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

Purpose: 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 witho ut a large increase in intravesical pressure. The current study utiliz ed an in vitro whole bladder model to determine the effects of hypoxia , alterations in extracellular calcium concentration, carbachol and at ropine on bladder capacity and compliance. Methods: Mature male New Ze aland White rabbits were used in this study. The urinary bladder was e xcised from the rabbit together with a short segment of proximal ureth ra and mounted in a 400 mi. isolated bath containing Tyrode's buffer. Bladder filling was started by opening the bladder to a saline reservo ir placed 80 cm. above the bladder. Intravesical pressure, rate of pre ssure increase, rate of volume increase, and maximal volume were digit ally recorded. The bladder filling was repeated while the whole bladde r was subjected to hypoxia, high calcium concentration, the presence o f EGTA, carbachol, atropine and tetrodotoxin respectively. Results: Re sults are summarized as follows: 1) Bladder filling was biphasic. Ther e was an initial rapid rise in intravesical pressure followed by a slo wer rise. The final bladder volume averaged 46 mi. 2) Hypoxia signific antly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and increased bladder volume b y 43%. 3) Incubation of the bladder in the presence of EGTA also signi ficantly decreased the initial rate of intravesical pressure rise, inc reased the rate of filling and increased bladder volume by 39%. 4) Hig h concentrations of calcium increased the initial rate of rise in intr avesical pressure. 5) Carbachol significantly increased the rate of in travesical pressure rise, decreased the rate of bladder filling, and d ecreased bladder volume. 6) Atropine and tetrodotoxin (TTX) had no eff ects on bladder filling. Conclusion: In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.