Serum thyroid hormone, guanine and protein profiles during smoltification and after thyroxine treatment in the masu salmon, Oncorhynchus masou

Abstract

Changes in serum thyroid hormones (thyroxine:T 4, triiodothyronine:T 3), skin and serum guanine, total serum protein and albumin-like protein (α 1-protein) concentrations were investigated during smoltification in yearling masu salmon, Oncorhynchus masou. Moreover, the effects of T 4 on their concentrations were examined in the underyearling fish. Skin and serum guanine levels increased as smoltification progressed. T 4 and T 5 levels followed skin and serum guanine profiles. At least four guanine-binding proteins were found in the serum. One of them was identified immunologically as a 1-protein. T 4 treatment caused increase in guanine levels in skin and serum. However, T 4 led to no change of a 1-protein concentrations. The present results suggest a possible pathway whereby guanine is induced by T 4 and transported to the skin by guanine-binding protein in the blood.