Unsuppressed Prolactin Secretion in the Male Rat is Pulsatile

Abstract

The pattern of prolactin (PRL) secretion was studied in several different situations. In normal and castrated male rats, the plasma PRL level gently fluctuated along the course of time. When the presumed hypothalamic PRL inhibitory factor was suppressed by treatment with a pharmacological agent, pimozide (Pim), the plasma PRL concentration was elevated and the elevated plasma level fluctuated in an irregular and pulsatile manner. Baseline PRL concentration was elevated by implantation of estradiol, which also caused a moderate fluctuation of the circulating PRL level. The PRL level was then lowered from the elevated plateau level by administration of a dopaminergic receptor agonist, ergocristine. During this partial blockade, the plasma PRL level fluctuated in episodic bursts. The inherent, unsuppressed secretion of PRL may be pulsatile in nature, but this pulsatile pattern may be normally suppressed under the inhibiting influence of the hypothalamus.