Insulin blockade of norepinephrine tachyphylaxis in the perfused kidney

Tachyphylaxis to norepinephrine (NOR) was determined in the rabbit kidney perfused with Krebs-Henseleit solution by using different calcium concentrations (2.5 mM; 5 mM; 12.5 mM) in the perfusate. The addition of insulin to the perfusion fluid causes a reversion of the tachyphylaxis which is seen at those Ca2+ concentrations. This effect is demonstrated mainly at 5 mM Ca2+. When kidneys were perfused with 12.5 mM calcium there was disappearance of NOR-mediated tachyphylaxis, both in the absence and in the presence of insulin. In this calcium concentration, insulin decreases vascular reactivity to NOR. These results suggest that insulin blockade of alpha adrenergic tachyphylaxis is a calcium-mediated effect which is thought to be due to an enhancement of calcium pumping inside the cells.