Jg. Gong et al., EFFECTS OF RECOMBINANT BOVINE SOMATOTROPIN, INSULIN-LIKE GROWTH-FACTOR-I AND INSULIN ON BOVINE GRANULOSA-CELL STEROIDOGENESIS IN-VITRO, Journal of Endocrinology, 143(1), 1994, pp. 157-164
Our previous studies have demonstrated that physiological concentratio
ns of metabolic hormones, including recombinant bovine somatotrophin (
BST), insulin-like growth factor-I (IGF-I) and insulin, can significan
tly stimulate the proliferation of bovine granulosa cells cultured und
er serum-free conditions. In this study we investigated the effects of
these factors on bovine granulosa cell steroidogenesis using the same
culture system. Bovine granulosa cells were obtained from antral foll
icles classified into three size classes: small, < 5 mm; medium-sized,
5-10 mm and large, > 10 mm in diameter. Whilst not affecting steroido
genesis by granulosa cells from small and medium-sized follicles, BST
(10-1000 ng/ml) stimulated the secretion of both oestradiol and proges
terone by granulosa cells from large follicles in a dose-dependent man
ner. Insulin (1-1000 ng/ml) and IGF-I (10-1000 ng/ml) stimulated the s
ecretion of oestradiol and progesterone by granulosa cells from all th
ree size categories of follicles in a dose-dependent manner. FSH (200
ng/ml) alone increased progesterone secretion by granulosa cells from
all three size classes of follicles, but had no effect on oestradiol s
ecretion by granulosa cells. Both IGF-I (200 ng/ml) and insulin (30 ng
/ml) acted in synergy with FSH (200 ng/ml) to stimulate steroidogenesi
s by granulosa cells from all three size categories of follicles, but
no such interaction was observed between BST (50 ng/ml) and FSH (200 n
g/ml). In conclusion, BST, IGF-I and insulin significantly influence t
he steroidogenic activity of bovine granulosa cells cultured under ser
um-free conditions. However, unlike their effects on cell proliferatio
n, the minimal effective concentrations of these factors required to s
timulate granulosa cell steroidogenesis were higher than those observe
d in our previous studies in vivo.