Dose response of luteinized porcine granulosa cells in vitro to prolactin: dependency on pre-exposure to human chorionic gonadotrophin

This study examined the hypothesis that human chorionic gonadotrophin (hCG) increases prolactin (PRL) stimulation of the utilization of lipoprotein-borne cholesterol by pig luteinized granulosa cells in culture. These cells, which luteinize in culture, were harvested from 6-mm or greater diameter follicles and cultured in the presence of 1% fetal calf serum and 1 microgram/mL insulin for 48 h. On the third day, the media were replaced with fresh serum-free media, with the same dose of insulin, and on the following day (day 4) the media were replaced with serum- and insulin-free media. At this time (day 4) hCG was added to some cultures. On day 5, cells from the group with hCG and cells from the group without hCG were treated with graded doses of ovine PRL (0.1-3.0 micrograms/mL). To a second set of cells, likewise treated, 100 micrograms of porcine low density lipoprotein (LDL) was added. Two days later (day 7) media were sampled and replaced with media alone or media containing hormones and (or) LDL. On day 9 cultures were terminated. In the cells pre-exposed to hCG, PRL (1 microgram/mL) in the presence of LDL increased progesterone production 1.7-fold (p less than 0.01) on day 7 and 2.2-fold (p less than 0.01) on day 9. In the granulosa cells in culture pre-exposed to hCG, the effect of PRL on LDL utilization was dose dependent and saturable at 1 microgram/mL on days 7 and 9. We conclude that brief pretreatment of luteinized pig granulosa cells with hCG results in a dose-dependent PRL-induced utilization of LDL for progesterone synthesis.