Influence of naloxone on inhibitory pudendal-to-bladder reflex in cats.
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.
Chen
Mang L
ML
Department of Urology, University of Pittsburgh, Pittsburgh, PA 15213, USA.
Shen
Bing
B
Wang
Jicheng
J
Liu
Hailong
H
Roppolo
James R
JR
de Groat
William C
WC
Tai
Changfeng
C
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
D009292:Narcotic Antagonists; D009270:Naloxone
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