Effect of radiographic contrast agents on leukocyte metabolic response.

Abstract

The use of radiographic contrast media in the setting of possible bowel ischemia and potential perforation is known to carry a risk of morbidity and mortality. However, studies of the effect of available contrast media on host immunological defense mechanisms are lacking. We have examined the effect of barium and of two water-soluble contrast agents of differing iodine concentration and osmolality, Conray 30 and Cysto Conray II, on leukocyte phagocytosis. Blood samples were incubated with the contrast media alone (termed the "resting state"), and in combination with a standard phagocytic challenge (Zymosan polysaccharide extract) and with Staphylococcus epidermidis, Streptococcus faecalis and Escherichia coli, to determine the effect of contrast media upon leukocyte phagocytic response. Incubation with saline was used as control. In the case of barium, the "resting state" and standard challenge experiments were repeated at nine dilutions, ranging from 1:1 to 1:1000. The leukocyte phagocytic response was measured in two ways: CO2 generation (an index of metabolic activity) and chemiluminescence (an index of generation of reactive oxygen species and bacterial killing). Barium, at clinical dilutions, causes a significant increase of baseline "resting state" phagocytic activity, which in turn leads to significant blunting of subsequent response to phagocytic challenge and adversely affects the response to all bacteria tested. There is no baseline activation of leukocytes by the water-soluble media, although there was some inhibition (rather than activation) of leukocyte metabolic activity. The effect of the water-soluble media on bacteria was more complex (although inhibition is minor compared to barium). Our data demonstrate that barium is a significant activator of phagocytic cells, which results in deactivation of phagocytic response when challenged; these data serve to explain the enhanced adverse effect of barium in cases of fecal peritonitis.