Kinetics of the generation and action of chemical mediators in zymosan‐induced inflammation of the rabbit peritoneal cavity

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Abstract
Acute inflammation was induced by intraperitoneal injection of zymosan (yeast cell walls) in the rabbit. Peritoneal inflammation was monitored by the local accumulation of intravenously‐injected Evans blue dye (which binds to plasma albumin) and of polymorphonuclear leukocytes (PMNLs). The zymosan‐induced exudate fluid contained a microvascular permeability‐increasing factor or factors which, unlike histamine and bradykinin, had a long duration of action when tested in rabbit skin and was dependent on circulating PMNLs. Using radioimmunossay, high levels of rabbit C5a, or C5a des Arg, were detected in the exudate fluid and accounted for much of the permeability‐increasing activity, as judged by skin bioassay after separation on Sephadex G‐100. The vasodilator prostaglandin, prostaglandin I2 (PGI2), was generated in the inflammatory reaction, as judged by the presence of high levels of 6‐oxo‐PGF1α detected in the exudate by radioimmunossay. However, in contrast to observations in rabbit skin, inhibition of prostaglandin generation had a relatively small effect on peritoneal oedema formation. C5a and C5a des Arg increase microvascular permeability by a PMNL‐dependent mechanism in the rabbit. However, in response to zymosan, protein leakage was detected considerably earlier than PMNL accumulation. A hypothesis to account for this difference is proposed.