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Clinically relevant concentrations of beta2-adrenergic agonists stimulate maximal cyclic adenosine
Daniel F McAuley1, James A Frank, Xiaohui Fang
1Cardiovascular Research Institute, University of California, San Francisco, CA, USA.
Objective:
To determine whether clinically relevant airspace concentrations of beta2-adrenergic agonists stimulated maximal alveolar fluid clearance rates and to determine whether beta2 agonist therapy decreased pulmonary edema in experimental acute lung injury.
Design:
Prospective randomized laboratory investigation.
Setting:
University-affiliated laboratory.
Subjects:
Sprague Dawley rats.
Interventions:
Dibutyryl cyclic adenosine monophosphate (cAMP), salmeterol, albuterol, and isoproterenol in normal rat lung. Salmeterol in a rat model of acid-induced lung injury.
Measurements And Main Results:
Basal alveolar fluid clearance was 7.6 +/- 2.2 %/hr. Maximal cAMP-dependent alveolar fluid clearance rate was 32.9 +/- 10.9 %/hr (p <.05). Racemic albuterol 10(-5) M, salmeterol 10(-6) M, and isoproterenol 10(-6) M each stimulated alveolar fluid clearance to a level comparable to maximal cAMP-dependent alveolar fluid clearance. Compared with basal rates, alveolar fluid clearance was increased by both racemic albuterol 10(-6) M (14.5 +/- 3.0%, p <.05) and R-enantiomer 10(-6) M (15.0 +/- 4.6%, p <.05), but there was no difference between the two groups. Intra-alveolar salmeterol 10 (-6) M attenuated the degree of pulmonary edema following acid-induced lung injury. Extravascular lung water increased to only 180 +/- 30 microL with salmeterol treatment, compared with 296 +/- 65 microL in saline-treated rats 4 hrs after acid injury (p <.05). This decrease in lung water was accompanied by a 2.4-fold increase in the rate of alveolar fluid clearance at 4 hrs in the salmeterol-treated group. Lung endothelial permeability, expressed as extravascular plasma equivalents, was reduced to 64 +/- 9 microL with salmeterol compared with 119 +/- 51 microL in saline-treated rats 4 hrs after acid injury (p <.05).
Conclusions:
Clinically relevant airspace concentrations of beta2-adrenergic agonists a) stimulate maximal cAMP-dependent airspace fluid clearance in normal lungs and b) reduce pulmonary edema in acid aspiration-induced lung injury by increasing alveolar fluid clearance and decreasing endothelial permeability. Clinical studies are required to determine whether beta2-adrenergic agonists improve outcome in patients with acute lung injury.