Factors influencing T-3 transport into red blood cells of rainbow trout, Oncorhynchus mykiss

We exposed rainbow trout, Oncorhynchus mykiss, to various environmental con ditions known to alter thyroid function in order to determine their effects on the in vitro carrier-mediated transport rate (J) of 3,5,3'-triiodo-L-th yronine (T-3) into red blood cells (RBC). Values for J (fmol T-3 transporte d/(10(6) cells min)) were (i) increased by assay temperature from 0 to 12 d egrees C but not from 12 to 21 degrees C, (ii) unaltered by acclimation for 14 d at 5 or 12 degrees C, (iii) depressed by a restricted food ration (0. 5% of mean body mass/d) but unaltered by 14 d of fasting, (iv) depressed by a T-3 challenge created by feeding T-3-supplemented food (12 ppm T-3) for 14 d, and (v) depressed 10 d after transport to our laboratory. We conclude that certain conditions that alter thyroid function also alter the rate of T-3 transport into trout RBC, with possible consequences for exchange of T -3 between plasma and RBC.