Postmortem changes in the rat kidney. I. Histopathological, electron microscopical, and enzyme histochemical studies of postmortem changes at room temperature.

Abstract

In the first part of this study, we reported that the postmortem changes in rat kidneys at room temperature proceed most rapidly in the epithelial cells of the distal tubule and thick ascending limb of the loop of Henle, and that one of the factors which determine the rapidity of the postmortem changes at room temperature is the intensity of K-NPPase (Na, K-ATPase) activity. In the present study, the postmortem changes in rat kidneys maintained at 0°C for 20, 48, and 72hr after death were studied histopathologically, electron microscopically, and histo- and cytochemically to obtain further information on the mechanisms of postmortem changes. At 0°C, the postmortem changes in the distal tubules and thick ascending limb of the loop of Henle were delayed considerably, and only mild changes were observed electron microscopically even 72hr after death. Contrary to the results at room temperature, the postmortem changes in the proximal tubules were quicker than those in the distal tubules at 0°C, and the proximal tubules show obvious cytolysis 48hr or more after death. Electron microscopy revealed swelling of the lysosomes, and in enzyme cytochemistry, reaction products indicating ACPase activity increased in the cytoplasm around the lysosomes 48hr after death. These findings suggest that the lysosomal enzymes leak out from the lysosomes at least 48hr after death at 0°C. The lysosomal enzymes were considered to have activity even at 0°C, because ACPase activity could be detected cytochemically at 0°C in the lysosomes. The cytolysis observed in the proximal convoluted tubules at 0°C was not seen in the kidneys flushed with chlorpromazine, a membrane stabilizer, and was severe in the kidneys flushed with Triton X-100, a membrane labilizer. From these results, the postmortem cytolysis observed especially in the proximal convoluted tubules 48hr or more after death even at 0°C is considered to be autolysis caused by the lysosomal enzymes which leak out from the lysosomes. Together with the result of the previous part of this study, it is concluded that there are at least two biological factors which determine the rapidity of the postmortem changes in the cells of the rat kidney, the intensity of cellular Na, K-ATPase activity and the lability of the lysosomal membrane.