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We investigated the effects of chronic treatment with the CB1 receptor antagonist rimonabant (10 mg/kg/day p.o. for 10 weeks) in mice with established obesity (5-month high-fat diet). Untreated obese mice showed a weight gain of 46% (45.0 +/- 0.6 g vs. 30.8 +/- 0.5 g) compared with age-matched animals fed a standard diet. Rimonabant treatment, commencing after 5-month high-fat diet, produced a marked and sustained decrease in body weight (34.5 +/- 0.8 g vs. 47.2 +/- 0.5 g in the high-fat vehicle group, p < 0.001). The anti-obesity effect of rimonabant was similar to that obtained by switching obese mice from high-fat diet to standard laboratory diet during 10 weeks (final weight 33.7 +/- 0.6 g) and was associated with only transient (14 days) reduction in energy intake. Serum leptin, insulin and glucose levels were markedly elevated in obese animals. Rimonabant treatment significantly reduced these elevations (leptin -81%, insulin -78%, glucose -67%, p < 0.001 in all cases vs. high-fat vehicle group). In addition, rimonabant treatment modestly but significantly increased serum adiponectin levels (+18%, p < 0.05 vs. high-fat vehicle group). Obese mice demonstrated abnormal serum lipid profiles. Although rimonabant did not modify high-density lipoprotein cholesterol (HDLc) and had modest effects on total cholesterol, it significantly reduced triglycerides and low-density lipoprotein cholesterol (LDLc) and, notably, increased the HDLc/LDLc ratio (12.4 +/- 0.8 vs. 7.9 +/- 0.2 in high-fat vehicle group, p < 0.001). Therefore, in a model of established obesity, chronic rimonabant treatment produces a marked and sustained decrease in body weight (equivalent to that achieved by dietary change) which is associated with favourable modifications in serum biochemical and lipid profiles.

Obesity is a major risk factor in the development of chronic renal failure. Rimonabant, a cannabinoid CB1 receptor antagonist, improves body weight and metabolic disorders; however, its effect on mortality and chronic renal failure associated with obesity is unknown. Obese Zucker rats received either rimonabant or vehicle for 12 months and were compared to a pair-fed but untreated group of obese rats. Mortality in the obese rats was significantly reduced by rimonabant along with a sustained decrease in body weight, transient reduction in food intake, and an increase in plasma adiponectin. This was associated with significant reduction in plasma total cholesterol, low-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio, triglycerides, glucose, norepinephrine, plasminogen activator inhibitor 1, and preservation of pancreatic weight and beta-cell mass index. The cannabinoid antagonist attenuated the increase in proteinuria, urinary N-acetylglucosaminidase excretion, plasma creatinine, and urea nitrogen levels while improving creatinine clearance. Renal hypertrophy along with glomerular and tubulointerstitial lesions were reduced by rimonabant. Although the drug did not modify hemodynamics, it normalized the pressor response to angiotensin II. Our study suggests that in a rat model of chronic renal failure due to obesity, rimonabant preserves renal function and increases survival.

The peptide hormone ghrelin is the endogenous ligand for the type 1a growth hormone secretagogue receptor (GHS-R1a) and the only currently known circulating appetite stimulant. GHS-R1a antagonism has therefore been proposed as a potential approach for obesity treatment. More recently, ghrelin has been recognized to also play a role in controlling glucose-induced insulin secretion, which suggests another possible benefit for a GHS-R1a antagonist, namely, the role as an insulin secretagogue with potential value for diabetes treatment. In our laboratories, piperidine-substituted quinazolinone derivatives were identified as a new class of small-molecule GHS-R1a antagonists. Starting from an agonist with poor oral bioavailability, optimization led to potent, selective, and orally bioavailable antagonists. In vivo efficacy evaluation of selected compounds revealed suppression of food intake and body weight reduction as well as glucose-lowering effects mediated by glucose-dependent insulin secretion.

1 The antagonist dynamics of suramin were investigated at P21-receptors in isolated rings of endothelium-denuded ear artery from New Zealand White (NZW) rabbits. 2 a,,8-Methylene adenosine 5'-triphosphate (ATP) concentration-effect curves were constructed cumulatively in a paired curve design in the absence and presence of increasing concentrations of suramin, incubated for 45 min. The slope of the resulting Schild plot was significantly greater than unity (1.50 0.08). 3 Assuming that slow equilibration by suramin explains the steep Schild plot, further experiments were conducted using short (15 min) and long (3 h) incubation times. The resulting Schild plot slopes were 1.66 + 0.36 and 1.06 + 0.13 respectively confirming the assumption. However, after 3 h incubation, suramin also caused depression of a,,-methylene ATP curves. 4 In an attempt to minimize the depressant effect of suramin, a kinetic study was designed to calculate the minimum incubation times for each concentration of suramin used in the Schild analysis to achieve effectively complete equilibrium. Theoretically fractional occupancy for the antagonist is given by (r -1)/ r, where r is the dose-ratio. A plot of (r -1)/r against time allowed the apparent 'on' and 'off' rate constants to be calculated. 5 With the resulting rate constant estimates, an optimised antagonism study was carried out in which incubation times were chosen such that >95% occupancy by suramin could be achieved without agonist curve depression at each concentration of suramin used. 6 Under these conditions, suramin fulfilled all criteria for simple competition: parallel rightward displacement of a.B-methylene ATP curves and a Schild plot slope of unity (1.00 + 0.09). The resulting pKB estimate was 4.79 + 0.05. This estimate of affinity was shown to be independent of the agonist used in another experiment in which L-fy-methylene ATP was employed (pKB = 5.17).7 Under the same conditions, suramin was found to have no effect on KCI-induced contractions and only slight effects on phenylephrine-and histamine-induced responses. 8 This analysis provides the first evidence that suramin is a genuine competitive P21-receptor antagonist.

