Effect of contrast media on coronary vascular resistance: contrast-induced coronary vasodilation.

STUDY OBJECTIVES To determine if the vasodilatory response to the intracoronary injection of ionic and nonionic contrast media in intact pigs is dependent on nitric oxide (NO). The mechanisms responsible for inducing the increase in coronary blood flow in response to the intracoronary injection of contrast media during angiography are still not entirely understood. There is evidence to suggest that the response could be partially mediated by NO. PARTICIPANTS We studied 14 anesthetized, open-chested pigs receiving ventilation. MEASUREMENTS AND RESULTS Changes in coronary blood flow and coronary vascular resistance were measured in response to the coronary artery injection of saline solution (0.5 mol/L, isosmolar with plasma) and three different contrast agents: meglumine sodium ioxaglate (Hexabrix; Mallinckrodt Medical; Point-Claire, Quebec, Canada), a low osmolar ionic contrast agent; iohexol (Omnipaque 300; Sanofi Winthrop; Markham, Ontario, Canada), a nonionic contrast agent; and diatrizoate meglumine 66%, diatrizoate sodium 10% (MD-76; Mallinckrodt Medical), an ionic contrast agent. Measurements were made during three experimental conditions: the coronary artery infusion of (1) saline solution, control; (2) L-nitro-arginine (LNNA; 10(-3) mol/L and 10(-2) mol/L), a competitive inhibitor of NO synthase; and (3)L-arginine 10(-1) mol/L, a substrate for NO synthase. The infusion of LNNA produced an increase in baseline coronary vascular resistance (p < 0.001), but it did not attenuate the vasodilatory response to the infusion of the contrast agents. Both the high and low osmolar ionic and nonionic contrast media caused a decrease in baseline coronary vascular resistance. For all three conditions, MD-76, which has the highest osmolality, produced the greatest decrease in coronary vascular resistance. CONCLUSION The vasodilatory response of the coronary vasculature to contrast agents is directly related to osmolality and is not mediated by NO.