Endogenous estrogen modulates phenothiazine stimulated prolactin secretion.

The role of endogenous estrogen in the regulation of serum prolactin concentration in man is controversial. To evaluate the possible effect of endogenous fluctuations in serum estrogen on the regulation of prolactin secretion, the authors determined phenothiazine stimulated prolactin secretion in 12 women in the early follicular phase of the menstrual cycle when estrogen levels were low (mean +/- SE E1 + E2 = 82 +/- 7 pg/ml) and compared it to the response during the late follicular phase when estrogen levels were higher (mean E1 + E2 = 320 +/- 63 pg/ml). Mean basal serum prolactin concentrations were similar in the early and late follicular phases of the cylcle (17 +/- 4 and 20 +/- 2 ng/ml, respectively). The integrated prolactin response following phenothiazine administration was significantly higher at mid-cycle (402 +/- 46 ng-hr/ml) than in the early follicular phase (317 +/0 46 ng-hr/ml, P less than .02). Thus, these studies suggest that endogenous estrogen secretion may play a role in the regulation of serum prolactin concentration in man.