Catecholamine Clearance from Alveolar Spaces of Rat and Human Lungs

Abstract

Background: Although aerosolized β-adrenergic agonists have been used as a therapy for the resolution of pulmonary edema, the mechanisms of catecholamine clearance from the alveolar spaces of the lung are not well known. Objective: To determine whether catecholamine clearance from the alveolar spaces is correlated with the fluid transport capacity of the lung. Methods: Albumin solution containing epinephrine (10^–7M) or norepinephrine (10^–7M) was instilled into the alveolar spaces of isolated rat and human lungs. Alveolar fluid clearance rate was estimated by the progressive increase in the albumin concentration over 1 h. Catecholamine clearance rate was estimated by the changes in catecholamine concentration and alveolar fluid volume over 1 h. Results: The norepinephrine clearance rate was faster than the epinephrine clearance rate in the rat and human lungs. In the rat lungs, amiloride (a sodium channel blocker) caused a greater decrease in alveolar fluid clearance and epinephrine clearance rate than propranolol (a nonselective β-adrenergic antagonist). Although propranolol and phentolamine (an α-adrenergic antagonist), and 5-(N-ethyl-N-isoprophyl)amiloride (a Na⁺/H⁺ antiport blocker) changed neither the alveolar fluid clearance nor the norepinephrine clearance rate, amiloride and benzamil (a sodium channel blocker) decreased both clearance rates. As in the rat lungs, amiloride decreased alveolar fluid and norepinephrine clearance rates in the human lungs. Conclusion: These results indicate that the catecholamine clearance rate from the alveolar spaces is correlated with alveolar fluid clearance in rat and human lungs.