Effects of haloperidol on anorexia induced by l-norephedrine and d-amphetamine in adult rats.

Although amphetamine anorexia has been linked to activation of dopaminergic receptors within the lateral aspects of the hypothalamus, the receptor type by which phenylpropanolamine (PPA: the racemic mixture of d- and l-norephedrine) induces anorexia has not been identified. In the present experiment, separate groups of adult male rats were pretreated (IP) with either 0.9% saline or haloperidol (either 0.4 or 0.8 mg/kg) 45 minutes prior to treatment (IP) with either saline or 20 mg/kg l-NEP (the active enantiomer of PPA) and were then allowed 180 minutes access to food and water. Treatment with 20 mg/kg l-NEP induced comparable reductions in food intake of approximately 30% in rats pretreated with either dose of haloperidol or saline. In a sub-experiment, it was demonstrated that 1.0 mg/kg d-amphetamine sulfate reduced food intake by 25%, but this anorexic action was completely attenuated by 0.8 mg/kg haloperidol given 45 minutes prior to feeding. These results add to a growing body of literature that documents important differences between the mechanisms by which amphetamine and PPA produce their anorexic actions.