DIFFERENTIAL ACTIONS OF CORTICOSTERONE ON LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE BIOSYNTHESIS AND RELEASE IN CULTURED RAT ANTERIOR-PITUITARY-CELLS - INTERACTIONS WITH ESTRADIOL

Previous in vivo studies from our laboratory suggested that glucocorticoids antagonize estrogen-dependent actions on LH secretion. This study investigated whether corticosterone (B) may have similar actions on gonadotropin biosynthesis and secretion in vitro. Enzymatically dispersed anterior pituitary cells from adult female rats were cultured for 48 h in alpha-modified Eagle's medium containing 10% steroid-free horse serum with or without 0.5 nM estradiol (E2). The cells were then cultured for 24 h with or without B in the presence or absence of E2. To evaluate hormone release, 5 x 10(5) cells were incubated with varying doses of GnRH (0, 10(-11) - 10(-7) M) or pulsatile GnRH (10(-9) M; 20 min/h) for 4 h. Cell and medium LH and FSH were measured by RIA. To evaluate LH biosynthesis, 5 x 10(6) cells were incubated for an additional 24 h with 10(-10) M GnRH, 60-mu-Ci H-3-glucosamine (H-3-Gln), 20-mu-Ci S-35-methionine (S-35-Met), and the appropriate steroid hormones. Radiolabeled precursor incorporation into LH subunits was determined by immunoprecipation, followed by SDS-PAGE. Continuous exposure to GnRH stimulated LH release in a dose-dependent manner, and this response was enhanced by E2. B by itself had no effect on LH release, but inhibited LH secretion in E2-primed cells at low concentrations of GnRH (10(-10) M or less). Total LH content was not altered by GnRH or steroid treatment. Similar effects of B were observed in cells that were given a pulsatile GnRH stimulus. In contrast to LH, E2 or B enhanced GnRH-stimulated FSH release at the higher doses of GnRH, while the combination of E2 and B increased basal and further augmented GnRH-stimulated release. Total FSH content was also increased in the presence of B, but not E2 alone, and was further augmented in cells treated with both steroids. There were no effects of the steroids on the magnitude of FSH release in response to GnRH pulses, but the cumulative release of FSH was greater in the E2 + B group compared to controls, indicating an increased basal release. Independent of E2, B suppressed the incorporation of H-3-Gln into LH by more than 50% of control, with only subtle effects on the incorporation of S-35-Met. These results suggest the following: 1) At the level of the pituitary, B differentially affects the release and synthesis of LH and FSH, with the steroid being mainly inhibitory for LH and stimulatory for FSH; 2) The glucocorticoid inhibition of LH secretion occurs by antagonism of E2's positive feedback actions at the pituitary, whereas the stimulation of FSH synthesis and release of B is enhanced by E2; and 3) B alters LH subunit biosynthesis by decreasing glycosylation via E2-independent mechanisms.