Triiodothyronine and growth hormone exert an opposite effect on the binding of growth hormone and insulin by hepatocytes from dwarf mouse.

Body weight increase together with growth hormone and insulin binding to isolated hepatocytes was used to study the effect of a chronic treatment of dwarf mice with triiodothyronine (T3), bovine growth hormone (GH) and T3 + bovine GH. After 4 weeks of treatment, the body weight increase was similar in all treated groups. However, the T3 and T3 + bovine GH treatment causes a more rapid increase in weight than bovine GH, from the first week of treatment. The binding of growth hormone was four times higher in T3 and T3 + bovine GH than in bovine GH and saline-injected mouse liver cells. This increase was mainly accounted for by a higher number of receptor sites in these cells. At low hormone concentrations, the binding of insulin expressed per unit of cell surface area was 1.3-fold lower in liver cells from bovine GH and T3 + bovine GH than in T3 and saline-injected mice. This decrease was mainly accounted for by a lower number of insulin receptors in these cells. The results presented indicate that bovine GH and T3 treatment affect the body weight increase in dwarf mice according to two mechanisms: (1) T3 increases the number of GH receptors in liver and probably GH content and secretion in pituitary; (2) GH increases the synthesis of somatomedins in liver. In addition, bovine GH treatment decreases the number of insulin receptors.