[Effect of thyroidectomy on the beta-cell function of the pancreatic islet apparatus]

The functional activity of the insular apparatus of the pancreas with varying function of beta-cells and body sensitivity to insulin were studied in vivo and in vitro in an experimental hypothyroidal condition produced by total removal of the thyroid from rabbits and rats. Insulin was detected by radioimmunoassay, whereas insulin biosynthesis was assessed from 3H-leucin incorporation into the de novo formed islet proteins with insulin immunoreactivity (proinsulin plus insulin). The insulin test (0.3 Units/kg mass, intravenously) was made to study glycemia and the level of non-esterified fatty acids in the blood serum. Thirty days after thyroidectomy glucose homeostasis was not disturbed, and the body sensitivity to sugar-reducing and antilypolytic insulin actions did not undergo any changes. The deficiency of thyroid hormones produced an increase in basal and glucose-induced insulinemia (intravenous glucose tolerance test) and a rise in the exogenous insulin break down rate. No changes in the biosynthesis of insulin by the islets were detected. The increase in the secretory response of beta-cells to glucose with undisturbed insulin formation presents a compensatory reaction aimed at making normal glycemia possible. The regulating effect of thyroid hormones on the secretory response of beta-cells and the essential role of the latter in glucose homeostasis under deficiency of thyroid hormones are discussed.