ROLE OF A CENTRAL MUSCARINIC CHOLINERGIC PATHWAY FOR RELAXATION OF THE PROXIMAL URETHRA DURING THE VOIDING PHASE IN RATS

Inhibitory roles of peripheral nitrergic mechanisms in capsaicin-induced detrusor overactivity in the rat

OBJECTIVES

To investigate the peripheral role of nitric oxide (NO) in capsaicin-induced detrusor overactivity (DO), as exogenously applied vanilloids can evoke NO release in urothelial cells but its functional role has not yet been reported.

MATERIALS AND METHODS

The effects of N(G)-nitro-l-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), on bladder activity during intravesical capsaicin (30 microm) instillation were examined by using continuous infusion cystometry in urethane-anaesthetized rats. L-NAME was administered intravenously (i.v., 20 mg/kg), intrathecally (i.t., 270 microg/rat), intracerebroventricularly (i.c.v., 270 microg/rat) or intravesically (10 mg/mL) before or during capsaicin instillation.

RESULTS

During cystometry with intravesical saline infusion, L-NAME injected i.v., i.t. and i.c.v., but not intravesically, significantly increased the intercontraction intervals (ICI) and L-NAME injected i.v., but not i.t., i.c.v. or intravesically, increased the maximum voiding pressure (MVP) without affecting the baseline pressure. Capsaicin instillation induced DO evidenced by a significant reduction in the ICI. L-NAME administered i.v. further decreased the ICI and increased the MVP and the baseline pressure during capsaicin instillation. Co-intravesical application of capsaicin and L-NAME also similarly enhanced capsaicin-induced DO. However, L-NAME injected i.t. or i.c.v. had no effect on capsaicin-induced DO. The excitatory effects of i.v and intravesical L-NAME on the ICI, MVP and baseline pressure during capsaicin infusion were significantly suppressed by desensitization of C-fibre afferent pathways by capsaicin pretreatment (125 mg/kg s.c., 4 days before cystometry).

CONCLUSION

These results indicate that locally released NO can suppress DO induced by capsaicin-mediated C-fibre activation and that central NO pathways are not involved in capsaicin-induced DO.

The effects of ageing on the distribution of vesicular acetylcholine transporter immunoreactive inputs to pelvic motoneurons of male Wistar rats

Age-related changes in the number and size of large cholinergic terminals immunoreactive for vesicular acetylcholine transporter (VAChT), were documented for the dorsolateral nucleus (DLN), retrodorsolateral nucleus (RDLN) and spinal nucleus of the bulbospongiosus (SNB) of the lumbosacral spinal cord of male rats. The most significant changes were a large increase in the number and size of cholinergic terminals within the DLN of aged animals, together with a small decrease in terminal number within the RDLN. No significant age-associated differences in VAChT labeling were seen within the SNB. In both age groups, SNB motoneurons projecting to the levator ani muscle received about 9 to 10 contacts from large cholinergic terminals. Ultrastructural examination of the terminals revealed structures likely to be postsynaptic subsurface cisterns that are characteristic of type C terminal boutons. Since both the DLN and SNB contain motoneurons innervating pelvic muscles and sphincters, these findings provide further evidence for a central cholinergic influence on micturition and sexual reflexes and suggest that this may remain robust in the face of ageing.

Central Muscarinic Receptor Subtypes Regulating Voiding in Rats

PURPOSE

Muscarinic receptors are distributed widely in the brain. A recent study revealed that central muscarinic receptors are involved in voiding regulation. However, to our knowledge the role of each muscarinic receptor subtype has not been resolved. Therefore, we evaluated the effect of intracerebroventricular administration of selective muscarinic M1 to M4 receptor antagonists on voiding function in rats.

MATERIALS AND METHODS

Female Sprague-Dawley rats were cannulated for intracerebroventricular infusion under halothane anesthesia. In experiment 1 cystometry was performed in conscious rats, and BC and maximal voiding pressure were measured. In experiment 2 a catheter was inserted via the bladder dome to the bladder neck and UPP was measured by saline infusion. Repeat cystostomy was performed, and saline infusion and discharge saline, BC, maximal IVP and minimal UPP were measured in conscious rats. Pirenzepine, methoctramine, pFHHSiD and MT-3 were used as selective M1, M2, M3 and M4 muscarinic receptor antagonists, respectively, which were injected intracerebroventricularly.

