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A Qualitative Transition in the Luteotropic Mechanism of Early Pregnancy^*

Department of Obstetrics and Gynecology, Washington University School of Medicine St. Louis, Missouri 63110

Address requests for reprints to: Dr. Walter G. Wiest, Washington University School of Medicine, Department of Obstetrics and Gynecology, 4911 Barnes Hospital Plaza, St. Louis, Missouri 63110.

Abstract

Secretion of progesterone and 20-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 to a maximum on the 5th day of pregnancy, which was 1.4 times that observed on the 2nd day. Beyond the 5th day, luteal cell density remained constant until the 9th day and decreased thereafter. These changes in gonadotropic response and luteal cell density seem to account accurately for changes seen in peripheral plasma progesterone levels observed during early pregnancy and further define a qualitative transition in the luteotropic mechanism occurring between days 5–8 of pregnancy, paralleling observations made in vivo.

Footnotes

^* This work was supported in part by NICHD Specialized Population Research Center Grant P50-HD-08235.

Received August 15, 1977.