Autophosphorylation of the insulin receptor in rat adipocytes is modulated by thyroid hormone status

The effect of thyroid status on the in vitro autophosphorylation of the insulin receptors was studied in triton-solubilized adipocyte plasma membranes obtained from normal and thyroidectomized rats. Thyroidectomy results in an increase (two to three times) of the in vitro insulin-dependent phosphorylation of the insulin beta-subunit receptor. Phosphorylation occurred on tyrosine residues. In vivo injection of triiodothyronine to thyroidectomized rats restored plasma membranes autophosphorylation of the beta-subunit to the values obtained for control euthyroid rats. This effect was independent of the number and affinity of the insulin receptors, which were not modified regardless of thyroid status.