Investigation of Iodothyronine Binding to Plasma Proteins in Brook Trout, Salvelinus fontinalis, Using Precipitation, Dialysis, and Electrophoretic Methods

Abstract

Over 95% of 3,5,3′-triiodo-L-thyronine (T₃) or L-thyroxine (T₄) up to added hormone levels of at least 5 μg/ml, were precipitated by trichloroacetic acid with plasma proteins of brook trout using a semimicro method. Hormone recovery in the precipitate was higher than with precipitation methods previously used on fish plasma.Equilibrium dialysis showed over 99% of T₄ or T₃ bound to plasma proteins of trout up to added hormone levels of at least 5 μg/ml.Acrylamide gel was superior to paper and particularly cellulose polyacetate as a medium for electrophoretic separation of proteins responsible for binding T₃ or T₄. In vitro studies at high hormone levels showed that T₃ and T₄ bound mainly to prealbumin-like proteins. In vivo studies at more physiological levels showed T₄ bound to fast prealbumin-like, albuminlike, and β-globulin-like proteins, while T₃ bound to slow prealbumin-like and probably the same albumin-like and β-globulin-like proteins as T₄.