnmt3A-Dnmt3L effectively reduced Gal-3 expression in SMC isolated from MCT rat PA and reversed the excessive proliferation. These results advance an important role of methylation-dependent mechanisms in Gal-3 signaling and provide a mechanism for the enduring changes in vascular cell behavior observed in PAH.

Obesity is a major risk factor for hypertension. The copresentation of hypertension and insulin resistance (IR) suggests a role for IR in blood pressure (BP) dysregulation. To test this hypothesis, peripheral IR has been genetically subtracted in a model of obesity by crossing leptin receptor mutant mice (K db H PTP ) with mice lacking protein tyrosine phosphatase 1B (insulin desensitizer, H db K PTP ) to generate obese insulin-sensitive mice (K db K PTP ). BP was recorded in lean (H db H PTP , H db K PTP ) and obese (K db H PTP , K db K PTP ) mice via telemetry, and a frequency analysis of the recording was performed to determine BP variability. Correction of IR in obese mice normalized BP values to baseline levels (H db H PTP : 116±2 mm Hg; K db H PTP : 129±4 mm Hg; K db K PTP : 114±5 mm Hg) and restored BP variability by decreasing its standard deviation and the frequency of BP values over the upper autoregulatory limit of the kidneys. However, although IR-induced increases in proteinuria (versus 53±13 μg/d, H db H PTP ) were corrected in K db K PTP (112±39 versus 422±159 μg/d, K db H PTP ), glomerular hypertrophy was not. IR reduced plasma aldosterone levels ruling out a role for mineralocorticoids in the development of hypertension. Taken together, these data indicate that correction of IR prevents hypertension, BP variability, and microalbuminuria in obese mice. Although the mechanism remains to be fully determined, increases in aldosterone or sympathoactivation of the cardiovascular system seem to be less likely contributors.

Diseases of the coronary circulation remain the leading cause of death in Western society despite impressive advances in diagnosis, pharmacotherapy and post-event management. Part of this statistic likely stems from a parallel increase in the prevalence of obesity and metabolic dysfunction, both significant risk factors for coronary disease. Obesity and diabetes pose unique challenges for the heart and their impact on the coronary vasculature remains incompletely understood. The vascular endothelium is a major interface between arterial function and the physical and chemical components of blood flow. Proper function of the endothelium is necessary to preserve hemostasis, maintain vascular tone and limit the extent of vascular diseases such as atherosclerosis. Given its central role in vascular health, endothelial dysfunction has been the source of considerable research interest in diabetes and obesity. In the current review, we will examine the pathologic impact of obesity and diabetes on coronary function and the extent to which these two factors impact endothelial function. This article is part of a Special Issue entitled “Coronary Blood Flow”.

Arginase can cause vascular dysfunction by competing with nitric oxide synthase for l-arginine and by increasing cell proliferation and collagen formation, which promote vascular fibrosis/stiffening. We have shown that increased arginase expression/activity contribute to vascular endothelial cell (EC) dysfunction. Here, we examined the roles of the two arginase isoforms, arginase I and II (AI and AII, respectively), in this process. Experiments were performed using streptozotocin-induced diabetic mice: wild-type (WT) mice and knockout mice lacking the AII isoform alone (AI+/+AII−/−) or in combination with partial deletion of AI (AI+/−AII −/−). EC-dependent vasorelaxation of aortic rings and arterial fibrosis and stiffness were assessed in relation to arginase activity and expression. Diabetes reduced mean EC-dependent vasorelaxation markedly in diabetic WT and AI+/+AII−/− aortas (53% and 44% vs. controls, respectively) compared with a 27% decrease in AI+/−AII −/− vessels. Coronary fibrosis was also increased in diabetic WT and AI+/+AII−/− mice (1.9- and 1.7-fold vs. controls, respectively) but was not altered in AI+/−AII −/− diabetic mice. Carotid stiffness was increased by 142% in WT diabetic mice compared with 51% in AI+/+AII−/− mice and 19% in AI+/−AII −/− mice. In diabetic WT and AI+/+AII−/− mice, aortic arginase activity and AI expression were significantly increased compared with control mice, but neither parameter was altered in AI+/−AII −/− mice. In summary, AI+/−AII −/− mice exhibit better EC-dependent vasodilation and less vascular stiffness and coronary fibrosis compared with diabetic WT and AI+/+AII−/− mice. These data indicate a major involvement of AI in diabetes-induced vascular dysfunction.

