[Effect of beta-adrenergic agonist on alveolar fluid clearance in acute lung injury: an experiment with rats].

Objective: To determine the effect of dobutamine, a beta-adrenergic agonist, on the alveolar fluid clearance (AFC) in acute lung injury (ALI).
Methods: Thirty two male Sprague-Dawley rats were randomly divided into four equal groups: normal control group; ALI group, infused with endotoxin to induce ALI; dobutamine control group, receiving sustained intravenous injection of dobutamine at the dose of 5 microg/kg/min, and dobutamine treatment group, receiving sustained intravenous injection of dobutamine at the dose of 5 microg/kg/min after the administration of endotoxin. Experiment began 45-60 minutes after the circulation was stable. Blood pressure was measured and blood gas analysis was conducted at the beginning of the experiment and one hour later. Perfusion fluid with (125)I-albumin with the radioactivity of 1.5 microCi/ml was perfused into the lung. One hour after the mechanical ventilation the mice were killed and their lungs were taken out. Alveolar fluid was taken out to calculate the AFC by single nuclide tracer technique. RT-PCR was used to detect the expression of alpha, beta, and gamma-rat epithelial sodium channel (rENaC) mRNA.
Results: (1) The AFC of ALI group was 14.0 +/- 1.2%, significantly lower than that of the normal control group (21.0 +/- 3.9%, P < 0.05). (2) The AFC of the dobutamine control group was 26.6 +/- 1.6%, significantly higher than that of the normal control group (P < 0.05). and the AFC of the dobutamine treatment group was 20.0 +/- 3.9%, significantly higher than that of the ALI group (P < 0.05). (3) The expression of a-rENaC mRNA was 1.40 +/- 0.40 in the ALI group and was 1.38 +/- 0.13 in the dobutamine treatment group, both significantly higher than those in the dobutamine control group (1.01 +/- 0.14) and in the normal control group (0.44 +/- 0.11, all P < 0.05). The expression of beta-rENaC mRNA was 0.70 +/- 0.8 in the ALI group was 0.71 +/- 0.17 in the dobutamine treatment group, both significantly higher than those in the dobutamine control group (0.58 +/- 0.12) and in the normal control group (0.44 +/- 0.11, all P < 0.05). There were not significant differences in expression of alpha and beta-rENaC mRNA between the normal control group and dobutamine control group, and between the ALI group and dobutamine treatment group (both P > 0.05). (4) The gamma-rENaC mRNA expression was 0.90 +/- 0.19 in the dobutamine control group and was 0.97 +/- 0.15 in the dobutamine treatment group, both significantly higher than that in the normal control group (0.69 +/- 0.10) and in the ALI group (0.70 +/- 0.32) (all P < 0.05).
Conclusion: Able to upregulate the gamma-rENaC expression and improve the AFC in acute lung injury, beta-adrenergic agonist may be beneficial to reduce lung edema in ALI patients.