A marked increase in plasma TNF-alpha has been described in patients with chronic heart failure (CHF). Nevertheless, little is known about the direct role of this cytokine early after myocardial infarction (MI) and its possible effects on the subsequent development of CHF. Wistar rats were subjected to permanent in vivo coronary artery ligation. At 5, 7, and 9 days after MI, cardiac function, passive compliance of the left ventricle (LV), and cardiac geometry were evaluated. The same model was used to perform pharmacological studies 7 days and 10 wk after MI in rats treated with monomeric recombinant human soluble TNF-alpha receptor type II (sTNF-RII, 40 microg/kg iv) or a placebo on day 3. Maximal alterations of cardiac function and geometry occurred 7 days after MI, which correlated chronologically with a peak of cardiac and serum TNF-alpha, as shown by immunohistochemistry and ELISA, respectively. sTNF-RII improved LV end-diastolic pressure under basal conditions and after volume overload 7 days and 10 wk after MI. Moreover, a significant leftward shift of the pressure-volume curve in the sTNF-RII-treated group 7 days after MI indicated a preservation of LV volume. Infarct expansion index was also significantly improved by sTNF-RII 7 days after MI (P < 0.01). Nevertheless, 10 wk after MI, geometric indexes and passive pressure-volume curves were not significantly improved by the treatment. In conclusion, TNF-alpha plays a major role in cardiac alterations 7 days after MI in rats and contributes to hemodynamic derangement, but not to cardiac remodeling, in subsequent CHF.

1 Dopexamine is an agonist at peripheral dopamine receptors and at P2-adrenoceptors.2 Dopexamine has approximately one-third the potency of dopamine in stimulating the vascular DA,-receptor in the dog, resulting in a fall in renal vascular resistance of 20% at 2.3 x 10-8 mol kg-' (i.a.). 3 Prejunctional DA2-receptors are also stimulated by dopexamine, resulting in a reduction of neurogenic vasoconstriction in the rabbit isolated ear artery (IC5o of 1.15 x 10-6 M) and of neurogenic tachycardia in the cat (ID5o of 5.4 x 10-8mol kg-', i.v.), with a potency six and four times less respectively than that of dopamine. 4 By contrast, dopexamine is approximately 60 times more potent than dopamine as an agonist at the P2-adrenoceptor of the guinea-pig isolated tracheal chain, with an EC50 of 1.5 x 10-6 M.5 Both dopexamine and dopamine are weak agonists at the guinea-pig atrial P,-adrenoceptor over the concentration range 10-7 to 10-4 M, but dopexamine has an intrinsic activity ofonly 0.16 relative to dopamine. 6 Dopexamine does not stimulate postjunctional a,-or M2-adrenoceptors in the canine isolated saphenous vein, whereas dopamine is an agonist, approximately 120 times less potent than noradrenaline. 7 Unlike dopamine and salbutamol, dopexamine does not cause arrhythmias in the guinea-pig isolated perfused heart at doses of up to 10 5mol, which is a thousand times the minimum cardiostimulant dose.8 The combination of agonist properties at peripheral dopamine receptors and at V2-adrenoceptors, with little or no activity at a-and P3-adrenoceptors gives dopexamine a novel pharmacological profile. This may confer advantages over dopamine in the treatment of acute heart failure.

Mitochondrial dysfunction has been identified as a possible early event in ischemia-reperfusion damage. The peripheral benzodiazepine receptor, a mitochondrial inner membrane protein, has already been proposed to play a role in mitochondrial regulation, although its exact function remains unclear. The aim of this work was to determine the role of peripheral benzodiazepine receptor in ischemia-reperfusion injury and to test the potential beneficial effect of a novel potent peripheral benzodiazepine receptor ligand, 7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino [4,5-b]indole-1-acetamide (SSR180575). To characterize and link the mitochondrial, cellular, and cardiac consequences of ischemia-reperfusion, we examined the effects of SSR180575 in several in vitro and in vivo models of oxidative stress. Hydrogen peroxide decreased mitochondrial membrane potential, reduced oxidative phosphorylation capacities, and caused cytochrome c release, caspase 3 activation, and DNA fragmentation. SSR180575 (100 nM-1 M) prevented all these effects. In perfused rat hearts, SSR180575 administered in vitro (100 nM-1 M) or by oral pretreatment (3-30 mg/kg) greatly reduced the contractile dysfunction associated with ischemia-reperfusion. Furthermore, in anesthetized rats, SSR180575 (3-30 mg/kg p.o.) produced significant reductions in infarct size after coronary artery occlusion/reperfusion. In conclusion, we have demonstrated that peripheral benzodiazepine receptor play a major role in the regulation of cardiac ischemia-reperfusion injury and that SSR180575, a novel peripheral benzodiazepine receptor ligand, is of potential interest in these indications.