Unexpected Adrenergic Effect of Chlorpromazine: Eating Elicited by Injection into Rat Hypothalamus
Chlorpromazine (CPZ), a tranquilizing agent, is probably the most widely used drug in the treatment of mental illness. Although chlorpromazine is believed to block adrenergic transmission, injection of this drug into the hypothalamus of satiated rats does not block norepinephrine-elicited eating, but instead mimics norepinephrine by eliciting eating. The classical view has been that CPZ is pharmacologically an adrenergic blocking agent and clinically a tranquilizer. These effects are supposed to be opposite to those of imipramine, a potentiator of adrenergic effects and an antidepressant. In addition to having no apparent effect upon norepinephrine (NE)-induced eating, CPZ itself elicited eating. Peripheral injections of CPZ have been found to both increase and decrease food intake in human patients and in animals. For the good NE eaters, the mean latency of the eating response after injection of CPZ was 25 minutes, whereas the mean response latency after injection of NE was 4 minutes.