Obesity is a risk factor for stroke, but the determinants of increased stroke risk in obesity are unknown. We have previously reported that obese Zucker rats (OZRs) have a worse stroke outcome and display evidence of remodeling of the middle cerebral artery (MCA), in parallel with hypertension, compared with lean controls. This study tested the hypothesis that hypertension is an essential determinant of cerebral vascular remodeling and increased stroke damage in OZRs. Blood pressure was measured by telemetery in lean and obese rats with and without hydrochlorthiazide (HCT; 2 mg·kg−1·day−1) from 8 to 15 wk of age. A separate group of rats was also chronically fed a low-sodium (LS) diet. Vessel structure was assessed in isolated, pressurized MCAs. Cerebral ischemia was induced for 60 min using an intralumenal suture technique, followed by 24 h of reperfusion. HCT treatment effectively prevented the increase in blood pressure in obese rats; however, the LS diet did not lower pressure. Importantly, infarct size was normalized by HCT after ischemia-reperfusion injury. Additionally, HCT improved the changes in MCA structure observed in untreated OZRs. There were no benefits of the LS diet on stroke injury or vessel structure. These results indicate that increased pressure is essential for driving the changes in infarct size in OZRs.

Background— Obesity causes hypertension and sympathoactivation, a process proposed to be mediated by leptin. Protein tyrosine phosphatase 1B (PTP1B), a major new pharmaceutical target in the treatment of obesity and type II diabetes mellitus, constrains the metabolic actions of leptin, but the extent to which PTP1B regulates its cardiovascular effects is unclear. This study examined the hypothesis that PTP1B is a negative regulator of the cardiovascular effects of leptin. Methods and Results— PTP1B knockout mice had lower body fat but higher mean arterial pressure (116±5 versus 105±5 mm Hg, P P P P 1 -adrenergic receptor subtypes, consistent with blunted constriction to phenylephrine. Conclusions— These data indicate that PTP1B is a key regulator of the cardiovascular effects of leptin and that reduced vascular adrenergic reactivity provides a compensatory limit to the effects of leptin on mean arterial pressure.

Impairment of vascular growth is a hallmark of diabetic complications, but the progression and mechanisms are poorly understood. To determine whether obesity and early diabetes impair endothelium-dependent vasodilatation and vascular response to ischemia, microvascular function as well as angiogenic responses to ischemia were assessed in young (C57) and 6-month-old lean mice (old C57), in obese (db-C57) mice, and in mice suffering an early (db-KsJ) and sustained type 2 diabetes (old db-KsJ). Glycemia gradually increased from the db-C57 to the old db-KsJ. Early and established type II diabetes significantly reduced the level of insulin that was significantly increased in obese mice. Endothelial function was assessed in isolated resistance arteries while the angiogenic response induced by unilateral hindlimb ischemia was analyzed, after 28 days, with a laser Doppler flowmeter and angiography. Aging (-21%), obesity (-45%), as well as early (-58%) and sustained type II diabetes (-69%) induced a progressive impairment of the endothelium-dependent relaxation of the gracilis artery. Laser Doppler measurements demonstrated that only early and sustained type II diabetes impaired skin blood flow recovery. Vascular collateralization was reduced with aging and severely impaired in older db-KsJ mice, the two strains of mice in which ischemia reduced eNOS expression. These results demonstrate that endothelial dysfunction induced by obesity is insufficient to alter the angiogenic response to ischemia. Furthermore, the development of frank type II diabetes or increasing age is required to impair the vascular response to hindlimb ischemia. We conclude that additional risk factors or severe endothelial dysfunction may be requisite to impede the angiogenic response to ischemia.

Obesity is a risk factor for stroke, but the mechanisms by which obesity increases stroke risk are unknown. Because microvascular architecture contributes to the outcome of stroke, we hypothesized that middle cerebral arteries (MCAs) from obese Zucker rats (OZRs) undergo inward remodeling and develop increased myogenic tone compared with those in lean Zucker rats (LZRs). We further hypothesized that OZRs have an increased infarct after cerebral ischemia and that changes in vascular structure and function correlate with the development of hypertension in OZRs. Blood pressure was measured by telemetry in LZRs and OZRs from 6 to 17 weeks of age. Vessel structure and function were assessed in isolated MCAs. Stroke damage was assessed after ischemia was induced for 60 minutes followed by 24 hours of reperfusion. Although mean arterial pressure was similar between young rats (6 to 8 weeks old), mean arterial pressure was higher in adult (14 to 17 weeks old) OZRs than in LZRs. MCAs from OZRs had a smaller lumen diameter and increased myogenic vasoconstriction compared with those from LZRs. After ischemia, infarction was 58% larger in OZRs than in LZRs. Before the development of hypertension, MCA myogenic reactivity and lumen diameter, as well as infarct size, were similar between young LZRs and OZRs. Our results indicate that the MCAs of OZRs undergo structural remodeling and that these rats have greater cerebral injury after cerebral ischemia. These cerebrovascular changes correlate with the development of hypertension and suggest that the increased blood pressure may be the major determinant for stroke risk in obese individuals.

Obesity is an emerging epidemic worldwide and threatens cardiovascular health due to the complications of accompanying metabolic dysfunction. One potential mechanism by which these complications are advanced is structural alteration in the microcirculation perfusing target organs. In this brief review, the authors focus on the structural adaptations that occur in the microcirculation, with specific focus on changes in basement membrane thickness and vascular structure. By delineating changes in end-stage disease and recent insights from animal studies, they hope to convince the reader (1) that diabetic disease in the limb is associated with profound changes in arteriolar structure and (2) that parallel changes in microvascular architecture precede the onset of frank type II diabetes.

