Influence of Induced Changes in Blood Plasma Osmotic Activity on Intestinal Absorption

Abstract

Summary and Conclusions

Experiments are reported in which the volume, osmotic activity, chloride and sulfate contents of plasma and ileal loop segments are measured, before and after raising the plasma osmotic activity by hypertonic sodium chloride solution injection by vein. The osmotic activity of originally isotonic sodium chloride-sodium sulfate solutions placed in the ileum rises above the pre-injection plasma osmotic activity after 100 cc of 5% sodium chloride solution was injected intravenously. In view of the fact that in more than a hundred control experiments with equiosmotic mixtures of sodium chloride and sodium sulfate the gut fluid osmotic activity has never exceeded the plasma osmotic activity except when poisons were present, the results of these experiments are believed to constitute satisfactory proof that the effect observed was due to the hypertonic salt solution injection.

After the elevation of the plasma osmotic activity the gut fluid values did not approach the former as closely as occurred before the elevation was produced. The net water absorption was not increased in proportion to the increase in osmotic gradient. In fact in one case the direction of net movement was reversed in spite of the larger osmotic gradient. These data add to previous evidence that although normal osmotic forces are probably contributing factors in the transport of water across the intestinal epithelium they are not the primary driving forces determining the direction and magnitude of net water transfer.