Mediators of C5a-induced bronchoconstriction in the guinea pig.
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 C5ades 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 C5ades 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.
Regal
J F
JF
Department of Pharmacology, University of Minnesota-Duluth, School of Medicine.
Bell
R L
RL
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001980:Bronchi / Q000187:drug effects; D001986:Bronchial Spasm / Q000139:chemically induced*; D002867:Chromones / Q000494:pharmacology; D003182:Complement C5 / Q000502:physiology*; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology*; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D010654:Phenylbutyrates / Q000494:pharmacology; D011738:Pyrilamine / Q000494:pharmacology; D013189:SRS-A / Q000502:physiology
D002867:Chromones; D003182:Complement C5; D010654:Phenylbutyrates; D013189:SRS-A; D001285:Atropine; D006632:Histamine; C006312:FPL 55712; C050033:L 649923; D011738:Pyrilamine; D000109:Acetylcholine; D007213:Indomethacin