The effect of follicle-stimulating hormone on follicular development, granulosa cell apoptosis and steroidogenesis and its mediation by insulin-like growth factor-I in the goat ovary.

The effect of FSH on goat follicular development, granulosa cell apoptosis and steroidogenesis and its mediation by insulin-like growth factor (IGF)-I were studied through both in vivo and in vitro experiments. The FSH treatment was begun on Day 9 after estrus and consisted of injections twice a day for 3 days in decreasing doses (7.5-7.5-5.0-5.0-2.5-2.5 mg). Does in both treatment and control groups were slaughtered for ovaries on Day 12. Granulosa cell apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). Expression of IGF-I and IGF-II mRNA was determined by RT-PCR, while concentrations of progesterone (P4), estradiol (E2), IGF-I and IGF-II were measured by radioimmunoassay (RIA). Following parameters increased significantly (P<0.05) after the FSH treatment: follicle number (5.0+/-1.5 versus 9.0+/-2.0 per ovary), the level of E2 (0.1+/-0.1 ng/ml versus 0.7+/-0.2 ng/ml), the E2/P4 ratio (0.7+/-0.4 versus 4.7+/-3.0) and the concentrations of IGF-I (0.5+/-0.2 ng/ml versus 119.4+/-15.1 ng/ml) and IGF-II (0.12+/-0.03 ng/ml versus 40.9+/-18.7 ng/ml) in follicular fluid of the medium sized (3-5 mm) follicles and in the ovarian cortex the relative quantity of IGF-I mRNA (0.37+/-0.17 versus 0.90+/-0.12 Max OD). In contrast, the ratio of apoptotic granulosa cells in these follicles was reduced significantly (0.53+/-0.1 versus 0.10+/-0.01, P<0.05). In large (>5 mm) follicles, however, only the follicle number (2.3+/-0.7 versus 7.0+/-1.5 per ovary) and the level of IGF-I (38.4+/-11.0 ng/ml versus 87.3+/-13.9 ng/ml) increased significantly (P<0.05), whereas other values did not change. In vitro culture of granulosa cells showed that FSH significantly (P<0.05) enhanced IGF-I production (12.7+/-2.1 ng/ml versus 26.+/-21.9 ng/ml) by these cells, and both FSH and IGF-I reduced the ratios of apoptotic cells (from 0.7+/-0.07 to 0.3+/-0.1 and 0.2+/-0.04, respectively) and the effect was additive when both were used together. H89, the PKA pathway inhibitor, blocked the effect of FSH on granulosa cell apoptosis and IGF-I production in vitro. These results indicated that FSH mainly enhanced the development of medium sized follicles in the goat by suppressing the apoptosis of granulosa cells via increasing production of IGF-I and steroids, possibly through the PKA pathway.