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Aim: This study aimed to chart the time course and durability of the effects of rosiglitazone, a potent thiazolidinedione-based peroxisome proliferator-activated receptor γ agonist, on hepatic steatosis and intramyocellular lipid in an animal model of obesity, the Zucker Fatty (ZF) rat. Methods and Results: Rosiglitazone (3 mg/kg/day p.o.) significantly reduced both liver fat content (by 59%; p

Hindlimbs of mature age obese fa/fa Zucker rats were perfused and found to be markedly insulin-resistant when compared to the hindlimbs of age-matched lean Fa/? animals. Hindlimb analysis also showed a greater content of fat and a lower content of muscle in the obese. Treatment of the obese animals for 7 days with the thiazolidinedione, BRL 49653 (3 mumol/kg/day) significantly decreased the insulin resistance of the hindlimb and significantly increased the rate of weight gain in the whole rat. However, the decreased insulin resistance due to BRL 49653 could not be accounted for by an increase in the proportion of hindlimb muscle to fat or by an increase in the hindlimb muscle mass perfused.

Thiazolidinediones (TZDs) are relatively new agents for the treatment of type 2 diabetes. They act as agonists at the PPAR-gamma nuclear receptor and their therapeutic effects include decreased insulin resistance and hyperglycaemia, an improved plasma lipid, inflammation and pro-coagulant profile, and amelioration of hypertension, microalbuminuria and hepatic steatosis. The most common side effects of TZDs include weight gain and oedema, with occasional reports of congestive heart failure (CHF). This review discusses the benefit-risk profile of TZDs in treating patients with type 2 diabetes, with particular reference to the heart. To provide context, we explore briefly the epidemiology and pathophysiology of heart failure in patients with type 2 diabetes, touch on the association of heart disease and cardiovascular mortality with antihyperglycaemic treatment modalities other than TZDs, and then focus on the effects of TZDs on the heart, cardiovascular risk factors and outcomes. We describe the cluster of host factors, which seems to predispose patients with type 2 diabetes to TZD-induced or TZD-exacerbated oedema and CHF and then provide an overview of the putative mechanisms of these TZD-related side effects. We also propose that certain diuretics (amiloride and spironolactone), by targeting the distal nephron that expresses PPARgamma in collecting duct cells, might be of benefit in ameliorating the fluid retention and oedema associated with TZDs.

Aim: Consumption of a palatable diet can induce hyperphagia, leading to weight gain (dietary obesity) and insulin resistance in rats. Thiazolidinediones (TZDs) can also induce hyperphagia in rats but conversely have an insulin-sensitizing effect. The aim of this study was to investigate whether preventing TZD-induced hyperphagia (i.e. energy restriction) in dietary obese (DIO) rats would enhance the insulin-sensitizing effects of treatment at a therapeutic dose; and, within this paradigm, to produce an original survey of candidate TZD-gene targets in the clinically relevant visceral white adipose tissue (WAT) depot. Methods: DIO rats that were either freely fed or energy restricted (i.e. pair-fed to the level of untreated controls) were treated with rosiglitazone maleate (RSG; 3 mg/kg/day) for 2 weeks, the restricted group controlling for treatment-induced hyperphagia and weight gain. The outcome measures were circulating concentrations of various biochemical markers of insulin resistance, and gene expression was measured in epididymal WAT. Results: In both freely fed and pair-fed groups, compared to untreated DIO controls, RSG reduced plasma levels of insulin (−29% and −43%; p < 0.05 and p < 0.001, respectively), free fatty acids (FFAs; −45% and −48%; p < 0.01 and p < 0.001, respectively) and triglycerides (TGs; −63% and −72%; both p < 0.001), reflected in improved insulin sensitivity, as measured by homeostasis model assessment (−29% and −43%; p < 0.01 and p < 0.0001). RSG also increased the expression of the fatty acid transport/synthesis genes, fatty acid transport protein (2.4–3.2-fold), epidermal fatty acid–binding protein (FABP; 1.7–2.0-fold), heart FABP (25–29-fold) and fatty acid synthase (2.3–2.9-fold; all p < 0.05) in both groups. Adipocyte FABP was also increased by RSG treatment, but only in combination with energy restriction (1.52-fold; p < 0.05) as was hexokinase II expression (p < 0.001). In contrast, the drug had no effect on expression of several genes associated with lipolysis. Although obesity-induced hyperleptinaemia was normalized only in the energy-restricted group, leptin messenger RNA (mRNA) expression was reduced in both treated groups (all p < 0.01). Resistin and tumour necrosis factor-alpha expression was also reduced, though in the latter case, only with energy restriction (p < 0.05). Other adipokines were unaffected by RSG treatment. Conclusion: Our results clearly show that energy restriction enhances the therapeutic efficacy of TZDs and suggest that this occurs, at least in part, through a modulatory effect on gene expression in visceral WAT. These findings improve our understanding of the underlying mechanistic basis for the clinical usefulness of dietary restriction as an adjunct to TZD therapy in type 2 diabetes.

