THE INHIBITORY EFFECT OF NOCICEPTIN ON THE MICTURITION REFLEX IN ANESTHETIZED RATS

1 We have investigated the effect of nociceptin on the micturition ref lex evoked by distension or topical application of capsaicin on the ur inary bladder of urethane-anaesthetized rats. 2 Nociceptin produced a dose-dependent (3-100 nmol kg(-1) i.v.) transient suppression of the d istension-evoked micturition reflex: its effect was not modified by gu anethidine (68 mu mol kg(-1) s.c.) nor by bilateral cervical vagotomy, alone or in combination, and by naloxone (1.2 mu mol kg(-1) i.v.). 3 Nociceptin (100 nmol/kg i.v.) slightly (about 30%) inhibited the contr actions of the rat bladder produced by pre- or postganglionic electric al stimulation of the pelvic nerve. 4 Nociceptin almost totally abolis hed the reflex component of the response to topical capsaicin (1 mu g in 50 mu l). 5 In the rat isolated bladder, submaximal contractions pr oduced by electrical held stimulation were slightly reduced (25+/-4% i nhibition) by 1 mu M nociceptin. Nociceptin did not affect the contrac tion of the rat bladder induced by acetylcholine (10 mu M) or ATP (1 m M). 6 These findings indicate that nociceptin exerts a naloxone-resist ant suppression of the volume-evoked micturition reflex which involves inhibition of transmitter release from postganglionic bladder nerves. An inhibitory effect on bladder afferent nerves is also suggested.