Neutrophils generate oxygen free radicals in rat mesenteric microcirculation after abdominal irradiation

Oxygen free radicals have been invoked as mediators of tissue injury in gastrointestinal diseases. This study determines whether oxygen radicals are generated in the mesenteric microvasculature after abdominal irradiation and defines the cellular source of these radicals.

Leukocyte adherence and emigration in mesenteric venules were measured using intravital microscopy at 2 or 6 hours after abdominal irradiation. Oxygen radical production was measured using the oxidant-sensitive fluorochrome dihydrorhodamine 123 (DHR-123).

Relative to control microvessels, irradiated venules exhibited a significant increase in adherent leukocytes 2 hours after irradiation, whereas both adherent and emigrated leukocytes were increased at 6 hours. An increased oxidation of DHR-123 was noted within venules at 2 hours after irradiation, with a more marked response, associated with leukocytes emigrated into the interstitium, observed at 6 hours after irradiation. Treatment with an anti-CD18 antibody blocked irradiation-induced leukocyte adherence and emigration and prevented the DHR-123 oxidation, normally observed at 6 hours, with a partial attenuation of DHR-123 oxidation at 2 hours. Neither the leukocyte-independent component of DHR-123 oxidation nor the leukocyte recruitment normally observed at 2 hours postirradiation was blunted by the xanthine oxidase inhibitor allopurinol.

These findings indicate that activated leukocytes represent the major source of oxidants generated in the mesentery after abdominal irradiation.