A morphologic and biochemical study of nutritional nephrocalcinosis in female rats fed semipurified diets

Nephrocalcinosis occurred in weanling female rats fed a semipurified diet for 8 weeks. Mineralization of the inner cortex began after 3 weeks on the semipurified diet, and was most severe after 8 weeks. Intraluminal calcification was observed first in the pars recta of the proximal convoluted tubule; calcification of cytoplasmic organelles or basement membranes of the tubular epithelium was not observed. At the end of 8 weeks, some mineral deposits were seen within Henle's loops of the outer medulla. Histochemical studies demonstrated that the deposits contained calcium and phosphorus and had a glycoprotein matrix; electron diffraction studies indicated that the main mineral phase was hydroxyapatite. No differences in serum calcium or phosphorus or in the ultrastructural characteristics of the thyroid parafollicular cells and the parathyroid parenchymal cells were observed between animals fed the semipurified diet and those fed a commercial chow. The urinary excretion of calcium and magnesium was less and urinary citrate excretion was greater in animals fed the semipurified diet.