Bronchial vasodilatory response to ionic and nonionic contrast media.

It has recently been shown that bronchial arterial injection of conventional contrast medium causes a significant increase in bronchial blood flow (Qbr) and that this response is partially attenuated after infusion of N omega-nitro-L-arginine (L-NNA). However, the precise mechanism for this increase in Qbr is unknown. In this study we examined the effect of bronchial arterial injection of conventional ionic as well as nonionic contrast media. We measured Qbr in nine anesthetized, ventilated, open-chest sheep. Qbr was recorded before (baseline) and at the peak response to injection of 0.5 ml of either 0.9% saline (control; isosmolar with plasma), Omnipaque 300 (iohexol; nonionic), Conray 66 (sodium iothalamate; ionic), or 50% dextrose (viscous control). Measurements were made during a control period, after infusion of the alpha-agonist phenylephrine (5 x 10(-6) to 5 x 10(-7) M), and after bronchial arterial infusion of L-NNA (10(-2) M). The results were as follows: bronchial arterial injection of saline, Omnipaque, Conray, and dextrose caused an increase in Qbr (P < 0.05). During the control period, increases in peak Qbr on injection of saline, Omnipaque, Conray, and dextrose were 55 +/- 29, 112 +/- 62, 280 +/- 99, and 388 +/- 125% of baseline, respectively. Bronchial arterial infusion of L-NNA lowered baseline Qbr and partially attenuated the response to injection of saline, Omnipaque, and Conray (P < 0.05). Phenylephrine, in doses that decreased baseline Qbr to the same extent as did L-NNA, did not attenuate the bronchial vasodilation. There was a linear relationship between osmolality and the percentage increase in bronchial blood flow. We conclude that an osmolar stress is the trigger for the contrast-induced bronchial vasodilation and that the response is partially mediated by endothelial release of nitric oxide.