Pudendal nerve stimulation induces urethral contraction and relaxation.
In this study we measured urethral pressure changes in response to efferent pudendal nerve stimulation in rats. All other neural pathways to the urethra were transected, and the urethra was continuously perfused. We found fast twitch-like contractions, superimposed on a slow relaxation. The amplitude of the twitches was independent of the stimulation frequency below 26 Hz, whereas the relaxation depended highly on this frequency. The twitches were caused by striated urethral muscles, and the relaxation was caused by smooth muscles. Both were mediated by acetylcholine. We calculated the effective urethral relaxation as the absolute relaxation multiplied by the time fraction between the twitches. Maximum effective relaxation occurred at 8-10 Hz, exactly the frequency of spontaneous oscillations during bladder voiding in rats. Although the oscillatory sphincter contractions in rats during voiding may be needed in other mechanisms for efficient voiding, our data suggest that they may be a side effect of the actual purpose: urethral relaxation.
le Feber
J
J
Department of Urology-Urodynamics, Erasmus University Rotterdam, 3000 DR Rotterdam, The Netherlands. lefeber@udn.fgg.eur.nl
van Asselt
E
E
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009130:Muscle, Smooth / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009424:Nervous System Physiological Phenomena; D018377:Neurotransmitter Agents / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D014521:Urethra / Q000187:drug effects / Q000294:innervation* / Q000502:physiology*
D004791:Enzyme Inhibitors; D018727:Muscarinic Antagonists; D018377:Neurotransmitter Agents; D001285:Atropine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester