Blockade of the Dopamine-Inhibitory Control of Prolactin Secretion in Rats by 3,4-Dimethoxyphenylethylamine (3,4-di-O-methyldopamine)1

Abstract

The aim of this study was to examine the possibility that the O-methylated dopamine derivative, dimethoxyphenylethylamine (DMPEA), is able to release prolactin secretion from dopamine inhibition. The effect of DMPEA on plasma radioimmunoassayable (RIA) prolactin levels in normal male rats was examined when administered alone, or together with L-dopa or 5-hydroxy-L-tryptophan (S-HTP). Acute intraperitoneal (ip) administration of DMPEA to normal male rats causes a highly significant elevation of plasma RIA prolactin levels at 30 min following injection. This effect is observed whether or not the animals are anesthetized with urethane, an anesthetic found to cause suppression of plasma RIA prolactin levels of control animals when compared with unanesthetized controls. L-dopa administration causes a significant reduction in plasma RIA prolactin but if it is administered together with DMPEA in unanesthetized animals there is no significant change in prolactin levels due to mutual antagonism. Acute ip administration of S-HTP to normal male rats under urethane anesthesia does not significantly alter plasma RIA prolactin levels nor does it prevent the elevation of prolactin levels if given together with DMPEA. These results thus support the hypothesis that prolactin secretion is under tonic dopamine-inhibitory control and reveal that DMPEA administration results in prolactin secretion by releasing it from dopamine inhibition. We postulate that DMPEA exerts its effect by competing with dopamine for hypothalamic receptor sites. (Endocrinology93: 147, 1973)