Blocking effect of diltiazem on thiopentone-induced vasoconstriction in isolated canine internal carotid arteries

Stainless-steel cannulas were inserted into isolated internal carotid arteries of the dog to observe vasoconstrictor responses to thiopentone. Thiopentone at a relatively large dose (100-3,000 micrograms) induced vasoconstrictor responses in a dose-dependent manner. A dose of 1 mg thiopentone usually produced a definite increase in perfusion pressure of greater than 50 mm Hg. These effects were not influenced by treatment with phentolamine in doses that significantly suppressed noradrenaline-induced vasoconstrictor responses. Diltiazem inhibited the constriction in response to thiopentone as well as that to potassium chloride in a noncompetitive antagonistic manner. It is suggested that the constriction induced by thiopentone may be due in part to activation of the calcium-inward channel in the wall of the internal carotid artery.