Orlistat 120 mg appears to improve glycaemic control more than would be predicted by weight loss alone in overweight or obese patients with type 2 diabetes. Postulated mechanisms underlying this effect include an improvement of insulin sensitivity, a slower and incomplete digestion of dietary fat, reduction of postprandial plasma non-esterified fatty acids, decreased visceral adipose tissue, and stimulation of glucagon-like peptide-1 secretion in the lower small intestine.

To quantify the potential of brown adipose tissue as a target organ for glucose oxidation, O2 consumption and glucose metabolism in isolated rat brown adipocytes were measured in the presence and absence of insulin, by using the beta-agonists isoprenaline or Ro 16-8714 to stimulate thermogenesis. Basal metabolic rate (278 mumol of O2/h per g of lipid) was maximally stimulated with isoprenaline (20 nm) and Ro 16-8714 (20 microM) to 1633 and 1024 mumol of O2/h per g respectively, whereas insulin had no effect on O2 consumption. Total glucose uptake, derived from the sum of [U-14C]glucose incorporation into CO2 and total lipids and lactate release, was enhanced with insulin. Isoprenaline and Ro 16-8714 had no effect on insulin-induced glucose uptake, but promoted glucose oxidation while inhibiting insulin-dependent lipogenesis and lactate production. A maximal value for glucose oxidation was obtained under the combined action of Ro 16-8714 and insulin, which corresponded to an equivalent of 165 mumol of O2/h per g of lipid. This makes it clear that glucose is a minor substrate for isolated brown adipocytes, fuelling thermogenesis by a maximum of 16%.

AY 9944 [trans-1,4-bis(2-chlorobenzylaminomethyl) cyclohexane dihydrochloride] is an amphiphilic cationic molecule. This chemical is an established inhibitor of cholesterol synthesis and is teratogenic in rats. The mechanisms of this teratogenicity remain to be clarified. This study used cultured rat whole embryos to ascertain whether AY 9944 had a direct effect on embryos, or whether its action was indirect, via the maternal cholesterol metabolism. Four experimental conditions were investigated: (A) controls; (B) 10 day untreated embryos were cultured in serum of treated rats; (C) 10 day untreated embryos were cultured in serum containing added AY 9944 (0-1,000 micrograms/ml); and (D) 10 day embryos from females treated on day 4 of gestation were cultured in normal serum. In group B there was no growth retardation; some slight nonspecific abnormalities were not significant. In group C, direct addition of AY 9944 to culture medium retarded growth and differentiation in a dose-dependent manner. No malformation was observed, but histological examinations showed numerous areas of cell necrosis, especially in the CNS. In group D, not only was growth retardation observed, but also characteristic malformations of AY 9944 teratogenesis, including pituitary agenesis. These results show that AY 9944 teratogenicity is initiated prior to day 10.

Objective: To determine the effect of rimonabant on energy expenditure (O 2 consumption) in rats at different metabolic states and in cannabinoid CB1 receptor-deficient (CB1R À/À ) mice. Design: Animals were exposed to light-dark cycles and fed only during dark cycles. Rimonabant or vehicle was administered together with food (absorptive), following overnight feeding (postabsorptive) or following a whole day of no food (fasting). Indirect calorimetric measurements, physical activity and food intake were measured continuously. Results: Compared with vehicle-treated rats, rats administered 3 and 10 mg kg À1 rimonabant showed an 18 and 49% increase in O 2 consumption, respectively after 3 h. A second dose of rimonabant administered 9-14.5 h after the first one failed to affect O 2 consumption, suggesting the development of tolerance. Similarly, stereotypic behaviors and ambulatory activity increased following the first dose but these effects were not observed after the second dose. Respiratory quotients revealed no effect of rimonabant on rates of carbohydrate and fat oxidation. Analysis of the correlation between O 2 consumption and physical activity indicated that factors other than increased physical activity may contribute to the increase in O 2 consumption. Similar studies in mice demonstrated that wild type but not CB1R À/À mice showed a change in O 2 consumption and physical activity following rimonabant administration, suggesting that these effects are mediated by the cannabinoid CB1 receptor. Conclusion: Previous studies suggested that reduced food intake alone may not explain the weight reduction observed with rimonabant. Our studies suggest that rimonabant stimulates significant acute energy expenditure in non-obese rodents, which could not be completely accounted for by an increase in physical activity. However, with the observation that there is rapid development of tolerance, these results suggest that there may be additional mechanism(s) that lead to weight loss in these rodents.

Orlistat, a selective inhibitor of gastrointestinal lipases, was used to investigate triacylglycerol absorption. Using mice and a variety of emulsified dietary lipids we found that the absorption of radiolabelled tripalmitin (containing the fatty acid 16: 0), but not of triolein (18 : ln-9) or tri-y-linolenin (18:3n-6), was incomplete from meals rich in esterified palmitate. Further, the absorption of radiolabelled triq-linolenin, from both saturated and unsaturated dietary triacylglycerols, was 1.3-to 2 fold more potently inhibited by orlistat than that of triolein and tripalmitin. These radiolabelled triacylglycerols, which have the same fatty acid in all three positions, may not always be accurate markers of the absorption of dietary triacylglycerols. Orlistat was more effective at inhibiting the absorption of radiolabelled triacylglycerols with which it was codissolved than those added separately, which indicates that equilibration between lipid phases in the stomach may not always be complete. The saturation of the dietary lipid had little or no effect on the potency of orlistat. Orlistat provides a novel approach for studying the role of triacylglycerol hydrolysis in the overall process of triacylglycerol absorption.Lipase inhibitor: Triacylglycerol: Absorption: Mice