Increased intra-abdominal pressure alters the contractile properties of rabbit bladder

Objective To evaluate the effects of increased intraabdominal pressure (IAP ) on the contractility of the rabbit bladder, as the dynamics of the bladde r may be impaired in conditions associated with a high IAP, e.g. constipati on and pregnancy. Material and methods The study comprised 22 adult male New Zealand rabbits; six served as the control group, eight had an IAP of 7 cmH(2)O imposed for 10 days by instilling air into the abdominal cavity and this IAP was maint ained for 60 days in a further eight rabbits. After treatment, the rabbits were killed, and the bladders removed and cut into 3 x12 mm strips. The con tractile activity of the muscle strips was then recorded isometrically, Ele ctrical field stimulation (EFS) was applied using a pair of platinum ring e lectrodes in trains of 3 s duration every 100 s (1 ms, 100 V, 2-100 Hz). Co ntractile responses to carbachol and isotonic KCl were also evaluated. Results EFS induced a frequency-dependent increase in contractile activity in all bladder strips, Ten days of high IAP resulted in an increased respon siveness to EFS, but high IAP for 60 days reduced the EFS-induced responses to the control levels, Carbachol (10(-9)-10(-3) mol/L) elicited concentrat ion-dependent contractions in all groups. From the concentration-response c urves of carbachol, the log EC50 values (the concentration producing half t he maximum effect) of the control and 60-day treated animals were comparabl e, at -6.24(0.05) and -6.25 (0.04), respectively. However, the log EC50 of the 10 day-treated group was -4.97 (0.08) and significantly (P < 0.01) lowe r than that of both groups. Isotonic KCl produced contractions in all prepa rations; these contractions in the control and 60-day treated animals were similar, while the 10 day-treated group had significantly (P < 0.05) higher contraction amplitudes. Conclusion Increased IAP alters the contractile properties of the bladder a nd its responsiveness to carbachol and KCl. As the intravesical pressure cl osely reflects the IAP, both should be increased in the present experimenta l design.