Effect of thyroid hormone on insulin action in cultured arterial smooth muscle cells

The effect of triiodothyronine (T3) on insulin action in cultured smooth muscle cells of the rat aorta were studied. Insulin binding to smooth muscle cells was increased by T3. The Scatchard analysis indicated an increase of insulin binding sites and an elevation of the affinity of insulin to its binding sites. T3 alone had no significant effect on DNA, RNA and protein synthesis in smooth muscle cells and did not increase the transport of 3-O-methylglucose into the cells. However, the insulin-induced 3-O-methylglucose transport into the cells was stimulated. The insulin-stimulated protein synthesis was not significantly altered by T3 treatment, whereas the effect of insulin on DNA and RNA synthesis was even reduced in the presence of T3. The study suggests, that T3 treatment produces predominantly a stimulation of processes which are necessary for the production of energy. The anabolic effect of insulin is decreased and must by inferior to the credit of energy production.