Inhibition by Naloxone of Prolactin Release Induced by L-5-Hydroxytryptophan in Rats 1

Abstract

Abstract

Intravenous injection of l-5-hydroxytryptophan (l-5-HTP), but not l-5-HTP, resulted in an increase in plasma prolactin (PRL) levels in anesthetized rats. l-5-HTP-induced PRL release was blunted by naloxone, a specific opiate antagonist. In rats pretreated with either reserpine or α-methyl-p-tyrosine (α-MT), basal plasma PRL levels were elevated and l-5-HTP injection caused a further increase in plasma PRL concentrations. However, PRL release induced by l-5-HTP was not blunted by naloxone in these animals pretreated with reserpine and α-MT. These results suggest that PRL release induced by serotonin is modulated, at least in part, by opioid peptidergic mechanisms, which are closely related to brain catecholamines.