Effect of treatment with interleukin-1 receptor antagonist on the development of carrageenan-induced pleurisy in the rat

Pretreatment of rats with the human interleukin-1 receptor antagonist (IL-1ra) by the subcutaneous route at –0.5 h, relative to the intrapleural injection of carrageenan (CG), suppressed the infiltration of cells into the pleural cavity of intact and adrenalectomized rats at 5 h (28 and 74% reduction in intact animals at 0.3 and 10 mg/kg, respectively). Exudate volume at 5 h was also suppressed at dosages of IL-1ra 3 mg/kg. IL-1ra was still effective as an antiinflammatory agent in the 5-h pleurisy model when administered 1 or 2 h, but not 3 h, after CG. The addition of IL-1ra to a maximally effective antiinflammatory dosage of indomethacin (5 mg/kg) resulted in further reductions of cell number and exudate volume, suggesting that the antiinflammatory effects of IL-1ra in the 5-h model were not due solely to inhibition of IL-1-induced prostaglandin biosynthesis. The antiinflammatory effects of suboptimal dosages of IL-1ra and dexamethasone, administered in combination, were essentially additive. In 24-h pleurisy, IL-1ra reduced exudate volume and PMN number after a single dosage of 10 mg/kg, subcutaneously at –0.5 h and after dosages of 3 mg/kg at –0.5 and 5 h. Additional dosages of IL-1ra (3 mg/kg) at 10 and 15 h did not further inhibit PMN accumulation. Treatment with IL-1ra did not affect macrophage accumulation in 24-h CG-induced pleurisy. IL-1ra was not active as an antiinflammatory agent in the 24-h pleurisy model after three dosages of IL-1ra (3mg/kg) at 5, 10 and 15 h.