Sympathetic inhibition of reflex activation of bladder motility during filling at a physiological‐like rate in urethane anaesthetized rats

The mean volume of saline (infused at a physiological‐like rate) required to elicit neurogenic rhythmic contractions of the detrusor muscle (micturition threshold) in urethane anaesthetized rats was reduced by reserpine pretreatment, as well as by chemical (6‐hydroxydopamine) or surgical sympathectomy (bilateral section of the hypogastric nerves). Propranolol pretreatment had no significant effect on micturition threshold but increased the intraluminal pressure at which the rhythmic contractions occurred. In spinal rats (T12L1) a flat pressure volume curve was obtained with only a minor phasic contractile activity. Propranolol administration or bilateral section of the hypogastric nerves significantly increased the intraluminal pressure response to saline filling in spinal rats. Topical tetrodotoxin increased the intraluminal pressure response to saline filling in control spinal rats but not following propranolol administration or bilateral section of the hypogastric nerves. These findings provide evidence for a sympathetic inhibition of the reflex activation of the detrusor muscle in response to a physiological‐like filling of the urinary bladder.