Histopathological analysis of initial change on tubular injury with glycerol-induced rhabdomyolysis in rats

Rhabdomyolysis is a disorder of striped (skeletal) muscle and is caused by several factors,and acute renal failure (ARF) associated with myoglobinuria is the most serious complication of rhabdomyolysis. However, the mechanism of tubule damage caused by myoglobin (Mb) is still unclear. The early histopathological changes were not examined, and Mb reabsorption by the renal tubules have not been reported to contribute to cellular damage. We performed histological analysis in a rat rhabdomyolysis model with administration of cytochalasin B (CB), which is an inhibitor of motile cell motile processes. Method; We intramuscularly injected 10 mg/kg of 50% glycerol in saline into the hind limbs of 6 rats. Another 6 animals received an intraperitoneal injection of 150 μg/kg CB just before the glycerol injection. A third group of 6 animals were administered injections of saline. At 24 hours after the injection, BUN was assayed. At 6 or 24 hours after the injections, their kidneys were removed. The specimens were prepared for light and electron microscopic observation. The extent of tubular injury was evaluated histological damage on HE staining. Result; CB inhibits the endocytosis of myoglobin in the proximal renal tubules and the increase in the BUN level, and decreased the percentage of area that had undergone tubular necrosis. On the other hand, initial degenerative changes (shortening of microvilli and protrusion of the cytoplasm) were observed on the cell surface of the proximal tubules with glycerol- induced cellular injury, and were not inhibited by the administration of CB. Moreover, the initial changes of the injury of the cell membrane and the leakage of the intracellular organelle (mitochondria and lysosome) were observed in the distal renal tubule. Conclusion; Initial glycerol- induced cellular injury of the renal proximal tubules may be caused by free iron, which is isolated from Mb in urine. Moreover, Mb in urine may also cause the initial change of the distal renal tubules, which is a cell membrane injury, as same as that of the proximal renal tubules. Further, the combination of the free iron in urine and the myoglobin reabsorbed by tubular cells may lead to cell necrosis.