Whole-body hyperthermia-induced renal atrophy of mice as evinced by obstruction and degeneration of renal tubules caused by acute ischemia.

Effects of microwave-induced whole-body hyperthermia (WBH) on the mouse kidney were examined histologically for acute and late effects up to 150 days after WBH treatment at 43.5 degrees C (rectal temperature) for 20 min or 42 degrees C for 40 min. As a whole the damage could be divided into two types. One was the damage to distorted epithelial cells in the subcapsular region. This lesion was common in most animals, possibly caused by direct hyperthermic effect of microwave. The other was general renal atrophy accompanied with aqueous or protein-rich cysts due to a chain of physiological reactions of the whole body to WBH. The first reaction was characterized by general stasis of the blood stream in all parts of the kidney, which resulted in acute ischemia of some tissues. This was seen immediately by dilatation of the renal and interlobular veins as well as the bundles of capillaries in the medulla region. The subsequent event was rather specific cell necrosis of distal and collecting tubular epithelium as compared to proximal tubules. The cell destruction induced cell proliferation of the proximal tubular epithelia after two days. Later on, in accord with the recovery of the blood circulation, the proliferated cells were carried away into the lumen, these processes then resulting in obstruction of tubules through formation of protein casts in the lumen. The block incidentally led to the destruction of nephrons. The degenerated area sometimes consisted of aqueous or protein-rich cysts of various sizes after 7 to 30 days. Thereafter these cysts degenerated, decreasing in both number and size. Thus irreversible atrophy of the kidney developed after WBH.