Scanning and transmission EM of rat kidney following low dose mercuric chloride administration.

The development of necrosis and the subsequent regeneration of the proximal tubular epithelium located in the cortex and the outer medulla of the rat kidney following subcutaneous injection of 2 mg of mercuric chloride per kilogram of body weight was observed utilizing light micromicroscopy (LM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The cortical proximal tubules were largely free of injury. In the medullary proximal tubules, the residual, undamaged cells underwent a change in phenotype appearance involving loss of the microvillus border, a decrease in cell height, and an increase in cytoplasmic ribosomes. These cells phagocytosed luminal debris. With time the cell height gradually increased, specialized organelles returned, and the luminal microvilli progressed from short, sparse profiles, to tufts of longer microvilli and finally the brush border was completely reformed. Some kidneys contained calcified tubules which regenerated more slowly than damaged but uncalcified tubules. Similarly, the medullary segments of the proximal tubules regenerated more slowly than the juxtamedullary region. Clusters of epithelial cells were occasionally seen growing into the tubular lumina during regeneration. Marked intersitial leukocyte infiltrations were observed.