The effect of radiographic contrast media on the chemotaxis of granulocytes.

The direct in vitro effect of radiographic contrast media (RCM) on granulocyte locomotion was assayed using an under agarose technique. All RCM tested inhibited the chemotactic response to N-fmlp, a synthetic chemotactic N-formylated tripeptide, which is an analogue of natural bacterial products. The inhibition was most pronounced for diatrizoate, the most hyperosmolar of the RCM, but hyperosmolality per se was not the only inhibitive factor, since 0.5 M NaCl, which has an osmolality comparable to the RCM used, did not inhibit chemotaxis significantly. Furthermore, the inhibition was not caused by a nonspecific sticky effect of RCM on granulocytes, since spontaneous migration was normal. We propose that the inhibition might be caused by competitive binding of RCM to the N-fmlp receptor sited on leukocytes because the third amino acid in N-fmlp is phenylalanine, which, like the RCM, contains a benzene ring.