Further studies on the motor response of the human isolated urinary bladder to tachykinins, capsaicin and electrical field stimulation

H2O2 enhances the spontaneous phasic contractions of isolated human-bladder strips via activation of TRPA1 channels on sensory nerves and the release of substance P and PGE2

Several studies have indicated that reactive oxygen species (ROS) can lead to detrusor overactivity (DO), but the underlying mechanisms are not known. Hydrogen dioxide (H2O2) is used commonly to investigate the effects of ROS. In present study, we investigated the effects of H2O2 on phasic spontaneous bladder contractions (SBCs) of isolated human-bladder strips (iHBSs) and the underlying mechanisms. Samples of bladder tissue were obtained from 26 patients undergoing cystectomy owing to bladder cancer. SBCs of iHBSs were recorded in organ-bath experiments. H2O2 (1μM-10mM) concentration-dependently increased the SBCs of iHBSs. These enhancing effects could be mimicked by an agonist of transient receptor potential (TRP)A1 channels (allyl isothiocyanate) and blocked with an antagonist of TRPA1 channels (HC030031; 10 μM). H2O2 induced enhancing effects also could be attenuated by desensitizing sensory afferents with capsaicin (10 μM), blocking nerve firing with TTX (1 μM), blocking neurokinin effects with NK2 receptor antagonist (SR48968, 10 μM), and blocking PGE2 synthesis with indomethacin (10 μM), respectively. Our study: (i) suggests activation of TRPA1 channels on bladder sensory afferents, and then release of substance P or PGE2 from sensory nerve terminals, contribute to the H2O2-induced enhancing effects on SBCs of iHBSs; (ii) provides insights for the mechanisms underlying ROS leading to DO; (iii) indicates that targeting TRPA1 channels might be the promising strategy against overactive bladder in conditions associated with excessive production of ROS.

The dual function of capsaicin-sensitive sensory nerves in the bladder and urethra

The sensory innervation of the urinary bladder and urethra plays a key role in a variety of reflexes involved in urine storage and voiding. Dysfunction of these systems is a possible cause of many disturbances related to urine continence but basic knowledge in this field has been hampered by the lack of tools for studying sensory nerves. The use of capsaicin, the pungent ingredient of red peppers, allowed us to investigate the anatomical and functional properties of a specific subset of sensory neurons in the lower urinary tract. These 'capsaicin-sensitive' neurons play a dual sensory and 'efferent' function, determined by transmitter release from their central and peripheral nerve endings. Tachykinins, including substance P, and other neuropeptides such as calcitonin gene-related peptide, mediate the functions of these sensory neurons. The 'sensory' function includes regulation of micturition threshold, activation of cardiovascular reflexes and perception of pain from the urinary bladder. The 'efferent' function includes local regulation of muscle cell activity, nerve excitability, blood flow and plasma protein extravasation. Recent data suggest that capsaicin-sensitive sensory nerves could be present in the human bladder.

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.

Effects of capsaicin on visceral smooth muscle: a valuable tool for sensory neurotransmitter identification

Studying the visceral effects of the sensory stimulant capsaicin is a useful and relatively simple tool of neurotransmitter identification and has been used for this purpose for approximately 25 years in the authors' and other laboratories. We believe that conclusions drawn from experiments on visceral preparations may have an impact on studies dealing with the central endings of primary afferent neurons, i.e. research on nociception at the spinal level. The present review concentrates on the effects of capsaicin--through the transient receptor potential vanilloid receptor type 1 (TRPV1) receptor--on innervated gastrointestinal, respiratory and genitourinary smooth muscle preparations. Tachykinins and calcitonin gene-related peptide (CGRP) are the most widely accepted transmitters to mediate "local efferent" effects of capsaicin-sensitive nerves in tissues taken from animals. Studies more and more frequently indicate a supra-additive interaction of various types of tachykinin receptors (tachykinin NK(1), NK(2), NK(3) receptors) in the excitatory effects of capsaicin. There is also evidence for a mediating role of ATP, acting on P(2) purinoceptors. Non-specific inhibitory actions of capsaicin-like drugs have to be taken into consideration while designing experiments with these drugs. Results obtained on human tissues may be sharply different from those of animal preparations. Capsaicin potently inhibits tone and movements of human intestinal preparations, an effect mediated by nitric oxide (NO) and/or vasoactive intestinal polypeptide.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Human tachykinin NK2 receptor: a comparative study of the colon and urinary bladder

