Electrical activities of urethral circular muscle and bladder detrusor and their control, examined by in vivo dogs.

Abstract

While the micturition reflex was induced in dog by infusion of Ringer solution into the bladder, the following four types of electrical activity were picked up by two bipolar wire electrodes, embedded in the posterior wall of bladder and in the prostatic part of male urethra; 'intravesical ureter potential' and 'detrusor spike' by bladder electrode, and 'slow wave' and 'external sphincter spike' by urethral electrode. The relative size, respective rhythm and timing of discharge during voiding cycle were specific for each of them and they were readily identifiable for their own sources. The 'ureter potential' was not actively related to the voiding cycle but its triphasic wave form was dissociated at the maximum contraction phase of the bladder. Unexpected finding was the 'quasi-synchronization' of discharges between detrusor and external sphincter. The entire discharges in both muscles were consisted of 'initial burst', 'intermittent inhibition' and 'prolonged after-discharge'. The initial burst of detrusor was definitely delayed in comparison with that of external sphincter, but the end of prolonged after-discharges was again synchronized in both muscles. The possible mechanism for synchronization was discussed. The 'slow wave' was sometimes superposed on the tonic discharge of external sphincter recorded by same wire-electrode in urethral wall, therefore, their properties were analyzed under the condition of 'immobilization' of external sphincter. The sustained waxing and waning 'slow waves', observed in all female urethrae and one-fifth of male urethrae, were markedly suppressed by elicitation of isovolumetric rhythmic contractions of bladder with fall of intraurethral pressure. This bladder-dependent behavior of 'slow wave' was interpreted as a sign of 'urinary' sphincteric activity of urethral circular muscle. On the other hand, 'spontaneous' cyclic activation of 'slow wave' which was seen in about four-fifths of male urethrae and was not dependent upon the state of bladder, was interpreted as a sign of 'genital' sphincteric activity of the same circular smooth muscle.