The effect of 4-nonylphenol on the synthesis of vitellogenin in the flounder Platichthys flesus

Abstract

Dose–response effects of the putative estrogenic compound 4-nonylphenol (4-NP) on the de novo synthesis of vitellogenin were investigated in the flounder Platichthys flesus. Male flounders received intraperitoneal injections during a period of 2 weeks with 10, 50, 100, 150 and 200 μg g −1 week −1 of 4-NP. Controls received the peanut oil vehicle only. The dose–response effects of the treatment were investigated on different plasma indicators of vitellogenin, alkali-labile protein phosphorous, total calcium and protein. Increased concentrations of these indicated a dose–response induced synthesis of vitellogenin in the liver of the 4-NP-treated male flounders. Vitellogenin from plasma of estradiol-treated male flounders was purified by gel filtration followed by ion-exchange chromatography and subsequently subjected to native gel electrophoresis. The purified vitellogenin fraction appeared as a high molecular protein band of 540 kDa in the electropherograms. The presence of vitellogenin in the plasma of the 4-NP-treated fish could then be directly detected by the native gel electrophoresis method. A high molecular weight vitellogenin band from plasma of the 4-NP-treated males appeared in the electropherograms in exactly the same position as the purified vitellogenin and vitellogenin in plasma of estradiol-treated male flounders. No vitellogenin band could be detected in the plasma of control males. The dose–response effect of the 4-NP-treatment was also reflected by an increased thickness of the vitellogenin band of the electropherograms by increasing doses of the 4-NP. De novo induction of vitellogenin synthesis in the liver was also indicated by increases of the hepatosomatic indices and of hepatic total RNA in the 4-NP-treated fish. No changes could be observed in the hepatic DNA concentrations. A significant increase of plasma GPT-concentrations indicated that 4-NP also elicited toxic effects on the fish. This was further indicated by a high mortality in the group treated with the highest dose of 4-NP (200 μg g −1). No effect could be observed on the gonadosomatic indices of the treated fish when compared to the peanut oil-injected controls. The present experiments were carried out towards the end of the reproductive season with testicular size observed to be near maximal in the control group. This is the most likely reason why no effect of the 4-NP injections could be observed on the testicular morphology or growth in the present experiments.