A Single Dose of the Ovotoxicant 4-Vinylcyclohexene Diepoxide Is Protective in Rat Primary Ovarian Follicles

Abstract

Repeated dosing of rats with the ovotoxic chemical, 4-vinylcyclohexene diepoxide (VCD), destroys primordial and primary ovarian follicles via apoptosis (physiological cell death) by accelerating the normal rate of atresia. The present study investigated the effect of a single dose (1×) of VCD. Immature (d28) female Fischer 344 rats were dosed 1× or 15× with VCD (80 mg/kg ip). Ovaries were collected 24 h or 15 days following 1× VCD or after 15× for classification and evaluation. Following 1× VCD the number of healthy primary follicles was greater (p < 0.05) than control 24 h and 15 days later. This effect reflected a slowing of the normal rate of atresia seen in control ovaries. There was no effect of a single dose on primordial or growing follicles at any time. Expression of mRNA encoding the cell death gene bax was reduced (p < 0.05) on d1 after 1× VCD in isolated primordial and primary follicles. These observations were in contrast to a decreased (p < 0.05) number of healthy primary and primordial follicles in ovaries and increased (p < 0.05) bax mRNA in isolated follicles from rats dosed 15× for 15 days. Immunofluorescence staining revealed that, the distribution of Bax protein was similar between ovaries from controls and 1× or 15× VCD-treated rats. These data provide evidence for a “protective” response against the normal rate of atresia in primary ovarian follicles following exposure to 1× VCD. Additionally, changes in expression of bax mRNA paralleled alterations in the rate of atresia.