Effect of Chronic Electrostimulation of the Sacral Roots on the Striated Urethral Sphincter

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Abstract
Chronic electrostimulation of the sacral roots induces an increase in urethral resistance due to activation of muscles of the striated urethral sphincter. Histochemical study of the urethral striated musculature (nonstimulated) revealed 3 main varieties of fibers: slow twitch fibers (35% of the whole muscle); fast twitch fatiguable fibers (52%); and an intermediate type, fast twitch fatigue resistant (13%). Ten dogs with chronically implanted electrodes at the 2nd sacral root were subjected to a program of prolonged stimulation under anesthesia. After prolonged electrostimulation, hypertrophy of the striated muscle fibers of the urethra, anal sphincter and stimulated side of the tail was detected. The stimulated muscle fibers showed a higher overall oxidative activity than the controls. This occurred both in intact and spinalized animals. The urethral striated musculature should be more resistant to fatigue because of the increased oxidative activity. Stimulated fibers also had increased glycolytic activity as shown by the enhanced intermyofibrillar deposition, especially in the fast twitch fibers. The increased glycolytic activity may also increase fatigue resistance by producing energy during periods of low O2 supply at the peak of muscle contraction. As a consequence of increase in oxidative and glycolytic capacities and muscular hypertrophy, the striated musculature of the urethra will be not only more resistant to fatigue but also capable of generating higher tension. Both are important in achieving continence via electrostimulation of sacral nerve roots. By .apprx. 3 mo. after conclusion of the stimulation program these changes had gradually reverted to the normal prestimulation level.