Gonadal steroid modulation of LH secretion stimulated by LHRH, Ca2+ and cAMP

Primary cultures of enzymatically dispersed rat pituitary cells were used to examine steroid effects on LH secretion stimulated by LHRH, Ca2+ and cAMP. Cultures were pretreated for 48 h with testosterone (T) or 17 beta-estradiol (E) and then challenged for 4 h with various secretogogues. T did not affect basal LH secretion; it inhibited the responses to Ca2+ and LHRH; and it potentiated the response to cAMP. E stimulated both basal LH secretion and the responses to all secretogogues, without affecting cell LH content. Thus, T affects stimulus-secretion coupling, while E affects secretion per se. All steroid effects were blocked by steroid antagonists, indicating that steroid action is receptor-mediated regardless of the secretogogue involved. The similarity of steroid effects on the responses to LHRH and Ca2+ but not cAMP suggests that Ca2+ rather than cAMP is a second messenger for LHRH, and that steroid action occurs at some step subsequent to LHRH-stimulated Ca2+ mobilization.