Neonatal exposure to agonists and antagonists of sex steroid receptors induces changes in the expression of oocyte-derived growth factors and their receptors in ovarian follicles in gilts.

The objective of the present study was to examine the effects of neonatal exposure to either agonists or antagonists of androgen and estrogen receptors on the expression of growth and differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) and their cognate receptors (TGFBR1, BMPR1B, and BMPR2) in ovarian follicles of adult pigs. Piglets were injected subcutaneously with testosterone propionate (TP, an androgen, at 20 mg/kg bw), flutamide (FLU, an antiandrogen, at 50 mg/kg bw), 4-tert-octylphenol (OP, an estrogenic compound, 100 mg/kg bw), ICI 182,780 (ICI, an antiestrogen, 400 μg/kg bw), or corn oil (control) between postnatal Days 1 and 10 (n = 5/group). Ovarian follicles were excised from adult pigs on Days 8-11 of the estrous cycle. The expression of GDF9, BMP15, TGFBR1, BMPR1B and BMPR2 were examined in the population of preantral and small antral ovarian follicles using real-time PCR, Western blot and immunohistochemistry. In preantral follicles, the upregulation of GDF9 mRNA and protein expression was found in pigs that were neonatally exposed to TP or FLU, while administration of TP or ICI resulted in upregulation of BMP15. TGFBR1 and BMPR2 mRNA and protein expression were upregulated in preantral follicles of adult pigs that were neonatally exposed to TP or FLU, while administration of TP or ICI resulted in upregulation of BMPR1B. In small antral follicles, the mRNA and protein for TGFBR1 and BMPR2 were upregulated, while BMPR1B was downregulated in response to neonatal OP treatment. In addition, treatment with FLU upregulated BMPR1B and BMPR2 mRNA and protein expression, while downregulated the expression of TGFBR1. Moreover, GDF9 and BMP15 were immunolocalized in oocytes and granulosa cells of preantral follicles obtained from both control and treated ovaries. TGFBR1, BMPR1B and BMPR2 receptors were observed in the oocytes and granulosa cells of preantral follicles as well as in granulosa and theca cells of small antral follicles. In conclusion, the present study demonstrated neonatal exposure to either agonists or antagonists of androgen and estrogen receptors affected GDF9 and BMP15 signalling in ovaries of adult pigs. It seems that neonatal androgen excess or deficiency may lead to the acceleration of initial follicle recruitment, while neonatal exposure to compounds with antiandrogenic and estrogenic activity may disturb small antral follicles fate. Therefore, it confirms that neonatal window is critical for programming of ovarian function in pigs.