Comparison of cystometric methods in female rats

Rat cystometry is a common model used to investigate urinary storage and voiding function. The effect of cystometric instrumentation in rat studies might be a source of deviation from normal physiologic responses. We hypothesized that transurethral catheterization would produce obstruction-related changes, and that suprapubic catheterization would limit volume-related functions as well as disrupt normal urothelial sensory function. We investigated the influence of transurethral and suprapubic catheterization on storage and voiding in the rat model.

Three groups of female SD rats 250-300 g under urethane anesthesia were studied. Cystometric and pseudoaffective responses to physiologic voiding with and without suprapubic catheter placement, and cystometry via suprapubic and transurethral catheterization were studied.

In free-voiding animals, per-void volume was 1.8 +/- 0.2 ml with an average flow rate of 0.18 ml/sec, and intercontraction interval (ICI) 60 min. Suprapubic catheterization decreased the ICI and per-void volume consistent with capacity reduction. Suprapubic cystometry did not significantly alter parameters compared to voiding except for a shortened ICI. Bladder pressures and somatic responses were increased, and urine flow impaired by transurethral cystometry. Terazosin did not significantly improve voiding parameters.

Other than volume-related parameter changes probably related to surgical compromise of bladder capacity, suprapubic catheterization does not alter the cystometric and physiologic responses to voiding when compared to normal, uninstrumented voiding. Transurethral cystometry appears to be obstructive and may activate nociceptive reflexes. For this reason, whenever possible, urodynamic testing using the rat model should employ suprapubic catheterization.