Intestinal transport of water and electrolytes during extracellular volume expansion in dogs

Abstract

A B S T R A C T The effects of extracellular fluid volume expansion on intestinal transport of salts and water were studied in dogs by perfusing loops of bowel in vivo. Saline loading caused depression of duodenal and jejunal absorption with net secretion of salt and water into the lumen. Studies of unidirectional transport of 'Na' revealed that the negative net sodium flux was due primarily, and perhaps exclusively, to increased serosal to mucosal transport, for mucosal to serosal sodium transport was not changed during volume expansion. Net transport of water and potassium paralleled net sodium flux. Administration of deoxycorticosterone did not affect the intestinal response to saline loading. Hemodilution, accomplished by equilibrating the dogs' blood with a reservoir of saline, did not affect intestinal absorption, but isotonic, iso-oncotic expansion of the extracellular fluid produced by reinfusing the saline-blood mixture from the reservoir resulted in negative net transport of water, sodium, and potassium by the duodenum. It is suggested that the small bowel is capable of secreting salts and water through intercellular spaces, and that this process is stimulated by extracellular fluid volume expansion.

The mechanism of decreased intestinal sodium and water absorption after acute volume expansion in the rat

“…DISCUSSION The present studies demonstrate that volume expansion with an isotonic electrolyte solution decreases net absorption of Na' from rat small intestine, confirming recent observations of Richet and Hornych in the rat (18), Higgins in the dog (19), and Gutman and Benzakein in the cat (20). Moreover, this effect of saline infusion to depress net Na' absorption occurred under experimental circumstances expected to decrease the transport of Na+ from lumen to blood.…”

“…Furthermore, it has been demonstrated recently that saline infusion depresses the net absorption of Na4 and water from small intestine in rat (18), dog (19), and cat (20), a response resembling that of the renal proximal tubule. Therefore, it seems likely that information on the mechanism whereby saline infusion influences Na4 and H20 absorption by the small intestine would provide information applicable…”

A Study of Intercellular Spaces in the Rabbit Jejunum during Acute Volume Expansion and after Treatment with Cholera Toxin

“…Cholera toxin and expansion of extracellular fluid volume are both known to reverse net reabsorption of fluid in the small intestine and to cause fluid secretion (1)(2)(3)(4). Several explanations have been proposed to explain the mechanisms of these effects.…”

“…Stimulation of active anion secretion or secretion via a neutral coupled pump is possible, and it is uncertain whether the active sodium reabsorptive mechanism is or is not inhibited simultaneously. The mechanism of secretion during expansion of fluid volume is also controversial (4,11). The possibility of a natriuretic hormone causing decreased lumen-to-body sodium reabsorption has been postulated (12), as has the possibility that the effects are due to hydrostatic pressure changes and increased passive, body-to-lumen movement of water and electrolytes (11).…”

Mechanism of production of intestinal secretion by elevated venous pressure.

“…The Journal of Clinical Investigation Volume 57 April 1976 *904915blocked (1), and extracellular volume expansion by saline infusion (5). Expansion of the extravascular space has been found to increase the small intestinal permeability to glucose (6), sucrose (6), and inulin (7).…”