Calcium-entry blockade and pressor effect of angiotensin II in normal and nephrectomized rats.

The pressor effect of intravascular boli of 1.5 micrograms/kg angiotensin II was studied in untreated and in verapamil-pretreated intact rats and in rats 24 h after bilateral nephrectomy. An initial i.v. dose of 250 micrograms/kg verapamil was followed by a continuous infusion of 7 micrograms/min per kg. This resulted, within 2 min, in an average decrease in mean arterial pressure of 19 +/- 3 (SE) mm Hg and 18 +/- 3 (SE) mm Hg in intact and bilaterally nephrectomized rats, respectively. This continuous dose of verapamil did not significantly prevent the pressor effect of angiotensin II. When the continuous infusion of verapamil was increased to 50 micrograms/min per kg, the rise in blood pressure following angiotensin II administration was significantly lower than in the untreated rats: 21 +/- 2 (SE) mm Hg in intact rats, compared with 39 +/- 3 (SE) mm Hg (P less than 0.001) in the untreated animals and 31 +/- 3 (SE) mm Hg in rats in the renoprival state, compared with 47 +/- 6 (SE) mm Hg (P less than 0.01) in the corresponding untreated group. The present study suggests that verapamil can be used as a calcium blocker to reduce blood pressure associated with, or caused by, an increased renin-angiotensin system activity.