EFFECTS OF ACTIVATED NEUTROPHILS ON ISOLATED RINGS OF RAT THORACIC AORTA

Local inflammation and respiratory burst of polymorphonuclear leukocytes generate reactive oxygen species (ROS). The aim of our study was to analyze the effects of peritoneal neutrophils on changes of the muscle tension of isolated aorta and compare their effects with those of different ROS. While native neutrophils did not influence muscle tension, the N-formyl-methionyl-leucyl-phenylalanine activated ones evoked a biphasic response on the KCl-precontracted aorta. The effects of activated neutrophils were in both respects similar to those evoked by xanthine/xanthine oxidase (X/XO) and differed from the effects evoked by H2O2 and Fe2SO4/H2O2. Using H2O2 we demonstrated that the effects of ROS were dependent on the KCl induced initial tension. To exclude the effect of extensive depolarization the action of different ROS was studied also on tissues precontracted by phenylephrine. Under such condition activated neutrophils caused a marked contraction similar to that evoked by X/XO. Their effects differed however, from those of H2O2 and Fe2SO4/ascorbic acid. These findings and elimination of activated neutrophil-induced contractions as well as the chemiluminiscence by superoxide dismutase suggest that the primarily activated neutrophil-released ROS was superoxide, which can be transformed to peroxynitrite, and other ROS including H2O2. Reduction of all followed-up contractions caused by nordihydroguaiaretic acid, indicate that 5-lipoxygenase metabolites unselectively reduce contractions. In contrast, selective inhibition of activated neutrophil-evoked contraction by indomethacin suggests that cyclooxygenase metabolites are involved mainly in their action on vascular smooth muscle.