RESULTS

In experiment 1 pirenzepine and pFHHSiD increased BC and decreased maximal voiding pressure. Methoctramine and MT-3 decreased BC. In experiment 2 pirenzepine and pFHHSiD increased BC and minimal UPP, and decreased maximal IVP. Methoctramine and MT-3 decreased BC and maximal IVP. Minimal UPP remained unchanged.

CONCLUSIONS

Intracerebroventricular administration of muscarinic M1 and M3 receptor antagonists inhibited urination in conscious rats, while M2 and M4 receptor antagonists induced excitatory changes.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Modulation of urethral alpha-sympathetic by parasympathetic before and following bethanechol chloride injection

INTRODUCTION AND OBJECTIVES

Chagas' disease causes specific parasympathetic denervation and in its digestive clinic form promotes also functional alterations in bladder. Thus, the aim was to investigate the existence of balance between sympathetic and parasympathetic systems in lower urinary tract, as occurs in other organs. We verified the urethral closing pressure before and following parasympathetic stimulus.

PATIENTS AND METHODS

For that, the urethral closure pressure was studied before and after the injection of 5 mg of bethanechol chloride subcutaneously in 28 voluntary female patients, divided into 4 groups. The constitution of theses groups was: A) normal control = 6 patients; B) Chagas' disease with positive serology only = 5 patients; C) Chagas' disease with cardiac disease = 6 patients, and D) Chagas' disease with digestive disease and vesical hyporeflexia = 11 patients. Urethral profilometry was performed through perfusion urethral catheter with a 6.5 ml/minute flow and a traction rate of 5 mm/minute.

RESULTS

Means and standard deviations for urethral closure pressure before bethanechol chloride were respectively: group A = 67.3 +/- 7.1; group B = 69.2 +/- 7.4; group C = 95.8 +/- 5.1; group D = 82.1 +/- 8.4. After bethanechol chloride they were: group A = 66.0 +/- 6.6; group B = 77.0 +/- 7.6; group C = 98.3 +/- 8.8; group D = 45.9 +/- 6.2. The Kruskal Wallis statistical test did not show statistically significance difference between groups A, B, C. However, it was statistically significant between groups C and D with p = 0.003. Wilcoxon test showed p = 0.001, only for values in group D before and following bethanechol chloride.

CONCLUSIONS

Chagas' disease in its intestinal form seems to alter urethral function as well. Parasympathetic stimulation decreased urethral pressure, indicating potential modulation by the parasympathetic system over the sympathetic system.

Functional role of central muscarinic receptors for micturition in normal conscious rats

PURPOSE

Antimuscarinic agents, which are used in to treat urgency and urge incontinence, have well-known effects on peripheral muscarinic receptors. However, some currently used drugs may have effects on muscarinic receptors in the brain and/or spinal cord involved in voiding control. We tested if muscarinic receptors within the central nervous system mediate a tonic excitatory influence on voiding in rats and if these receptors can be differently influenced by antimuscarinic drugs.

MATERIALS AND METHODS

The effects on cystometrography of intracerebroventricular atropine, oxybutynin, tolterodine and darifenacin were investigated in normal conscious rats.

RESULTS

Atropine (0.2 to 2 nmol.) dose dependently affected urodynamic parameters. At 2 nmol. in 6 rats the drug decreased voiding pressure (p <0.01), and increased bladder capacity (p <0.001), voided volume (p <0.05) and post-void residual volume (p <0.05). In 6 rats oxybutynin (6 to 40 nmol.) given at a dose of 6 nmol. caused no change in cystometric parameters, while at 20 nmol. the drug decreased voiding pressure (p <0.01). Tolterodine (2 to 20 nmol.) dose dependently changed urodynamic parameters, while at 20 nmol. in 6 rats the drug decreased voiding pressure (p <0.01) and increased bladder capacity (p <0.05) and voided volume (p <0.05). Darifenacin given at a dose of 20 nmol. in 6 rats caused no change in cystometric parameters.

CONCLUSIONS

Muscarinic receptor mechanisms in the central nervous system mediate a tonic excitatory influence on voiding in rats, while nonsubtype selective antimuscarinic drugs may have an inhibitory effect on these mechanisms.