The Biphasic Regulation of Prolactin Secretion by Dopamine Agonist-Antagonists*

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Abstract
The in vitro secretion of PRL [prolactin] by the [rat] pituitary gland is inhibited by low concentrations of dopamine. Dopamine receptor-blocking agents, haloperidol and pimozide, in concentrations between 10-100 nM, neutralize virtually completely the dopamine-mediated inhibition of PRL secretion. At these concentrations, the dopamine antagonists alone are without effect on PRL secretion. Higher concentrations of these agents, however, have a powerful action to inhibit PRL secretion. Perphenazine was without direct effect on the in vitro secretion of PRL. These observations may be of general importance to the study of dopamine action in other organ systems.