Insulin alters the effects of follicle stimulating hormone on aromatase inbovine granulosa cells in vitro

It is known that follicle-stimulating hormone (FSH) and insulin stimulate e stradiol secretion from cultured non-luteinizing granulosa cells. The inter action between these hormones is less well understood. Granulosa cells from small (2-4 mm) bovine follicles were cultured in serum-free medium to dete rmine if L cytochrome P450 aromatase activity is regulated by FSH in the pr esence of different concentrations of insulin. Insulin significantly stimul ated aromatase activity in the absence of FSH. There was a significant inte raction between insulin and FSH on aromatase activity, such that FSH stimul ated activity at low (0.5, 1 and 10 ng/ml) doses of insulin, whereas at hig her (100 ng/ml) doses of insulin FSH failed to stimulate aromatase activity . To determine if the lack of a response to FSH with higher doses of insuli n is related to gene expression, the effect of FSH on p450 aromatase mRNA l evels was measured. An 'uncoupling' of mRNA and enzyme activity was observe d for cells cultured with 100 ng/ml insulin, as FSH significantly increased P450 aromatase mRNA abundance without affecting estradiol secretion or aro matase activity. We conclude that in the presence of hi h doses of insulin, FSH decreases aromatase activity, and an uncoupling of P450 aromatase mRNA and aromatase activity occurs. This may have implications for infertility treatments when there is a risk of hyperinsulinemia. (C) 2001 Elsevier Scie nce Inc. All rights reserved.