Testosterone induces activation of porcine primordial follicles in vitro.

Purpose: The mechanism underlying primordial follicle activation is poorly understood. In this study, in-vitro culture and subsequent xenotransplantation were conducted to determine whether testosterone promotes the activation of porcine primordial follicles.
Methods: Prepubertal porcine ovarian cortical strips containing primordial follicles were cultured in the presence of testosterone for 7 days, and subsequently transplanted to immunodeficient mice for 2 months. After culture and transplantation, development of follicles was examined histologically. The presence of androgen receptors in oocytes was assessed by use of western blot and immunohistochemical analyses.
Results: Testosterone at 10-6 m induced the primordial follicle transition to the intermediate (19 ± 4%) and primary (3 ± 1%) stages after 7-day culture, while 56 ± 5% of primordial follicles remained in the initial pool. Higher concentrations, above 10-5 m, or lower concentrations, below 10-6 m, did not induce follicle transition to the primary stage. After 7-day culture with 10-6 m testosterone, ovarian cortical strips were transplanted to immunodeficient mice. Some of the follicles developed to the secondary (15 ± 3%) and antral (10 ± 3%) stages, whereas 44 ± 7% of primordial follicles remained in the initial pool. In the culture experiment, estradiol-17β (10-7-10-5 m) had no significant effect on follicle activation. The androgen receptor antagonist, cyproterone acetate, inhibited the stimulatory effect of testosterone on primordial follicle activation, suggesting an androgen receptor-mediated action of testosterone. Western blot and immunohistochemical analyses revealed that androgen receptors were present in the oocytes of primordial follicles. Conclusions: These results suggest that testosterone at 10-6 m promotes the activation of porcine primordial follicles in vitro through the androgen receptors in the oocytes.