In vitro induction/inhibition of germinal vesicle breakdown (GVBD) in frog (Euphlyctis cyanophlyctis) oocytes by endocrine active compounds.

Oocyte maturation is transformation of oocytes into a fertilizable egg. This study examined the effects of four classes of chemicals: 1) acephate (organophosphate); 2) atrazine (herbicide); 3) cypermethrin and fenvalerate (synthetic pyrethroids); and 4) carbaryl (carbamate) on in vitro germinal vesicle breakdown (GVBD) of Euphlyctis cyanophlyctis oocytes. Follicles were isolated and defolliculated from surgically removed ovaries of E. cyanophlyctis and exposed to either progesterone (1 μM/mL) or graded concentrations (1, 5, 10, 15, and 20 μg/mL) of test chemicals. GVBD was evident by the presence of a white spot in the animal pole as well as the absence of germinal vesicles in sectioned heat-fixed oocytes. Percent GVBD was scored every 4 hours until 24 hours. Progesterone induced 77-84% GVBD, compared to 29-33% in controls, at 24 hours. Acephate induced 46-67% GVBD, whereas atrazine elicited 58-77% of GVBD. In cypermethrin or carbaryl- or fenvalerate-exposed oocytes, GVBD was limited to 22-28, 17-29 and 18-24%, respectively. The study infers that some chemical contaminants in the aquatic system may interfere with GVBD in amphibians. Because oocyte maturation is a prerequisite for the production of fertilizable eggs, any alteration in this process potentially impairs the fecundity of females.