Some effects of hydrocortisone on the early development of the rat cotton pellet granuloma.

Differential cell counts, DNA levels, cellular proliferation (studied by in vitro ³H]thymidine incorporation) and hydrolytic enzyme release into inflammatory exudates were investigated in sterile cotton wool pellets at various times after subcutaneous implantation in rats. At 2 days (the earliest time studied) the predominant cell type was the polymorphonuclear leucocyte (PMNL), but by 5 and 7 days increasing numbers of mononuclear cells (macrophages and lymphocytes) were present. Total DNA levels were almost constant, usually increasing slightly with time. DNA synthesis did not occur before day 3 and was still increasing at day 7. The two lysosomal hydrolases measured (N-acetyl-glucosaminidase) and β-glucuronidase) were present in the cell-free pellet exudate in high concentrations, suggesting that they had been released during phagocytosis. Treatment with hydrocortisone (10 mg/kg/day p.o.) during the earlier phase of the response reduced dry granuloma weight, total DNA levels and release of hydrolytic enzymes, and delayed the onset of cellular proliferation. Steroid treatment during the later proliferative phase only (days 3 to 6), reduced dry granuloma weight, total DNA level and hydrolytic enzyme release but did not affect ³H]thymidine incorporation.