COMPARISONS BETWEEN THE EFFECTS OF 5-HT AND DL-FENFLURAMINE ON FOOD-INTAKE AND GASTRIC-EMPTYING IN THE RAT

5-Hydroxytryptamine (5-HT) dose-dependently increased gastric emptying in rats, whereas DL-fenfluramine produced a biphasic dose response cu rve for gastric emptying. Thus, fenfluramine increased gastric emptyin g at a dose of 0.1 mg/kg but decreased it at doses of 1 and 3 mg/kg. B oth 5-HT and DL-fenfluramine produced significant decreases in food in take. As 5-HT produced opposing effects on gastric emptying and food i ntake, it appears that the anorectic effect of 5-HT may not depend on changes in the rate of gastric emptying. In contrast, doses of DL-fenf luramine that decreased feeding also decreased gastric emptying, which suggests that reduced food intake may at least partly result from dec reased gastric emptying. Taken together, these results suggest that th e effects of 5-HT and DL-fenfluramine on feeding and gastric emptying may be mediated by different mechanisms.