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The present study examines the indomethacin-provoked aggravation of chronic ulceration induced by acetic acid in rats. The drug was administered in a single dose, 7 and 14 days after provocation of ulceration. The changes induced by indomethacin in other groups of animals that had been treated for 7 and 14 days with hydroxyurea (which provokes a marked leucopenia) were also studied. The results obtained demonstrate that indomethacin does not significantly modify the macroscopic index of ulceration nor vascular permeability in the majority of the groups tested. Only in the group that received hydroxyurea for 14 days was there an increase in both parameters. Myeloperoxidase activity was assayed and used as an index of leucocyte infiltration in an attempt to relate the increase in this activity with a gastrolesive effect. Application of acetic acid produced a significant increase in this activity 7 days after induction of chronic injury. Administration of hydroxyurea intraperitoneally was associated with a decrease in the severity of chronic ulceration and neutrophil infiltration into the gastric mucosa. This effect was detectable enzymatically and microscopically. The groups that received indomethacin showed an increase in myeloperoxidase activity, although this increase was only significant in the animals treated with hydroxyurea for 7 and 14 days. The results suggest that the aggravation provoked by indomethacin is greater when the ulcer curing process is more advanced.

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