ABSTRACT
The effects of insulin-like growth factor-I (IGF-I) on aromatase P450 activity and steroid production in preimplantation pig conceptuses were evaluated in vitro. Conceptuses recovered from gilts on days 10 and 12 of pregnancy were incubated for 6 h in modified Eagle's Minimum Essential Medium (MEM) plus IGF-I (0·1 μg/ml) or insulin (8·5 μg/ml), and conceptuses were monitored for their ability to convert [1,2-3H]β-testosterone into oestrogens. Aromatase activity of day-10 conceptuses was low and unaffected by IGF-I or insulin. In contrast, basal aromatase activity in day-12 conceptuses was about threefold higher and was further increased by IGF-I (P < 0·02), but was unaffected by insulin. To determine whether higher aromatase P450 activity was associated with increased oestradiol production, concentrations of oestradiol were determined by radioimmunoassay in culture medium of day-11 and -12 conceptuses, after incubation in MEM alone or in the presence of dehydroepiandrosterone (DHA, 1 μg/ml) with or without IGF-I (0·1 μg/ml) or insulin (0·1 or 8·5 μg/ml) for 24 h. Conceptuses in MEM plus DHA produced more oestradiol (P < 0·01) than those in MEM alone. Addition of IGF-I or insulin did not increase the effect of DHA. Basal oestradiol production was dependent on conceptus size; however, IGF-I or insulin did not affect basal or DHA-stimulated oestradiol production regardless of conceptus size. These findings demonstrate that IGF-I can modulate aromatase activity in vitro, without affecting overall de-novo steroidogenesis. Thus, the developmental increase in conceptus oestradiol production observed during early pregnancy in the pig may reflect synergistic interactions between IGF-I and other regulatory factors present within the conceptus and/or uterine environment.
Journal of Endocrinology (1991) 130, 245–250
Kit ligand and insulin-like growth factor I affect the in vitro development of ovine preantral follicles
