Urothelium-dependent and urothelium-independent detrusor contractility mediated by nitric oxide synthase and cyclooxygenase inhibition

The role of the mucosa in modulation of evoked responses in the spinal cord injured rat bladder

Aims

Mounting evidence indicates that a variety of factors released from the urothelium or suburothelium can modulate smooth muscle activity. Although the relationship between the mucosa and smooth muscle has been investigated, little is known about the pathophysiologic changes in detrusor‐mucosa interactions in neurogenic bladders. The goal of the study was to determine the impact of the mucosa on evoked responses in spinal cord injured (SCI) bladders.

Methods

Urinary bladders were obtained from 6wk SCI rats or age‐matched uninjured controls. Ex vivo isometric tension studies were performed and muscarinic receptor expression was measured in bladder tissue with and without mucosa.

Results

The magnitude and area of nerve evoked responses in SCI tissue with mucosa was higher than without mucosa. The duration and decay time of nerve‐evoked responses were longer in SCI than control tissue irrespective of the mucosa. The level of the muscarinic M₂ receptor was decreased in the mucosa of SCI bladders.

Conclusions

Detrusor‐mucosa interactions are substantially altered in the neurogenic bladder. After spinal cord injury, an excitatory modulation of smooth muscle contraction by the mucosa emerges, and could be targeted via intravesical treatment in the context of neurogenic bladder dysfunction.

Changes in Adenosine Triphosphate and Nitric Oxide in the Urothelium of Patients with Benign Prostatic Hyperplasia and Detrusor Underactivity

PURPOSE

We investigated changes in the levels of adenosine triphosphate and nitric oxide in the urothelium of men with detrusor underactivity and benign prostatic hyperplasia.

MATERIALS AND METHODS

We prospectively enrolled in study 30 men who planned to undergo surgical treatment for benign prostatic hyperplasia. The 15 patients with a bladder contractility index less than 100 were assigned to the detrusor underactivity group while the 15 with a bladder contractility index more than 100 were assigned to the no detrusor underactivity group. Bladder mucosal specimens were collected at surgical prostate resection, and adenosine triphosphate and endothelial nitric oxide synthase were analyzed in these specimens. The levels of adenosine triphosphate and endothelial nitric oxide synthase were compared between the 2 groups. The correlation of urodynamic parameters with adenosine triphosphate and endothelial nitric oxide synthase was assessed in all patients.

RESULTS

Mean ± SEM endothelial nitric oxide synthase did not significantly differ between the detrusor underactivity and no underactivity groups (3.393 ± 0.969 vs 1.941 ± 0.377 IU/ml, p = 0.247). However, the mean level of adenosine triphosphate in the detrusor underactivity group was significantly lower than in the no detrusor underactivity group (1.289 ± 0.320 vs 9.262 ± 3.285 pmol, p = 0.011). In addition, in all patients adenosine triphosphate positively correlated with the bladder contractility index (r = 0.478, p = 0.018) and with detrusor pressure on maximal flow (r = 0.411, p = 0.046).

CONCLUSIONS

Adenosine triphosphate was significantly decreased in the urothelium in men with detrusor underactivity and benign prostatic hyperplasia, reflecting the change in detrusor function.

Altered detrusor contractility in MPTP-treated common marmosets with bladder hyperreflexia

Bladder hyperreflexia is a common non-motor feature of Parkinson's disease. We now report on the contractility of the isolated primate detrusor strips devoid of nerve input and show that following MPTP, the amplitude and frequency of spontaneous contraction was increased. These responses were unaffected by dopamine D1 and D2 receptor agonists A77636 and ropinirole respectively. Contractions by exogenous carbachol, histamine or ATP were similar and no differences in the magnitude of noradrenaline-induced relaxation were seen in detrusor strip obtained from normal and MPTP-treated common marmosets (Callithrix jacchus). However, the neurogenic contractions following electrical field stimulation of the intrinsic nerves (EFS) were markedly greater in strips obtained from MPTP treated animals. EFS evoked non-cholinergic contractions following atropine were also greater but the contribution of the cholinergic innervation as a proportion of the overall contraction was smaller in the detrusor strips of MPTP treated animals, suggesting a preferential enhancement of the non-cholinergic transmission. Although dopaminergic mechanism has been proposed to underlie bladder hyperreflexia in MPTP-treated animals with intact bladder, the present data indicates that the increased neurogenically mediated contractions where no extrinsic innervation exists might be due to long-term adaptive changes locally as a result of the loss of the nigrostriatal output.

Mucosal modulation of contractility in bladder strips from normal and overactive rat models and the effect of botulinum toxin A on overactive bladder strips

AIMS

To investigate the local, regulatory role of the mucosa on bladder strip contractility from normal and overactive bladders and to examine the effect of botulinum toxin A (BoNT-A).

METHODS

Bladder strips from spontaneously hyperactive rat (SHR) or normal rats (Sprague Dawley, SD) were dissected for myography as intact or mucosa-free preparations. Spontaneous, neurogenic and agonist-evoked contractions were investigated. SHR strips were incubated in BoNT-A (3 h) to assess effects on contractility.

