Alpha 1 adrenergic bronchomotor tone in guinea-pigs

The bronchial reactivity of fifty-one Hartley strain guinea-pigs, anesthetized with pentobarbital, was tested for aerosolized norepinephrine (NE) or phenylephrine (PE) in 1% saline solutions (total inhaled dose: 2 mg in 2 min). No changes in their total airways resistances was observed at the end of the tests. When the same animals were pretreated by inhalation of nebulized propanolol (4 mg in 5 min), NE provoked a significant increase in these airway resistances in 72% of the animals for a mean inhaled dose of 1.07 mg. The NE challenge was stopped as soon as ventilatory asynchronism developed. Similar responses were induced by PE inhalation. These increases in airways resistance were prevented when phentolamine aerosol (1.3 mg inhaled in 5 min) was inhaled before NE or PE tests. An alpha 1-adrenergic bronchoconstriction is thus provoked by NE or PE when the protection resulting from the bronchial beta-adrenergic dilation has been suppressed. This constriction presents important individual variations depending on the activity or on the number of the corresponding alpha-receptors; in 28% of the guinea-pigs, the bronchomotor tone remained unaffected by NE in spite of beta-antagonist pretreatment.