Inhibition of angiotensin-converting enzyme by contrast media. I. In vitro findings.

There is increasing evidence that activation of the plasma contact system that results in the production of bradykinin plays an important role in contrast material systemic reactions. The effects of bradykinin in anaphylaxis depend on its rate of destruction and its rate of production. The highest percentage of contrast material reactions occur after intravenous injections, and the major enzyme hydrolyzing bradykinin (kininase II; angiotensin-converting enzyme) is found on pulmonary vascular endothelial surfaces. The inhibitory effects of numerous ionic and nonionic contrast material solutions on the enzyme have been determined. Additionally, the role in this inhibition of the chelators found in all commercial contrast material vials has been studied. In vitro, all such preparations combined with their chelators inhibit angiotensin-converting enzyme. Whether this inhibition plays a role in vivo remains to be established.