The impact of sex steroid agonists and antagonists on folliculogenesis in the neonatal porcine ovary via cell proliferation and apoptosis

The objective of the study was to examine the effects of androgen and estrogen agonists or antagonists on the follicle formation, ovarian cell proliferation and apoptosis as well as plasma steroid concentration in neonatal pigs. Piglets were injected with testosterone propionate (TP, 20 mg/kg bw), flutamide (FLU, 50 mg/kg bw), 4-tert-octylphenol (OP, 100 mg/kg bw), ICI 182,780 (ICI, 400 μg/kg bw), methoxychlor (MXC, 100 mg/kg bw) or corn oil (CTR, controls) between postnatal Days 1 and 10 (n = 4/group). Heart blood was collected and ovaries were excised from the 11-day-old piglets. The lower percentage of oocytes within an egg nest and higher ovarian expression of active caspase 3 were found in TP (androgen excess) piglets compared to controls. FLU-induced androgen deficiency decreased the percentage of primordial follicles, increased that of early primary follicles and diminished ovarian cell proliferation. OP-induced estrogen action increased the percentage of primordial and developing follicles as well as cell proliferation. ICI-induced estrogen deficiency decreased the percentage of transitional follicles and ovarian cell proliferation, while increased the percentage of primordial follicles and the abundance of active caspase 3. Treatment with MXC, exhibiting estrogenic, antiestrogenic, and antiandrogenic activities, declined the percentage of developing follicles and cell proliferation. Moreover, the investigated compounds differentially affected plasma steroid level. In conclusion, the present study demonstrated clear effects of TP and FLU during the earliest stages of folliculogenesis in pigs (nest breakdown and follicle assembly), whereas OP and ICI influenced also the subsequent stages of follicle initial recruitment and growth. Therefore, the androgen and estrogen seems to be important for the follicle assembly and follicle growth in neonatal porcine ovaries.