High-potassium diets can improve vascular function, yet the effects of potassium supplementation on ischemic stroke have not been studied. We hypothesized that dietary potassium supplementation would reduce ischemic cerebral infarct size by reversing cerebral artery hypertrophy. Six-week-old male stroke-prone spontaneously hypertensive rats (SHRSP) were fed diets containing 0.79% potassium (LK) or 2.11% potassium (HK) for 6 wk; Wistar-Kyoto (WKY) rats were fed the LK diet. The HK diet did not reduce blood pressure, as measured by telemetry, in the SHRSP. Cerebral ischemia was induced by middle cerebral artery (MCA) occlusion. The resultant infarct was smaller in the HK-SHRSP than in the LK-SHRSP: 55.1 ± 6.3 vs. 71.4 ± 2.4% of the hemisphere infarcted ( P < 0.05). Infarcts were smaller in WKY rats (33.5 ± 4.8%) than in LK-SHRSP or HK-SHRSP. The vessel wall of MCAs from LK-SHRSP was hypertrophied compared with WKY rats; this was reversed in HK-SHRSP. RT-PCR analysis of the cerebral vessels showed that expression of platelet-derived growth factor receptors-α and -β, epidermal growth factor receptor, and collagen I and III was increased in the vessels from LK-SHRSP compared with WKY rats and reduced in HK-SHRSP. These results suggest that potassium supplementation provides neuroprotection in a model of ischemic stroke independent of blood pressure and possibly through changes in vascular structure.

Clinical studies have demonstrated that the pressor response to acute stress is larger in obese versus lean individuals. We therefore tested the hypotheses that the pressor response to behavioral stress is greater in obese (OZRs) versus lean Zucker rats (LZRs) and that reduced β-adrenergic–mediated vasodilation contributes to the enhanced pressor response. Animals were restrained and subjected to acute pulsatile air jet stress (3 minutes), followed by a poststress period of 20 minutes; β-adrenergic blockade was achieved with propranolol (5 mg/kg, IV) given 15 minutes before the start of air jet stress. Mean arterial pressure (MAP) was continuously monitored by telemetry. Untreated OZRs responded with a greater integrated pressor response (area under the curve [AUC]) to acute stress (41.2±6.1 versus 21.2±3.3 mm Hg×3 minutes, OZR versus LZR; P P

1. Obesity is rapidly increasing in Western populations, driving a parallel increase in hypertension, diabetes and vascular disease. Prior to the development of overt diabetes or hypertension, obese patients spend years in a state of progressive insulin resistance and metabolic disease. Mounting evidence suggests that this insulin-resistant state has deleterious effects on the control of blood flow, thus placing organ systems at a higher risk for end-organ damage and increasing cardiovascular mortality. 2. The purpose of the present review is to examine the current literature on the effects of obesity and insulin resistance on the acute control of vascular tone. Effects on nitric oxide (NO)-mediated control of vascular tone are particularly examined with regard to proximal causes and distal mechanisms of the impaired NO-mediation of vasodilation. 3. Finally, novel pathways of impaired control of perfusion are summarized from the recent literature to identify new avenues of exploring impaired vascular function in patients with metabolic disease.

Obesity causes whole body insulin resistance and impaired vasodilation to nitric oxide (NO). Because NO is a major contributor to the regulation of mesenteric blood flow, the mesenteric circulation of obese animals is faced with reduced capacity to increase flow and increased demand for flow associated with elevated consumption of food. This study hypothesized that insulin resistance impairs NO-mediated dilation but that constrictor reactivity would be reduced to compensate in obese animals. We further hypothesized that elevated superoxide levels caused impaired responses to NO in insulin resistance. Vasodilator reactivity and vasoconstrictor reactivity of mesenteric resistance arteries from lean (LZR) and obese (OZR) Zucker rats were examined in vitro using videomicroscopy. Insulin resistance independent of obesity was induced via fructose feeding in LZR (FF-LZR). Endothelium-dependent NO-mediated dilation was reduced in OZR and FF-LZR compared with LZR. Impairments in NO-mediated dilation were reversed with 1 mM tempol, a SOD mimetic. Constrictor reactivity to norepinephrine was reduced in OZR but not in FF-LZR relative to LZR. Basal mesenteric vascular resistance was similar in LZR and OZR despite impaired NO-dependent dilation in OZR. Mesenteric vascular resistance was increased in FF-LZR relative to LZR. These data indicate that there is reduced constrictor reactivity in OZR that may offset the impaired NO-mediated dilation and preserve mesenteric blood flow in hyperphagic, obese animals.

