Acute effect of calcium and insulin on hyperfiltration of early diabetes

We examined the effect of calcium administration on renal hyperfiltration in streptozotocin-treated diabetic rats. Rats were studied 7–10 days after streptozotocin injection. Intrarenal infusion of CaSO4 in Ringer's solution had no effect on the hyperfiltration of the diabetic kidney. Infusion of insulin in a dose that did not effect hyperglycemia also had no effect on the hyperfiltration. However, when insulin and calcium were infused together, a rapid decrease in glomerular filtration rate, single-nephron filtration rate, glomerular hydraulic pressure, and renal plasma flow occurred. The contralateral control kidney was unaffected. Verapamil infusion had no significant effect in untreated diabetic rats, but immediately reversed the vasoconstriction induced by insulin plus calcium. Similar intrarenal insulin and calcium infusions had no effect in euvolemic or chronically salt-loaded nondiabetic rats. The observations indicate that renal vascular cells (probably preglomerular) are hyperresponsive to calcium in early insulin-dependent diabetes mellitus and that this response requires insulin. We suggest that decreased renal vascular tone in early insulin-dependent diabetes mellitus may be due in part to defective transmembrane calcium flux across vascular smooth muscle cells. Insulin appears to be required for calcium entry or mobilization, to initiate renal vascular smooth muscle contraction in diabetes.