Hypercalcemic Effect of Insulin in Thyroparathyroidectomized Alloxan-Treated Rats

Abstract

The acute effect of a hypoglycaemic dose of 0.5U/100g BW insulin administered intramuscularly on calcium metabolism was investigated in fasted alloxan-treated rats. It was found that the hypercalcaemic effect of insulin was evident only in thyroparathyroidectomized (TPTX) and not in parathyroidectomized (PTX) rats. A subcutaneous administration of 180 MRC mU/100g BW calcitonin abolished the calcium raising effect of insulin in TPTX rats suggesting a protective role of calcitonin against insulin action in intact rats. In an attempt to elucidate the mechanism of the calcium raising effect of insulin 45 Ca administered intravenously was used to indicate the movement of calcium from the plasma pool. Insulin administration delayed the plasma 45 Ca disappearance rate but had no effect on bone 45 Ca uptake within 120min. In contrast, insulin administration resulted in a 31% reduction of urinary 45 Ca excretion while the urine volume remained unchanged. However, the insulininduced reduction of urinary calcium excretion could not totally accunt for the calcium raising effect of insulin in TPTX animals. © 1986, The Japan Endocrine Society. All rights reserved.