Mediators of C5a-Induced Bronchoconstriction in the Guinea Pig

Abstract

The effect of intravenous injection of C5a on pulmonary resistance and dynamic lung compliance was determined in anesthetized, artificially respirated guinea pigs. A mixture of C5a plus C5a_{des arg} was purified from yeast-activated guinea pig serum and is referred to as C5a. Intravenous injection of C5a caused a dose-related bronchoconstriction as evidenced by a decrease in compliance and increase in resistance. Conversion of the C5a in the mixture to C5a_{des arg} by carboxypeptidase B digestion did not significantly alter the magnitude of the bronchoconstriction. Pharmacological antagonists were employed to determine if histamine, acetylcholine or products of the arachidonate metabolism were mediators of C5a-induced bronchoconstriction. The histamine H₁ antagonist pyrilamine inhibited the C5a-induced bronchoconstriction, suggesting the involvement of histamine. The cholinergic receptor antagonist atropine in combination with pyrilamine caused an inhibition of the C5a-induced increase in resistance but not compliance, suggesting acetylcholine does not play a major role in C5a-induced bronchoconstriction beyond its known role in participating in histamine-induced bronchoconstriction. Involvement of arachidonate metabolites was suggested by the ability of the cyclooxygenase inhibitor, indomethacin, to prevent the C5a-induced bronchoconstriction. Because indomethacin also caused a delay in the leukotriene C₄ (LTC₄)-induced bronchoconstriction, the participation of peptidoleukotrienes in the C5a-induced bronchoconstriction could not be ruled out. The leukotriene antagonists FPL 55712 and L-649,923 were evaluated for their specificity in inhibiting LTC₄-induced bronchoconstriction. FPL 55712 was nonselective since it inhibited prostaglandin D₂ and histamine-induced bronchoconstriction as well as LTC₄-induced bronchoconstriction. L-649,923 inhibited only the LTC₄-induced bronchoconstriction and was without effect on the C5a-induced bronchoconstriction, suggesting that peptidoleukotrienes are not important mediators of C5a-induced bronchoconstriction. Using radioimmunoassay, the change in peptidoleukotriene levels detected in plasma during C5a-induced bronchoconstriction was not significantly different from 0. Thus, these studies have quantitated the C5a-induced decrease in dynamic lung compliance and increase in pulmonary resistance and suggest that histamine and cyclooxygenase products, but not peptidoleukotrienes, play a major role in C5a-induced bronchoconstriction.

Enhancement of Antigen-Induced Bronchoconstriction in the Guinea Pig after Intravascular Complement Activation with Cobra Venom Factor

“…Pulmonary resistance and dynamic lung compliance were mea sured continuously in mechanically respirated, pentobarbitalanesthetized male guinea pigs (300-450 g. Dunkin-Hartley des cendants; Bio-Lab, St. Paul, Minn. USA) as described previously [10]. Results are expressed as the m ean±SE of the percentage of change from the control compliance or resistance before addition of the bronchoconstricting stimuli.…”

“…Purification of guinea pig C5a utilized a modification of the method of Gerard and Hugli [13], as in our previously reported studies [10], The C5a used in these studies was a mixture of C5a plus C5adc, Arp, as verified by cellulose acetate electrophoresis.…”

“…When the com plement system is activated by either the classical or alternative pathways, the C5 molecule is cleaved, gen erating the polypeptide anaphylatoxin C5a. Included among the known biological activities of C5a is its ability to contract isolated respiratory smooth muscle [7,8] and to cause bronchoconstriction in vivo in the guinea pig [9][10][11], Thus, the suggestion that the com plement system may be activated on antigen chal lenge in acute asthmatics, coupled with the ability of C5a to cause bronchoconstriction in experimental an imals, indicates that an investigation into a role for the complement system in antigen-induced broncho constriction is warranted. To begin to test the hypo thesis that the complement system is important for an tigen-induced bronchoconstriction, we employed the complement-depleting agent cobra venom factor (CVF).…”

C5a-Induced Bronchoconstriction: Absence of a Role of Circulating White Blood Cells and Platelets

“…Guinea pig C5a was purified as previously described [3], The material referred to as C5a throughout this paper is a mixture of C5a plus C5adcs.Arg. A spectrophotometric scan after cellulose ace tate electrophoresis indicated that C5a was approximately 26% of the C5a plus C5ades.Arg present.…”

“…Included among the bio logic activities of C5a is the ability to cause broncho constriction in the guinea pig [1][2][3] as well as to cause chemotaxis and aggregation of granulocytes [4], Pre vious studies by ourselves [3,5] and others [2,6] had suggested that histamine and cyclo-oxygenase prod ucts, but not leukotriene B4 or peptidoleukotrienes, play a major role in bronchoconstriction induced by intravenous administration of C5a. As an extension of the studies on mediators, the purpose of the present study was to determine if circulating white blood cells and platelets played a major role in the ability of in travenously injected C5a to cause bronchoconstric tion.…”