This study aimed to chart the time course and durability of the effects of rosiglitazone, a potent thiazolidinedione-based peroxisome proliferator-activated receptor gamma agonist, on hepatic steatosis and intramyocellular lipid in an animal model of obesity, the Zucker Fatty (ZF) rat.Rosiglitazone (3 mg/kg/day p.o.) significantly reduced both liver fat content (by 59%; p0.05) and size (11.5%; p0.05) in male ZF rats that received between 3 days and 1 week of treatment, and these reductions were maintained for at least 12 weeks. Liver fat content measured by magnetic resonance spectroscopy (MRS) correlated closely and positively with plasma insulin levels (reduced by 89% within a week, r = 0.8) and with postmortem histological fat fractional volume (r = 0.89). Similarly, liver volume measured by magnetic resonance imaging (MRI) correlated closely with postmortem wet weight (r = 0.99). MRS also showed, and numbers of lipid vacuoles counted in transmission electron micrographs confirmed, that rosiglitazone significantly reduced the elevated intramyocellular lipid seen in ZF rat skeletal muscle by at least 40% (p0.05).Localized MRS and MRI showed that rosiglitazone reversed the hepatic steatosis, hepatomegaly and intramyocellular lipid, characteristic of the ZF rat, an animal model of obesity.

To clarify whether centrally delivered leptin can access the circulation and to determine to what extent the effects of i.c.v. h-leptin and m-leptin on body weight and plasma corticosterone are due to reduced food intake.Male lean Zucker rats were infused i.c.v. with recombinant m-leptin or h-leptin (42 microg/day) for 7 days. Terminal plasma leptin levels were measured using selective r-leptin, m-leptin and h-leptin RIA. Plasma h-leptin and corticosterone levels were determined on days 0, 2, 4 and 6 of h-leptin infusion. Interscapular brown adipose tissue weight and UCP-1 mRNA expression (an indicator of thermogenic capacity) were also measured.The terminal plasma leptin level was elevated (from 2.2 +/- 0.4 to 42.7 +/- 20.2 ng/ml) in the h-leptin-treated lean rats to levels similar to those in vehicle i.c.v. infused fa/fa rats (72.2 +/- 4.7 ng/ml), but this was only detectable when the h-leptin radioimmunoabsorbent assay (RIA) was used. Further, both m-leptin and h-leptin infusions in lean rats elevated terminal plasma corticosterone (352 +/- 37 and 389 +/- 55 ng/ml, respectively) to levels similar to those in i.c.v. rats (386 +/- 62 ng/ml), whereas diet-restriction by pair-feeding, with the h-leptin group, in lean rats had no effect (207 +/- 45 ng/ml). The increase in plasma corticosterone level coincided with the maximum hypophagic effects of leptin and preceded the appearance and sustained elevation of exogenous human leptin in the circulation. Both m-leptin and h-leptin i.c.v. infusion reduced body weight gain (3% and 4%, respectively, compared to pair-fed group) and increased UCP-1 expression (11-fold and 16-fold, respectively) in lean rats. However, h-leptin elicited an earlier effect than m-leptin on body weight, manifested as an earlier reduction in food intake and greater increase in UCP-1 expression. h-Leptin also elicited a greater reduction in body weight gain than did pair-feeding.Intracerebroventricular-infused m-leptin or h-leptin was detected in the circulation. Furthermore, m-leptin and h-leptin elevated plasma corticosterone levels and h-leptin caused some weight loss in lean rats independently of its suppression of food intake. The elevation of corticosterone levels in the lean rats may be a mechanism whereby they resist excessive weight loss in response to leptin.

