Effect of ventilation on vascular permeability and cyclic nucleotide concentrations in ischemic sheep lungs.
Ventilation during ischemia attenuates ischemia-reperfusion lung injury, but the mechanism is unknown. Increasing tissue cyclic nucleotide levels has been shown to attenuate lung ischemia-reperfusion injury. We hypothesized that ventilation prevented increased pulmonary vascular permeability during ischemia by increasing lung cyclic nucleotide concentrations. To test this hypothesis, we measured vascular permeability and cGMP and cAMP concentrations in ischemic (75 min) sheep lungs that were ventilated (12 ml/kg tidal volume) or statically inflated with the same positive end-expiratory pressure (5 Torr). The reflection coefficient for albumin (sigmaalb) was 0.54 +/- 0.07 and 0.74 +/- 0. 02 (SE) in nonventilated and ventilated lungs, respectively (n = 5, P < 0.05). Filtration coefficients and capillary blood gas tensions were not different. The effect of ventilation was not mediated by cyclic compression of alveolar capillaries, because negative-pressure ventilation (n = 4) also was protective (sigmaalb = 0.78 +/- 0.09). The final cGMP concentration was less in nonventilated than in ventilated lungs (0.02 +/- 0.02 and 0.49 +/- 0. 18 nmol/g blood-free dry wt, respectively, n = 5, P < 0.05). cAMP concentrations were not different between groups or over time. Sodium nitroprusside increased cGMP (1.97 +/- 0.35 nmol/g blood-free dry wt) and sigmaalb (0.81 +/- 0.09) in nonventilated lungs (n = 5, P < 0.05). Isoproterenol increased cAMP in nonventilated lungs (n = 4, P < 0.05) but had no effect on sigmaalb. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester had no effect on lung cGMP (n = 9) or sigmaalb (n = 16) in ventilated lungs but did increase pulmonary vascular resistance threefold (P < 0.05) in perfused sheep lungs (n = 3). These results suggest that ventilation during ischemia prevented an increase in pulmonary vascular protein permeability, possibly through maintenance of lung cGMP by a nitric oxide-independent mechanism.
Pearse
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DB
Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins Medical Institutions at the Asthma and Allergy Center, Hopkins Bayview Medical Center, Baltimore, Maryland 21224, USA.
Wagner
E M
EM
Permutt
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D000818:Animals; D002199:Capillary Permeability / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D007511:Ischemia / Q000378:metabolism / Q000503:physiopathology; D008168:Lung / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000494:pharmacology; D011652:Pulmonary Circulation / Q000502:physiology; D012121:Respiration, Artificial; D012756:Sheep; D014655:Vascular Resistance / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology
D004791:Enzyme Inhibitors; D014665:Vasodilator Agents; D009599:Nitroprusside; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester