Metabolic aspects of urinary bladder filling

Urinary bladder compliance allows the bladder to fill to near capacity with out a large increase in intravesical pressure. Bladder compliance is compos ed of two interrelated factors: passive characteristics of the connective t issue elements of the bladder, and active properties of the smooth muscle e lements. The tension generated by the smooth muscle elements can significan tly affect bladder compliance. This study utilized an in-vitro whole-bladde r model in rabbits to determine the effects of hypoxia, alterations in calc ium concentrations, and muscarinic agonists and antagonists on bladder capa city and compliance. The urinary bladder was excised together with a short segment of proximal urethra. A catheter was inserted into the bladder via t he dome and the urethra was canulated with a saline-filled tube. The bladde r was mounted in an isolated bath containing Tyrode's buffer. The catheter was connected to a pressure transducer to monitor the intravesical pressure and connected to a saline-filled i.v. bag. The weight of the saline bag wa s continually monitored. The height of the saline bag was set to 80 mmH(2)O above the baseline intravesical pressure. Bladder filling was started by o pening the bladder to the saline reservoir. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digital ly recorded. The bladder filling was repeated while the whole bladder was s ubjected to hypoxia, high calcium concentration, the presence of EGTA, carb achol, atropine and tetrodotoxin, respectively. Results are summarized as f ollows: (a) control bladder filling was biphasic, there was an initial rapi d rise in intravesical pressure followed by a slower linear rise to the pre -set pressure; (b) hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and s ignificantly increased final bladder volume; (c) incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of in travesical pressure-rise, increased the rate of filling and also significan tly increased the final bladder volume; (d) high concentrations of calcium increased the initial rate of rise in intravesical pressure; (e) carbachol significantly increased the rate of intravesical pressure rise, decreased t he rate of bladder filling, and significantly decreased final bladder volum e; (f) atropine and tetrodotoxin (TTX) had no effects on bladder filling. I n summary, alterations in muscle tone had significant effects on bladder ca pacity and compliance.