Effects of exogenous 17β‐estradiol on follicular development in the neonatal and immature mouse in vivo

Purpose The study was aimed to examine the effects of exogenous 17β‐estradiol (E 2 ) on oocyte nest breakdown and follicular growth in the ovary of neonatal and immature mice. Methods The effect of E 2 on primordial follicle formation and differentiation were examined by treating neonatal mice with E 2 in mineral oil at a dose of 10 mg/kg by sc injection each day from postnatal days 1 (PND1) to 10 (PND10). This investigation was conducted by using histological observation and immunohistochemical staining of proliferating cell nuclear antigen (PCNA); the numbers of follicles at each stage were examined to assess the follicular development. Results The results indicated that such dose of E 2 inhibited oocyte nest breakdown from PND1 to PND10 significantly and enhanced the oocyte staining intensity of PCNA in the ovary by PND3, 5 and 10. PCNA staining was mainly detected on growing follicles (stages later than primary follicle). Our results also revealed that E 2 decreased the size of the reproductive tract at PD10. Conclusions This dose of E 2 treatment inhibits oocyte nest breakdown and primordial follicle assembly, and causes follicle losses after PND5. Effects of exogenous E 2 on follicular development in the neonatal and immature mouse may through a PCNA‐dependent pathway.