Intestinal fluid and electrolyte transport in man during reduced circulating blood volume

The effect on intestinal net transport of fluid and electrolytes of a reduced circulating blood volume was studied in the human jejunum with the triple lumen perfusion technique. The blood volume was reduced by changing the lower extremities from an elevated to a dependent position combined with a venous stasis. The tilting manoeuvre, probably resembling a bleeding of about 600-800 ml, significantly increased net absorption of fluid, sodium and chloride while glucose transport was unaffected. Concomitantly the blood flow decreased and vascular resistance increased in the forearm vascular bed. The results are consistent with the hypothesis that activity in the sympathetic nervous system initiated from unloading of the cardiopulmonary volume receptors enhances intestinal absorption of fluid and electrolytes. The results also indicate that the human intestines are an important target organ in the compensatory mechanisms activated during hypovolaemia due to - for example, haemorrhage.