Angiographic contrast media (CM) may cause both vasodilatation and vasoconstriction. This study evaluates a contrast mediuminduced vasoconstriction that occurs when isolated arteries are exposed directly to a CM. Segments of rabbit coronary arteries were mounted in tissue baths containing buffer solution. During the experiments the buffer solution was exchanged with iohexol iso-osmolar with plasma, which caused a temporary vasoconstriction of the vessel segments. The constriction did not depend on the degree of oxygenation of iohexol. The endothelium was not involved in the vasoconstriction. Prazosin slightly decreased the vasoconstriction and a small part of the constriction might thus depend on liberation of norepinephrine by iohexol. The constriction was totally inhibited by the calcium antagonist nifedipine, while it was augmented by addition of low concentrations of KCI to ihoexol. It is concluded that the otherwise safe CM iohexol causes vasoconstriction in vitro by depolarizing the smooth muscle cells and the nerve terminals in the vessel wall.

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