Effect of endocrine disruptors on the oocyte maturation and ovulation in amphibians, rana dybowskii

Abstract

Recently, we have shown that some endocrinedisruptors, heavy metals, organotins and azoles suppressedsteroidogenic enzymes such as P450 side-chain cleavageenzyme (P450sc) and aromatase in bullfrog ovarian follicles.In the present study, by using an amphibian ovarian follicleculture system, we examined the effects of these endocrinedisruptors on maturation and ovulation of oocytes fromRana dybowskii in vitro. Ovarian fragments or isolatedfolicles were cultured for 24 h in a medium containing frogpituitary homogenate (FPH) or progesterone (P4) with orwithout endocrine disruptors, and oocyte maturation (germinalvesicle breakdown, GVBD) and ovulation were examined.Among the organotins, tributyltin (TBT) strongly inhibitedboth FPH- and P4-induced oocyte maturation (ED500.7M, respectively); however, tetrabutyltin (TTBT) anddibutyltin (DBT) showed only partial suppression, whilemonobutyltin (MBT) showed no inhibitory effect. All of theorganotins suppressed P4-induced oocyte ovulation veryeffectively at a low concentration, and TBT and DBT exertedan inhibitory effect on FPH-induced ovulation. Among theheavy metals, mercury (Hg), cadmium (Cd) and cobalt (Co)were very effective in inhibiting FPH-induced oocytematuration and ovulation, while lead (Pb), arsenite (As) andmetals suppressed FPH-induced oocyte ovulation at a highdose (100 M). Among the azoles, itraconazole (ICZ),ketoconazole (KCZ) and clotrimazole (CTZ) effectivelyinhibited FPH-induced oocyte maturation and ovulation,while econazole (ECZ), miconazole (MCZ) and fluconazole(FCZ) were considerably less effective. These resultsdemonstrated that the abovementioned endocrine disruptorsexhibited diferential effects on oocyte maturation andovulation in amphibian follicles and that the frog ovarianculture system could be used as an effective experimentaldisruptors in vitro.