Effects of GH on IGF-II-induced progesterone accumulation by cultured porcine granulosa cells.

A total of seven experiments were conducted to investigate the potential facilitative interaction of growth hormone (GH) and insulin-like growth factor II (IGF-II) in stimulating steroidogenesis by cultured porcine granulosa cells and to examine the possible nature of this action. Porcine granulosa cells were cultured in serum-free medium in the presence or absence of GH or prolactin, with or without IGF-II or IGF-I. IGF-II by itself dose (with peak progesterone production of 498 ng/mg DNA/24 h being observed at 100 ng of IGF-II/mL) and time- (with minimum time requirement of 24-48 h) dependently increased progesterone accumulation (P < 0.01). Neither GH (dose range 0, 5, 10, 50, 100, and 150 ng/mL) nor prolactin (dose range 0, 0.01, 0.1, 1, 5, 10 micrograms/mL) alone stimulated progesterone accumulation when compared with the control (P > 0.05). However, in the presence of IGF-II, GH proved to be a potent amplifier of IGF-II in progesterone production (P < 0.01) with a minimum GH time requirement of 24-48 h. In contrast, prolactin did not influence IGF-II-induced progesterone accumulation (P > 0.05). An inhibitory study showed that the presence of cycloheximide (3 micrograms/mL) or actinomycin D (1 microgram/mL) blocked both the stimulatory effect of IGF-II on progesterone accumulation and the amplification of GH on IGF-II induced production (P > 0.01), suggesting GH amplification of IGF-II-induced progesterone accumulation is a process involving gene transcription and translation. Northern blot analysis further demonstrated that GH amplification of IGF-II-induced steroidogenesis can be attributed, at least partially, to enhanced IGF-II-induced cytochrome P450 cholesterol side-chain cleavage mRNA by GH.