Triiodothyronine increases glucose transporter isotype 4 mRNA expression, glucose transport, and glycogen synthesis in adult rat cardiomyocytes in long-term culture.

Effects of T3 treatment (day 2-day 12) on the expression of the insulin-regulated GLUT4, on 2-deoxyglucose uptake, and on glycogen synthesis were studied in ARC after 12 days of culture in T3-depleted 20% fetal calf serum. GLUT4 mRNA expression was low in controls, but increased in a dose-dependent manner by T3 treatment up to 2.8-fold at 100 nM. In parallel, 100 nM T3 increased basal 2-deoxyglucose uptake 1.95-fold and insulin-stimulated uptake 1.75-fold. In addition, T3 enhanced basal and insulin-stimulated [14C] glucose incorporation into glycogen 1.86- and 1.5-fold, respectively. Hence, ARC may meet part of their increased energy requirements in response to T3 by enhancing GLUT4 expression.