VASODILATOR AND HYPOTENSIVE EFFECTS OF THE OPTICAL ISOMERS OF NICARDIPINE (YC-93), A NEW Ca2+-ANTAGONIST

Vasodilator and hypotensive effects of (+) and (−) nicardipine were investigated in anesthetized dogs. When administered intravenously, (+) nicardipine was 3 times as potent as the (−) isomer in increasing vertebral blood flow and in lowering mean blood pressure. When injected into the vertebral artery, (+) nicardipine was also 3 times as potent as the (−) isomer in increasing vertebral blood flow. Upon both routes of administration, the duration of the action after (+) nicardipine was longer than that after the (−) isomer. However, there were no differences of plasma nicardipine levels after intravenous injection of both isomers to conscious beagle dogs. The LD50 values of (+) nicardipine in mice and rats upon intravenous injection were only 1.5-2 times smaller than those of the (−) isomer. These results indicate that there exists a stereoselectivity of vasodilator and hypotensive actions among the nicardipine isomers.