EFFECTS OF HYPOXIA, CALCIUM, CARBACHOL, ATROPINE AND TETRODOTOXIN ON THE FILLING OF THE IN-VITRO RABBIT WHOLE BLADDER

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Abstract
The urinary bladder stores urine at low intravesical pressure and empties the urine efficiently and completely. Bladder compliance is the property that allows the bladder to fill to near capacity without a large increase in intravesical pressure. The current study utilized an in vitro whole bladder model to determine the effects of hypoxia, alterations in extracellular calcium concentration, carbachol and atropine on bladder capacity and compliance. Mature male New Zealand White rabbits were used in this study. The urinary bladder was excised from the rabbit together with a short segment of proximal urethra and mounted in a 400 ml. isolated bath containing Tyrode's buffer. Bladder filling was started by opening the bladder to a saline reservoir placed 80 cm. above the bladder. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin respectively. Results are summarized as follows: 1) Bladder filling was biphasic. There was an initial rapid rise in intravesical pressure followed by a slower rise. The final bladder volume averaged 46 ml. 2) Hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and increased bladder volume by 43%. 3) Incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and increased bladder volume by 39%. 4) High concentrations of calcium increased the initial rate of rise in intravesical pressure. 5) Carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and decreased bladder volume. 6) Atropine and tetrodotoxin (TTX) had no effects on bladder filling. In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.