Gonadotropin-sensitive progesterone production by rhesus monkey luteal cells in vitro: A function of age of the corpus luteum during the menstrual cycle

Progesterone production in vitro, in the presence and absence of exogenous gonadotropin, was examined in suspensions of luteal cells isolated by collagenase digestion of rhesus monkey corpus luteum at various stages of the menstrual cycle. Cells isolated during mid-luteal phase (days 15-19) of the cycle secreted progesterone for up to 6 h in vitro. Mid-luteal phase cells were responsive to physiologic concentrations of human chorionic gonadotropin (hCG), with progesterone production significantly (P < 0.05) enhanced by as little as 0.1 ng hCG/ml. Maximal stimulation was obtained with 100 ng hCG/ml. Both macaque chorionic gonado-tropin (mCG) and human luteinizing hormone (hLH) significantly (P 0< 0.01) increased progesterone production, while human follicle stimulating hormone (hFSH) did not. Under control conditions, in the presence of nutrient medium alone (no exogenous gonadotropin), the progesterone synthetic activity of mid-luteal phase cells was significantly (P < 0.01)greater than that of cells from late luteal phase (days 22-28) of the cycle. Moreover, progesterone production by mid-luteal phase cells was consistently stimulated (P < 0.01) by the presence of 100 ng hCG/ml, whereas late luteal phase cells were less sensitive or unresponsive to exogenous gonado-tropin. The progesterone synthetic activity of luteal cells in vitro correlated positively with both the wet weight of the excised corpus luteum (r = 0.82, P < 0.01) and the peripheral serum progesterone concentration immediately preceding luteectomy (r = 0.66, P < 0.01). These findings suggest that freshly isolated luteal cells reflect the functional capability of the corpus luteum in vivo. It is apparent that the age of the rhesus monkey corpus luteum of the non-fertile menstrual cycle is an important factor governing luteal cell progesterone synthetic capability and luteal cell responsiveness to gonadotropin in vitro.