Antihistamine activity of Bryophyllum calycinum.

1. The juice obtained by pressing the leaves of Bryophyllum calycinum (Crassulaceae) exhibited histamine-blocking activity. 2. The juice contains flavonoid compounds, carbohydrates and mineral salts. A flavonoid fraction (fraction B) obtained by partitioning the juice between n-butanol and water contained the substance responsible for the antihistamine activity. 3. When assayed on the isolated guinea pig ileum, 50 mg/ml juice and 0.15 mg/ml fraction B produced parallel and concentration-dependent rightward displacement of the concentration-response curve to histamine (EC50 (FL): 1.30 (0.26-5.28) x 10(-7) M, 15.80 (5.90-23.30) x 10(-7) M, 12.50 (7.62-14.90) x 10(-7) M, in the absence and presence of 50 mg/ml juice and 12 mg/ml fraction B, respectively) apparently in a competitive manner. The antagonism was specific for histamine, i.e., did not modify the response to acetylcholine, KCl and BaCl2 and was reversible upon washing. Vascular permeability responses of rats to intracutaneous 1.0, 5.0 or 10.0 micrograms histamine were decreased by about 20-25% in animals pretreated with 4 ml/kg of juice or with 12 mg/kg fraction B. The juice (4 ml/kg) protected guinea pigs from death by asphyxia induced by 5 mg histamine and the protection lasted at least 1 h. 4. However, since the juice was ineffective in protecting the gastric mucosa from histamine-induced ulceration, we conclude that the antihistamine effect of the juice and fraction B was produced by blockade of H1 and not H2 receptors.