the effect of 4-n-nonylphenol on vitellogenin synthesis and thyroid hormone concentrations in immature male yellowfin seabream (acanthopagrus latus)

nonylphenol (np) is a well-known compound as having the potential to mimic the natural hormone 17β-estradiol (e2) and disrupt the endocrine system in a wide range of organisms. however, the ability of different isomers of this compound is different in exerting estrogenic effects. the objectives of this study were to estimate the effects of a straight side-chain np isomer (4-n-np) on the vitellogenin (vtg) synthesis and thyroid hormone concentrations as estrogenic and non-estrogenic responses of yellowfin seabream’s (acanthopagrus latus) endocrine system. in this regard the total numbers of 30 immature male fish were intraperitonealy injectioned by 10, 50, 100 μg/g of 4-n- np over a period of one week. the induction of vtg synthesis in treated fish was investigated using alkali labile phosphate assay and measurement of total plasma calcium. the concentrations of thyroid hormones, thyroxin (t4) and triiodothyronine (t3), in the plasma were also quantified by radioimmunoassay. the result showed that the vtg levels in the plasma were significantly increased by injection of 50 and and 100 μg/g of 4-n-np (p<0.05). moreover, the total plasma calcium concentrations in fish exposed to the highest dose used exhibited a significant increase compared to the control (p<0.05). in addition, t4 concentration in fish received 50 and 100 μg/g of 4-n-np was significantly higher than the control group (p<0.05). while, the plasma levels of t3 in fish treated by 100 μg/g of 4-n-np was significantly lower than controls (p<0.05). the results of present study indicate the potential of 4-n-np to exert the estrogenic effect as well as disturbance in the balance of thyroid hormones in yellowfin seabream.