Fructose feeding has been widely reported to cause hypertension in rats, as assessed indirectly by tail cuff plethysmography. Because there are potentially significant drawbacks associated with plethysmography, we determined whether blood pressure changes could be detected by long-term monitoring with telemetry in age-matched male Sprague-Dawley rats fed either a normal or high-fructose diet for 8 weeks. Fasting plasma glucose (171±10 versus 120±10 mg/dL), plasma insulin (1.8±0.5 versus 0.7±0.1 μg/L), and plasma triglycerides (39±2 versus 30±2 mg/dL) were modestly but significantly elevated in fructose-fed animals. Using the hyperinsulinemic euglycemic clamp technique, the rate of glucose infusion necessary to maintain equivalent plasma glucose was significantly reduced in fructose-fed compared with control animals (22.9±3.6 versus 41.5±2.9 mg/kg per minute; P P

Excessive cellular proliferation is a major contributor to the pathological changes associated with the secondary complications of diabetes. In particular, hyperglycemia (HG)-induced growth of vascular smooth muscle cells (VSMC) and glomerular mesangial cells (GMC) are characteristic features of the cardiovascular and renal complications of diabetes. VSMC and GMC respond to traditional growth factors, however in diabetes this occurs in the context of an environment, enriched in circulating vasoactive mediators and HG. For example, signaling via the angiotensin II (Ang II) pathway has been implicated in the pathogenesis of diabetic vascular disease. Recent findings indicate that HG and Ang II activate intracellular processes, including the polyol pathway and the generation of reactive oxygen species. These pathways activate the JAK (janus kinase)/STAT (signal transducers and activators of transcription) signaling cascades in both VSMC and GMC. Activation of the latter signaling cascade can stimulate excessive proliferation and growth of these cells, contributing to the accelerated atherosclerosis and nephropathy seen in the diabetic state. This review focuses on key factors in the diabetic microenvironment, in particular the interplay between HG, accumulation of advanced glycation end products and Ang II mediated signaling events both in vitro and in vivo.

DEY, APARAJITA, ROGER S. WILLIAMS, DAVID M. POLLOCK, DAVID W. STEPP, JOHN W. NEWMAN, BRUCE D. HAMMOCK, AND JOHN D. IMIG. Altered Kidney CYP2C and cyclooxygenase-2 levels are associated with obesity-related albuminuria. Obes Res. 2004;12: 1278 –1289. Objective: To determine cytochrome P450 (CYP450) and cyclooxygenase (COX) expression and metabolite regulation and renal damage in the early stages of obesity-related hypertension and diabetes. Research Methods and Procedures: Obese and lean Zucker rats at 10 to 12 weeks of age were studied. Blood pressure was measured in the conscious state using radiotelemetry. Blood glucose levels and body weight were measured periodically. Protein expression of CYP450 and COX enzymes in the kidney cortex, renal microvessels, and glomeruli was studied. The levels of CYP450 and COX metabolites in urine were measured, and urinary albumin excretion, an indicator of kidney damage, was measured. Results: Body weight and blood glucose averaged 432 20 grams and 105 5 mg/dl, respectively, in obese Zucker rats as compared with 320 8 grams and 91 5 mg/dl, respectively, in age-matched 10- to 12-week-old lean Zucker rats. Renal microvascular CYP4A and COX-2 protein levels were increased 2.3- and 17.0-fold, respectively, in obese Zucker rats. The protein expression of CYP2C11 and CYP2C23 was decreased 2.0-fold in renal microvessels isolated from obese Zucker rats when compared with lean Zucker rats. The urinary excretion rate of thromboxane B2 was increased significantly in obese Zucker as compared with lean Zucker rats (22.0 1.8 vs. 13.4 1.0 ng/d). Urinary albumin excretion, an index of kidney damage, was increased in the obese Zucker rat at this early age. Discussion: These results suggest that increased CYP4A and COX-2 protein levels and decreased CYP2C11 and CYP2C23 protein levels occur in association with microalbuminuria during the onset of obesity-related hypertension and type 2 diabetes.

Background A sedentary lifestyle is an independent risk factor for cardiovascular disease and exercise has been shown to ameliorate this risk. Inactivity is associated with a loss of muscle mass, which is also reversed with isometric exercise training. The relationship between muscle mass and vascular function is poorly defined. The aims of the current study were to determine whether increasing muscle mass by genetic deletion of myostatin, a negative regulator of muscle growth, can influence vascular function in mesenteric arteries from obese db/db mice. Methods and Results Myostatin expression was elevated in skeletal muscle of obese mice and associated with reduced muscle mass (30% to 50%). Myostatin deletion increased muscle mass in lean (40% to 60%) and obese (80% to 115%) mice through increased muscle fiber size ( P NO ) synthase inhibitor l ‐ NG ‐nitroarginine methyl ester ( l ‐ NAME) . Prostacyclin ( PGI 2 )‐ and endothelium‐derived hyperpolarizing factor ( EDHF)‐ mediated vasodilation were preserved in obese mice and unaffected by myostatin deletion. Reactive oxygen species) was elevated in the mesenteric endothelium of obese mice and down‐regulated by deletion of myostatin in obese mice. Impaired vasodilation in obese mice was improved by NADPH oxidase inhibitor ( GKT 136901). Treatment with sepiapterin, which increases levels of tetrahydrobiopterin, improved vasodilation in obese mice, an improvement blocked by l ‐ NAME . Conclusions Increasing muscle mass by genetic deletion of myostatin improves NO‐ , but not PGI 2 ‐ or EDHF‐ mediated vasodilation in obese mice; this vasodilation improvement is mediated by down‐regulation of superoxide.

