A study of the interaction of practolol with acetylcholine, histamine, serotonin and bradykinin in the guinea-pig, and with bean-sprout juice in the mouse.

1. The interactions of practolol with acetylcholine, histamine, serotonin and bradykinin were studied on the trachea and lung of the guinea-pig, an animal whose sensitivity to bronchoactive endogens is known to be similar to that of human asthmatic bronchi. 2. Practolol, like propranolol, potentiated the action of the first three agonists mentioned above, but, unlike propranolol, it did not potentiate the bronchospastic effect of bradykinin. 3. Practolol, in fact, antagonized the action of bradykinin, but this effect was unlike that produced by nonsteroidal anti-inflammatory drugs. 4. The possibility that beta-adrenoreceptor antagonists might show adverse interactions with certain foodstuffs was investigated, an is discussed. 5. It is suggested that the feasibility of the continued use of practolol (or the newer cardioselective beta-blockers) in asthmatics necessarily depends on the type of allergic reaction involved, and so it is not possible to generalize. Any drug or food that might cause a bronchospastic effect synergistically in the presence of a beta- adrenoreceptor antagonist, even a cardioselective one, should be regarded with suspicion.