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Corticosteroid regulation of Na+ and K+ transport in the rat distal colon during postnatal development
Insights
Corticosteroids regulate colonic sodium absorption in developing rats, with immature animals showing greater sensitivity. Glucocorticoids and mineralocorticoids act via distinct receptors, influencing sodium absorption before potassium secretion.
Area of Science:
- Gastroenterology
- Endocrinology
- Developmental Biology
Background:
- Corticosteroids play a crucial role in regulating electrolyte transport in the colon.
- Understanding the developmental changes in corticosteroid sensitivity is vital for pediatric gastroenterology.
Purpose of the Study:
- To investigate the role of corticosteroids in colonic electrogenic amiloride-sensitive sodium absorption (ISCNa) and barium-sensitive potassium secretion (ISCK) during rat development.
- To determine the differential effects of mineralocorticoids and glucocorticoids on colonic ion transport.
Main Methods:
- Adrenalectomized rats at different developmental stages (suckling, weanling, adult) were treated with aldosterone, corticosterone, or dexamethasone.
- Ion transport was measured electrophysiologically.
- Specific antagonists (spironolactone and RU 38 486) were used to differentiate receptor pathways.
Main Results:
- Adrenalectomy significantly reduced or abolished ISCNa in a developmental-dependent manner.
- Aldosterone, corticosterone, and dexamethasone restored ISCNa in young rats, with glucocorticoids showing a greater effect.
- Glucocorticoid and mineralocorticoid effects were mediated by distinct receptors, as shown by antagonist studies.
- The response to corticosteroids decreased with age, indicating higher sensitivity in immature rats.
- Potassium secretion (ISCK) was not acutely affected but stimulated after chronic corticosteroid treatment.
Conclusions:
- Corticosteroids regulate colonic sodium absorption and, with delayed effect, potassium secretion in developing rats.
- Distinct receptors mediate the colonic actions of mineralocorticoids and glucocorticoids.
- Immature rats exhibit heightened sensitivity to corticosteroid-induced colonic ion transport compared to adults.
Abstract:
To study the role of corticosteroids in the regulation of colonic electrogenic amiloride-sensitive Na+ absorption (ISCNa) and barium-sensitive K+ secretion (ISCK) during development, we investigated suckling (10-day old), weanling (25-day old) and adult (90-day old) adrenalectomized rats after they had received aldosterone, dexamethasone or corticosterone. Adrenalectomy reduced markedly ISCNa in suckling rats and completely inhibited ISCNa in weanling animals; the ISCNa was absent in intact adult rats. The doses of aldosterone, corticosterone and dexamethasone estimated to be equivalent to the endogenous production rate of aldosterone and corticosterone restored ISCNa after 1 day in both suckling and weanling rats. Compared with aldosterone, glucocorticoids produced a greater increase in ISCNa. Concurrent spironolactone treatment (a mineralocorticoid antagonist) completely prevented the effect of aldosterone but had no effect in dexamethasone-treated rats. The glucocorticoid antagonist RU 38 486 inhibited the dexamethasone-induction of ISCNa but had no effect on aldosterone. The response to corticosteroids, measured as the increase of ISCNa, declined from suckling to adult rats. In contrast to ISCNa, the same time of treatment and the same doses of corticosteroids did not influence ISCK. ISCK was stimulated only after chronic treatment (4 days). These findings suggest that, in the distal colon of young rats, (1) both corticosteroids may regulate amiloride-sensitive Na+ absorption and barium-sensitive K+ secretion, (2) different receptors mediate the colonic effects of glucocorticoids and mineralocorticoids, (3) immature rats are more sensitive to corticosteroids than adult animals, and (4) the acute effect of corticosteroids is an increase in Na+ absorption which is followed by delayed stimulation of K+ secretion.