Flow Starting Point and Voiding Mechanisms Measured by Simultaneous Registrations of Intravesical, Intra-abdominal, and Intraurethral Pressures in Awake Rats.

Purpose: The aim of this study was to apply a new surgical procedure that allows for the successful monitoring of intraurethral pressure (IUP) changes in the cystometry of awake Sprague-Dawley rats.

Methods: Twenty-six female Sprague-Dawley rats were grouped according to the catheterization method (bladder only; bladder and urethra; or bladder, urethra, and abdomen). Using an arbitrarily determined initial point of the first phase among four rat micturition phases on the simultaneous curves as a reference point, we compared the time differences to the points on an intravesical pressure (IVP) and those on IUP or a detrusor pressure (DP) curve from intra-abdominal pressure (IAP).

Results: In awake rat, the start of urethral flow on IUP curve corresponded to the initial point of the second phase, which is same to the results on the anesthetized rat. However, certain results, such as micturition pressure (MP) and intraluminal pressure high-frequency oscillations (IPHFOs), differed between awake and anesthetized rats. Most MP values were checked after the end of urethral flow on the IUP curve, which is due to the peculiar methodology such as transvesical catheterization. Urethral flow was not completely interrupted during the IPHFOs, which suggests the presence of urethral wall tension against the flow during voiding. After removal of the superimposed effects of IAP from IVP, the DP curve clearly showed a peculiar shape, highlighting the possibility of using IAP in place of IUP to detect the flow starting point on the IVP curve.

Conclusions: Awake rat cystometry results have been interpreted based on those in anesthetized rats. However, our awake cystometry data were substantially different in terms of voiding time compared to those of anesthetized rats. This discovery warrants careful interpretation of the voiding parameters in awake rat cystometry.