Differences between the anorexic actions of amphetamine and fenfluramine--possible effects on hunger and satiety.

The inhition of feeding in rats brought about by amphetamine and fenfluramine was continuously monitored for periods of up to 24 h using a pellet detecting eatometer. For rats tested under conditions of food deprivation the two drugs gave rise to distinctive anorexic profiles: amphetamine delayed the onset of eating whereas fenfluramine allowed eating to commence normally but brought about an early termination of the initial bout of feeding. When the drugs were administrated to rats with free access to food, analysis of the meal pattern showed that amphetamine gave rise to a small increase in the inter-meal interval while fenfluramine brought about a clear reduction tion in meal size. It is suggested that the contrasting modes of action of these drugs represent an effect of amphetamine upon hunger and an action of fenfluramine on satiety. This suggestion is in keeping with the proposed mechanisms of action of these drugs, amphetamine acting upon a hpothalamic motivational system and fenfluramine acting by means of a postulated serotoninergic satiety system. Use of the continuous monitoring technique has pointed pointed to certain limitations in the assessment of anorexic drug action by means of discrete food sampling periods.