Beta-adrenergic-mediated inhibition of feeding by mercaptoacetate in food-deprived rats.

This study investigated the effect of intraperitoneal (IP) injections of the fatty acid oxidation (FAO) inhibitor mercaptoacetate (MA, 45.6 mg/kg) on feeding in food-deprived rats. As previously, MA significantly stimulated feeding in ad libitum-fed rats. MA, however, reduced feeding in 18 and 36 h-fasted rats despite apparently antagonizing the fasting-induced increase in hepatic FAO. To test whether this anorectic effect involves beta-adrenergic stimulation, 36 h-fasted rats were IP injected with the nonspecific beta-adrenergic receptor antagonist propranolol (PROP, 0.5 mg/kg) just before MA injection. PROP attenuated MA's feeding-inhibitory effect, suggesting that MA anorexia is at least partially mediated by beta-adrenergic stimulation. Finally, we evaluated the role of subdiaphragmatic vagal afferent fibers in MA's feeding-inhibitory effect by testing the ability of MA to inhibit food intake in fasted rats after subdiaphragmatic vagal deafferentation (SDA). MA inhibited feeding similarly in SDA rats and sham-operated rats. These data demonstrate that subdiaphragmatic vagal afferents are not necessary for the feeding-inhibitory effect of peripheral MA. These results suggest that the FAO inhibitor MA elicits a feeding-inhibitory effect in fasted rats that is mediated by a different mechanism than its feeding-stimulatory effect.