Overview of adrenergic anorectic agents.

Adrenergic anorexic agents of the amphetamine class suppress appetite and reduce body weight via activation of beta-adrenergic and/or dopaminergic receptors within the perifornical hypothalamus (PFH). Although phenylpropanolamine (PPA) is often considered to be a member of the amphetamine class of anorexiants, this drug is an atypical adrenergic anorexiant. Unlike amphetamine, microinjection of PPA into the PFH does not suppress feeding. Moreover, PPA anorexia is not reversed by the dopamine antagonist haloperidol. The anorexic action of PPA may result, in part, from its interaction with alpha 1-adrenergic receptors within the paraventricular medial hypothalamus (PVN). This hypothesis is supported by prior research, which documents that PPA is a direct-acting agonist predominantly at alpha 1 adrenoceptors, that microinjections into the PVN of the alpha 1-adrenoceptor agonists PPA and l-phenylephrine suppress feeding, and that injections of alpha 1-adrenoceptor antagonists within the PVN enhance feeding behavior.