Pelvic floor muscles and the external urethral sphincter have different responses to applied bladder pressure during continence.
OBJECTIVE
To determine the functional innervation of the pelvic floor muscles (PFM) and whether there is PFM activity during an external pressure increase to the bladder in female rats.


METHODS
Thirty-one female adult virgin Sprague-Dawley rats received an external increase in bladder pressure until urinary leakage was noted while bladder pressure was recorded (leak point pressure [LPP]) under urethane anesthesia. Six of the rats underwent repeat LPP testing after bilateral transection of the levator ani nerve. Another 6 rats underwent repeat LPP testing after bilateral transection of the pudendal nerve. Simultaneous recordings of PFM (pubo- and iliococcygeus muscles), electromyogram (EMG), and external urethral sphincter (EUS) EMG were recorded during cystometry and LPP testing.


RESULTS
Thirteen rats (42%) showed tonic PFM EMG activity during filling cystometry. Eighteen rats (58%) showed no tonic PFM EMG activity at baseline, but PFM EMG could be activated by pinching the perineal skin. This activity could be maintained unless voiding occurred. The external increase in bladder pressure caused significantly increased EUS EMG activity as demonstrated by increased amplitude and frequency. However, there was no such response in PFM EMG. LPP was not significantly different after levator ani nerve transection, but was significantly decreased after pudendal nerve transection.


CONCLUSIONS
PFM activity was not increased during external pressure increases to the bladder in female rats. Experimental designs using rats should consider this result. The PFM, unlike the EUS, does not contribute to the bladder-to-urethra continence reflex. PFM strengthening may nonetheless facilitate urinary continence clinically by stabilizing the bladder neck.
Jiang
Hai-Hong
HH
Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA.
Salcedo
Levilester B
LB
Song
Bo
B
Damaser
Margot S
MS
D000009:Abdominal Muscles / Q000294:innervation / Q000502:physiology; D000818:Animals; D004195:Disease Models, Animal; D004576:Electromyography; D019160:Endosonography; D005260:Female; D009119:Muscle Contraction / Q000502:physiology; D017773:Pelvic Floor / Q000294:innervation* / Q000502:physiology; D011312:Pressure; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D014521:Urethra / Q000294:innervation* / Q000502:physiology; D001743:Urinary Bladder / Q000294:innervation* / Q000502:physiology