Regulation of Parathyroid Hormone Secretion: Proportional Control by Calcium, Lack of Effect of Phosphate

Measurement by radioimmunoassay of secretory rates for parathyroid hormone in the cow shows that hypocalcemia is the major stimulus for hormone production; hypercalcemia quickly abolishes secretion. Phosphate causes no direct effect on secretion of the hormone. Analyses for parathyroid hormone and calcium in peripheral plasma showed a simple linear inverse function of hormone concentration vs. plasma calcium in the range of 4 to 12 mg/100 ml. This led to the conclusion that calcium regulates hormonal secretion predominantly through a proportional control mechanism. The half-life of parathyroid hormone in the circulation was found to be approximately 20 min. The speed with which secretion responds to changes in blood calcium and the short half-life of hormone in plasma are consistent with recent studies showing that parathyroid hormone effects rapid changes in blood calcium. These findings emphasize the importance of the hormone in the minute to minute regulation of blood calcium. (Endocrinology 83: 1043, ...