ENDOTHELIN-I MEDIATED VASOCONSTRICTION - SPECIFIC BLOCKADE BY VERAPAMIL

The capacity of three vasodilators that act by distinct mechanisms to reverse endothelin-I-mediated vasoconstriction was studied in 11 healthy nonsmoking male subjects (mean age +/- SEM, 26 +/- 2 years; mean weight +/- SEM, 74 +/- 2 kg) by use of brachial artery infusion and forearm strain-gauge plethysmography. Isoproterenol (cyclic adenosine monophosphate-mediated vasodilation), sodium nitroprusside (cyclic guanosine monophosphate-mediated vasodilation), and verapamil (L-type calcium channel blocker) were compared for capacity to reverse endothelin-I-mediated increase in forearm vascular resistance (FVR). Endothelin-I infusion increased FVR 1.9-fold in the control state. Isoproterenol infusion decreased FVR with or without concurrent endothelin-I infusion; however, at comparable isoproterenol infusion rates, endothelin-I increased FVR similar to the control state (for 5 ng/min isoproterenol, endothelin-I increased FVR 1.85-fold; for 12.5 ng/min isoproterenol, endothetin-I increased FVR 2.03-fold). Similarly, sodium nitroprusside infusion decreased FVR with or without concurrent endothelin-I infusion; however, at comparable sodium nitroprusside infusion rates the endothelin-I increase in FVR was similar to control (for 0.48 mug/min sodium nitroprusside, endothelin-I increased FVR 1.89-fold, for 0.96 mug/min sodium nitroprusside, endothetin-I increased FVR 2.36-fold). In contrast, verapamil infusion decreased FVR with or without endothelin-I infusion. At a verapamil infusion rate of 19.1 mug/min, endothelin-I increase in FVR was comparable to control (for 19.1 mug/min verapamil, endothelin-I increased FVR 1.36-fold, less than the 1.9-fold increase in the control state; p < 0.05). Isoproterenol and sodium nitroprusside decreased FVR during concurrent endothelin-I infusion but did not reverse the endothelin-I effect. In contrast, verapamil reversed endothelin-I-induced vasoconstriction to control FVR, suggesting a specific antagonism of endothelin-I-mediated increase in FVR.