Cell proliferative activity in the kidney of young growing rat analyzed using flash and cumulative labeling with bromodeoxyuridine

We examined the cell proliferation activity of kidney in young growing rats using flash and cumulative labeling with bromodeoxyuridine (BrdU). Rats were subjected to the study at the age of 6 weeks, and cumulative labeling was carried out for periods of 7 to 28 days. BrdU-positive cells were observed after flash labeling and were increased by cumulative labeling. The positive epithelia were mainly distributed in the cortex and the outer stripe of the outer medulla and were scarce in the inner stripe of the outer medulla and inner medulla throughout all labeling periods. In the tubular epithelium, the majority of positive cells were found in the proximal tubule. In the proximal tubule, positive epithelia were abundant in the medullary rays and in the outer stripe of the outer medulla. In the intermediate tubule to collecting duct, positive epithelia were rare. In the renal corpuscle, positive nuclei were mainly found in the endothelial cells and the mesangial cells and were scarce in the parietal cells of the Bowman's capsule. BrdU-positive nuclei were not observed in podocytes. These results indicate that renal tubules actively grow relative to epithelial proliferation, and that the endothelial cells, the mesangial cells and the parietal cells in the renal corpuscle also proliferate at the age of 6 to 10 weeks in rats. For assessment of renal toxicity using young growing rats, not only the morphologic and physiologic features unique to the kidney but also the growing process of the kidney should be taken into account.