Endogenous factors modulating urinary bladder compliance in mice

The application of repeated cystometric measurements in longitudinal long-term studies both in patients and experimental animals requires detailed knowledge of factors causing intraindividual variability. In the present study, the effect of age, body weight, estrus cycle phase, rectal temperature and premeasurement bladder volume on the results of cystometry in mice have been assessed. No systematic changes in bladder compliance parameters were observed with age (75 to 344 days) or body weight (18 to 38 gm.). Also, the animal's position in the estrus cycle had no effect on bladder capacity. The abdominal temperature, adjusted to 32 to 37.3C under anesthesia, did not affect the outcome of cystometry either. When the bladder was emptied at 1.5 to 3.5 hours before cystometry, a significant drop in bladder capacity to about 60% of individual control values was observed. This initial emptying clearly decreased the intraindividual variability in absolute terms (standard deviation), but not the relative variability (coefficient of variance). Thus only a shift in absolute values, but no improvement in reproducibility of cystometric results, could be achieved. Bladder filling to 10 or 25 mm. Hg 40 minutes to 2 hours before cystometry increased the bladder capacity to 120 or 145%, respectively, when anesthesia was maintained throughout the experiment. When intervals longer than 2 hours were studied, animals were allowed to regain consciousness between initial bladder filling and cystometry. Under these conditions, the capacity data returned to normal or subnormal values.