Action of stobadine on respiratory and vascular smooth muscle in vivo: evidence for histamine receptor antagonist activity.

The effect of stobadine on respiratory smooth muscles, blood pressure, heart rate and gastric acid secretion was studied and compared with the action of other antihistamines in vivo. Stobadine, as diphenhydramine, dithiadene and promethazine, but in contrast to cimetidine and ranitidine, prevented histamine from producing bronchospasm both after i.v. and oral administration. Based on the potency of its pharmacological action, diphenhydramine had a lower bioavailability after oral administration than the other antihistamines. Both cimetidine and ranitidine reduced the gastric acid secretion while stobadine was ineffective in this respect. None of the drugs studied antagonized histamine in reducing blood pressure, but all of them, with exception of promethazine and diphenhydramine, reduced mean arterial blood pressure. The results suggest that the action of stobadine on the respiratory and vascular smooth muscle effects is intermediate between that of diphenhydramine and dithiadene. In view of the minimal effect of stobadine on gastric acid secretion and its marked activity on airways, it is concluded that this drug predominantly acts on H1-receptors.