Morphological correlates of urinary enzyme loss after extracorporeal lithotripsy

Urinary loss of the tubular marker enzyme N-acetyl-beta-D-glucosaminidase (NAG) immediately following extracorporeal lithotripsy suggests corresponding morphological changes in the kidney. To date, the morphological correlate of the enzymuria remains unclear. In this animal study with Wistar rats acute morphological changes in the tubulus cells beneath isolated tubulus necrosis were demonstrated. The mechanically induced lesions of the cell organelles included fragmentation of the lysosomes and severe alterations of the cell membrane. The tubulus damage was quantified. With the help of histochemical NAG staining and electron microscopic observations, a significant correlation between number and intensity of shock waves and tubular damage was found. The intracellular lesions described here are at least part of the morphological basis of shock-wave-induced enzymuria. The results show that enzymatic changes in urine reflect visible renal damage.