Mercuric chloride-induced tubulonecrosis in the rat kidney: the recovery phase.

Regeneration of the renal tubules in rats, after death of the cells of the pars recta caused by a dose of 1.5 mg HgCl2/kg, was examined by histological and radioautographic methods. The tubules regenerated from surviving squamoid cells at both ends of the necrotic segments, which often appeared to arise from epithelial cells that had cast off superficial "dead cytoplasm" to leave the basal parts containing the nucleus in a rim of cytoplasm. The tubular epithelium was reconstituted between the 2nd and 5th days by proliferation and sliding extension of the squamoid cells along the tubules and predominantly from the distal end of the necrotic segments where the cell proliferation was extremely active. Inflammation in reaction to the dead cells was insignificant. Although the majority of tubules regenerated in a regular fashion some degree of anomalous epithelial proliferation occurred in patches, predominantly in the junctional area between the pars recta and the loops of Henle and perhaps most frequently in reference to those nephrons with superficial and mid-cortical glomeruli. The exuberant proliferation led to scattered epithelial growths projecting into the lumen of the tubules, and there was evidence that these obstructed the discharge of necrotic debris. Tubular collapse and atrophy leading to the formation of small scars followed, more often affecting the short looped nephrons.