In vitro effects of 4-nonylphenol on oocyte maturation and ovarian steroid hormone dynamics in the catfish heteropneustes fossilis

Abstract

Alkylphenols are known endocrine-disrupting chemicals present in water bodies as contaminants, affecting aquatic life adversely. In this study, post vitellogenic follicles of the catfish Heteropneustes fossilis were in vitro exposed to 4-nonylphenol (4-NP) at concentrations of 0.1, 0.5, 1, 10, 100 and 200 ng/mL for 12 and 24 h. Germinal vesicle breakdown (GVBD), an indicator of final oocyte maturation (FOM), and the mortality of ovarian follicles were monitored. Levels of estradiol-17β (E2), testosterone (T), progestins; progesterone (P4), 17α-hydroxyprogesterone (17-P), 17α, 20β-dihydroxy-4-pregnen-3-one (17, 20β-DP), and cortisol (F) were measured by ELISA or HPLC. The exposure to lower concentrations of 4-NP (0.1, 0.5, 1 and 10 ng/mL) induced GVBD time dependently and the highest rate of induction was up to 25% in 0.5 ng/mL group. The higher concentrations decreased GVBD. 4-NP significantly increased the mortality rate of follicles in a dose-dependent manner. Concentrations ≥10 ng/mL produced more than 60% mortality. 4-NP elicited biphasic effects on all hormones measured, except in the level of 17-P. The levels of T, E2, P4, 17, 20β-DP and F increased at the lower concentrations and maximum increase was at 0.1 ng/mL dose for E2, P4 and 17, 20β-DP, at 0.5 ng/mL dose for F and at 1 ng/mL dose for T. Then, they were declined with increasing 4-NP concentration. In contrast, 17-P level exhibited a continuous decline in a dose-dependent manner. From the results, it is inferred that the low concentrations of 4-NP stimulated GVBD. Increase in E2 level might have lowered the rate of GVBD, despite the high level of 17,20β-DP, maturation-inducing steroid, and F. The cytotoxicity infused by 4-NP at higher concentrations adversely affected GVBD and steroid secretion, causing follicle mortality.