Urinary myelin figures in gentamicin. Treated vs. ischemic kidneys.

In view of the demonstrated occurrence of myelin figures in renal tubules and urine following gentamicin administration, we compared urinary excretion of myelin figures in dogs given nephrotoxic doses of gentamicin and in those undergoing clamping of renal arteries. Ten dogs weighing 15 to 20 kg were randomly divided into two experimental groups. Group I consisted of five dogs injected daily with 40 mg/kg body weight of gentamicin intramuscularly. Group II consisted of five dogs that were operated on and had their renal arteries clamped for one to two hours. Baseline studies, including body weight, serum creatinine, and analysis of urine sediment by light microscopy and electron microscopy, were obtained. Daily creatinines were obtained in both groups, and urine sediments were examined for epithelial cells and myelin figures at regular intervals and graded from 0 to 4+. The control serum creatinine levels were normal in all ten dogs, and no myelin figures were observed in the baseline examinations. In Group I, two out of five dogs developed frank renal impairment with creatine levels over 2 mg/dl and subsequently died. These two dogs had 1+ or more myelin figures in the urine sediment early in the treatment, and subsequently, a copious amount of myelin figures (4+) was excreted. The remaining dogs did not develop creatinine elevation greater than 2 mg/dl and showed only trace amounts of myelin figures. In Group II, two out of five dogs developed abnormal creatinine levels on the first postoperative day, but did not show myelin figures in their urine. Two other dogs with normal creatinine levels had trace myelin figures. The study shows that conspicuous urinary excretion of myelin figures occurs in gentamicin-induced renal failure in dogs, but myelin figures are absent or slight after renal vascular ischemia of 1 to 2 hours.