Segmental action of aldosterone on water and electrolyte transport across rabbit colon in vivo.

Water and electrolyte transport (Na, K, Cl) and the electrical potential difference were investigated simultaneously in five segments of rabbit colon in vivo, under control conditions and under the influence of aldosterone. A dialysis method was used. The solution was designed to mimic the electrolyte concentration of the lumen, and to simulate normal in vivo conditions. Under in vivo conditions (imposed gradients), marked segmental differences in water and electrolyte transport were present. The proximal colon secreted sodium and absorbed potassium, whereas the distal colon absorbed sodium and secreted potassium. Chloride was secreted in all segments. Aldosterone stimulated water and NaCl absorption in the proximal colon by an electroneutral mechanism, whereas in the distal colon a stimulation of electrogenic Na-absorption occurred. The results demonstrate the role of aldosterone in regulating rabbit colonic electrolyte transport. A uniform hormonal stimulation causes qualitatively and quantitatively different effects in the various segments.