Influence of plasma lipid changes in response to 17 beta-oestradiol stimulation on plasma growth hormone, somatostatin, and thyroid hormone levels inimmature rainbow trout

Plasma total lipids were significantly higher in 17 beta -oestradiol (E-2)- treated immature rainbow trout Oncorhynchus mykiss at week 4 after implanta tion, due to increases in polar and neutral lipids. The lipid classes respo nding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolam ine, sterols and sterol esters, in a proportion that approximately reflecte d the increase in plasma vitellogenin (VtG) levels as measured by a non-com petitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified f atty acids and triacylglycerol were not affected by E-2 treatment. Plasma g rowth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) l evels decreased in E-2-treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E-2 action on somato troph function is possible. Plasma T-4 concentrations were not affected by E-2 treatment, but plasma T-3 concentrations were significantly lower than in controls 1 week after implantation when plasma E-2 concentrations were t he highest; this is in support of the hypothesis that E-2 has a suppressive action on T-3 production. (C) 2001 The Fisheries Society of the British Is les.