A biochemical study of the cotton pellet granuloma in the rat. Effects of dexamethasone and indomethacin.

The subcutaneous implantation of a cotton pellet into a rat results in the formation of a granuloma at the site of the implant. The early events comprise an accumulation of fluid and protein-aceous material together with an infiltration of neutrophils. The granuloma formed by day 7 is characterized by the formation of a vascularized fibrous capsule containing fibroblasts and infiltrating mononuclear cells which are rich in N-acetyl-beta-D-glucosaminidase (NAG). Granuloma development was quantitated by dry weight measurements, and its cellular content was measured by assaying activity of NAG and total nucleic acid content. Nucleic acid determinations showed that cell infiltration into the granuloma took place at a virtually constant rate over a 7-day period. In contrast, the NAG activity did not change significantly until after day 5 when a large increase in the amount of enzyme extractable from the granuloma was seen. Systemic treatment of the animal with dexamethasone or indomethacin resulted in an inhibition of granuloma weight gain, NAG activity and nucleic acid levels. The data suggest that the two drugs acted during the early phase of granuloma development at the level of cell infiltration. Both drugs given on days 0-3 alone suppressed granuloma formation, whereas treatment on days 4-7 was without effect.