The effect of alpha adrenergic blockade on non-specific airways reactivity and exercise induced asthma.

In asthmatics, alpha-adrenergic blockage with oral phentolamine partially or completely blocked bronchospasm after maximal exercise challenge. Bronchial reactivity to isocapnic hyperventilation with conditioned cold air was also reduced. However, non-specific airways reactivity to inhaled histamine did not change. Therefore, exercise and cold induced bronchospasm in asthma may be partially mediated by alpha adrenergic neural mechanisms perhaps through sensitization of alpha receptors during airway cooling.