Vasoconstrictor agents correlatively alter diameter and tension development in isolated pig coronary arteries

Outer diameter of the isolated pig coronary artery was measured under isotonic conditions using a sonomicrometer, and tension development of a ring preparation was assessed isometrically by a strain gauge transducer. Potassium chloride (KCl), acetylcholine (ACh) and 5-hydroxytryptamine dose-dependently reduced the coronary outer diameter. There was a direct linear relation between the reduction of diameter and tension development by these agents (r = 0.91, n = 15, p less than 0.001). KCl was one of the most potent vasoconstrictors tested and reduced the outer diameter by 35 +/- 1% (n = 15, mean +/- SEM) at 120 mM. ACh produced a transient increase in isometric tension and the reduction of the coronary diameter by ACh was smaller than that seen with KCl, even with a dose which produced the similar peak level of isometric tension by KCl and ACh. It is concluded that changes in the coronary diameter do closely correlate with those in tension development, however, the reduction of coronary diameter after exposure to vasoconstrictive agents is less in phasic than tonic contraction. The latter evidence suggests the importance of both the strength and duration of active vasoconstriction in eliciting coronary spasm.