Water and electrolyte homeostasis in sheep without functional colons

Aldosterone enhances 11beta-hydroxysteroid dehydrogenase type 2 expression in colonic epithelial cells in vivo

OBJECTIVE

[corrected] 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) metabolizes glucocorticoids, thus enabling aldosterone to bind to the mineralocorticoid receptor. However, little is known about the regulatory mechanism of epithelial 11beta-HSD2 expression in the gut.

MATERIALS AND METHODS

Sprague-Dawley rats were maintained on a sodium-depleted diet or subjected to continuous aldosterone infusion for 4 weeks. Plasma aldosterone and arginine-vasopressin (AVP) levels were measured by radioimmunoassay. Expression of 11beta-HSD2 in colonic epithelia was evaluated by Northern blotting and immunohistochemistry. T84 and Caco2 cells were stimulated with aldosterone, dexamethasone and AVP alone or in combination, and 11beta-HSD2 mRNA was measured by quantitative reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Sodium-depleted and aldosterone-infused rats showed an increase of plasma aldosterone and AVP. Both treatments resulted in induction of 11beta-HSD2 in the colonic epithelia at mRNA and protein levels. Positive immunoreactivity was detected in the cytoplasm of the surface epithelia in control rats. In contrast, epithelial cells in the crypt also showed immunoreactivity for 11beta-HSD2 in the proximal colon of dietary sodium-depleted and aldosterone-infused rats. Induction of 11beta-HSD2 mRNA was observed when T84 cells were stimulated with corticosteroids plus AVP.

CONCLUSIONS

Aldosterone has a pivotal role by increasing expression of 11beta-HSD2 in epithelial cells of the colon. AVP may act as a synergistic hormone in aldosterone-mediated 11beta-HSD2 induction.

Induction of 11beta-hydroxysteroid dehydrogenase type 2 and hyperaldosteronism are essential for enhanced sodium absorption after total colectomy in rats

BACKGROUND

Patients who undergo total colectomy with ileopouch anal reconstruction often have persistent diarrhea and frequent bowel movements. Analysis of the intestinal adaptation after total colectomy may lead to developing novel therapies for postoperative diarrhea.

METHODS

Sprague-Dawley rats underwent total colectomy with ileoanal reconstruction and were sacrificed 4 and 8 weeks later. Mucosal response to aldosterone was evaluated with the use of ileal mucosa in an Ussing chamber by measuring short circuit current after in vitro stimulation with aldosterone. We investigated the expression of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD 2) in intestinal epithelial cells. To examine the role of hyperaldosteronism, we also evaluated rats treated with a sodium-deficient diet or subcutaneous aldosterone infusion.

RESULTS

Aldosterone levels increased 80-fold after total colectomy. A comparable amount of aldosterone dramatically increased aldosterone-mediated, amiloride-sensitive short circuit current in the mucosa from colectomized rats, but not in control rats. We measured an increase in 11beta-HSD 2 messenger RNA and protein in the distal ileum from colectomized rats. Circulating aldosterone appears to be essential for these functional and molecular changes because similar results were obtained by using the mucosa from both dietary sodium-depleted and aldosterone-infused rats.

CONCLUSIONS

Induction of 11beta-HSD 2 is essential for enhanced mineralocorticoid action in the remnant ileum after total colectomy in rats.

Effects of restorative proctocolectomy on renal and adrenal function

PURPOSE

Restorative proctocolectomy is a standard procedure in the surgical treatment of ulcerative colitis and familial adenomatous polyposis. The radical removal of the colorectum with construction of an ileostomy often results in high stoma losses. These may lead to changes in the electrolyte and acid-base balance and to alterations in renal and suprarenal gland function.

METHODS

In this study 33 patients who received an ileoanal pouch before and after proctocolectomy were investigated at different time intervals for electrolyte changes, alteration of the acid-base balance, kidney function, and hormonal changes of the suprarenal glands. Measurements were performed before proctocolectomy, ten days after proctocolectomy with ileal pouch-anal anastomosis under protective loop ileostomy, before ileostomy closure, and 6 to 12 months after ileostomy closure. Neither acute renal failure nor other vital complications were observed.

RESULTS

Statistical analysis showed a significant decrease of urine pH to 5.4 +/- 0.22 (before ileostomy closure) and metabolic acidosis (pH 7.32 +/- 0.04; base excess -1.3 +/- 5.6 (before ileostomy closure)). Likewise, we found a decrease in renal clearance to 86 ml/minute (before ileostomy closure) without signs of tubular damage. The most important change during the phase with ileostomy was a functional secondary hyperaldosteronism with aldosterone levels of 63.2 +/- 70.8 ng/dl (before ileostomy closure). In comparison with preoperative levels, there was a ten-fold increase in mineralocorticoid adrenal activity. Additionally, during the period with protective ileostomy, the hepatic synthesis of aldosterone-18-glucuronide was only slightly increased, and the cortisol/cortisone ratio was extremely decreased.

CONCLUSIONS

These results show that restorative proctocolectomy with ileal pouch-anal anastomosis and protective loop ileostomy significantly influences fluid, electrolyte, and acid-base balance. Functional secondary hyperaldosteronism is of central importance for subsequent renal recompensation. Approximately one-half year after ileostomy closure, the endogenous hormones with mineralocorticoid effects returned to normal levels.