Mercaptoacetate fails to block the feeding-inhibitory effect of the β3-adrenergic receptor agonist CGP 12177A

Peripherally administered β3-adrenergic receptor (β3-AR) agonists stimulate lipolysis and inhibit food intake. To test the hypothesis that this inhibition of feeding is due to a substrate-driven increase in hepatic fatty acid oxidation (FAO), we assessed the ability of the FAO inhibitor mercaptoacetate (MA) to reverse the feeding-inhibitory effect of the β3-AR agonist CGP 12177A (CGP). Adult male Sprague-Dawley rats received intraperitoneal injections of 1 mg/kg CGP, of 45.6 mg/kg MA, or of both drugs, and the effects on food intake, plasma free fatty acids (FFA), and plasma β-hydroxybutyrate (BHB), an indicator for hepatic FAO, were assessed. Control rats received saline injections. CGP significantly reduced food intake after 0.5 and 6 h and increased plasma FFA and BHB at 0.5 h, suggesting increased lipolysis and hepatic FAO. MA completely reversed the increase in plasma BHB and thus appeared to effectively abolish CGP's effect on hepatic FAO, but MA failed to affect CGP's feeding-inhibitory action. These findings do not support the hypothesis that the β3-AR agonist CGP inhibits feeding by enhancing hepatic FAO or ketogenesis. Although the β3-AR agonist CGP reduced saccharin intake in a one-bottle condition taste aversion test, it seems unlikely that the hypophagic effect of CGP is elicited by malaise.