AJP - Regulatory, Integrative and Comparative Physiology, Vol 264, Issue 6 1157-R1163, Copyright © 1993 by American Physiological Society
Changes in bladder and external urethral sphincter function after spinal cord injury in the rat
M. N. Kruse, A. L. Belton and W. C. de Groat
Department of Pharmacology, University of Pittsburgh, Pennsylvania 15261.
Spinal cord injury (SCI) in humans results in inappropriate contractions of
the external urethral sphincter muscle (EUS) during micturition
(bladder-sphincter dyssynergia), leading to urinary retention. The major
goal of this study was to determine whether SCI in rats has similar
detrimental effects on micturition. After chronic SCI, urethan-anesthetized
rats had a significantly (15-fold) increased bladder capacity and impaired
voiding (31-fold increase in residual volume) compared with control rats.
Bladder contractions in SCI rats were accompanied by abnormal tonic EUS
electromyographic activity, whereas the EUS electromyograms of control rats
exhibited a burst pattern (4-8 Hz) during voiding. Suppression of EUS
activity with neuromuscular blockade did not improve the fraction of urine
voided in SCI rats and reduced the fraction voided in control rats.
Therefore, both tonic activity and complete quiescence of the rat's EUS
appear to be detrimental to voiding, suggesting that the normal bursting
EUS activity facilitates bladder emptying. In summary, rats and humans
exhibit similar micturition dysfunctions after SCI (e.g., bladder-sphincter
dyssynergia and impaired voiding).
