Age and the development of nephrocalcinosis induced by injections of neutral phosphate in rats

A morphological characterization of nephrocalcinosis induced by injected neutral phosphate was made in both female weanling and young adult rats in order to determine the effects of age on the development of this type of phosphate-induced renal calcification. Nephrocalcinosis was induced by giving the rats single daily intraperitoneal injections of 0.5 M neutral phosphate (15.5 mg Pi/100 g bw/24 h) for 10 days. Following the experimental period, the kidneys of the animals were fixed and processed for general histology and for the histochemical localization of calcium-phosphate salts. The weanling rats developed nephrocalcinosis that was characterized mainly by large intraluminal calciferous deposits in terminal segments of proximal tubules at the junction of the outer and inner stripes of the outer medulla, and in collecting ducts and descending thin limbs and ascending thick limbs of Henle in the inner stripe of the outer medulla. In contrast, the young adult rats developed nephrocalcinosis that was characterized primarily by small granular calciferous deposits in the basement membranes of proximal tubules in the mid-cortex. The results of the present study indicate that some factor(s) associated with age and development of female rats influence(s) the development of nephrocalcinosis induced by injected neutral phosphate.