Quantification of nephrotoxicity in rabbits by automated morphometry of alkaline phosphatase stained kidney sections.

Male and female rabbits were injected intravenously with a single dose of either cefroxadine or cefsulodin or cephaloridine. Quantitative determinations of the activity of two brush border membrane enzymes, aminopeptidase and alkaline phosphatase, were made in homogenates of cortical kidney tissue, in the urine and morphometrically in proximal tubules of cryostat sections. Morphometry was done by classification and enumeration of proximal tubule sections with the same level of enzyme reaction product using a microscopic television analysis system. By comparison with the control values, no changes were detectable 24 h after the injection of up to 1.2 g cefroxadine or cefsulodin per kg body weight. By contrast, after 300 mg/kg cephaloridine, the concentrations of the two enzymes were decreased in a large number of proximal tubules, i.e. the brush border membranes, and concomitantly cell degeneration and necrosis took place. Alkaline phosphatase activity in sections and tissue homogenates was reduced to a greater extent than aminopeptidase activity. A corresponding, significant increase in enzymic activity in the urine was only demonstrable in respect of aminopeptidase. The classification of proximal tubules in sections by television analysis on the basis of alkaline phosphatase reaction product concentration appears to be a reliable measure for detecting and quantifying toxic effects on proximal tubules of kidney.