Antagonistic effects of xenobiotics on steroid-induced final maturation of Atlantic croaker oocytes in vitro

The antagonistic effects of Kepone (chlordecone) and o,pʹ-DDD on maturation-inducing steroid (17α,20β,21-trihydroxy-4-pregnen-3-one, 20β-S) induced final maturation of Atlantic croaker (Micropogonias undulatus). Oocytes were investigated in an in vitro germinal vesicle breakdown (GVBD) bioassay. Exposure to Kepone or o,pʹ-DDD (100 nM-100 μM) prevented the majority of the oocytes from completing GVBD in response to 20β-S; many of them were arrested at the lipid coalescence or germinal vesicle migration stages when exposed to high xenobiotic concentrations (100 μM). In addition, clearing of the ooplasm, oil droplet formation and hydration were incomplete in xenobiotic-exposed oocytes that underwent GVBD. The xenobiotics inhibited GVBD in a concentration-dependent manner. One minute exposure to either of the xenobiotics was sufficient to block GVBD. Washing the follicle-enclosed oocytes after xenobiotic exposure restored their ability to undergo GVBD in response to 20β-S. These results suggest that o,pʹ-DDD and Kepone exert antagonistic effects on 20β-S action, possibly by competing for the ovarian 20β-S membrane receptor.