Estrogen Reduces Sensitivity of Chicken Pituitary Cells to GnRH.

Primary monolayer culture cells prepared from the anterior pituitary of 1-day-old male chicks were used to examine the effect of estrogen on GnRH-induced LH release. The half-maximal response (ED50) values of several kinds of GnRH determined by dose-response incubations with day-4 culture cells were in the following ascending order (in nM) : (D-Lys6)GnRH (a synthetic analogue; 0.07), chicken GnRH-II (0.24), chicken GnRH-I (0.51), and mammalian GnRH (0.82). By the use of the most potent and stable GnRH, (D-Lys6) GnRH, at a dose (1 nM) less than that inducing a maximal LH release, the GnRH-induced LH release was found to decrease in day-4 culture cells which had been pre-incubated with estradiol-17β (E2) for 12, 24 or 48 h. Whereas basal LH secretion was not changed by pre-incubation with E2. Following pre-incubation with E2 or diethylstilbestrol for 24 h the dose-response curves for the GnRH-induced LH release were shifted to a higher concentration with the ED50 enhanced. The results suggest that estrogen reduces the sensitivity of the chicken anterior pituitary cells to GnRH in vitro.