Alveolar liquid clearance is increased by endogenous catecholamines in hemorrhagic shock in rats

The primary objective of this study was to test the hypothesis that hemorrhagic shock would stimulate alveolar liquid clearance by a catecholamine-dependent mechanism. Anesthetized rats were hemorrhaged to a mean arterial pressure of 30 mmHg for 90 min, but they were not resuscitated. Alveolar liquid clearance was measured by the concentration of labeled and unlabeled protein over 2 h in an isosmolar physiological solution of 5% albumin that had been instilled into one lung. Hemorrhaged rats developed a severe metabolic acidosis that was associated with a 5- to 10-fold rise in plasma epinephrine levels. There was a 60% increase in alveolar liquid clearance in the hemorrhaged rats compared with control rats (55 +/- 6 vs. 34 +/- 7%; P < 0.05). Amiloride (10(-4) M) or propranolol (10(-4) M) inhibited the increase in alveolar liquid clearance. Thus the endogenous release of catecholamines associated with hemorrhagic shock markedly stimulates alveolar fluid clearance by a beta-adrenergic-mediated stimulation of active sodium transport. These data suggest a new, previously unrecognized mechanism that may protect against alveolar flooding in the acute phase of hemorrhagic shock.