Neutrophils contribute to sympathetic nerve terminal-dependent plasma extravasation in the knee joint of the rat

Abstract

Infusion of bradykinin or 6-hydroxydopamine into the knee joint of the rat activates sympathetic postganglionic nerve terminals and increases plasma extravasation, a major sign of acute inflammation. Since bradykinin attracts and activates neutrophils in vivo and since neutrophils can release factors leading to plasma extravasation, we evaluated the contribution of the neutrophil to bradykinin-induced plasma extravasation. We report that perfusion of bradykinin into the rat knee joint produces a prolonged increase in plasma extravasation which is markedly reduced not only by sympathectomy (chronic pretreatment with systemic 6-hydroxydopamine) but also by depletion of circulating polymorphonuclear leukocytes (intravenous infusion of hydroxyurea combined with intraperitoneal glycogen). Depletion of polymorphonuclear leukocytes also reduced the plasma extravasation induced by intraarticular infusion of 6-hydroxydopamine, which acutely activates sympathetic postganglionic terminals. We next tested whether attraction of neutrophils into the joint, in the absence of bradykinin, was sufficient to enhance plasma extravasation. Although the classical neutrophil attractant glycogen attracted neutrophils into the knee joint, it did not increase plasma extravasation. Co-infusion of bradykinin and glycogen into the knee joint, however, provoked plasma extravasation that was significantly greater than that produced by bradykinin alone. We hypothesize, therefore, that bradykinin not only attracts neutrophils but also activates them, by an as yet undefined mechanism that requires the sympathetic terminal. The activated neutrophils release factors that lead to plasma extravasation. The next series of studies evaluated the role of the sympathetic nervous system in neutrophil attraction in vivo by bradykinin and glycogen. Since quantification of neutrophil attraction was not possible in the knee joint, we performed these studies in the peritoneal cavity, a site where neutrophils are readily attracted. We report that although intraperitoneal injection of either bradykinin or glycogen increased neutrophils into the peritoneal cavity, only that produced by bradykinin was significantly reduced by sympathectomy. These results support the hypothesis that the neutrophil contributes to bradykinin-induced plasma extravasation in the joint and suggest that the failure of bradykinin to attract neutrophils in vitro reflects the absence of substances released from the sympathetic postganglionic nerve.