Functional Studies of Aromatase Activity in Human Granulosa Cells from Normal and Polycystic Ovaries*

Abstract

To determine the basis of the reduced ovarian estrogen (E) production in polycystic ovary syndrome (PCO), the ability of granulosa cells from normal and polycystic ovaries to aromatize androgens was assessed both in vitro and in vivo. During a 5-h incubation in vitro with graded doses of aromatase substrate [androstenedione (Δ⁴), 10⁻¹⁰−10⁻⁶ M], a dose-related increase in E production was observed in granulosa cells from normal 8- to 15-mm follicles; the minimum and maximum effective doses of Δ⁴ were 10⁻¹⁰ and 10⁻⁷ M, respectively, and the ED₅₀ was approximately 10⁻⁸ M. In contrast, granulosa cells from 4- to 6-mm follicles of both normal and polycystic ovaries produced negligible amounts of E when incubated 5 h with graded doses of Δ⁴,suggesting that the aromatase enzyme had not been induced in follicles of this size. To test the functional relationship between gonadotropins and E production in PCO and normal granulosa cells from the aromatase-deficient 4- to 6-mm follicles, these granulosa cells were cultured in a chemically defined medium for 48 h with Δ⁴ (10⁻⁷ M) and FSH (100 ng/ml) or human LH (100 ng/ml). Cultured granulosa cells from both PCO and normal subjects responded significantly to FSH by showing 24- and 17-fold increases in E production, respectively. LH had little or no effect. Similarly, administration of human FSH to patients in vivo resulted in a rapid and dramatic increase in plasma estradiol and estrone levels. These results indicate that granulosa cells from PCO patients have an inherent ability to respond to the FSH induction of aromatase activity, but the Graafian follicles never develop to the size in which the aromatase enzyme is normally expressed. Such data strongly suggest that the absence of aromatase in PCO and the arrested follicle growth may be caused by a reduced local concentration of FSH and/or decreased bioactivity.