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

Abstract

To get a better understanding of the factors that are related to the rapidity of the postmortem changes, we studied the postmortem changes in various parts of the nephron in the rat kidney at room temperature histopathologically, electron microscopically, and enzyme histo-and cytochemically. We found that the rapidity of the postmortem changes in the tubular epithelia of the rat kidney, at room temperature, is related to the intensity of cellular K-NPPase activity, that is the partial phosphatase activity of Na, KATPase. The postmortem changes, characterized by cytoplasmic vacuolization and karyopyknosis, in the epithelial cells in the distal tubule and the thick ascending limb of the loop of Henle (TAL) with intense KNPPase activity began earlier and progressed faster than those in the epithelia of the proximal tubules, macula densa and other parts of the nephron with low K-NPPase activity. These postmortem changes were delayed by flushing the kidney with PBS containing ouabain, ATP, verapamil, or EDTA. It is probable that the cells with intense ATPase activity tend to consume intracellular ATP faster than the cells with low ATPase activity after death, and the resulting lack of intracellular ATP and calcium ion influx cause various postmortem changes. On the other hand, the postmortem changes in the proximal tubules, with a large number of lysosomes, are slower and milder than those in the distal tubules and TAL at room temperature. Enzyme cytochemistry revealed hardly any signs of leakage of acid phosphatase, one of the lysosomal hydrolytic enzymes, up to at least 10 hr after death, during which time, the postmortem changes in the proximal tubules are slight and those in the distal tubules and TAL are severe.These results suggest that the rapidity of the postmortem changes in the rat kidney at room temperature depends mainly on the intensity of cellular Na, K-ATPase activity and that lysosomes do not participate in the cellular postmortem changes to a great extent until at least 10 hr after death.In the histopathological examination in toxicity studies using laboratory animals, it is important to differentiate postmortem changes from toxic changes caused by the test compound when animals are found dead during the dosing period. Thus, an attempt was made in our laboratory to obtain data on the postmortem changes in various organs and tissues. We studied histopathologically the postmortem changes in various organs and tissues at room temperature up to 20 hr after death in rats sacrificed by ether anesthesia (15). During the course of that study, we found that the rapidity of the postmortem changes in the rat kidney varies with the part of the nephron: at room temperature, epithelial cells in the distal tubules and the thick ascending limb of the loop of Henle show faster postmortem changes, which were characterized by cytoplasmic vacuolization and karyopyknosis, than do other parts of the nephron (16,23).In the present study, postmortem changes in the various parts of the nephron in the rat kidneys were studied...

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