Effects of moderate hypothermia on alveolar capillary membrane permeability in endotoxin-induced acute lung injury in rats

Objective To investigate the effects of moderate hypothermia on the permeability of alveolar capillary membrane in acute lung injury (ALI) induced by lipopolysaccharide (LPS) .Methods Thirty-four adult male SD rats weighing 300-350g were randomly divided into 4 groups: control group (n = 8) ; LPS group (n = 10); hypothermia group (n = 8) and LPS + hypothermia group (n = 8) . The animals were anesthetized with intraperitoneal (i.p.) 1% pentobarbital 30 mg·kg-1, intubated and mechanically ventilated (RR 80 bpm, VT 20 ml·kg-1, I: E 1:2) . Right external jugular vein and left carotid artery were cannulated for BP and CVP monitoring and blood sampling. ALI was induced by LPS 1.0 mg·kg-1 i.p. and 16h later, intratracheal instillation of LPS 1.5 mg·kg-1. ALI was considered established when PaO2/FiO2 ≤300. Hypothermia was induced by surface cooling. Body T0 was reduced to 32.5-33.0℃. In control and hypothermia groups normal saline was given instead of LPS. Arterial blood samples were taken for blood gas analysis and MAP and CVP were recorded before (T0, baseline) and 1, 2, 3, 4 h after ALI (T1-4) . At the end of experiment (4h after ALI was established) the animals were killed by exsanguination. The lungs were removed. Lung lavage was performed and the concentration of albumin in bronchoalveolar lavage fluid (BALF), the left lung wet/dry weight ratio, myeloperoxidase (MPO) activity of lung tissue were measured. Lung tissue was also taken for histologic examination by transmission electron microscopy.Results There was no significant difference in hemodynamics among the 4 groups. PaO2/FiO2 and PaCO2 remained unchanged in the control group and hypothermia group. PaO2 /FiO2 was significantly decreased and PaCO2 was significantly increased as compared to the baseline values (T0) in LPS group (P 0.01). Hypothermia inhibited the increase in PaCO2 but had no effect on the decrease in PaO2/FiO2 induced by LPS. LPS significantly increased the lung W/D weight ratio, the concentration of albumin in BALF and MPO activity of the lung tissue as compared with the control group (P 0.01 or 0.05) . Moderate hypothermia significantly reduced the increase in lung W/D ratio, albumin concentration in BALF and lung tissue MPO activity induced by LPS but the lung W/D weight ratio in LPS + hypothermia group was still significantly higher than that in control group (P 0.05) . Electron microscopic examination showed that the alveolar capillary membrane was severely damaged in LPS group and moderate hypothermia significantly attenuated the injury to the alveolar capillary membrane. Conclusion Moderate hypothermia significantly decreases the increased permeability of alveolar capillary membrane in a rat model of ALI induced by LPS.