Increases in muscle mass, as observed with exercise, are positive influences of cardiovascular health. Recent studies from our lab have shown the increase muscle mass via deletion of myostatin improves vasodilation but the underlying mechanisms are unknown. Improving insulin resistance has been shown to improve oxidant stress, specifically via expression of NOX1. Hypothesis: Increasing muscle mass by deletion of muscle growth negative regulator myostatin, improves vascular function in mesenteric arteries from obese db/db mice via reducing NOX-mediated oxidant stress in the endothelium. Myostatin deletion increased muscle mass in both lean (gastrocnemius 57.93%, gluteus maximus 60.95%) and obese mice (gastrocnemius 79.64%, gluteus maximus 112.32%). Fasting glucose, HbA1c and glucose tolerance are improved in obese myostatin null mice. Obese mice demonstrate superoxide-mediated impairment of ACh-induced vasodilation compared to lean mice. Deletion of myostatin in obese mice improved ACh-induced vasodilation...

Increases in shear stress promote coronary vasodilation by stimulating the production of nitric oxide (NO). Whether shear stress-induced NO production also limits vasoconstriction in the coronary microcirculation in vivo is unknown. Accordingly, we measured microvascular diameter and flow velocity in the beating heart along with estimated blood viscosity to calculate shear stress during vasoconstriction with endothelin or vasopressin. Measurements were repeated in the presence of N G-monomethyl-l-arginine (l-NMMA) to inhibit NO production and BQ-788 to block NO-linked endothelin type B receptors. BQ-788 did not augment steady-state constriction to endothelin, suggesting that NO production via activation of this receptor is inconsequential. l-NMMA potentiated constriction to both agonists, particularly in small arteries (inner diameter >120 μm). Shear stresses in small arteries were elevated during constriction and further elevated during constriction after l-NMMA. These observations suggest that NO production limits vasoconstriction in the coronary microcirculation and that the principal stimulus for this governance is elevated shear stress. The degree of shear stress moderation of constriction is heterogeneously distributed, with small arteries displaying a higher degree of shear stress regulation than arterioles. These results provide the strongest evidence to date that shear stress-mediated production of NO exerts a “braking” influence on constriction in the coronary microcirculation.

For over 50 years, it has been recognized that coronary blood flow is precisely matched to cardiac metabolism. The interactions which govern this matching remain unknown. In the current review, 3 specific aspects of coronary flow regulation will be discussed: Specialization of function in different microvascular domains, influence of cardiac region on microvascular function and the interactions of vasoactive agents in control of coronary blood flow. Each level of the coronary microcirculation is affected by different physical and chemical forces within the heart. These forces place special demands on these vessels and are in turn met by specialized vasodilator responses, including metabolic and flow-mediated vasodilation. Perfusion of the heart is also profoundly affected by the region perfused. The endocardium is affected by forces, notably cardiac contraction, in a different manner than the epicardium. Thus, the microcirculation has specialized to meet these demands. Finally, the factors determining microvascular tone appear to be coordinated such that the loss of any individual dilator, such as nitric oxide, can be compensated for by the increased contribution of another, such as adenosine. This interplay may serve to protect the heart from ischemia during the early phases of coronary vascular disease when individual dilators may be impaired.

Background —Physical forces, such as pressure and flow, are well known to affect vascular function in the coronary circulation. Increases in shear stress produce vasodilation in coronary arterioles in vitro, and constant-flow preparations suggest a role for shear stress–induced vasodilation during adjustments to metabolic demand in vivo. Hypothetically, the regulation of shear stress can be viewed as a negative feedback control scheme (increased velocity → increased shear → vasodilation → decreased velocity → shear normalized). Therefore, we hypothesized that shear stress would be at least partially regulated during conditions of elevated flow. Methods and Results —We used fluorescence microangiography to measure microvascular diameters and velocities in the coronary circulation in vivo and used these variables to calculate shear stress. Measurements were obtained under basal conditions, during maximal coronary blood flow, and after inhibition of NO synthase. Basal shear stress in the coronary circulation averaged 10 dyn/cm 2 in small arteries and 19 dyn/cm 2 in arterioles. Regulation of shear stress was observed in small arteries during adenosine-induced increases in coronary blood flow, but arterioles showed minimal regulation. NO synthase blockade had no effect on basal shear stress but completely abolished its regulation in small arteries during vasodilation. Conclusions —Our data provide the first quantitative estimates of microvascular shear stress in the coronary circulation. Moreover, our results suggest that shear stress in small coronary arteries is regulated by NO release from the endothelium.

