Acute Stimulatory Effects of Progesterone on Luteinizing Hormone and Follicle-Stimulating Hormone Release in Rat Anterior Pituitary Cells in Culture

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Abstract
The acute effects of progesterone (P) on gonadotropin secretion were studied in anterior pituitary cells in primary culture. While P alone had no effect on LH release up to 48 h of incubation, it led to a rapid (between 3–8 h after its addition) 40–65% increase of the LH response to 0.1 nm LHRH, followed by a progressive decrease at later time intervals in 17β-estradiol (E2)-primed cells. In the same experiment, the effect of P on the FSH response to LHRH was quite different, the effect being exclusively stimulatory in the presence or absence of E2. Priming with E2 did, however, accelerate the stimulatory effect of P on FSH secretion. The acute stimulatory effect of P on the gonadotropin responses to LHRH in E2-primed cells is due to increased spontaneous LH and FSH release coupled to increased gonadotropin responsiveness to LHRH as reflected by the decreased LHRH ED50 values for both LH and FSH release in the presence of P. The absence of an acute effect of P on gonadotropin cell content indicates that the acute stimulatory effect of P, in analogy with that of E2, is due to parallel changes of the sensitivity of the secretory mechanisms in gonadotrophs. The stimulatory effect of P on LH and FSH responses to LHRH in E2-primed cells was observed at ED50 values of 2.0 and 1.5 nm, respectively. This stimulatory effect appears to be exerted through specific progestin action and can possibly serve as a biological assay for new synthetic progestins. (Endocrinology106: 684, 1980)