We investigated whether pair-feeding to prevent hyperphagia would potentiate the insulin-sensitizing effect of rosiglitazone in chow-fed and insulin-resistant dietary obese rats, and studied the role of leptin and hypothalamic neuropeptide Y as mediators of weight gain during treatment.Dietary obese and chow-fed rats (575 +/- 10 vs. 536 +/- 7 g; p0.01) were given rosiglitazone (30 mg/kg p.o.) or vehicle daily for 14 days.Energy intake and weight gain were greater in rosiglitazone-treated ad-lib-fed rats (body weight: chow + 24 +/- 2 g, rosiglitazone-treated + 55 +/- 2 g, p0.001; dietary obese + 34 +/- 2 g, rosiglitazone-treated + 74 +/- 7 g, p0.001). Half of each rosiglitazone-treated group were pair-fed to vehicle-treated controls. Rosiglitazone normalized circulating free fatty acids (FFAs) and insulin sensitivity in dietary obese rats (homeostasis model assessment (HOMA): chow-fed controls, 3.9 +/- 0.3; dietary obese controls, 6.7 +/- 0.7; rosiglitazone-treated, ad lib-fed dietary obese, 4.2 +/- 0.5; both p0.01). Insulin sensitivity improved further with pair-feeding (HOMA: 2.9 +/- 0.4; p0.05 vs. rosiglitazone-treated, ad lib-fed dietary obese), despite unchanged FFAs. Qualitatively similar findings were made in chow-fed rats. Pair-feeding prevented rosiglitazone-related weight gain in chow-fed, but not dietary obese rats (body weight: + 49 +/- 5 g, p0.001 vs. untreated dietary obese controls). Adipose tissue OB mRNA was elevated in dietary obese rats, reduced 49% (p0.01) by rosiglitazone treatment, and further (by 16%) with pair-feeding (p0.0001). Plasma leptin, however, only fell in the pair-fed group. Hypothalamic neuropeptide Y mRNA was unchanged throughout, suggesting that weight gain associated with high-dose rosiglitazone treatment is independent of hypothalamic neuropeptide Y.Food restriction potentiates the insulin-sensitizing effect of rosiglitazone in rats, and this effect is independent of a fall in FFAs.

The evolution of diabetes in the male leptin receptor-deficient (fa/fa) Zucker diabetic fatty (ZDF) rat is associated with disruption of normal islet architecture, beta-cell degranulation, and increased beta-cell death. It is unknown whether these changes precede or develop as a result of the increasing plasma glucose, or whether the increased beta-cell death can be prevented. Early intervention with thiazolidinediones prevents disruption of the islet architecture. To determine the specific effects of rosiglitazone (RSG) on beta-cell mass dynamics, male fa/fa (obese) and +/fa or +/+ (lean) rats age 6 weeks were fed either chow (control group [CN]) or chow mixed with rosiglitazone (RSG group) at a dosage of 10 micromol. kg(-1) body wt.day(-1). Rats were killed after 0, 2, 4, 6, or 10 weeks of treatment (at age 6, 8, 10, 12, or 16 weeks). Plasma glucose increased from 8.9 +/- 0.4 mmol/l at 0 weeks to 34.2 +/- 1.8 mmol/l (P = 0.0001) at 6 weeks of treatment in obese CN rats and fell from 8.0 +/- 0.3 to 6.3 +/- 0.4 mmol/l in obese RSG rats (P = 0.02). beta-cell mass fell by 51% from 2 to 6 weeks of treatment (ages 8-12 weeks) in obese CN rats (6.9 +/- 0.9 to 3.4 +/- 0.5 mg; P0.05), whereas beta-cell mass was unchanged in obese RSG rats. At 10 weeks of treatment (age 16 weeks), beta-cell mass in obese CN rats was only 56% of that of obese RSG rats (4.4 +/- 0.4 vs. 7.8 +/- 0.3 mg, respectively; P = 0.0001). The beta-cell replication rate fell from a baseline value of 0.95 +/- 0.12% in lean rats and 0.94 +/- 0.07% in obese rats (at 0 weeks) to approximately 0.3-0.5% in all groups by 6 weeks of treatment (age 12 weeks). After 10 weeks of treatment, beta-cell replication was higher in obese RSG rats than in CN rats (0.59 +/- 0.14 vs. 0.28 +/- 0.05%, respectively; P0.02). Application of our mass balance model of beta-cell turnover indicated that net beta-cell death was fivefold higher in obese CN rats as compared with RSG rats after 6 weeks of treatment (age 12 weeks). The increase in beta-cell death in obese CN rats during the 6-week observation period was well correlated with the increase in plasma glucose (r2 = 0.90, P0.0001). These results suggest that the development of hyperglycemia in ZDF rats is concomitant with increasing net beta-cell death. beta-cell proliferation compensates for the increased beta-cell loss at a time when plasma glucose is moderately elevated, but compensation ultimately fails and the plasma glucose levels increase beyond approximately 20 mmol/l. Treatment with rosiglitazone, previously shown to reduce insulin resistance, prevents the loss of beta-cell mass in obese ZDF rats by maintaining beta-cell proliferation and preventing increased net beta-cell death.