Obesity is a major cause of hypertension, but links between the obese and hypertensive states remain incompletely understood. A major component of cardiovascular function in obese individuals is a state of sympathoactivation. A postulated mechanism of this sympathoactivation is the activation of specific classes of neurons commonly associated with metabolic control, which also affect sympathetic outflow to cardiovascular targets. One class of neurons is characterized by expression of melanocortin-4 receptors (MC4R) which are activated by metabolic signals such as leptin and insulin. In this study, we examined the effects of deletion of MC4R in a novel rat model. MC4R knockout (KO) rats are obese and profoundly insulin resistant without frank diabetes. Despite these conditions, MC4R KO rats are normotensive. Moderate bradycardia and significant increases in peripheral resistance were evident in MC4R KO rats. To determine if the dissociation between hypertension and obesity was associated with changes in vascular function, in vitro reactivity to vasoactive agents and in vivo reactivity to sympathetic blockade were examined. Vasodilator function was not affected by obesity in MC4R KO rats. Reactivity to phenylephrine was reduced, suggesting desensitization of adrenergic signaling. In response to ganglionic blockade with mecamylamine, blood pressure and hindlimb resistance fell more in MC4R KO rats, suggesting that sympathoactivation of the vascular was still evident, despite the absence of hypertension. These findings suggest that obesity causes sympathoactivation of the vasculature despite the absence of MC4R. Dissociation of obesity from hypertension in this model may reflect more renal mechanisms of blood pressure control.

Protein tyrosine phosphatase 1B (PTP1B), a molecular brake on leptin and insulin signaling pathways, is an important regulator of metabolic functions. Due to the close proximity between the signaling pathways regulating the metabolic and the cardiovascular systems, it has been hypothesized that PTP1B might have a role in the control of cardiovascular functions in the context of metabolic disorders. Evidence from population-based studies demonstrates that polymorphisms of the human PTP1B gene, PTPN1, predispose to both type II diabetes and cardiovascular disease, including hypertension and atherosclerosis. Consistent with these findings, genetic deletion of PTP1B in lean and obese animal models has proven to be protective against obesity-induced hypertension and endothelial dysfunction. While both human and animals studies mostly support indirect effects of PTP1B on the cardiovascular system via its control of metabolic function, evidence from in vitro studies suggests direct effects of PTP1B on endothelial and vascular smooth muscle cell integrity. Taken together these data identify PTP1B as a major regulator of cardiovascular function and suggest that manipulation of PTP1B expression and activity could provide a novel therapeutic approach to prevent obesity-related cardiovascular disease.

The effect of exogenous and endogenous adenosine in controlling coronary flow was determined using an axially distributed mathematical model of the myocardium to estimate interstitial adenosine concentration from coronary arterial and venous adenosine values. The left main coronary artery was perfused at constant pressure in closed-chest, anesthetized dogs, and exogenous adenosine was infused intracoronary to increase coronary flow. Basal interstitial adenosine was 92 nmol/L, just at the threshold for increasing coronary flow. An increase in interstitial adenosine concentration of only 62% was sufficient to increase coronary flow from 5% to 50% of maximal flow. The possible contribution of an endothelial dilator secondary to activation of adenosine receptors on endothelial cells was tested by comparing the response to exogenous intracoronary adenosine infusion with increases in endogenous adenosine produced by inhibition of adenosine kinase and adenosine deaminase. If adenosine increases coronary flow by an endothelial mechanism, then the interstitial ED 50 of exogenous adenosine would be lower than that for endogenous adenosine due to the postulated additional endothelial dilator. The interstitial ED 50 for exogenous adenosine was 156 nmol/L, not different from the endogenous ED 50 of 150 nmol/L. In conclusion, basal interstitial adenosine concentration is at the threshold of a remarkably steep dose-response curve for increasing coronary blood flow. No evidence was found for an endothelium-mediated vasodilator mechanism secondary to adenosine receptor activation of endothelial cells in vivo. The steep adenosine dose-response curve indicates that measurements of adenosine concentration should be interpreted with caution, because small changes in adenosine concentration cause large changes in coronary flow.

Insulin resistance is a powerful predictor of cardiovascular disease; however, the mechanistic link remains unclear. This study aims to determine if early cardiovascular changes associated with short‐term fructose feeding in the absence of obesity manifest as abnormal blood pressure control. Metabolic dysfunction was induced in Lean Zucker rats by short‐term high‐fructose feeding. Rats were implanted with telemetry devices for the measurement of mean arterial blood pressure (MAP) and subjected to air jet stress at 5 and 8 weeks after feeding. Additional animals were catheterized under anesthesia for the determination of MAP and blood flow responses in the hind limb and mesenteric vascular beds to intravenous injection of isoproterenol (0.001–0.5 μm), a β‐adrenergic agonist. Metabolic dysfunction in high‐fructose rats was not accompanied by changes in 24‐h MAP. Yet, animals fed a high‐fructose diet for 8 weeks exhibited a marked impairment in blood pressure recovery after air‐jet stress. Dose‐dependent decreases in MAP and peripheral blood flow in response to isoproterenol treatment were significantly attenuated in high‐fructose rats. These data suggest that impaired blood pressure recovery to acute mental stress precedes the onset of hypertension in the early stages of insulin resistance. Further, blunted responses to isoproterenol implicate β 2‐adrenergic sensitivity as a possible mechanism responsible for altered blood pressure control after short‐term high‐fructose feeding.

