441 Perinatal hypoxia leads to primordial follicle activation and premature depletion of ovarian reserve: rat model

Abstract

The human ovary contains 6-million follicles during 20th week of embryonic development and 1-million at birth. The majority of these follicles are eliminated by atresia and only ∼300,000 reach reproductive age. Depletion of ovarian reserve is a serious cause for infertility and can be caused by various physiological, pathological and iatrogenic conditions. The rat ovary development at days 1-5 postpartum represents the human ovary development at the late perinatal period. Newborn Sprague Dawley rat pups(n=5) were exposed to hypoxia, 5%oxygen/95% nitrogen for 10 min three times daily from day 1 to day 5 postpartum. Control pups(n=5) received no hypoxic intervention. On day 5 ovaries were harvested and embedded in paraffin. H&E staining was used for follicle counts. Ki-67 staining was performed to detect stromal cellular proliferation. Apoptosis was assessed by TUNEL staining. The percentage of primordial follicles out of total follicles in ovaries of pups exposed to hypoxia was lower than in control ovaries (76±8.2% and 90.33±6.3% respectively, p<0.05). The percentage of primary and secondary follicles in ovaries of pups exposed to hypoxia was higher than in control ovaries (12.93±6% and 5.82±3.13%; 10.5±5.12 % and 3.28±2.42% respectively, p<0.05).The mean stromal Ki67 staining in ovaries of pups exposed to hypoxia was significantly lower than in the ovaries from the hypoxia group (1.67±0.58 and 2.5±0.55 respectively, p<0.05). There was no difference in stromal apoptosis rates between both groups. We provide evidence for the first time that perinatal hypoxia causes premature activation and growth initiation of dormant follicles leading to diminished ovarian reserve. These changes were associated with decreased stromal cell proliferation, indicating hypoxia-induced loss of the support cell pool as a possible mechanism for accelerated follicular activation.View Large Image Figure ViewerDownload Hi-res image Download (PPT)