Effects of Intrathecal Transmitters on the Pain-induced Micturition Reflex

Park, Jae Sik; Kim, Duk Yoon; Ahn, Dong Kuk

Abstract

PURPOSE: Irritations or painful stimuli to the bladde: may alter voiding behaviorand this may be associated with dysfunction of periurethral muscles. In our study, recording of bladder and sphincter activity in response to intravesical irritants(acetic acid, capsaicin) was done and the effects of Intrathecal administration of transmitters(enkephalin, susbtance P and its antagonist, or calcitonin gene related peptide and its antagonist) was analyzed
MATERIALS AND METHODS
Adult male Sprague-Dawley rats(400-500gm) were anesthetized with intraperitoneal urethane mixed with entobar. The left femoral artery and vein were cannulated for blood pressure monitoring and drug administration. A catheter(PE 50) was inserted into the bladder dome through a midline abdominal incision and bipolar electromyographic(EMG) needle electrodes were placed into the urethral sphincter. Peak contractile pressure and EMG activities were measured on a polygraph. Saline, acetic acid, or capsaicin was infused into the bladder at 50mu1/min and saline, enkephalin (ENK), substance P(SP) and its antagonist, or calcitonin gene related peptide (CGRP) and its antagonist was administered intrathecally.
RESULTS
Each micturition cycle started with an increase in bladder pressure which triggered the contraction of the external urethral sphincter. Fast Fourier transform(FFT) analysis of the external sphincter EMG revealed a peak activity at 500Hz. The inteNal and duration of EIOG bursts were 38+/-2 msec and 92+/-10 msec respectively. The interval of bladder contraction was 809+/-23 sec. Intravesical acetic acid and capsaicin activated micturition reflex earlier than in control group and intrathecal ENK, SP antagonist, and CGRP antagonist attenuated the parameters in activated micturition reflex.
CONCLUSIONS
Urethral sphincte EMG showed constant burst duration and interval in spite of the infusion of acetic acid or capsaicin. Intravesical acetic acid or capsaicin increased the peak amplitude of intravesical pressure, lowered voided volume, and shortened EMG spike duration and voiding interval significantly. Intrathecal injection of ENK, SP, SP antagonist, CGRP, and CGRP antagonist changed the parameters, especially the voiding interval, voiding duration and peak pressure of the bladder.