Oocyte number in newborn mice after prenatal octylphenol exposure

The aim of the present study was to investigate whether prenatal exposure to the suspected estrogenic compound 4-tert-octylphenol (OP), influences oocyte number in newborn female mice. In addition, effects on the percentage distribution of prefollicular, follicular, and atretic oocytes were investigated. Pregnant mice were subcutaneously injected with OP (1 or 250 mg/kg) or vehicle alone on embryonic day 11.5-16.5 (plug = embryonic day 0.5). As a positive control for estrogenic effects, a group of animals was injected with the synthetic estrogen diethylstilbestrol (DES, 100 microg/kg). Ovaries from the offspring were collected on the day of birth and a stereologic method, the optical fractionator, was used to estimate the number of prefollicular, follicular, and atretic oocytes in the ovaries. The total number of oocytes was calculated as the sum of the three subpopulation estimates. Neither OP nor DES exposure could be observed to affect the total number of oocytes or the percentage distribution of atretic, prefollicular, and follicular oocytes. Thus, prenatal OP exposure does not appear to cause a serious threat to fetal female germ cell proliferation and survival, or early follicle formation.