1. The present study compared the binding and functional characteristics of tachykinin NK2 receptors in human detrusor muscle with those in human colon circular muscle. 2. In radioligand binding studies, similar KD values were observed for tachykinin NK2 receptor radioligands [125I]-neurokinin (NK) A, [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10,]NKA(4-10) and [3H]-SR48968 in both human colon circular muscle (0.28-1.1 nmol/L) and human bladder detrusor (0.49-0.91 nmol/L), suggesting binding was primarily to tachykinin NK2 receptors. Receptor capacity (Bmax) was greater in colon compared with detrusor muscle. 3. In functional studies of isolated smooth muscle contraction, there was an excellent positive correlation between human bladder detrusor and colon circular muscle with respect to in vitro contractile potency (r = 0.97) and maximum responses (r = 0.98) to tachykinins, selective tachykinin receptor ligands and l-Ala-substituted NKA(4-10) analogues. 4. Species differences between the human and rat tachykinin NK2 receptors were apparent as observed by a low correlation for potency (r = 0.77) and efficacy (r = 0.32) of l-Ala-substituted analogues in isolated smooth muscle contractile studies. 5. Minor differences observed in the affinity and potency of NK2 receptor agonists between colon and bladder are dependent on the tissue of interest, the receptor-effector coupling and the presence of other tachykinin receptors. Overall, the NK2 receptors of human colon and urinary bladder smooth muscle appear pharmacologically identical.

Neurogenic inflammation of the bladder

Current evidence suggests multiple and redundant pathways through which the nervous system can initiate, amplify, and perpetuate inflammation. Many of the processes initiated by neurogenic inflammation have the capacity to recruit the participation of additional sensory nerves. These observations indicate that effective strategies for prevention or treatment of neurogenic inflammation of the bladder will entail or require intervention at multiple points. It has been observed that pain management in the future will be based on selective intervention tailored to the specific processes modulating pain perception in individual patients. It is exciting to contemplate the same approach to prevention and treatment of neurogenic bladder inflammation.

Urodynamic effects induced by intravesical capsaicin in rats and hamsters

This study compared the effect of acute intravesical capsaicin administration on transvesical cystometries in urethane-anesthetized rats and hamsters, and aimed to assess whether sensory neuropeptides (tachykinins; calcitonin gene-related peptide, CGRP) play a role in the urodynamic effects of capsaicin in these species. The following urodynamic parameters were evaluated: the mean micturition interval (MI), the pressure threshold for micturition (PT), and the mean amplitude of micturition contractions (MAC). Two concentrations of capsaicin (10 and 100 microM) were evaluated in both species. Here, we demonstrate that 10-microM capsaicin decreased the PT in both rats and hamsters, and 100-microM capsaicin decreased the PT in hamsters and decreased the MI in both species. In addition, 100-microM capsaicin increased the MAC in rats but decreased the MAC in hamsters. Administration of CGRP (10 nmol kg(-1) , i.v.) significantly decreased both MAC and PT in hamsters only, while capsaicin-induced desensitization of neuropeptide-containing afferents antagonized the urodynamic effects of intravesical capsaicin. In addition, administration of the tachykinin NK2 receptor antagonist, Nepadutant (100 nmol kg(-1), i.v.), reduced the effects of capsaicin (100 microM) only in rats. These results indicate that capsaicin induces bladder hyperactivity in both rats and hamsters, but the urodynamic characteristics of this hyperactivity markedly differ in these two species. The differences observed may be due to differential expression of sensory neuropeptides in capsaicin-sensitive bladder afferents or neuropeptide receptors in smooth muscle cells and in nerve fibers.

Effect of several bicyclic peptide and cyclic pseudopeptide tachykinin NK2 receptor antagonists in the human isolated urinary bladder

1. We have studied several tachykinin NK2 receptor antagonists, bearing a monocyclic pseudopeptide (MEN 10,508, MEN 10,573, MEN 10,581, MEN 10,612, MEN 10,619 and MEN 10,677), or bicyclic peptide (MEN 10,627, MEN 10,692, MEN 10,771, MEN 10,882 and MEN 10,993) structure, on the human isolated urinary bladder detrusor muscle against neurokinin A as an agonist, and compared their affinities in this preparation with those for NK2 receptors expressed in the rabbit isolated pulmonary artery and hamster isolated trachea. 2. In the human bladder, all the antagonists tested produced a concentration-dependent and competitive antagonism of neurokinin A-mediated contractions: among the cyclic pseudopeptides MEN 10,677 (pKB = 8.0) was the most potent antagonist, while among the bicyclic analogues it was MEN 10,993 (pKB = 8.8). 3. In general, the bicyclic peptide antagonists tested were more potent than the monocyclic pseudopeptide compounds, either in the human urinary bladder or in the rabbit pulmonary artery or hamster trachea, showing a nanomolar affinity for the human NK2 receptor. 4. A highly significant correlation was found between the estimated pKB values of all the antagonists tested in the human urinary bladder and rabbit pulmonary artery (r2 = 0.94, n = 12, P < 0.01), whereas no linear correlation was found between pKB values measured in the human urinary bladder and hamster trachea (r2 = 0.52, n = 12, P > 0.05): these observations provide further pharmacological evidence for receptor homology between the human and rabbit NK2 receptor. 5. The present results point out the class of NK2 receptor antagonists bearing a bicyclic peptide structure, like MEN 10,627, as candidates for testing in pathological conditions, such as bladder hyperactivity, for which preclinical evidence indicates that a therapeutic effect could result from the block of the tachykinin NK2 receptor.

