Effects of 17b-estradiol and 4-nonylphenol on osmoregulation and hepatic enzymes in gilthead sea bream (Sparus auratus)

Sexually immature Sparus auratus were injected intraperitoneally with coconut oil either alone (control) or containing 17b-estradiol (E sub(2), 10 kg/g body mass) or 4-nonyphenol (4-NP, 100 and 200 kg/g body mass) and sampled 10 days later. Gill and kidney Na super(+),K super(+)-ATPase activities, plasma levels of E sub(2) and cortisol, plasma osmolites (osmolality, sodium and chloride) and metabolites (glucose, lactate, proteins and triglycerides) were examined. Livers were used for measuring hepatosomatic index (HSI) and determinations of the activities of antioxidant defences catalase (CAT) and total glutatione peroxidase (t-GPX), the CYP1A-dependent, 7-ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST). HSI and plasma levels of E sub(2) were significantly increased in E sub(2)-treated fish. E sub(2) treatment enhanced plasma osmolality, glucose, triglycerides and proteins, but had no effect on plasma cortisol, and gill and kidney Na super(+),K super(+)-ATPase activities. Hepatic activities of EROD, GST and CAT were significantly decreased after E sub(2) administration, whereas t-GPX remained unaffected. Treatment with 200 kg/g 4-NP caused a slight increase in plasma E sub(2) relative to the control group. Plasma glucose and protein levels were not affected by 4-NP, while triglycerides were increased. Fish treated with the higher dose of 4-NP displayed a clear reduction in kidney Na super(+),K super(+)-ATPase activity, together with increases in plasma osmolality, relative to the control group. High 4-NP also caused a significant decrease in EROD and an increase in GST activity. Our results confirm the regulation of the natural estrogen E sub(2) and the weak xenoestrogen 4-NP on osmoregulation and biotransformation enzymes in a partially similar manner. The actions of xenoestrogens on critical physiological processes may have an ecological significance as it can reduce adaptability and capacity to metabolise xenobiotics under stressful conditions.