Dose‐related effects of 17βoestradiol (E₂) on liver weight, plasma E₂, protein, calcium and thyroid hormone levels, and measurement of the binding of thyroid hormones to vitellogenin in rainbow trout, <i>Salmo gairdneri</i> Richardson

Abstract

Administration of 17β‐oestradiol (E 2 ) to rainbow trout, in the form of hydrogenated coconut oil implants produced a stable, long‐term elevation in plasma E 2 levels. The elevation was doserelated (over the range 1–10mg kg‐ 1 body weight) both 4 and 8 weeks after implantation. Dose‐related increases were also observed with respect to liver weight‐body weight ratios and plasma protein levels. Plasma T 3 and total calcium levels were depressed and elevated, respectively, by E 2 treatment but the responses were not linearly related to the dose of E 2 administered; there was no significant effect of E 2 on plasma T 4 levels. E 2 induced a shift in the binding of T 3 to plasma proteins, with T 3 binding to smaller molecular weight proteins; neither T 4 nor T 3 bound to vitellogenin which was present at high levels in the plasma of E 2 ‐treated fish.