Serum vitellogenin levels and reproductive impairment of male Japanese medaka (Oryzias latipes) exposed to 4-tert-octylphenol

The induction of synthesis of the "female" yolk precursor protein vitelloge nin (VTG) in male fish by estrogenic chemicals in the environment has been demonstrated in many recent reports. However, little is known about the org anismal and biological significance of this phenomenon. To examine the rela tionship between VTG production in male fish and reproductive impairment, a dult male medaka were exposed to 4-tert-octylphenol (OP), a known environme ntal estrogen, in concentrations ranging from 20 to 230 ppb for 21 days, un der flow-through conditions. Following exposure, male fish were mated, in t he absence of OP, with unexposed females. Breeding groups composed of expos ed males and control females produced about 50% fewer eggs than control gro ups. VTG levels in serum of male fish increased with increasing OP exposure concentration and decreased after OP exposure was discontinued. Neverthele ss, significant correlations (p<0.01) were observed between VTG levels in e xposed male fish and 1) OP exposure concentrations, 2) percent of fertilize d eggs, and 3) survival of embryos. OP-induced VTG synthesis and reproducti ve impairment appear to be closely linked phenomena. Histological examinati on indicated spermatogenesis in OP-exposed fish was inhibited, and some exp osed fish had oocytes in their testes. Finally, OP caused a significant inc rease in the number of abnormally developing embryos, suggesting that OP ma y be genotoxic as well as estrogenic.