Detrusor-sphincter dyssynergia induced by cold stimulation of the urinary bladder of rats.

Instillation of cold water into the urinary bladder has been used as a diagnostic test to evaluate neurogenic dysfunctions of the lower urinary tract (LUT). This study examined the effects of cold stimulation on the LUT of urethan-anesthetized rats. Urinary bladder pressure and external urethral sphincter (EUS) electromyogram (EMG) were recorded during cystometrograms in which body- or room-temperature saline was infused continuously into the bladder and voided through the urethra. Subsequent infusion of cold saline (6-8 degrees C) into the bladder increased by approximately 100% the duration and amplitude of supraspinal reflex bladder contractions, increased baseline bladder pressure, increased the pressure threshold for inducing micturition, and increased EUS EMG activity. Blocking EUS activity by transecting the pudendal nerves or by administering a neuromuscular blocking agent markedly reduced or eliminated the effect of cold stimulation. Capsaicin pretreatment suppressed the effect of cold stimulation. It is concluded that cold temperatures stimulate capsaicin-sensitive C fiber bladder afferents that reflexly activate the EUS, producing detrusor and sphincter dyssynergia and increasing urethral outlet resistance. This in turn increases the amplitude and duration of bladder contractions during voiding.