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

The influence of aldosterone upon water and sodium transport properties of the distal colon was studied in long-term adrenalectomy (11-29 days).2. Six groups of rats were used: I, normal (control); II, adrenalectomized; III, adrenalectomized, acutely substituted with aldosterone (200 mug/kg 4 h); IV, adrenalectomized rats receiving aldosterone simultaneously with the specific inhibitor spironolactone (40 mg/kg within 4 h); V, adrenalectomized, substituted chronically with aldosterone (2 x 75 mug/kg day); VI, adrenalectomized, substituted chronically with dexamethasone (120 mug/kg day).3. Distal colon segments were perfused in vivo with isotonic Ringer solution. In addition, a hypotonic electrolyte solution (Na(+) 111 mM) was used in groups I and II.4. In adrenalectomy (group II), net water absorption (J(v)) was significantly decreased from (normal) 54.4 mul/h cm(2)+/-10.5 (n = 9) to 41.2 mul/h cm(2)+/-7.3 (n = 4), and net Na(+) absorption (J(Na)) was decreased from 13.6 mumol/h cm(2)+3.5 to 8.5 mumol/h cm(2)+/-0.9 (isotonic perfusate). Similarly, J(v) was decreased from 54.0 mul/h cm(2)+/-8.3 (n = 4) to 37.3 mul/h cm(2)+/-4.2 (n = 7), and J(Na) from 8.6 mumol/h cm(2)+/-2.1 to 4.2 mumol/h cm(2)+/-2.1 (hypotonic perfusate).5. Acute aldosterone substitution in adrenalectomy (III) had no effect upon J(v) (37.1 mul/h cm(2)+/-10.3; n = 5) but increased J(Na) to 10.3 mumol/h cm(2)+/-0.3.6. The luminal Na(+) steady-state concentration was higher in group II (11.2 mmol l(-1)+/-3.6; n = 6) than in group I (3.3 mmol l(-1)+/-1.4; n = 29). Acute aldosterone substitution restored this value to normal (3.0 mmol l(-1)+/-1.2; n = 4). The aldosterone effect was partly blocked by spironolactone: the Na(+) steady-state concentration was 6.4 mmol/l+/-0.6 (n = 3) in group IV.7. At the steady-state luminal Na(+) concentration, the osmotically driven net water fluxes were not different in groups I and II, indicating that the hydraulic permeability coefficient is not altered in adrenalectomy.8. In group V, J(v) (54.9 mul/h cm(2)+/-10.9; n = 7) and J(Na) (11.9 mumol/h cm(2)+/-1.7; n = 6) were not significantly different from normal.9. In group VI, J(v) (37.3 mul/h cm(2)+/-6.0; n = 5) and J(Na) (8.0 mumol/h cm(2)+/-1.4) were not significantly different from group II.10. The mineralocorticoid effects of aldosterone in long-term adrenalectomy appear to represent the principal determining factors of colonic J(v) and J(Na).