Effects of insulin on urinary calcium excretion by diabetic rats in the absence of blood glucose control.

Male rats weighing approximately 250 g were given streptozotocin (STZ), 60 mg/kg, i.p., on two successive days. Six h after the last STZ injection, some STZ-diabetic rats began receiving daily injections of insulin (NPH, 1.5 U, s.c.). At various times after the above treatments the following studies were performed: control rats, STZ-diabetic rats and NPH-treated STZ-diabetic rats were injected s.c. with calcium-45 and housed individually in metabolic cages. Urine from each rat was collected at 24 h intervals for two weeks. Volumes, osmolalities, glucose concentrations, total calcium and radioactivity due to calcium-45 were measured. The results of the studies showed that: STZ-diabetes caused rapid urinary excretion of the injected 45Ca and increased renal excretion of 40Ca; 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, significantly reduced the diabetes-induced calcium loss.