The Effect of Triiodothyronine on Insulin Binding and Action in Rat Adipocytes

Abstract

The effects of a short term (2 hour) incubation of 5 microM triiodothyronine (T3) on 125I-insulin binding and insulin stimulated (14C)-2-deoxy-D-glucose uptake in rat adipocytes was investigated. In the presence of 5 microM T3, (14C)-2-deoxy-D-glucose uptake was significantly decreased by 11 to 24% at insulin concentrations of 5 to 1000 microU/ml. The concentration of insulin eliciting a half maximal response for insulin stimulated (14C)-2-deoxy-D-glucose uptake was 11.5 microU/ml in the control, and 14.3 microU/ml in the T3 treated cells (p less than 0.01). T3 treated adipocytes bound 9 to 22% less 125I-labeled insulin yet the concentration of native insulin necessary to displace 50% of the bound 125I-labeled insulin was the same in the control and T3 treated cells (75 and 70 ng/ml, respectively). These studies indicate that the decreased sensitivity of T3 treated cells to insulin is in accordance with a decreased number of receptors with the same binding characteristics as those of the control cells. The decreased maximal uptake of (14C)-2-deoxy-D-glucose at saturating insulin levels is likely to be independent of receptor number and result from a second, undetermined alteration in the hexose transport system of adipocytes treated with T3.

The Effect ofIn VivoThyroxine Treatment on Insulin Receptors, Glucose Transport and GLUT4 in Rat Adipocytes

“…It seems that this general statement is not universal, particularly with regard to glucose utilization, since the tissue specific differences may occur. Czech and Amatruda (6) showed that in vitro addition of T3 to isolated adipocytes lowered both, the insulin receptors and glucose uptake as well.…”

Metabolic Development of Porcine Fetal Adipose Tissue

“…These hormones are reduced or absent from decapitated pig serum [18] as are cate cholamines [unpublished data]. The absence of these potent insulin antagonists [3,4,13,22] during the developmental period of glu cose-sensitive insulin secretion [8] suggests that these insulin antagonists may contribute to the observed differences between tissues from decapitated and control animals as ges tation proceeds.…”