C5a and antigen-induced tracheal contraction: effect of a combination of an antihistamine and cyclo-oxygenase inhibitors

The role of C5a in hypersensitivity reactions in the lung

What role the complement system in general, and C5a in particular play in hypersensitivity reactions in the lung is unknown. A review of the available studies indicates that C5a can mimic hypersensitivity reactions in the lung by virtue of its ability to cause cell infiltration and edema in the lung, cause a short lived airway hyperreactivity and cause bronchoconstriction. Its ability to cause contraction of isolated airways and in vivo bronchoconstriction in the guinea-pig is due to the release of histamine and arachidonate metabolites, mediator systems similar to those evoked by antigen-antibody reactions in the guinea-pig lung. To begin to determine if C5a generation with complement system activation was an important contributor to antigen-induced bronchoconstriction, the response to antigen was assessed in animals depleted of complement by cobra venom factor and unresponsive to C5a. Unexpectedly, these animals responded to antigen with a much greater bronchoconstriction than did animals with an intact complement system. This suggested that an intact complement system was somehow important in limiting allergic bronchoconstriction or conversely that allergic bronchoconstriction might be heightened when preceded by complement system activation. Thus, the data implicates C5a and/or complement system activation as a modulator of antigen-induced bronchoconstriction rather than directly contributing to the bronchoconstrictor component of hypersensitivity reactions in the lung.

Bronchoconstriction induced by N-formyl-methionyl-leucyl-phenylalanine in the guinea pig; involvement of arachidonic acid metabolites

The chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (F-met-leu-phe) was shown to be a potent myotropic agent on the guinea-pig parenchymal strip (IC50, 2 X 10(-7)M). The response was unaffected by the histamine (H1) antagonist, mepyramine, but in the presence of the cyclooxygenase inhibitor, indomethacin, the dose response curve was shifted to the left (IC50, 4 X 10(-8)M) and the maximal response reduced. Injection of F-met-leu-phe into perfused guinea pig lungs resulted in the release of leukotriene-like activity which was detected by superfusion over guinea-pig ileum preparations in the presence and absence of FPL-55712. Intravenous injection of F-met-leu-phe to spontaneously breathing anaesthetized guinea pigs resulted in transient increases in pulmonary resistance and blood pressure and decreases in dynamic compliance and heart rate. The pulmonary parameters were significantly inhibited by BW 755C, indomethacin, FPL-55712 and a contractile prostanoid antagonist, L-640,035. These results demonstrate that F-met-leu-phe is a potent bronchoconstrictor in the guinea pig and that the peptide may induce these changes through the generation of products of the cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism.

Indomethacin alters the effects of substance-P and VIP on isolated airway smooth muscle

Both substance-P and vasoactive intestinal peptide (VIP) have previously been demonstrated to contract and relax, respectively, the isolated guinea pig trachea. In addition, substance-P and VIP have been localized within the pulmonary innervation of various species. In the present studies, substance-P was found to cause a concentration-related contraction of isolated lung parenchymal strips of the guinea pig, as well as isolated tracheal strips. VIP caused a significant concentration-related relaxation of the isolated tracheal strip, but not the lung parenchymal strip. Indomethacin, a prostaglandin synthetase inhibitor, potentiated the contractile response of the trachea to substance-P and inhibited the VIP- and isoproterenol-induced relaxation. These studies are potentially important in understanding the pathogenesis of bronchospastic disorders, since alterations in prostaglandin biosynthesis may result in hyperreactivity of airways to contractile agonists such as neurotransmitters, as well as an inhibition of relaxation induced by endogenous substances such as VIP or beta agonists.