Gentamicin-induced hypercalciuria in the rat.

A study was made of the effects of gentamicin (40 mg/kg/day for 7 days) on the excretion of sodium, potassium, calcium and magnesium in the urine of rats. Volume of urine, protein excretion and the urinary activities of the enzymes alanine aminopeptidase, lactate dehydrogenase and N-acetyl-beta-glucosaminidase were also monitored. There were no significant changes in the excretion of sodium or potassium and the excretion of magnesium was too variable to permit a meaningful interpretation of changes in its excretion. Significant changes occurred in the excretion of calcium and protein and in the 24 hr urine osmolarity. The earliest of these changes, on day 4, was an increase in calcium excretion (P less than 0.01) which progressed until the drug was stopped and persisted throughout the 5 follow-up days. The increase in protein excretion was significant (P less than 0.01) by day 5 and the decrease in osmolarity (P less than 0.01) by day 6. These changes were preceded, on day 1, by a significant (P less than 0.001) rise in the activities in urine of all three enzymes. This early enzymuria suggests that considerable perturbation of cell integrity occurred before the increase in calcium excretion. Further studies are required to elucidate what role, if any, the loss of calcium plays in the genesis of tubular cell injury.