Transcapillary fluid movement in human calf after drinking hypertonic saline.

1. Transcapillary absorption of interstitial fluid was demonstrated with a pressure plethysmograph applied to the human calf after the ingestion of 200 ml. hypertonic (5.1%) saline. Capillary absorption began within 15 min after ingestion and lasted for about 2 hr. The maximum rate of absorption (0.019 ml./min. 100 ml. tissue) was attained 30-75 min after ingestion.2. The total amount of fluid absorbed into capillary blood vessels in the calf was 1.11 ml./100 ml. tissue. The amount of fluid thus absorbed in the whole body was estimated to be 677 ml.3. The capillary filtration coefficient (CFC) of the calf was also measured by the pressure plethysmograph. This was 0.0038 ml./min. mm Hg. 100 ml. tissue.4. The peak value of capillary absorption pressure was 5.2 mm Hg.5. The total osmotic pressure of the plasma rose by 12.6 m-osmole/kg H(2)O after ingestion. This rise was accompanied by transcapillary fluid absorption.6. The plasma protein concentration and packed cell volume were almost unchanged by ingestion, indicating that the plasma volume was unaltered.7. It was estimated that the net shift of fluid between intracellular and interstitial compartments during the period of transcapillary fluid absorption was very small.8. It is concluded that the volume of fluid moving from plasma into intestinal lumen is the same as that flowing from interstitial fluid into plasma, and that the transcapillary absorption is caused by a difference in osmotic pressure between the plasma and the interstitial fluid.