P450 aromatase expression and estradiol secretion in bovine granulosa cells in vitro

Folliculogenesis is a highly complex process which involves hormone-induced proliferation and differentiation of both theca and granulosa cells, leading ultimately to the increased ability of follicles to produce estradiol and to respond to gonadotropins. The ability to synthesize estradiol is an essential characteristic of a healthy ovarian follicle. Estradiol is synthesized in granulosa cells from thecal androgens; a process catalized by the enzyme P450 aromatase (P450arom). In cattle, the study of the hormonal regulation of P450arom gene expression and estradiol secretion has been hampered because of the lack of a cell model in which estradiol secretion can be maintained. Recently, a cell culture system has been developed in which bovine granulosa cells maintain aromatase activity in vitro. Thus, the aim of the present study was to examine the mechanisms involved in the regulation of P450arom gene expression and estradiol secretion by FSH, insulin and IGF-I in bovine granulosa cells in vitro.;The objective of the first study was to study the time course and the effects of FSH on P450arom, P450scc mRNAs, and estradiol and progesterone secretion. Estradiol secretion increased with time of culture, and this was correlated with an increase in P450arom mRNA abundance. Progesterone secretion also increased with time of culture, but P450 scc mRNA did not. We conclude that in the present culture cell model, P450arom mRNA and estradiol secretion can be maintained with low FSH concentrations, whereas higher doses of FSH downregulated P450arom mRNA levels. Contrary to P450arom mRNA, P450scc mRNA and progesterone secretion increased with highest FSH concentrations.;The objective of the second study was to determine the relative importance of FSH, IGF-I and insulin to maintain P450arom mRNA and estradiol secretion in cultured bovine granulosa cells.;The objective of the third study was to understand the intracellular mechanisms utilized by insulin and FSH to induce P450arom mRNA and estradiol secretion in granulosa cells.;The results of these studies showed that P450arom mRNA abundance and estradiol secretion can be induced and maintained by physiological FSH and insulin concentrations, and they are differentially regulated in bovine granulosa cells in vitro. (Abstract shortened by UMI.).