The Effects of Calcium, Phosphate, and Vitamin D

Abstract

Secondary hyperparathyroidism is characterized by an increase in parathyroid (PT) cell number, and parathyroid hormone (PTH) synthesis and secretion. It is still unknown as to what stimuli regulate PT cell proliferation and how they do this. We have studied rats with dietary-induced secondary hyper- and hypoparathyroidism, rats given 1,25dihydroxyvitamin D3 (1,25(OH)2D3) and rats after 5/6 nephrectomy for the presence of PT cell proliferation and apoptosis. PT cell proliferation has been measured by staining for proliferating cell nuclear antigen (PCNA) and apoptosis by in situ detection ofnuclearDNA fragmentation and correlated with serum biochemistry and PTH mRNA levels. A low calcium diet led to increased levels of PTH mRNA and a 10-fold increase in PT cell proliferation. A low phosphate diet led to decreased levels of PTH mRNA and the complete absence of PT cell proliferation.