In Vivo Bronchodilator Activity of Nifedipine in the Guinea Pig

We administered histamine subcutaneously to anesthetized guinea pigs to induce prolonged bronchoconstriction and then tested the effect of intravenously administered nifedipine on pulmonary resistance (RL) and dynamic compliance (Cdyn). One mg of subcutaneously administered histamine caused RL to increase by an average of more than 250% and Cdyn to fall on average to 26% of baseline; mean RL remained more than twice baseline, and mean Cdyn remained less than half baseline for 80 min. Intravenously administered nifedipine 3 ng/kg and ethanol (diluent) administered 25 min after histamine had no effect on RL but caused a slightly greater fall in Cdyn than in the control animals treated with histamine alone. Nifedipine 30 µg/kg, however, exhibited significant bronchodilator activity: 35 min after nifedipine 30 µg/kg, RL decreased on average to 41 ± 17% above baseline (p < 0.02), and Cdyn increased to 49 ± 5% below baseline (p < 0.0001). By comparison, isoproterenol (0.3 to 3.0 µg/kg) caused bronchodilation of...