TIME COURSE AND DEGREE OF CHANGE IN ALVEOLAR-CAPILLARY MEMBRANE-PERMEABILITY INDUCED BY ASPIRATION OF HYDROCHLORIC-ACID AND HYPOTONIC SALINE

Abstract

A change in alveolar capillary membrane permeability was induced in anesthetized rabbits by intratracheal injection of either HCl or hypotonic saline (2 ml/kg body wt). The degree of increase in permeability was measured from the relative extraction from the lung into arterial blood of 2 .gamma.-emitting tracers, 125I antipyrine and 51Cr EDTA instilled into the airways either in isotonic saline or mixed with the acid or hypotonic saline. The permeability index of the membrane was expressed as the ratio of total counts of 51Cr EDTA to 125I antipyrine in arterial blood in the first 5 min after intratracheal instillations. For the normal lung, this ratio was 0.022 .+-. 0.007. After aspiration of 2 ml of 10-1 M HCl (pH 1)/kg body wt, there was a 44 .times. increase in the ratio to 0.974 .+-. 0.110. There was a similar increase after aspiration of 10-4 M NaCl, to 0.990 .+-. 0.090 (isotonic saline being 1.5 .times. 10-1 M NaCl). The change in permeability after HCl persisted for at least 60 min, whereas the change in permeability due to osmotic damage with hypotonic saline was transient, completely resolving within 15 min after aspiration. There was a graded effect with different concentrations of HCl and NaCl. Minimal changes in permeability were found with 10-3 M HCl (pH 3), and no abnormality was demonstrated after aspiration of 10-4 M HCl (pH 4) due to rapid neutralization of acid in the alveoli. No abnormality was found after intratracheal injection of 10-1 M NaCl. This method provides a simple technique for assessing alveolar capillary membrane permeability. The results with HCl are consistent with previous reports that major lung damage in humans and animals only occurs with pH < 2.5. The technique provides new information about the time course of osmotic damage to the alveolar membrane.