Although the anorexic effects of leptin are lost in obesity, leptin-mediated sympatho-activation is preserved. The cardiovascular consequences of leptin-mediated sympatho-activation in obesity are poorly understood. We tested the hypothesis that 32 weeks of high-fat diet (HFD) induces metabolic leptin resistance but preserves leptin-mediated sympatho-activation of the cardiovascular system. HFD in mice significantly increased body weight and plasma leptin concentrations but significantly reduced the anorexic effects of leptin. HFD increased heart rate, stroke volume, cardiac output, and plasma aldosterone levels but not blood pressure. As reflected by the contractile response to phenylephrine measured both in vivo and ex vivo, vascular adrenergic reactivity was reduced by HFD, suggesting that reductions in sympathetic tone to the periphery vasculature may mitigate sympatho-activation of the heart and the renin-angiotensin-aldosterone system. Tachyphylaxis was partially restored by symptho-inhibition and not present in ob/ob and db/db mice, despite obesity, arguing for a sympatho-mediated and leptin-specific mechanism. Although infusion of leptin in HFD mice had no effect on heart rate or blood pressure, it further increased aldosterone levels and further reduced vascular adrenergic tone in the absence of weight loss, indicating persistent leptin-mediated stimulation of the cardiovascular system in obesity. In conclusion, these data indicate that, despite metabolic leptin resistance, leptin-mediated stimulation of the heart, the vasculature, and aldosterone production persists in obesity. Blood pressure effects in response to leptin may be limited by a tachyphylactic response in the circulation, suggesting that failure of adrenergic desensitization may be a requisite step for hypertension in the context of obesity.

Obesity and diabetes are major risk factors for the development of vascular disease in the lower limbs. Previous studies have demonstrated reduced nitric oxide (NO)-mediated vasodilation, increased adrenergic constriction, and inward, atrophic remodeling in the limb circulation of obese Zucker rats, but the component of the "metabolic syndrome" driving these changes is unclear. Because insulin resistance precedes the state of frank diabetes, the current study hypothesized that insulin resistance independent of obesity induced by fructose feeding would impair microvascular function in the skeletal muscle circulation in lean Zucker rats (LZR). A 66% fructose diet impaired glucose tolerance and induced moderate insulin resistance with no changes in whole-body hemodynamics of anesthetized rats (FF-LZR), compared to control LZR. NO-mediated vasodilation of isolated gracilis arteries, assessed in vitro with acetylcholine and sodium nitroprusside, was reduced approximately 20% in FF-LZR vs. LZR. NO-independent cGMP-mediated vasodilation was unimpaired. Pretreatment of isolated vessels with the superoxide scavenger, tempol, improved responses to both vasodilators. Reactivity to adrenergic stimulation was unaltered in FF-LZR vs. LZR, although constriction to endothelin was increased. Structural and passive mechanical characteristics of isolated gracilis arteries were similar in both LZR and FF-LZR. Taken together, these findings indicate that moderate insulin resistance is sufficient to impair endothelial function in an oxidant-dependent manner in the rat hindlimb circulation. Other aspects of skeletal muscle vascular function documented in obese models, specifically adrenergic tone and inward remodeling, must reflect either severe insulin resistance or other aspects of obesity. The factors accounting for nonendothelial vasculopathies remain unknown.

Background— Cardiovascular disease is the leading cause of death for both men and women in the United States and the world. A profound pattern exists in the time of day at which the death occurs; it is in the morning, when the endothelium is most vulnerable and blood pressure surges, that stroke and heart attack most frequently happen. Although the molecular components of circadian rhythms rhythmically oscillate in blood vessels, evidence of a direct function for the “circadian clock” in the progression to vascular disease is lacking. Methods and Results— In the present study, we found increased pathological remodeling and vascular injury in mice with aberrant circadian rhythms, Bmal1-knockout and Clock mutant. In addition, naive aortas from Bmal1-knockout and Clock mutant mice exhibit endothelial dysfunction. Akt and subsequent nitric oxide signaling, a pathway critical to vascular function, was significantly attenuated in arteries from Bmal1-knockout mice. Conclusions— Our data reveal a new role for the circadian clock during chronic vascular responses that may be of significance in the progression of vascular disease.

