Role of histamine in the spasmogenic effect of the complement peptides C3a and C5a-desArg (classical anaphylatoxin)

The role of endogenous histamine in the spasmogenic effect of the complement-derived peptides C3a and C5a-desArg (isolated from yeast-activated hog serum) was studied in strips of terminal guinea-pig ileum. The effect of C3a is apparently histamine-independent; it neither induces histamine release from the test organ nor is its spasmogenic action inhibited by the H1-antihistaminics pheniramine and triprolidine, used in concentrations effective against histamine. However, endogenous histamine may be involved in the spasmogenic effect of C5a-desArg; when applied repeatedly C5a-desArg induces histamine release during its first and second application. Furthermore, both H1-antihistaminics inhibited C5a-desArg-induced contractions considerably, though less efficiently than those of added histamine.