Mechanisms of action of contrast media on cranial vessels. Comparison of diatrizoate, ioxaglate, iohexol, mannitol, and NaCl on rabbit basilar and ear arteries.

The relaxant effects of the ionic contrast media diatrizoate and ioxaglate and the nonionic agent iohexol on the vascular wall were examined by a sensitive in vitro system. Control solutions of NaCl and mannitol were used to evaluate the relative importance of osmolality to the vasodilation response. The rabbit central ear artery and the basilar artery were precontracted by (1) potassium, causing depolarization of the sarcolemmal membrane, (2) noradrenaline, causing activation of alpha 1-adrenoceptors, and (3) histamine, causing activation of histamine H1 receptors. The contrast media caused concentration-dependent relaxation of both types of arteries; this effect was relatively insensitive to the agent used to precontract the vessels. Histamine-contracted arteries were thought more sensitive to the relaxant agents used than arteries contracted by potassium or noradrenaline. The relaxation induced by the contrast media correlates with the relaxation induced by equiosmolar amounts of NaCl or mannitol. Our results suggest that the artery dilator response seen after exposure to currently used contrast media is due primarily to changes in local osmolality rather than to a specific receptor involvement.