Effect of mechanical ventilation on urine volume and expression of aquaporins in rabbits

To explore biological mechanisms underlying the traditional Chinese medicine theory of “lung governing the regulation of water passage” by observing effects of mechanical ventilation on urine volume and related bioactive substances.A total of 16 male rabbits were randomly divided into control and lung expansion model groups (n = 8 per group), which were examined during the following four respiratory intervention stages (10 minutes each): (1) free breathing without any respiratory intervention; (2) lung expansion induced by mechanical ventilator; (3) free breathing without ventilator intervention; (4) cutting of bilateral sympathetic, vagus, and depressor nerves with mechanical ventilation. Data for breathing rate, blood pressure, and urine drops were recorded with a Medlab data acquisition system. Levels of nitric oxide (NO), antidiuretic hormone (ADH), endothelin 1 (ET-1), angiotensin II (AngII), prostaglandin E₂ (PGE₂), and atrial natriuretic peptide (ANP) were detected in lung tissue, kidney tissue, and serum by enzyme-linked immunosorbent assay. Protein expression of aquaporins 1 and 2 (AQP1 and AQP2) was detected in kidney tissue by immunohistochemistry, while Aqp1 mRNA and Aqp2 mRNA levels in kidney tissue were detected by real-time quantitative polymerase chain reaction. Histopathological changes in lung and kidney tissues were examined by hematoxylin and eosin staining.Compared with the control group, number of urine drops during the second and fourth stages is significantly decreased in the model group (P < .05). In addition, NO and PGE₂ content in lung and kidney tissues was significantly decreased in the model group (P < .05). ANP content in model group lung and kidney tissues was significantly increased (P < .05), while ET-1 content in these tissues was significantly decreased (P < .05). AngII content in kidney tissue was significantly decreased in the model group (P < .05), while serum AngII content of the animals was significantly increased (P < .05). Expression of AQP1 and AQP2 proteins in kidney tissue was significantly higher in the model group than in the control group (P < .05). No obvious histopathological changes were observed in lung or kidney tissues of animals in either group.Mechanical ventilation reduced urine volume, increased expression of AQP1 and AQP2 in kidney tissue, and altered levels of NO, ADH, ET-1, AngII, PGE₂, and ANP in lung tissue, kidney tissue, and serum. These results provide an experimental basis for preliminary studies of mechanisms under pinning the theory of “lung governing the regulation of water passage”.