A qualitative transition in the luteotropic mechanism of early pregnancy.

Abstract

Secretion of progesterone and 20α-dihydroprogesterone by dispersed rat luteal cells was studied as a function of the age of the corpora lutea from which the cells were derived and the gonadotropic hormone content of the perifusion medium employed. Progesterone secretion by luteal cells gradually declined during 5-h perifusion under conditions simulating tonic in vivo PRL-LH levels. Initial rates of progesterone secretion from cells obtained from the 5th and 8th days of pregnancy were double that from the 2nd day. Supplementation of tonic gonadotropin levels with a simulated PRL surge maintained initial progesterone secretion by day 5 cells. PRL withdrawal markedly reduced progesterone secretion, while supplemental LH was ineffective. Conversely, progesterone secretion from day 8 cells could be maintained undiminished with supplemental LH, but PRL was ineffective. Total deprivation of LH from day 8 cells resulted in acute decline of progesterone secretion. Luteal cell density of the corpora lutea increased...