Individual differences in PCA response in the guinea pig

Experiments were carried out to determine the cause of individual differences in the passive cutaneous anaphylaxis (PCA) response in guinea pigs. The intensity of 4-h homologous PCA produced by anti-penicillin G serum was not markedly different among eight reactive sites on the back of a specified animal, whereas considerable individual differences were observed in the PCA response, even at a specified reactive site. PCA was significantly inhibited by an antihistaminic agent, promethazine, and the tissue histamine content was significantly reduced after PCA, suggesting histamine release as a mediator. The intensity of PCA in individual animals was highly correlated with that of the histamine-induced cutaneous reaction elicited at a site adjoining the PCA but was unrelated to skin histamine content. These results suggest that the difference in susceptibility to histamine has a considerable effect on individual differences in the PCA response in guinea pigs.