1. The blood glucose-lowering efficacy of rosiglitazone (RSG) and the mechanisms of associated weight gain were determined in dietary obese rats (DIOs). DIO and chow-fed rats received RSG 0.3-30 mg kg-1 daily for 21 days. 2. In DIOs, plasma glucose and insulin concentrations were reduced by RSG at dosages of 3 and 10 mg kg-1, respectively. Homeostasis model assessment (HOMA) indicated the threshold for a reduction of insulin resistance was 1 mg kg-1. Neither glucose nor insulin levels were affected by treatment in chow-fed rats. 3. RSG 0.3 mg kg-1 lowered free fatty acids (FFAs) in DIOs, whereas for plasma triglycerides (TGs), the threshold was 3 mg kg-1. By contrast, the threshold for reducing packed red cell volume (PCV) and increasing cardiac mass was 10 mg kg-1. Thus, the therapeutic index for RSG in DIOs was3 andor = 10. 4. Energy intake and weight gain increased in treated DIOs (by 20% and 50 g, at 30 mg kg-1) and chow-fed rats (by 25% and 35 g, at 30 mg kg-1). In DIOs, these increases coincided with falls in plasma leptin (40% lower at 30 mg kg-1) and insulin (43% lower at 30 mg kg-1). By contrast, in chow-fed rats, weight gain and hyperphagia occurred without changes in either leptin or insulin. However, reductions in FFAs below 0.4 - 0.3 mM were associated with hyperphagia and weight gain in DIO and chow-fed rats. 5. We conclude that increased energy intake and body weight did not attenuate the improved metabolism evoked by RSG in DIO rats, and that insulin action was enhanced at a dose3 fold below the threshold for causing haemodilution and cardiac hypertrophy in DIO rats.

BRL 49653 (rosiglitazone) and troglitazone are thiazolidinedione insulin-sensitizing agents, which are undergoing clinical evaluation as treatments for NIDDM. Potential side effects of thiazolidinediones include edema and hemodilution. Although the underlying mechanisms are presently unclear, animal and human studies have demonstrated a vasodilator action of troglitazone, which could in theory cause fluid retention. This in vitro study compared the direct vasodilator effects of troglitazone and BRL 49653 in small arteries (n = 44) from human subcutaneous fat. In arterial rings with a functioning endothelium and preconstricted with norepinephrine (NE; 6 micromol/l), troglitazone (n = 22 vessels), but not BRL 49653 (1-100 micromol/l), caused a concentration-related relaxation (69.4 +/- 5.2% at 100 micromol/l; P < 0.01). In the presence of indomethacin (IM; 10 micromol/l; n = 12), this vasorelaxant effect of troglitazone was abolished (P < 0.01 vs. troglitazone alone) and replaced by enhanced vasoconstriction (58.5 +/- 39.5% over the NE baseline) similar in magnitude to that produced by troglitazone vehicle (ethanol) alone (n = 16; NS vs. ethanol vehicle). By contrast, BRL 49653 (100 micromol/l; n = 22) and an equivalent volume of ethanol alone (n = 12) caused similar degrees of vasoconstriction (18.7 +/- 14.6 and 22.5 +/- 8.0%, respectively; NS). In the presence of IM (10 micromol/l; n = 10), the vasoconstrictor effect of BRL 49653 was enhanced (41.5 +/- 14.4%), although not significantly (NS vs. BRL 49653 alone or ethanol alone). Additional studies in Wistar rat arteries showed a similar vasodilator effect of troglitazone that was not inhibited by L-NAME (100 micromol/l). The alpha-tocopherol moiety alone had no vasorelaxant effect at concentrations up to 300 micromol/l. Thus, in human arterial resistance vessels in vitro, BRL 49653 does not possess the direct, IM-sensitive vasorelaxant action of troglitazone. This vasodilation could, in theory, permit transmission of systemic pressure to the capillary bed.

