Role of Aldosterone for Control of Colonic NaKATPase Activity in Weanling Rats

Abstract

ABSTRACT. Ex~eriments were ~erforrned to examine MATERIALS AND METHODShow aldosterone ;noddates coloniE NaKATPase activity during the weaning period. NaKATPase activity was determined in proximal and distal colon in control rats aged 16, 20, and 40 days, in rats aged 20 and 40 days fed low sodium diet for 4 days and in 20-day-old rats adrenalectomized on day 16. In some protocols net sodium and water transport was determined with in vivo perfusion technique. In control rats colonic NaKATPase activity increased significantly between day 16 and 20. This increase was abolished by adrenalectomy but restored by aldosterone substitution, 5 pg/lOO g body weight112 h. No significant increase in NaKATPase activity occurred between day 20 and 40. Serum levels of both aldosterone and of corticosterone were low until day 14 and increased to peak level at day 18-20. In 20-and 40-day-old rats fed a low sodium diet, NaKATPase activity increased significantly in proximal and distal colon in both age groups but the increases were significantly greater in the 20-than the 40-day-old animals. A low sodium diet increased serum aldosterone, but not serum corticosterone levels in both age groups: also the low sodium diet significantly increased net sodium and water transport in 20-but not in 40-day-old rats. Aldosterone is of physiological importance for the regulation of Pi, inorganic phosphorousAt the time of weaning there is an accelerated maturation of gastrointestinal enzymes and this maturation is attenuated by adrenalectomy (1). It is generally assumed that it is the glucocorticoid hormone which triggers the maturation. The serum levels of glucocorticoid hormones increase rapidly at the time of weaning (2) and treatment with large doses of glucocorticoid in suckling rats results in precocious development of enzymes in the gastrointestinal tract (3-6).There are few developmental studies of the large intestine. The adult large intestine has a high concentration of mineralocorticoid receptors (7,8), and the activity of NaKATPase enzyme in the adult colon can be modulated by mineralocorticoid (9). The present study was designed to explore the influence of mineralocorticoid hormone on colonic NaKATPase activity at the time of weaning. Animals. Sprague-Dawley rats from Anticimex, Sollentuna, Sweden were used. The animal quarters were air-conditioned (2 1 + lo C) with a 12-h light cycle (0700-1900 h) and a 12-h dark cycle. The litter sizes were maintained at four to six animals.Experimental Groups. Zn~act rats. The animals were kept with lactating dams. They had free access to ordinary rat food (Ewos R3) containing 0.13 mmol Na/g and tap water ad libitum until 20 days. Thereafter they were kept in litters without dams. Their body weight increased from a mean of 21.5 g at 10 days to a mean of 170 g at 40 days. Sodium depletion. These animals were fed a low sodium diet (Ewos) for 4 days. The diet was similar to the ordinary rat food but contained 0.009 mmol Na/g. Animals aged 16 days were separated from the dams and fed a low salt diet...

Mechanisms for Colonic Sodium Transport during Ontogeny: Loss of an Amiloride-Sensitive Sodium Pathway

“…We have also shown that, if endogenous aldosterone production is stimulated by a low salt Table I. Effect of dBcAMP administered intraarterially on the intake, the net colonic sodium absorption and NaKATPase net sodium andjluid absorption in 14-to 40-day-old rats (mean activity increase more in young than in adult rats (6).…”

Differential Effects of Glucocorticoids and Mineralocorticoids on the mRNA Expression of Colon Ion Transporters in Infant Rats

“…It is well established that the circulating levels of GC and MC increase during the 3rd wk of life (3,4). To evaluate whether the temporary up-regulation of the Na,K-ATpase, H,K-ATPase, and Na-channel mRNA is due to corticoids, rats were given a single injection of betamethasone or aldosterone at 10 d of life-i.e.…”

“…These results suggest that an increased synthesis of ion transporters occurs during weaning. In the rat, the circulating level of GC and MC increases in the preweaning period (3,4), and it has been shown that the maturation of colon Na,K-ATPase activity can be accelerated by GC and MC (4, 11). To determine whether the up-regulation of the colon transporter mRNA is due to corticosteroids, betamethasone, and aldosterone were injected into 10-d-old rats-i.e.…”

“…Adrenal corticosteroids are known to have pronounced effects in the mammalian colon (15)(16)(17)(18). The activity of colon Na,K-ATPase is low in infancy, and both aldosterone and GC have been shown to stimulate maturation of the enzyme activity (4,19). The rat distal colon contains abundant MC and GC receptors which are expressed in epithelial surface and crypt cells (20,21).…”

“…Several studies have suggested that such effects are mediated by modulating the level or the activity of certain key enzymes involved in metabolic and physiologic processes (1, 2). The maturation of several ion transporters is developmentally regulated in the kidney and the intestine during the preweaning period, at the time when the circulating levels of both G C and M C hormones increase (3,4). A deficiency of corticoids (e.g.…”