title: Effects of beta-adrenergic agents in lungs of normal and air-embolized awake sheep.
abstract: It is unclear whether beta-adrenergic agonists or antagonists affect lung liquid and protein exchange by changing pulmonary hemodynamics or microvascular leakiness. In 23 unanesthetized, instrumented sheep with long-term lung lymph fistulas, we assessed the effect of the beta-agonist terbutaline or the beta-antagonists propranolol, nadolol, and atenolol, all infused intravenously, on lung lymph flow under base-line conditions and during the acute lung injury caused by 4 h of venous air embolism. Under base-line conditions, neither beta-stimulation nor blockade had any effect. During air embolism, terbutaline decreased pulmonary vascular resistance and lymph flow by 25%. Propranolol and nadolol (non-selective beta 1,beta 2-antagonists) but not atenolol (selective beta 1-antagonist) also decreased lymph flow by 22% on average. We favor the more conservative (hemodynamic) over the more liberal (altered permeability) explanation for our results. First, beta-stimulation clearly caused vasodilation, which lowered the pulmonary microvascular pressure at the site of injury. beta-blockade caused changes similar to alpha-stimulation (J. Appl. Physiol. 62: 2147-2153, 1987). We therefore interpret the beta-blockade as unmasking pulmonary arterial alpha-receptors stimulated by the air-embolism injury, thus allowing vasoconstriction upstream to the site of injury. We do not believe the explanation of the beta-agent effects requires any modulation of lung microvascular leakiness by beta-adrenergic agents.
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001262:Atenolol / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D001798:Blood Proteins / Q000032:analysis; D002302:Cardiac Output / Q000187:drug effects; D004618:Embolism, Air / Q000503:physiopathology*; D005260:Female; D008168:Lung / Q000187:drug effects / Q000502:physiology* / Q000503:physiopathology; D008196:Lymph / Q000187:drug effects / Q000502:physiology; D009248:Nadolol / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011506:Proteins / Q000032:analysis; D011652:Pulmonary Circulation / Q000187:drug effects*; D012016:Reference Values; D012756:Sheep
chemical_list: D000318:Adrenergic beta-Agonists; D001798:Blood Proteins; D011506:Proteins; D009248:Nadolol; D001262:Atenolol; D011433:Propranolol