Peroxisome development in the regenerating pars recta (P₃ segment) of proximal tubules of the rat kidney

The development of peroxisomes, lysosomes and endocytic vacuoles in regenerating cells of the pars recta (P₃ segment) of proximal tubules, in rats given a single intraperitoneal injection of d serine (80 mg/100 g.b.wt), was studied by light and electron microscopy using cytochemical methods. Rapid proliferation of cells occurred between 2 and 5 days after d serine induced tubular necrosis; by day 6 almost all injured tubules were re epithelialized with flat or low cuboidal cells. Peroxisomes and lysosomes were not observed during the period of rapid cell multiplication i.e., between 2 and 6 days after d serine injection. Restitution of mitochondrial population preceded the development of peroxisomes in the newly regenerated cells of P₃ tubules. Maximum development of peroxisomes occurred between 9 and 14 days after d serine injection. The formation of peroxisomes appeared to correlate closely with the differentiation of apical endocytic vacuoles and the brush border. Lysosomes in the regenerated cells of P₃ tubules were the last to develop.