Studies on the Biosynthesis of Rat Parathyroid Hormone and Proparathyroid Hormone: Adaptation of the Parathyroid Gland to Dietary Restriction of Calcium1

Abstract

Proparathyroid hormone (proPTH) and parathyroid hormone (PTH) have been separated from rat gland extracts by a combination of methods including chemical fractionation, gel nitration and ion exchange chromatography. The 2 peptides were shown to be similar to bovine proPTH and PTH, respectively, in their immunoreactivity, molecular weight and size and elution position during chromatography. In radioisotope incorporation studies, they exhibited a precursorproduct relationship comparable to that observed for the bovine prohormone and hormone. After 13 days on a diet containing 0.02% calcium, parathyroid gland weight, size and capacity to synthesize general proteins did not change. In such glands, the content of immunoreactive PTH and synthetic rate for PTH doubled. In contrast, the synthetic rate of proPTH and the half-life of its cellular pool did not change. These data indicate that the parathyroid glands adapted to the low-calcium diet by increasing the efficiency of conversion of proPTH to PTH and suggest that the control of PTH biosynthesis by calcium may occur at the level of intracellular turnover and degradation of the prohormone. (Endocrinology93: 915, 1973)