Parathyroid hormone secretion in vivo. Demonstration of a calcium-independent nonsuppressible component of secretion

ABSTRA CT The response of normal bovine para-thyroid glands to hypercalcemia was assessed in vivo by radioimmunoassay of immunoreactive parathyroid hormone concentrations in parathyroid effluent blood ob-tained by surgical cannulation of both anesthetized and nonanesthetized calves. Hypercalcemia was induced for periods of 0.3-35 h by intravenous infusion of a solution of calcium chloride. Assessment of immunoreactivity in effluent and peripheral blood included measurements of selected samples by use of a radioimmunoassay specific for a site residing in the biologically active portion of the hormone molecule. In all instances, the concentration of immunoreactive parathyroid hormone in hypercalcemic venous effluent from a superior parathyroid gland ex-ceeded that of the peripheral blood. Failure of hyper-calcemia to suppress completely secretion by normal parathyroids indicates that a portion of parathyroid hormone secretion occurs independent of blood calcium concentration. Consequently, continued parathyroid hor-mone secretion despite hypercalcemia can no longer be regarded as a unique feature of parathyroid neoplasia