Effect of epinephrine on alveolar liquid clearance in the rat

Endogenous epinephrine has been found to increase alveolar liquid clearance (ALC) in several pulmonary edema models. In this study, we infused epineph rine intravenously for Ih in anesthetized rats to produce plasma epinephrin e concentrations commonly observed in this species under stressful conditio ns and measured ALC by mass balance. Epinephrine increased ALC from 31.5 +/ - 3.2 to 48.9 +/- 1.1 (SE)% of the instilled volume (P < 0.05). The increas ed ALC was prevented by either propranolol or amiloride. To determine wheth er ALC returns to normal after plasma epinephrine concentration normalizes, we measured ALC 2 h after stopping an initial 1-h epinephrine infusion and found ALC to be at baseline values. Finally, to determine whether desensit ization of the liquid clearance response occurs, we evaluated the effects o f both repeated 1-h infusions and a continuous 4-h infusion of epinephrine on ALC and found no reduction in ALC under either condition. We conclude th at epinephrine increases ALC by stimulating beta-adrenoceptors and sodium t ransport, that the increase is reversible once plasma epinephrine concentra tion normalizes, and that desensitization of the ALC response does not appe ar to occur after 4 h of continuous epinephrine exposure.