Biology of Reproduction, Vol 25, 673-682, Copyright © 1981 by Society for the Study of Reproduction

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

¹ MRC Group in Reproductive Biology, Department of Physiology, and Department of Obstetrics and Gynecology, The University of Western Ontario, London, Ontario, Canada N6A 5A5
² Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1

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-17 (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.

Note:
ACKNOWLEDGMENTS We greatly appreciate the technical assistance of Ms. Barbara Atkinson and Dr. Susan Huntley. We thank the NIH Hormone Distribution Office (USA) for donating the LH and FSH.

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