Inhibition of cyclic gonadotropin secretion by endogenous human prolactin.
The resumption of cyclic uterine bleeding reportedly accompanies the use of human prolactin (HPRL)-suppressing agents in postpill galactorrhea-amenorrhea. In this laboratory, HPRL suppression with L-dopa was variable and short lived. Basal plasma HPRL levels were elevated before and after as much as five months of therapy. Galactorrhea persisted and mean gonadotropin concentrations were subnormal. An immediate and sustained attenuation of HPRL secretion ( less than 200 per cent) followed the use of 2-Br-alpha-ergocryptine (CB-154). Cyclic gonadotropin secretion resumed and was accompanied by ovulation and, in one instance, pregnancy. The cessation of galactorrhea was positively correlated with the rise in the daily concentration of 17 beta-estradiol. Cyclic postovulatory menstruation continued after the cessation of CB-154 treatment. HPRL levels remained normal. The daily patterns of human follicle-stimulating hormone (HFSH) and human tuteinizing hormone (HLH) secretion created by the suppression of HPRL displayed an inherent rhythmicity identical to that observed at the time of menarche. The inhibitory effects of HPRL appeared directed at cyclic rather than tonic gonadotropin secretion. At the same time, diminished ovarian estrogen production seemed to increase mammary gland sensitivity to HPRL, leading to lactation. One may postulate, therefore, that the ingestion of sex steroids is associated with an over-all suppression of endogenous cyclic and, to a lesser extent, tonic gonadotropin secretion secondary to which ovarian function is attenuated. Without physiologic concentration of circulating estrogen, HPRL induces mammary alveolar function with the production of a milklike secretion.