Concentration-dependent effects of allopregnanolone on bovine pre-antral follicles in ovarian cortical tissue cultured in vitro.

Allopregnanolone (ALLO) is a neuroactive steroid derived from progesterone that plays well-established roles in the nervous system. However, its impact on ovarian physiology remains underexplored. This study investigated the concentration-dependent effects of allopregnanolone on bovine pre-antral follicles in vitro. Ovarian cortical tissue from Aberdeen Angus heifers was cultured with ALLO at concentrations of 5, 10, 50, 100, 500, and 1000 nM for 24 h. Histomorphometric parameters, stromal and granulosa cell counts, and markers of proliferation (PCNA) and apoptosis (TUNEL) were analyzed. Primary follicle density increased at 100 nM and decreased at 10 nM, while secondary follicle density increased at 10 nM and 100 nM. Degenerated primordial follicle density increased at 5, 50, and 100 nM, primary follicle density increased at 50, 100, and 500 nM, and secondary follicle density increased at all concentrations except at 10 nM and 1000 nM. Follicular diameter increased at 100 nM in primordial and primary follicles and decreased at 5 nM and 500 nM in the same types. In secondary follicles, it decreased at 50 and 100 nM. Oocyte diameter decreased at all concentrations in primordial and primary follicles except at 50 nM and in secondary follicles at 5 nM, 10 nM, 50 nM, and 500 nM. Chromatin diameter decreased in primordial and primary follicles at 5, 100, and 500 nM and in secondary follicles at 5 and 500 nM. Granulosa cell counts increased at 500 nM in primordial follicles and at 100 nM and 500 nM in primary and secondary follicles. PCNA increased at 10 and 500 nM in primary follicles, and apoptosis increased at 50 nM in primordial and primary follicles and at 10 and 1000 nM in secondary follicles. These findings reveal a concentration-dependent effect of ALLO on early folliculogenesis and stromal remodeling, highlighting its relevance in ovarian tissue culture and fertility preservation.