Effect of contrast media on coronary vascular resistance - Contrast-induced coronary vasodilation

Study objectives: To determine if the vasodilatory response to the intracor onary injection of ionic and nonionic contrast media in intact pigs is depe ndent on:nitric oxide (NO), The mechanisms responsible for inducing the inc rease 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 venti lation, Measurements and results: Changes in coronary blood flow and coronary vascu lar resistance were measured in response to the coronary artery injection O f Saline solution (0.5 mol/L, isosmolar with plasma) and three different co ntrast agents: meglumine sodium iosaglate (Hexabrix; Mallinckrodt Medical; Point-Claire, Quebec, Canada), a low osmolar ionic contrast agent; iohexol (Omnipaque 300; Sanofi Winthrop; Markham, Ontario, Canada),: a nonionic con trast agent; and diatrizoate meglumine 66%, diatrizoate sodium 10% (MD-76; Mallinckrodt Medical), an ionic contrast agent. Measurements were made duri ng three experimental conditions: the coronary artery infusion of (1) salin e solution, control; (2) L-nitro-arginine (LNNA; 10(-3) mol/L and 10(-2) mo l/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 i n baseline coronary vascular resistance (p < 0.001), but it did not attenua te the vasodilatory response to the infusion of the contrast agents. Both t he 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 corona ry vascular resistance, Conclusion: The vasodilatory response of the coronary vasculature to contra st agents is directly related to osmolality and is not mediated by NO.