Role of 5-HT receptors in the effect of d-fenfluramine on feeding patterns in the rat.

The effect of d-fenfluramine, 1.5 mg/kg i.p., on meal patterns was studied in rats treated i.p. with 1 mg/kg metergoline or 0.5 mg/kg ritanserin or s.c. with 3 mg/kg (+/-)cyanopindolol. d-Fenfluramine significantly reduced eating rate, meal size and total intake in the first 4 h of testing and the effects were antagonized by metergoline. (+/-)Cyanopindolol reduced total intake and the effect of d-fenfluramine on this measure; the effect of d-fenfluramine on meal size (but not on eating rate) was also reduced by (+/-)cyanopindolol. Ritanserin only reduced the rate of eating and the effect of d-fenfluramine on this measure. The results suggest that 5-HT1 receptors, possibly of the 5-HT1B type, are involved in the ability of d-fenfluramine to cause satiety in freely feeding rats.