Estrogen, Androgen, and Progesterone Biosynthesis by Theca and Granulosa of Preovulatory Follicles in the Pig1

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Abstract
Prepubertal gilts were treated with 1000 IU PMSG and slaughtered at 0, 36, or 72 h, or at 75 h following treatment with 500 IU of hCG at 72 h. Theca and granulosa were isolated from preovulatory follicles and cultured for 24 h alone or with FSH or LH and in combination with or without testosterone. In vitro accumulation of estradiol-17β (E2), progesterone (P), testosterone (T), and androstenedione (A) was measured for each culture. On a per follicle basis, theca produced E2 in quantities comparable to granulosa, but granulosa required an exogenous aromatizable substrate (T) whereas theca did not. Theca was the sole source of androgen, predominantly A, and produced significant quantities of P, though granulosa was the primary producer of P. Theca was responsive to LH but not FSH, particularly in the early stages of follicular development, in production of all steroids except E2. The overall thecal production of all steroids increased with development of the follicle to 72 h, and in vivo hCG treatment further stimulated the production of P, A, and T but inhibited E2 biosynthesis. In culture in the absence of exogenous steroid, there was a net depletion of A and T by granulosa, matching the accumulation of E2. Granulosa cell androgen content prior to culture was correlated with thecal androgen synthetic activity, providing indirect evidence that thecal androgen is transferred to granulosa cells in vivo. In the presence of T, granulosa production of E2 declined with development of the follicle but was enhanced 3 h after hCG treatment in vivo; there was no effect of gonadotropin on in vitro E2 synthesis. The granulosa biosynthesis of P increased with follicular development, and was highly responsive to both LH and FSH in the early stages; P production was unaffected by addition of T. We conclude that, in the porcine preovulatory follicle, theca is an important source of E2 and the sole source of androgen. After transfer from theca to granulosa cells, A is converted to T and thence to E2. Granulosa is also the predominant site of P synthesis.