Reservoir characteristics of Mainz pouch studied in animal model: Osmolality of filling solution and effect of oxybutynin

In a canine model of the Mainz pouch, intracavitary pressure and compliance were measured during instillation of isosmotic and hyperosmotic (900 mmol/kg water) solutions of saline. Wall properties of small- and large-bowel segments of the pouch were assessed individually by sonomicrometry. Intraluminal pressures increased more steeply during filling with hyperosmotic solution, resulting in reduced distensibility of small- and large-bowel segments. Additionally, instillation of the hyperosmotic solution resulted in increased amplitudes and frequency of intracavitary pressure waves. The results indicate that this was the result of a combination of intensified bowel contractions and an increased mural tension. Topical application of oxybutynin abolished these effects. These findings are reviewed in light of the nocturnal increase in urine osmolality, its correlation with nocturnal incontinence in patients with enterocystoplasty, and possible treatment choices.