The effect of aldosterone and the renin‐angiotensin system on sodium, potassium and chloride transport by proximal and distal rat colon in vivo.

Abstract

SUMMARY1. The roles of aldosterone and angiotensin in the direct control of epithelial sodium transport in vivo have been investigated by measurement of electrical p.d. changes and of the fluxes of sodium, potassium and chloride in rat colon, an organ actively involved in electrolyte homoeostasis. Exogenous angiotensin and aldosterone were given by both short-and long-term infusions and endogenous secretion of the hormones was varied by dietary sodium variation and by nephrectomy and/or adrenalectomy.2. In vitro angiotensin has been shown to influence colonic salt and water absorption but in the present in vivo experiments administered angiotensin had no significant action on p.d. or on the ionic fluxes of the proximal or distal colon. The increase in p.d. produced by infusing aldosterone was unaffected by giving angiotensin concurrently. The effect of sodium depletion in stimulating sodium absorption and potassium secretion was completely abolished by adrenalectomy but was unaffected by nephrectomy.3. During prolonged infusion of angiotensin into adrenalectomized rats, a small fall in faecal fluid and sodium content was observed, but this change would have little significance in sodium homoeostasis.4. Aldosterone and sodium depletion stimulated sodium absorption in both proximal and distal colon but significant increase in potassium secretion was demonstrable only in the distal colon. Bicarbonate secretion (by calculation) was unaffected. In the proximal colon, the increased sodium absorption appeared to be accompanied by increased chloride absorption while in the distal colon it was principally the sodium-potassium exchange that was increased.

Regulation of cation transport by low doses of glucocorticoids in in vivo adrenalectomized rat colon.

“…As previously described (1,19,22,31), adrenalectomy markedly depressed the rate of sodium absorption in proximal colon (Fig. 1) dry tissue, a value similar to that found in intact animals (P < 0.001 compared with adrenalectomy alone).…”

“…The normal rat colon has significant amiloride-resistant net sodium absorption which decreases markedly with adrenalectomy (1,2,5,15,16,(19)(20)(21)(22). This adrenal dependent sodium absorption could be under the control of circulating physiologic levels of glucocorticoid.…”

Aldosterone on sodium transport of rat distal colon in long‐term adrenalectomy during acute and chronic substitution

“…Distal colon Na+ absorption was not significantly depressed after adrenalectomy, although it was somewhat lower than control (Dolman & Edmonds, 1975); by contrast, JNa of the proximal colon was clearly decreased (Dolman & Edmonds, 1975), and JNa as well as Jv of the entire colon were lower after adrenalectomy (Bastl, Binder & Hayslett, 1980). Aldosterone in physiological amounts increased both JNa and Jv in adrenalectomized rats (Edmonds & Marriott, 1967).…”

The effect of lithium on the transport of sodium, potassium and chloride by the colon of normal and sodium‐depleted rats.

“…In all the remaining experiments, the dialysis method, previously described (Dolman & Edmonds, 1975), was used. All solutions were prepared freshly from stock solutions immediately before the experiments.…”