Stimulation of the uptake of alpha-aminoisobutyric acid in rat thymocytes by L-triiodothyronine: a comparison with insulin and dibutyryl cyclic AMP.

L-Triiodothyronine in vitro increased the uptake of the non-metabolizable amino acid, alpha-aminoisobutyrate, into isolated rat thymocytes. This effect was evident at extracellular free hormone concentrations of 10-7 to 5 times 10-8M and was due to a marked inhibition of amino acid efflux. In contrast, insulin and dibutyryl cyclic AMP, which also increased uptake in these cells, acted to stimulate amino acid influx. When L-triiodothyronine was added to maximally effective concentrations of either insulin or dibutyryl cyclic AMP, the resultant effect was the sum of the effect of each hormone added individually. These studies extended previous observations which indicate that thyroid hormones stimulate the cellular uptake of amino acids, and they provide a convenient system for the study of thyroid hormone action in vitro.