Protein and gene expression of VTG in response to 4-nonylphenol in rockfish (Sebastes schlegeli)

To investigate the in vivo estrogenic activity of 4-nonylphenol (4-NP) on reproductive function, we have measured the expression level of rockfish vitellogenin (rVTG) mRNA, concentration of plasma VTG and levels of plasma estradiol-17β (E2) and testosterone (T) by radioimmunoassay (RIA). An rVTG mRNA transcript of approximately 4.0 kb was extracted from hepatic tissue for Northern blot analysis, and the effects of 4-NP on rVTG mRNA expression in vivo with both male and female juvenile rockfish were examined. The level of rVTG mRNA expression was increased 48 h after injection with 4-NP of 10 mg/kg body mass and after injection in both male and female rockfish. The level of rVTG mRNA expression was increased 24 h after injection in male rockfish injected with 4-NP of 25 mg/kg body mass, while the level of rVTG mRNA expression was increased 12 h after injection in female injected with same dosage. Concentrations of plasma rVTG in female injected with 4-NP of 10 and 25 mg/kg b.w. were increased 72 h after injection and reached 35 and 66 mg/mL, respectively. In male, rVTG concentrations with the dosage of 25 mg/kg body mass were increased 72 h after injection and reached to 14 and 65 mg/mL at 168 h, respectively. Plasma concentrations of T and E2 in female and male injected with 4-NP were not significantly different between two 4-NP dosages. These results suggest that 4-NP may disrupt the reproductive system of immature rockfish by acting directly on vitellogenesis. Immature females injected with 4-NP were more sensitive than immature males, but VTG in immature males is likely to return to normal conditions slowly. There are obviously large interspecies differences in response of fish to 4-NP.