Progesterone production by human granulosa cells cultured in serum free medium: effects of gonadotrophins and insulin-like growth factor I (IGF-I)

There is evidence that insulin-like growth factor I (IGF-I) is a potent regulator of oestradiol synthesis by human granulosa and luteal cells; however, the question of whether IGF-I regulates progesterone synthesis by these cell types has yet to be answered. As a first step towards this goal, we have compared the effects of IGF-I, follicle stimulating hormone (FSH), and human choriomc gonadotrophin (HCG) on progesterone production by human granulosa cells obtained from individual dominant and cohort follicles, and granulosa luteal cells from preovulatory follicles of patients undergoing in-vitro fertilization (IVF). Granulosa cells from normal, unstimulated follicles cultured in serum-free medium as controls (no additions) produced some progesterone spontaneously. In all cases, FSH stimulated basal progesterone levels (10-fold average increase) and the effect was dose-dependent (ED of FSH = 9.1 ± 3.9 ng/ml). Similar effects were observed when granulosa cells from large follicles were incubated with HCG (ED50 of HCG = 6.9 ± 2.8 ng/ml). By comparison, the effects of IGF-I on progesterone production were not marked, being absent in 80% of the follicles tested. However, granulosa cells from healthy follicles co-incubated with IGF-I and FSH or HCG produced more progesterone compared with cells treated with the gonadotrophins alone; this effect of IGF-I was dose dependent (ED of IGF-I = 10 ng/ml). When the effect of each agonist was tested on LVF granulosa luteal cells, HCG but not FSH or IGF-I stimulated basal progesterone levels but the HCG effect required a two-day lag phase. In expen ments in which IGF-I was added together with FSH or HCG, there was a greater stimulation of progesterone production by IVF cells at 4 and 6 days compared to their matched controls. In summary, these results with cultured human granulosa and luteal cells indicate that IGF-I itself does not have a marked effect on progesterone production but incuba tion of physiological amounts of IGF-I with FSH and HCG does produce a marked effect on the relative rate of progesterone synthesis, specifically by granulosa cells in healthy follicles. These findings are consistent with the hypothesis that IGF-I may play a role in regulating the progesterone potential of the human ovary by amplifying the stimulatory signals of FSH and LH/HCG in healthy follicles.