RESULTS

Spontaneous contraction amplitude, force-integral or frequency were not significantly different in SHR mucosa-free strips compared with intacts. In contrast, spontaneous contraction amplitude and force-integral were smaller in SD mucosa-free strips than in intacts; frequency was not affected by the mucosa. Frequency of spontaneous contractions in SHR strips was significantly greater than in SD strips. Neurogenic contractions in mucosa-free SHR and SD strips at higher frequencies were smaller than in intact strips. The mucosa did not affect carbachol-evoked contractions in intact versus mucosa-free strips from SHR or SD bladders. BoNT-A reduced spontaneous contractions in SHR intact strips; this trend was also observed in mucosa-free strips but was not significant. Neurogenic and carbachol-evoked contractions were reduced by BoNT-A in mucosa-free but not intact strips. Depolarisation-induced contractions were smaller in BoNT-A-treated mucosa-free strips.

CONCLUSIONS

The mucosal layer positively modulates spontaneous contractions in strips from normal SD but not overactive SHR bladder strips. The novel finding of BoNT-A reduction of contractions in SHR mucosa-free strips indicates actions on the detrusor, independent of its classical action on neuronal SNARE complexes.

Low concentrations of niflumic acid enhance basal spontaneous and carbachol-induced contractions of the detrusor

PURPOSE

The urinary bladder expresses Ca(2+)-activated Cl(-) channels (CACC), but its physiological role in governing contractility remains to be defined. The CACC modulator niflumic acid (NFA) is widely used despite the variable results arisen from different drug concentrations used. This study was designed to examine the effects of NFA at low concentrations on detrusor strip contractility.

METHODS

Rat detrusor strips with mucosa-intact (+MU) and mucosa-denuded (-MU) were prepared in transverse (Tr) and longitudinal (Lg) with respect to the bladder orientation. Isometric force measurements were made at baseline (for spontaneous phasic contractile activity) and during drug stimulation (by carbachol, CCh) with and without NFA.

RESULTS

NFA (1 and 10 μmol/L) pretreatment enhanced CCh-induced contractions more in +MU than -MU strips with no selectivity on contractile direction. For spontaneous phasic contractions, NFA-treated strips in the Tr direction showed increased phasic amplitude, while phasic frequency was unchanged.

CONCLUSIONS

The findings suggest low concentrations of NFA having a potentiating effect on detrusor contractions that was sensitive to the MU and contractile direction.

The effect of indomethacin on the muscarinic induced contractions in the isolated normal guinea pig urinary bladder

Background

To investigate the effect of prostaglandin depletion by means of COX-inhibition on cholinergic enhanced spontaneous contractions.

Methods

The urethra and bladder of 9 male guinea pigs (weight 270–300 g) were removed and placed in an organ bath with Krebs’ solution. A catheter was passed through the urethra through which the intravesical pressure was measured. The muscarinic agonist arecaidine, the non-selective COX inhibitor indomethacin, and PGE₂ were subsequently added to the organ bath. The initial average frequency and amplitude of spontaneous contractions in the first 2 minutes after arecaidine application were labelled F_ini and P_ini, respectively. The steady state frequency (F_steady) and amplitude (P_steady) were defined as the average frequency and amplitude during the 5 minutes before the next wash out.

Results

Application of 1 μM PGE₂ increased the amplitude of spontaneous contractions without affecting frequency. 10 μM of indomethacin reduced amplitude but not frequency.

The addition of indomethacin did not alter F_ini after the first application (p = 0.7665). However, after the second wash, F_ini was decreased (p = 0.0005). F_steady, P_steady and P_ini were not significantly different in any of the conditions. These effects of indomethacin were reversible by PGE₂ addition._.

Conclusions

Blocking PG synthesis decreased the cholinergically stimulated autonomous contractions in the isolated bladder. This suggests that PG could modify normal cholinergically evoked response. A combination of drugs inhibiting muscarinic receptors and PG function or production can then become an interesting focus of research on a treatment for overactive bladder syndrome.

Airway epithelium-derived relaxing factor: myth, reality, or naivety?

The presence of a healthy epithelium can moderate the contraction of the underlying airway smooth muscle. This is, in part, because epithelial cells generate inhibitory messages, whether diffusible substances, electrophysiological signals, or both. The epithelium-dependent inhibitory effect can be tonic (basal), synergistic, or evoked. Rather than a unique epithelium-derived relaxing factor (EpDRF), several known endogenous bronchoactive mediators, including nitric oxide and prostaglandin E2, contribute. The early concept that EpDRF diffuses all the way through the subepithelial layers to directly relax the airway smooth muscle appears unlikely. It is more plausible that the epithelial cells release true messenger molecules, which alter the production of endogenous substances (nitric oxide and/or metabolites of arachidonic acid) by the subepithelial layers. These substances then diffuse to the airway smooth muscle cells, conveying epithelium dependency.

