EFFECTS OF HYPERINSULINEMIA UNDER THE EUGLYCEMIC CONDITION ON CALCIUMAND PHOSPHATE-METABOLISM IN NONOBESE NORMOTENSIVE SUBJECTS

The effect of acute insulin infusion on the metabolism of calcium (Ca) and phosphate (P) was examined in 17 healthy subjects. They mere hosp italized and kept on a constant diet for 5 days, and an euglycemic hyp erinsulinemic glucose clamp was applied. Synthetic human insulin was i nfused at the rate of 40 mU/m(2)/min for 2 hr, and glucose was also in fused to maintain basal glucose levels of each subject. The control st udy was performed in 8 of the 17 subjects, into whom 10% xylitol was i nfused for 2 hr at the rate of 100 ml/hr. The plasma insulin concentra tions were 7.94+/-0.35 and 62.3+/-14.3 mU/liter before and after the g lucose clamp technique, but serum free Ca ion was increased significan tly (p<0.05), and serum P and serum parathyroid hormone (PTH) mere dec reased significantly (p<0.001). Creatinine clearance did not change du ring the glucose clamp technique. Urinary excretion of Ca (UCaV) was s ignificantly higher after the glucose clamp than the control study. Fr actional excretion of Ca (FECa) was increased significantly (p<0.05), and urinary excretion of P (UPV) and fractional excretion of P (FEP) w ere decreased significantly (p<0.05) under the hyperinsulinemic condit ion. The results suggested that, under the conditions of euglycemic hy perinsulinemia by glucose clamp technique, insulin increased the serum free Ca ion, and as a result, PTH was suppressed. Decreased PTH might induce calciuresis and enhance tubular P reabsorption under hyperinsu linemia. Insulin increased serum free Ca ion might relate to the vasod ilating action of insulin by its decrease of intracellular free Ca ion in vascular smooth muscle.