Male rats were injected with streptozotocin (STZ), 60 mg/kg, i.p., on 2 successive days. Six hours after the last STZ injection, some STZ-diabetic rats began receiving daily injections of insulin that were insufficient to control blood glucose. Another group of STZ-diabetic rats received insulin injections after 2 wk duration of untreated diabetes. Still other STZ-diabetic rats received no insulin treatment. Under sodium pentobarbital anesthesia, kidneys from each treatment group were isolated and perfused with an artificial“plasma”containing 45Ca. As urine was collected, urine-to-per-fusate ultrafiltrate (U/P) ratios for 45Ca were determined. The results of the studies showed that: STZ diabetes reduced 45Ca reabsorption by the kidney; the increased urinary excretion of calcium was not due to an osmotic effect or to a direct nephrotoxic action of STZ; and insulin therapy instituted early, but insufficient to control blood glucose, reduced the diabetes-induced calcium loss via a direct action on the kidney, whereas insulin therapy instituted late failed to reverse renal loss Of calcium.

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