Circannual variations in carrageenan-induced paw edema and in the anti-inflammatory effect of phenylbutazone in the rat.

Circannual variation in the edema produced by intraplantar injection of carrageenan (carr) was examined over a period of 31 months. The anti-inflammatory effect of a dose of 30 mg/kg of phenylbutazone (PHZ) was also determined over a period of 1 year. Carr-induced edema was significantly larger in spring while it was smaller in winter. PHZ induced a pronounced reduction of paw edema throughout the year except in spring when the anti-inflammatory effect of the drug could not be detected. Mechanisms responsible for these circannual variations are discussed.