Effects of nicardipine on the cross-perfused canine atrium.

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Abstract
Effects of nicardipine, a newly synthesized dihydropyridine vasodilator exhibiting cyclic phosphodiesterase inhibitory properties, were studied in the isolated canine atrium cross-perfused with blood from a donor dog. When nicardipine (1.0-10 .mu.g/kg) was administered i.v. to the donor dog, the systemic blood pressure decreased and the heart rate did not significantly change. The contraction and beat rate of the isolated atrium were slightly decreased. At larger doses (30-100 .mu.g/kg, i.v.), the systemic blood pressure fell markedly and was usually accompanied by marked bradycardia, greater than that of the isolated atrium. Nicardipine injected into the sinus node artery of the isolated atrium caused dose-related negative chronotropic and inotropic effects which were less pronounced than those of verapamil. Papaverine increased right atrial rate and contractile force. Nicardipine like verapamil and unlike Mn2+ caused greater inhibition of the right atrial contraction at higher than lower pacing frequencies. Nicardipine may produce predominantly cardiac depressant properties as a Ca2+ antagonist, and may not be related to phosphodiesterase inhibition in cardiac tissues.

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