Abstract
Bronchodilator effects of diltiazem were investigated in the isolated guinea pig tracheal chain and in the anesthetized cat. Interaction of diltiazem with isoproterenol (iso) was also examined. Diltiazem (10-4g/ml) relaxed by 70% the tracheal chain contracted by histamine, 10-5g/ml. This effect of diltiazem was not affected by pretreatment with propranolol, 3×10-8g/ml. Diltiazem (400 μg/kg, i.v.) diminished by 20% the elevation of intratracheal pressure induced by serotonin aerosol, the effect of which lasted for approximately 20 min. On the other hand, diltiazem (10-5g/ml) produced no influence on the iso-induced relaxation of the guinea pig trachea. In the anesthetized dog, diltiazem (20 μg/kg/min, i.v.) did not affect the iso-induced bronchodilation when histamine was used as a spasmogen, while the positive chronotropic action of iso was diminished. On the contrary, propranolol (30 μg/kg, i.v.) potentiated the bronchoconstrictor effect of histamine and suppressed both the bronchodilating and positive chronotropic actions of iso. Thus, the effects of diltiazem differed from those of propranolol. In summary, diltiazem showed bronchodilation both in vitro and in vivo, although the activity was not so potent. With regard to the iso-induced bronchodilation, diltiazem had no effect at a dose which diminished the positive chronotropic action of iso.
