The effect of diltiazem, a calcium channel blocking agent, on vasoconstrictor responses to norepinephrine, serotonin and potassium depolarization in canine coronary and femoral arteries.

1. Diltiazem produced a dose-dependent inhibition of contractions due to norepinephrine (NE), serotonin (5HT) and high potassium depolarization in both coronary and femoral artery rings. 2. Diltiazem was a more potent and efficacious blocker of all 3 agonists in the coronary arteries. 3. Dose response curves to NE and 5HT indicated that diltiazem produced a noncompetitive type of blockade. 4. Diltiazem blocked contractions produced by 5HT more easily than those produced by NE in both coronary and femoral artery rings. 5. That diltiazem was more potent in coronary than femoral arteries suggests a basic difference in calcium regulation in the two vessels.