Enzymatic histamine catabolism in vertebrate ontogenesis. A comparative study.

1. The synthesizing and degrading activities of histamine were determined in the liver and small intestine of developing guinea pig and chick embryos. 2. Though increasing with age, HDC values were always 2-3 orders of magnitude lower than those of degrading enzymes. 3. DAO activity on the other hand was 10-100 fold higher than HMT at all ages studied, suggesting a decisive role for oxidative deamination in control of tissue histamine levels. 4. Generally histamine levels were higher in tissues of developing guinea pig than chick embryo, however, in the laying hen intestine histamine concentration was approximately 5 times greater than in the adult guinea pig intestine.