A comparison of the effects of aspirin and histamine of fluid balance in the recruited lung.

Salicylate administration has been reported to increase the flow of protein-rich lymph from the lungs of animals, however, the mechanism of this response is unclear. In the present study we measured pulmonary hemodynamics and lung fluid and protein flux in anesthetized sheep, surgically prepared for the collection of lung lymph, in order to examine the possible effect of aspirin (ASP) on lung vascular permeability. ASP was given during recruitment of pulmonary microvascular surface area induced by sustained elevation of left atrial pressure (Pla) (Group 1) or continuous infusion of adenosine triphosphate (ATP) (Group 2). We compared the results of ASP administration to those found in similarly prepared animals given histamine (H) during like periods of increased Pla (Group 3) or ATP infusion (Group 4). ASP administration resulted in increased lymphatic protein clearance (Cp) in both Groups 1 and 2. In Group 1, following the characteristic increase in lung lymph flow (Q1) and fall in the ratio of lung lymph to plasma protein concentration (L/P) produced by Pla elevation, ASP administration resulted in a further increase in Q1 and a significant increase in L/P. The results found in ASP animals are qualitatively similar to those observed in Groups 3 and 4 after H. While we cannot specifically rule out a hemodynamic effect of the drug, our results suggest the increased protein flux observed following ASP administration was mediated at least in part through an increase in lung microvascular permeability.