title: Influence of naloxone on inhibitory pudendal-to-bladder reflex in cats.
abstract: To determine the involvement of opioid receptors in the inhibitory pudendal-to-bladder reflex, the effect of naloxone (0.01-1 mg/kg, i.v.), an opioid receptor antagonist, on the inhibition of bladder activity evoked by pudendal nerve stimulation was investigated in alpha-chloralose anesthetized cats. The inhibition of reflex isovolumetric bladder contractions induced by pudendal nerve stimulation (5-10 Hz) at intensity threshold (T) for producing complete inhibition was significantly suppressed by naloxone at a high dose (0.3 mg/kg). However, the inhibition elicited at higher intensities (1.5-3 T) was not changed. Naloxone (1 mg/kg) did not alter the frequency dependence of the inhibitory effect of pudendal stimulation. During cystometrograms (CMGs) pudendal nerve stimulation significantly increased bladder capacity to 155.1+/-24.5% and 163.4+/-10% of the control at stimulation intensities of 1 T and 1.5-3 T, respectively. After administration of naloxone (1 mg/kg), the bladder capacity during pudendal nerve stimulation at inhibition threshold (1 T) was not significantly different from control, but it was significantly increased at higher intensities (1.5-3 T). Naloxone alone markedly reduced bladder capacity to 43+/-11.1% of the control, and pudendal stimulation completely reversed this facilitatory effect. This study revealed that activation of opioid receptors contributes to or facilitates the inhibitory pudendal-to-bladder reflex. The reduction in bladder capacity after naloxone treatment also indicates that endogenous opioid peptides mediate a tonic inhibition of micturition. Understanding the neurotransmitter mechanisms involved in the inhibitory pudendal-to-bladder reflex could promote the development of new treatments for bladder overactivity and incontinence.
authors.affiliation: Department of Urology, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Mang L
authors.initials: ML
authors.lastname: Chen
authors.forename: Bing
authors.initials: B
authors.lastname: Shen
authors.forename: Jicheng
authors.initials: J
authors.lastname: Wang
authors.forename: Hailong
authors.initials: H
authors.lastname: Liu
authors.forename: James R
authors.initials: JR
authors.lastname: Roppolo
authors.forename: William C
authors.initials: WC
authors.lastname: de Groat
authors.forename: Changfeng
authors.initials: C
authors.lastname: Tai
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005260:Female; D008160:Lumbosacral Plexus / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D012018:Reflex / Q000187:drug effects* / Q000502:physiology; D001743:Urinary Bladder / Q000187:drug effects / Q000294:innervation*; D014554:Urination / Q000187:drug effects* / Q000502:physiology
chemical_list: D009292:Narcotic Antagonists; D009270:Naloxone
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