Mechanism of the Hypercalcemic Effect ofl-Valine in Parathyroidectomized Rats

The mechanism of the hypercalcemic effect of l-valine was studied in parathyroidectomized rats. Although a definite hypercalcemic effect of l-valine was demonstrated in parathyroidectomized rats fed a diet containing 1.85% calcium, this effect was almost completely abolished in parathyroidectomized rats fed a calcium-free diet, and also in rats in which the total intestinal tract was removed prior to parathyroidectomy. The hypercalcemic effect of valine was observed following removal of the distal jejunum, ileum or colon but was abolished by removal of the duodenum or proximal jejunum. These findings, together with the observation that subcutaneous injection of l-valine increased the speed of appearance of 45Ca in plasma following oral administration, suggest that the resulting hypercalcemia may be primarily due to enhanced intestinal absorption, although participation of other factors cannot be ruled out entirely. (Endocrinology80: 200, 1967)