We determined 1) whether the previously observed induction of estradiol secretion in bovine granulosa cells cultured in serum-free conditions is associated with an increase in cytochrome P450 aromatase (P450_arom) mRNA abundance and 2) whether P450_arom mRNA levels are responsive to FSH in vitro. Granulosa cells from small (2–4-mm) follicles were cultured in serum-free medium. Estradiol secretion increased with time in culture and was correlated with increased P450_arom mRNA abundance. Progesterone secretion also increased with time in culture, but P450 cholesterol side-chain cleavage (P450_scc) mRNA abundance did not.

FSH stimulated estradiol secretion and P450_arom mRNA abundance; the effect was quadratic for both estradiol and P450_arom mRNA. Estradiol secretion and P450_arom mRNA levels were correlated. FSH stimulated progesterone secretion and P450_scc mRNA abundance, although the minimum effective dose of FSH was lower for estradiol (0.1 ng/ml) than for progesterone (10 ng/ml) production. Insulin alone stimulated estradiol secretion and P450_arom mRNA levels but not progesterone or P450_scc mRNA abundance. We conclude that this cell culture system maintained both estradiol secretion and P450_arom mRNA abundance responsiveness to FSH and insulin, whereas P450_scc mRNA abundance and progesterone secretion were responsive to FSH but not insulin.