Nonspecificity of the Chloride Impoverishing Mechanism of Small Intestine

Abstract

Burns and Visscher 1 have shown that an isotonic solution of a mixture of sodium chloride and some other sodium salt with an indiffusible anion when placed in a loop of the small intestine becomes practically chloride-free in 1½ hours. This movement of sodium chloride, against a diffusion gradient into the blood through the intervention of the intestinal epithelium, resembles the removal of chloride by the kidney tubules from the glomerular filtrate. The intestinal preparation affords a convenient method of studying salt movement which may be of general importance.

As a step in elucidating this mechanism it was decided that the specificity of mechanism should be determined. Sodium bromide was chosen as an example of a salt similar chemically to sodium chloride but not a usual constituent of body fluid. It is the purpose of these experiments to see if, in the presence of an indiffusible anion, sodium bromide will diffuse from a certain concentration in the intestinal fluid to the blood where a higher concentration exists.

Dogs were fed 10 gm. of sodium bromide per day for 3 days. At the end of this time about two-thirds of total plasma halides was bromide. Sodium amytal was used as an anesthetic. A loop of the lower portion of the ileum, sufficient in size to hold about 50 cc. of fluid, was tied off, cannulated and flushed with warm saline. The test solution, containing 40 mM/1 sodium chloride, 40 mM/1 sodium bromide and balance to isotonicity of sodium sulphate, was placed in the loop and allowed to remain 1½ hours. Samples were withdrawn at intervals for analysis of chloride and bromide in plasma and intestinal fluid by the electrometric technique of Hastings and Van Dyke. 2