Dual action of antihistamines on histamine release

1. Quantitative examinations were made on the effect of benadryl and neoantergan on the histamine release in vitro from chopped skin of dogs and in vivo from rat skin. For estimation of the in vitro histamine release by biological method, a chemical procedure for separating the diffused-out histamine from mixed antihistamines was carried out. 2. Both antihistamines caused a fairly marked release of histamine from chopped skin tissues in comparatively higher concentrations. This action was synergistic with histamine-releasing effect of sinomenine and anaphylatoxin. 3. In lower concentrations, however, both antihistamines inhibited the in vitro histamine-releasing effect of sinomenine and anaphylatoxin. 4. Administration of a comparatively large amount of benadryl markedly depleted the skin histamine of a rat in vivo but smaller amount clearly suppressed the histamine depletion by subsequently administered sinomenine. 5. Based on the evidence of such dual action of antihistamines, some considerations were made on the site of action of these agents.