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

Plasma total lipids were significantly higher in 17 beta -oestradiol (E-2)-treated immature rainbow trout Oncorhynchus mykiss at week 4 after implantation, due to increases in polar and neutral lipids. The lipid classes responding were phosphatidylcholine, phosphatidylinositol, phosphatidylethanolamine, sterols and sterol esters, in a proportion that approximately reflected the increase in plasma vitellogenin (VtG) levels as measured by a non-competitive enzyme-linked immunosorbent assay (ELISA). Plasma non-esterified fatty acids and triacylglycerol were not affected by E-2 treatment. Plasma growth hormone GH levels were increased, and plasma somatostatin-14 (SRIF) levels decreased in E-2-treated fish, responses which could be secondary to elevated plasma lipid (VtG) content, although a direct E-2 action on somatotroph 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 the 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 Isles.