1. Insulin resistance is associated with hypertension but the underlying mechanism is unclear. We tested the hypothesis that insulin-induced vasodilatation is impaired in insulin-resistant obese Zucker rats. We studied mesenteric artery (≈ 220 μm diameter) function before the development of hypertension in 3-month old obese Zucker rats and age-matched lean rats. 2. In vessels from lean rats, insulin at concentrations of 50, 500 and 5000 m-units/l attenuated the constriction in response to noradrenaline (50 m-units/l: 8 ± 3%, P < 0.05; 500 m-units/l: 13 ± 3%, P < 0.02; 5000 m-units/l: 13 ± 2%, P < 0.02). 3. Vessels from obese rats failed to show any such response to insulin (2 ± 6% increase in maximal tension with 5000 m-units/l; not significant), both in the presence and absence of l-arginine (3 mmol/l). 4. Vessels from obese rats showed slight but significant impairment in the vasodilator response to acetylcholine (5 × 10−8−10−4 mol/l) (obese: 64.1 ± 3.7% relaxation; lean: 77.3 ± 3.7% relaxation; P < 0.05); however, relaxation in response to A23187 was not significantly different between the phenotypes (obese: 81.3 ± 10.6% relaxation; lean: 79.1 ± 9.7% relaxation; not significant). 5. Systolic blood pressure was not significantly different in lean (126 ± 8 mmHg) and obese (127 ± 7 mmHg) rats at the time of study (not significant). 6. We conclude that insulin-induced attenuation of noradrenaline-mediated vasoconstriction is impaired in the obese Zucker rat and that this defect precedes and therefore could contribute to the development of hypertension in this insulin-resistant model. The defect in insulin action could reside in the endothelial generation of nitric oxide, as endothelial function is also abnormal.

The present studies describe the blood pressure lowering, and some other haemodynamic effects, of the potassium channel activator, BRL 38227 ((-) enantiomer of cromakalim, CAS 94470-67-4) in various animal models. BRL 38227 was a potent antihypertensive agent following oral administration to conscious spontaneously hypertensive rats, SHR, (0.038, 0.075 and 0.15 mg/kg), renal hypertensive cats (0.035 and 0.05 mg/kg) and renal hypertensive dogs (0.05 and 0.1 mg/kg). The (+) enantiomer of cromakalim (BRL 38226) was without effect on blood pressure in the conscious rat and cat confirming the stereospecific mode of action of this potassium channel activator. Tachycardia accompanied the antihypertensive effect of BRL 38227 in these models and in the rat this effect could be abolished by pretreatment with atenolol (conscious SHR), diltiazem, verapamil, propranolol and alinidine (anaesthetised rats). In addition to reflex tachycardia, BRL 38227 also increased plasma renin activity and aldosterone levels in the conscious renal hypertensive cat. In both the anaesthetised normotensive cat (0.001 mg/kg/min i.v.) and dog (0.0025 to 0.02 mg/kg i.v.) BRL 38227 lowered blood pressure and total peripheral resistance while increasing cardiac output via increased heart rate and stroke volume in the cat and via increased heart rate alone in the dog. BRL 38227 reduced renal vascular resistance in both conscious (0.01, 0.015 and 0.02 mg/kg p.o.) and anaesthetised (0.001 mg/kg/min i.v.) cats and the effect was maintained despite marked reductions in blood pressure. In the anaesthetised dog, BRL 38227 was a potent coronary arterial dilator and this effect was also maintained in the face of marked blood pressure lowering activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The antihypertensive effects of Clonidine (0.15 mg kg−1, i.p.) were studied in conscious DOCA/saline hypertensive rats having chronically implanted arterial cannulae. The response to Clonidine was markedly reduced by simultaneously administered desipramine (3 mg kg−1, i.p.), antagonized dose-dependently by piperoxan (2–10 mg kg−1, i.v.) and prevented by pretreatment with phentolamine (0.2 mg, i.c.v.). Pretreatment with 6-hydroxydopamine (3 × 250 μg, i.c.v.), halo-peridol (1 mg kg−1, i.p.), p-chloro-N-methylamphetamine (3.5 mg kg−1, i.p.) or 5, 6-dihydroxytryptamine (50 μg and 25 μg, i.c.v.) did not significantly modify the antihypertensive response. It is concluded that the antihypertensive response to Clonidine is mediated via stimulation of central α-adrenoceptors and is independent of central dopaminergic receptors and intact central serotoninergic neurons. The necessity for intact central noradrenergic neurons remains uncertain.