In vitro effects of radiographic contrast media on the complement system

The effect of several radiographic contrast media on the complement system in vitro was examined using quantitative crossed immunoelectrophoresis. Diatrizoate, iothalamate, metrizoate, and methiodal did not cause electrophoretic conversion of C3 or properdin factor B. In fact, the small degree of spontaneous conversion occurring when serum is incubated in polypropylene tubes was inhibited by these contrast media or by hypertonic sodium chloride. Metrizamide caused enhanced conversion of C3 and factor B that was only partially inhibited by ethylene glycol tetracetic acid (EGTA) but completely inhibited by ethylenediaminetetraacetic acid (EDTA). Iodipamide caused a unique electrophoretic alteration of C3 that was not affected by EDTA or several other inhibitors and that was not identical with the usual products of C3 activation. Iodipamide in very low concentrations inhibited complement activation through the classical pathway.