1. In the present study, we determined the role of hypertension, oxidative stress and inflammation on kidney damage in a rodent model of obesity and diabetes. Hypertension was induced in male obese (db/db) mice and lean (db/m) mice by implantation of deoxycorticosterone acetate (DOCA) pellets and mice were allowed to drink water containing 1% salt. Mice were divided into six groups as follows: obese and lean control, obese and lean 1% salt (salt) and obese and lean DOCA plus 1% salt (DOCA-salt). 2. Blood pressure was significantly increased in lean and obese DOCA-salt groups relative to their respective controls; however, there was no difference in blood pressure between the lean and obese control and salt groups. Urinary 8-isoprostane was increased in obese control compared with lean control mice (1464 +/- 267 vs 493 +/- 53 pg/micromol creatinine, respectively) and this elevation was further increased in the obese DOCA-salt treated mice (2430 +/- 312 pg/micromol creatinine). Urinary monocyte chemoattractant protein-1 excretion and CD68-positive cells were also increased in both obese and lean DOCA-salt groups compared with their respective controls. Furthermore, DOCA-salt treatment increased collagen IV excretion in both obese and lean mice compared with controls, but there was no difference between obese and lean DOCA-salt groups. Urinary albumin excretion was significantly increased in the obese compared with the lean DOCA-salt mice (507 +/- 160 vs 202 +/- 48 microg/day, respectively). 3. These data suggest that obese DOCA-salt hypertensive mice exhibit greater renal injury than lean DOCA-salt hypertensive mice in a manner independent of blood pressure and that this renal injury is associated with obesity related pre-existing renal oxidative stress.

Adult obese Zucker rats (OZRs) have elevated sympathetic vasomotor tone and arterial pressure (AP) with blunted baroreflex-mediated changes in heart rate (HR) compared with adult lean Zucker rats (LZRs). The present study examined whether compromised cardiac baroreflexes are indicative of attenuated sympathetic responses. In addition, because juvenile OZRs have a normal mean AP, we determined whether baroreflexes are fully functional prior to hypertension. At 13 wk, adult OZRs had an elevated baseline mean AP compared with LZRs (137 ± 3 vs. 123 ± 5 mmHg, P < 0.05) under urethane anesthesia. Phenylephrine-induced increases in AP evoked smaller inhibitions of splanchnic sympathetic nerve activity (SNA) and HR in OZRs compared with LZRs. In addition, sympathoexcitatory responses to nitroprusside-induced hypotension were also blunted in OZRs. Sigmoid analysis revealed a decreased gain, a higher mean AP at the midpoint of the curve (AP50), and a reduced range of changes in SNA in OZRs. In contrast, at 7 wk of age, although juvenile OZRs weighed more than LZRs (313 ± 13 vs. 204 ± 4 g, P < 0.05), mean AP was comparable in both groups (122 ± 5 vs. 121 ± 4 mmHg, not significant). In these rats, rapid changes in AP evoked comparable changes in SNA and HR in OZRs and LZRs. Sigmoid analysis revealed that, although the gain of the reflex was blunted in OZRs ( P < 0.05), the mean AP50 and range of changes in SNA were comparable in OZRs and LZRs. Together, these data indicate that in adult OZRs, sympathetic responses to acute changes in AP are smaller than those observed in adult LZRs and that impairment of baroreceptor reflexes in OZR is not limited to the regulation of HR but extends to sympathetic vasomotor control. In addition, most of these deficits in baroreflex control of SNA develop in adulthood long after the onset of obesity and when other deficits in cardiovascular regulation are present.

Obesity is an emerging risk factor for renal dysfunction, but the mechanisms are poorly understood. Obese patients show heightened renal vasodilation to blockade of the renin-angiotensin system, suggesting deficits in vascular responses to angiotensin II (ANG II). This study tested the hypothesis that obesity augments renal vasoconstriction to ANG II. Lean (LZR), prediabetic obese (OZR), and nonobese fructose-fed Zucker rats (FF-LZR) were studied to determine the effects of obesity and insulin resistance on reactivity of blood pressure and renal blood flow to vasoconstrictors. OZR showed enlargement of the kidneys, elevated urine output, increased sodium intake, and decreased plasma renin activity (PRA) vs. LZR, and renal vasoconstriction to ANG II was augmented in OZR. Renal reactivity to norepinephrine and mesenteric vascular reactivity to ANG II were similar between LZR and OZR. Insulin-resistant FF-LZR had normal reactivity to ANG II, indicating the insulin resistance was an unlikely explanation for the changes observed in OZR. Four weeks on a low-sodium diet (0.08%) to raise PRA reduced reactivity to ANG II in OZR back to normal levels without effect on LZR. From these data, we conclude that in the prediabetic stages of obesity, a decrease in PRA is observed in Zucker rats that may lead to increased renal vascular reactivity to ANG II. This increased reactivity to ANG II may explain the elevated renal vasodilator effects observed in obese humans and provide insight into early changes in renal function that predispose to nephropathy in later stages of the disease.