Variations in carbachol- and ATP-induced contractions of the rat detrusor: effects of gender, mucosa and contractile direction

PURPOSE

Contractile characteristics of the bladder may depend on variables such as gender, mucosa (MU) and direction of the contractions. However, definitive information is not yet available despite earlier studies on the effects of one variable or another. Here, we explored the differences in the rat detrusor attributable to gender, mucosa and contractile direction.

METHODS

K+, carbachol (CCh) and ATP were used as contractile stimuli on rat detrusor strips with and without MU. Contractility was monitored using a myograph system. Both tonic and phasic contractile activities were analyzed.

RESULTS

MU-independent contractions induced by CCh were more potent in females, an effect specific to the longitudinal direction only. The maximal CCh response was larger also in females when MU was removed, suggesting a stronger MU-independent component in the contraction. The larger area under curves of the females under ATP stimulation showed dependence on MU and contractile direction as well. ATP-induced contractions in the males were affected more by MU in the transverse direction than in the females. Direction- and MU-dependent variability of ATP responses was also observed in the males but not in females.

CONCLUSIONS

Findings here added new information to the understanding of bladder contractile physiology, providing insights into the quest for better drugs in managing bladder disorders.

Regional distribution and molecular interaction of caveolins in bladder smooth muscle

What's known on the subject? and What does the study add? Caveolae are specialised regions of bladder smooth muscle (BSM) cell membranes where specific signalling pathways are regulated. Caveolin proteins are involved in caveolar biogenesis and function as signal transduction regulators. Expression of caveolin-1, -2, and -3 has been previously identified in the bladder; however, the distribution and relative expression of these proteins have not been defined. The present data show significant differences in the spatial distribution of caveolin proteins throughout the bladder wall. Region dependent variations in the co-localisation of caveolin subtypes in detrusor SM were also detected. These findings support the premise that the unique spatial pattern of caveolin proteins associated with BSM cells may enable regionally distinct functional responses to common stimuli.

OBJECTIVE

• To determine the regional expression profile of caveolin isoforms (integral membrane proteins abundant in caveolae), the spatial relationships among caveolin proteins within specific smooth muscle (SM) regions and the extent of their molecular interactions in bladder SM (BSM).

MATERIALS AND METHODS

• Regional differences in the expression of caveolin family members were determined by quantitative reverse transcriptase-polymerase chain reaction and Western blot of RNA and protein extracted from the base, body and dome of rat bladders. • To evaluate the distribution of caveolin-1 (Cav-1), Cav-2 and Cav-3 within the bladder, longitudinal tissue sections from the base to dome were processed for confocal microscopy and quantified for intensity of immunoreactivity (IR) and extent of co-localisation. • Interactions among Cav-1, Cav-2 and Cav-3 were determined by co-immunoprecipitation.

RESULTS

• Differential expression of Cav-1 and Cav-3 was detected among bladder regions, with lowest expression in the bladder base relative to the dome. • Cav-1 was highly expressed in all regions, although an increase in IR from submucosa to serosa was detected in each region. • The distribution of Cav-2 IR generally paralleled Cav-1, but progressively decreased from submucosa to serosa in each region. • Cav-3 expression predominated in the medial region of BSM increasing progressively from base to dome, but was poorly expressed in the outer SM layer particularly in the dome. • Cav-1 co-precipitated extensively with both Cav-2 and Cav-3. Co-precipitation between Cav-3 and Cav-2 was also detected.

CONCLUSIONS

• The isoform-specific spatial distribution and distinct molecular interactions among caveolins in BSM may contribute to the contractile heterogeneity of BSM cells and facilitate differential modulation of responses to local stimuli. • As BSM caveolae regulate key signalling processes involved in contraction, altered expression of caveolin proteins may generate a regional imbalance in contraction/relaxation responses, thus leading to bladder dysfunction.

Gastrodia elata decreases isoprenaline potency and enhances spontaneous phasic activity in the rat detrusor

Gastrodia elata (Tianma) is a traditional Chinese herb with demonstrated vasodilatory effects. This pilot study examined the effects of Tianma treatment on bladder smooth muscle contractility. Rats were treated with 2.5 g Tianma per kg body weight over 7 weeks. Contractility was measured in detrusor strips isolated in both transverse (Tr) and longitudinal (Lg) directions with the urothelium intact (+UE) or denuded (-UE). Spontaneous phasic activity was enhanced in longitudinal +UE strips. No differences between control and Tianma-treated detrusor strips were detected in contractions elicited by K+-Krebs' solution or carbachol. Isoprenaline (IPNA)-induced relaxation remained unchanged in -UE strips after Tianma treatment. However, potency of IPNA was lower in Tianma-treated +UE strips in the longitudinal direction. These findings provided an initial assessment of how Tianma altered bladder smooth muscle function. It will be of interest in future investigations to elucidate the mechanisms via which Tianma exerts its actions on the bladder.