Bradykinin, the end product of activation of the plasma contact system, may play a significant role in reactions to contrast material and in other forms of anaphylactoid and anaphylactic responses to drugs or antigens. Activation of factor XII initiates activity in the plasma contact system, and we have identified factors (negatively charged surfaces) present in elevated concentrations in the plasma of patients who are asthmatic or allergic that can "prime" their plasma for the initiation and/or potentiation of factor XII activation. In other studies, we have shown that persons who react to contrast material and persons who are asthmatic or allergic share both a potential for accelerated contact system activity and evidence of an increased mean concentration of low-level contact system products. Recently, we have found that contrast media can inhibit angiotensin-converting enzyme, the substance that hydrolyzes bradykinin and limits its systemic effects. Thus, a number of factors suggest that it is the potential for increased production of bradykinin in persons who are allergic or asthmatic that may account for the greatly increased susceptibility of these patients to contrast material. This susceptibility may be critically triggered by the contrast media-induced inhibition of angiotensin converting enzyme. In view of these findings, the possibility exists that most, if not all, significant reactions to contrast material require an underlying allergic diathesis that may, or may not, be apparent by history and conventional diagnostic testing.
AJR. American journal of roentgenology