Altered parathyroid response to calcium in hypercalcemic neonatal calves.

Abstract

Calves are born with hypercalcemia which recedes within 2–3 weeks. To assess the role of the parathyroids in this condition, immunoreactive parathyroid hormone (iPTH) secretion rate was measured during induced alterations of plasma calcium concentration in six anesthetized calves which were 1–3 days of age. The technique involved RIA of parathyroid venous blood which was collected during timed intervals and measured volumetrically. Elevation of plasma calcium concentration decreased PTH secretion rate but above 12 mg/100 ml, a nonsuppressible rate of secretion was maintained despite any further increase in plasma calcium concentration. Between 9.5–12 mg/100 ml, iPTH secretion rate and plasma calcium concentration were inversely related. A maximal rate of secretion was attained when plasma calcium concentration was reduced to 9.5 mg/100 ml, and it did not increase when plasma calcium was reduced to a lower level. The sigmoid relationship between iPTH secretion rate and plasma calcium conce ntration is simi...