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

1. 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 μg/kg 4 h)...

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Veröffentlicht in:The Journal of physiology 1983-07, Vol.340 (1), p.503-511
Hauptverfasser: Michael Horster, Andreas Lückhoff
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Sprache:eng
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Zusammenfassung:1. 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 μg/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 × 75 μg/kg day); VI, adrenalectomized, substituted chronically with dexamethasone (120 μg/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 μl/h cm 2 ±10·5 ( n = 9) to 41·2 μl/h cm 2 ±7·3 ( n = 4), and net Na + absorption ( J Na ) was decreased from 13·6 μmol/h cm 2 +3·5 to 8·5 μmol/h cm 2 ±0·9 (isotonic perfusate). Similarly, J v was decreased from 54·0 μl/h cm 2 ±8·3 ( n = 4) to 37·3 μl/h cm 2 ±4·2 ( n = 7), and J Na from 8·6 μmol/h cm 2 ±2·1 to 4·2 μmol/h cm 2 ±2·1 (hypotonic perfusate). 5. Acute aldosterone substitution in adrenalectomy (III) had no effect upon J v (37·1 μl/h cm 2 ±10·3; n = 5) but increased J Na to 10·3 μmol/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 μl/h cm 2 ±10·9; n = 7) and J Na (11·9 μmol/h cm 2 ±1·7; n = 6) were not significantly different from normal. 9. In group VI, J v (37·3 μl/h cm 2 ±6·0; n = 5) and J Na (8·0 μmol/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 .
ISSN:0022-3751
1469-7793
DOI:10.1113/jphysiol.1983.sp014776