Urethral closure mechanisms under sneeze-induced stress condition in rats: a new animal model for evaluation of stress urinary incontinence

Abstract

The urethral closure mechanism under a stress condition induced by sneezing was investigated in urethane-anesthetized female rats. During sneezing, while the responses measured by microtip transducer catheters in the proximal and middle parts of the urethra increased, the response in the proximal urethra was almost negligible when the bladder response was subtracted from the urethral response or when the abdomen was opened. In contrast, the response in the middle urethra during sneezing was still observed after subtracting the bladder response or after opening the abdomen. These responses in the middle urethra during sneezing were significantly reduced approximately 80% by bilateral transection of the pudendal nerves and the nerves to the iliococcygeous and pubococcygeous muscles but not by transection of the visceral branches of the pelvic nerves and hypogastric nerves. The sneeze leak point pressure was also measured to investigate the role of active urethral closure mechanisms in maintaining total urethral resistance against sneeze-induced urinary incontinence. In sham-operated rats, no urinary leakage was observed during sneeze, which produced an increase of intravesical pressure up to 37 +/- 2.2 cmH2O. However, in nerve-transected rats urinary leakage was observed when the intravesical pressure during sneezing exceeded 16.3 +/- 2.1 cmH2O. These results indicate that during sneezing, pressure increases elicited by reflex contractions of external urethral sphincter and pelvic floor muscles occur in the middle portion of the urethra. These reflexes in addition to passive transmission of increased abdominal pressure significantly contribute to urinary continence mechanisms under a sneeze-induced stress condition.

Electromyography of Pelvic Floor Muscles in Rats

“…Pelvic floor inhibition during voiding suggests similarities between rats and humans in the neural control of micturition. Some studies in rats have shown that levator ani denervation decreases urethral pressure and that neurectomized rats leak at sneeze (Conway et al 2005;Kamo et al 2003). However, we could not demonstrate a pelvic floor response during a LPP test and the LPP value did not decrease after levator ani nerve transection .…”

“…Knowledge of the pathways of peripheral innervation is an important tool to study EUS function in preclinical studies (Cruz & Downie 2005;Jiang et al 2009aJiang et al , 2009bKamo & Hashimoto 2007;Kamo et al 2009;Kamo et al 2003;Kerns et al 2000;Lee et al 2003;Peng et al 2008aPeng et al , 2008b). Animal models have been used to estimate the damage to nerves during simulated childbirth and to test pharmacological and neuromodulation strategies to promote neuroregeneration and recovery of EUS function Cannon et al 2002;Jiang et al 2009aJiang et al , 2009bPeng et al 2008a;Streng et al 2001;Thor 2003;Thor et al 1989;Thor et al 2007;Vera & Nadelhaft 2001).…”

“…EMG EUS activity, or contraction, is usually measured along with bladder pressure, urethral pressure, leak point pressure and/or voiding frequency before and after a lesion to or stimulation of one or more of the nerves that innervate the EUS (Cruz & Downie 2005;Jiang et al 2009b;Peng et al 2006;Peng et al 2008aPeng et al , 2008b. However, it is difficult to compare results because some studies do not describe the site of the nerve lesion and the dissection procedures to access the nerves differ between studies (Cruz & Downie 2005;Damaser et al 2007;Furuta et al 2008;Kamo et al 2003;Kim et al 2009;Peng et al 2006;Wai et al 2004). A procedure commonly used to eliminate EUS activity is to make a lesion to the pudendal nerve.…”

“…Visceral dysfunction, such as prolapse and fecal and urinary incontinence, are related to pelvic floor muscle disorders. However, to date there are only few preclinical studies focused on EMG activity of pelvic floor muscles during excretory function Kamo et al 2006;Kamo et al 2009;Kamo et al 2003). The experimental conditions and results differ between studies.…”

Animal Models of Female Stress Urinary Incontinence

“…Kamo et al reported that opening the abdomen significantly decreases bladder pressure during a sneeze, indicating that the abdominal musculature contributes to the pressure increase during a sneeze. 8 The middle urethra generates a high pressure response to a sneeze that commences before the increase in abdominal pressure and is maintained relatively long after bladder pressure has returned to baseline, suggesting a sneeze induced active reflex muscle contraction to maintain continence activated directly by sneezing, rather than by afferent pathways from the bladder. By selectively transecting nerves Kamo et al determined that the reflex involved in maintaining continence during sneeze generation in urethane anesthetized female rats involves the pudendal nerve, and the nerves to the iliococcygeus and pubococcygeus muscles but not the visceral branches of the pelvic nerve or the hypogastric nerve.…”