Nonimmunologic Immediate Contact Reactions to Three Isomers of Pyridine Carboxaldehyde

Summary

Pyridine carboxaldehyde (PCA) has recently been found to be one of the many substances able to produce nonimmunologic immediate contact reactions (NIICRs). This study investigated the ability of three isomers of PCA, 2-, 3- and 4-PCA, all in ethyl alcohol, to produce NIICRs in the guinea pig and man. In the guinea pig ear swelling test, five animals were used for each concentration of each test substance. 2-PCA did not cause swelling of the ear, 50 mM 4-PCA produced slight and 1 M moderate swelling, whereas 3-PCA was the most active in inducing slight to moderate swelling at a concentration as low as 1.6 mM. The results of the NIICR test (open application) on the upper back skin of ten healthy untanned Caucasians agreed with those of the guinea pig ear swelling test. The results indicate marked differences between the three isomers of PCA in the ability to produce NIICRs in both man and the guinea pig.