Effects of two new Ca-entry blockers bepridil and nitrendipine on isolated vessels.

The effects of nitrendipine and bepridil were studied in isolated rings of human crural veins contracted by noradrenaline (NA) or potassium (K). Both drugs had a concentration dependent inhibitory effect on active tone and shifted the NA and K concentration-response curves to the right in a non-parallel manner and reduced the maximum contractile response. Both drugs had a more potent inhibitory effect on K than on NA-induced contractions. Nitrendipine was far more potent in inhibiting the K-induced contractions than bepridil while the drugs were equipotent in inhibiting NA-induced contractions. Human veins were less sensitive than rat aorta to the inhibitory effect of nitrendipine. In contrast to nitrendipine the effect of bepridil was gradual and slow in onset. The inhibitory effect of both drugs was strong and long-lasting and resistant to washout procedures. Both drugs effectively eliminated spontaneous mechanical activity and reduced K-induced contractions in rat portal veins. The results support that nitrendipine and bepridil are effective vasodilators in arteries as well as in veins. The main action of both nitrendipine and bepridil seems to be attributed to an inhibitory effect on cellular Ca-entry.