Effects of dl-fenfluramine and xylamidine on gastric emptying of maintenance diet in freely feeding rats.

Freely feeding rats received an anorexigenic dose of dl-fenfluramine HCl (5 mg/kg). Two hours following injection, their stomachs retained significantly greater dry weight contents than saline-injected controls. The same dose of fenfluramine decreased the rate of gastric emptying over a 2 h period to a similar extent in mildly food-deprived rats. The peripherally acting serotonin antagonist xylamidine counteracted the effect of fenfluramine in prolonging the satiating effect of an ad libitum meal of a given size. We propose therefore that the principal mechanism by which fenfluramine reduces food consumption in freely feeding rats is through a prolongation of the satiating effect of absorption as a result of slowing of gastric emptying, presumably via enhanced release of serotonin from nerve terminals in the wall of the gastrointestinal tract.