Effects of insulin-like growth factor-I on aromatase cytochrome P450 activity and oestradiol biosynthesis in preimplantation porcine conceptuses in vitro.
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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 microgram/ml) or insulin (8.5 micrograms/ml), and conceptuses were monitored for their ability to convert [1,2-3H]beta-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 less than 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 microgram/ml) with or without IGF-I (0.1 microgram/ml) or insulin (0.1 or 8.5 micrograms/ml) for 24 h. Conceptuses in MEM plus DHA produced more oestradiol (P less than 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 conceptuses 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.(ABSTRACT TRUNCATED AT 250 WORDS)
