The effects of calcium antagonists and prostaglandin E_l on isolated canine coronary arterial tension

The effects of calcium antagonists (nifedipine, nicardipine, diltiazem, and verapamil) and prostaglandin E₁ (PGE₁) on the tension of isolated canine coronary arterial strips were studies. In a solution containing 20 mEq/L of K⁺, 127 mEq/L of Na⁺, the tension was increased by 500-1,000 mg with 4 mEq/L of Ca²⁺. This increase in tension was suppressed by Ca-antagonists and PGE₁ dose-dependently. Nifedipine 10^-5M, nicardipine 3 X 10^-7M, diltiazem 3 X 10^-6M, and verapamil 3 X 10^-6M completely suppressed the increased tension. The maximal suppression of the tension produced by PGE₁ was about 40% at 10^-10M. In 20 mEq/L K⁺ solution (0 mEq/L Ca²⁺, 37°C), the reduction of the Na⁺ concentrations from 127 mEq/L to 12 mEq/L increased the tension by 50 to 100 mg. This increase in tension was not suppressed by Ca-antagonists or PGEI. In conclusion, this study demonstrated that Ca-antagonists and PGE₁ suppressed an increase in the tension caused by Ca²⁺ but did not suppress an increase in the tension caused by Na⁺ reduction.