Neural 5-HT4 receptors in the human isolated detrusor muscle: effects of indole, benzimidazolone and substituted benzamide agonists and antagonists

1. In strips of human isolated detrusor muscle, the 5-hydroxytryptamine (5-HT) receptor (5-HT4) that mediates facilitation of neuromuscular cholinergic transmission was further characterized by using 5-HT and a series of ligands known for their 5-HT4 agonist (5-methoxytryptamine: 5-MeOT, cisapride, (R,S)-zacopride, BIMU 8) or antagonist (RS 23597, GR 125487, DAU 6285) properties. 2. In the presence of methysergide (1 microM) and ondansetron (3 microM) to isolate pharmacologically the 5-HT4 receptors, 5-HT (0.3 nM-1 microM), 5-MeOT (10 nM -30 microM), BIMU 8 (10 nM-3 microM), cisapride (0.1-10 microM) and (R,S)-zacopride (0.1-30 microM) potentiated cholinergic contractions to electrical field stimulation in a concentration-dependent manner. RS 23597 (10 nM-10 microM), a competitive 5-HT4 receptor antagonist in other systems, also showed agonist properties. The following rank order of potency as an agonist was obtained: 5-HT (pEC50 = 8.0) > RS 23597 (7.0) = BIMU 8 (6.9) > or = cisapride (6.6) > 5-MeOT (6.0) > or = (R,S)-zacopride (5.7). Relative to 5-HT (intrinsic activity = 1), 5-MeOT acted as a full agonist (1.03), while BIMU 8 (0.76), (R,S)-zacopride (0.61), RS 23597 (0.60) and cisapride (0.41) behaved as partial agonists. 3. The potentiation by 5-HT was competitively antagonized by the selective 5-HT4 receptor antagonist GR 125487 (0.3-3 nM) with a pA2 estimate of 9.75 (Schild slope of 1.09), and by DAU 6285 (1 microM; pK3 = 6.45). Additionally, GR 125487 (3 nM) antagonized the responses to 5-MeOT (pKB = 9.72) and reversed the potentiation induced by RS 23597. As an antagonist, RS 23597 (10, 30 and 100 nM) inhibited the response to 5-HT. In addition, 30 and 100 nM RS 23597 reduced the 5-HT response maximum by 30 and 50%, respectively. The pKB value calculated at 10 nM was 8.0. 4. Thus, in the human isolated detrusor muscle, the 5-HT4 receptors mediating facilitation of cholinergic neuromuscular transmission are activated by indoleamines (5-HT, 5-MeOT), substituted benzamide (cisapride, (R,S)-zacopride), benzoate (RS 23597) and benzimidazolone (BIMU 8) derivatives. The activities (in terms of both potency and efficacy) of most agonists, as well as the affinity estimates of the antagonists GR 125487 and DAU 6285, are comparable to those found in other peripheral tissues. Exceptions are RS 23597, which acted either as a partial agonist or as an antagonist of the response to 5-HT1 and 5-MeOT that showed an unusually low potency. The latter findings may be ascribed to differences in the efficiency of receptor coupling mechanisms and/or in the molecular structure (i.e. splice variants) of the 5-HT4 receptor.

Characterization of the 5-HT receptor potentiating neuromuscular cholinergic transmission in strips of human isolated detrusor muscle

In human isolated detrusor strips, submaximal contractile responses evoked by electrical stimulation were resistant to hexamethonium (30 microM) and abolished by tetrodotoxin (0.6 microM) and hyoscine (1 microM), indicating the activation of postganglionic cholinergic nerves. In methysergide (1 microM) and ondansetron (3 microM) pretreated tissues, 5-hydroxytryptamine (5-HT) (0.3 nM-1 microM) caused a concentration-dependent increase in the amplitude of contractions (pEC50 = 8.1), which was antagonized by the selective 5-HT4 receptor antagonist GR 113808 (3, 10 and 30 nM) in a competitive manner. Schild analysis yielded a pA2 estimate of 8.9, a value comparable to that reported for GR 113808 in other animal and human peripheral tissues (8.8-9.7). Our findings indicate that neuromuscular cholinergic transmission in human isolated detrusor muscle is facilitated by neural 5-HT receptors belonging to the 5-HT4 subtype. The human urinary bladder can thus be regarded as an additional site in which 5-HT4 receptors are distributed.

Omega conotoxin and prejunctional modulation of the biphasic response of the rat isolated urinary bladder to single pulse electrical field stimulation

1. Single pulse electrical field stimulation (EFS) produces a biphasic response of muscle strips of the rat isolated urinary bladder consisting of an early and a late contraction which were atropine-resistant and atropine-sensitive, respectively. Repeated application of desensitizing doses of the P2 purinoceptor agonist, alpha, beta-methylene ATP (mATP) inhibited the early response while leaving unaffected the late component. 2. Omega conotoxin (CTX, 0.1 microM) inhibited both the early and the late response either in control conditions or after enhancement by physostigmine (0.1 microM). The effect of CTX was, in both cases, more pronounced on the late than the early response to EFS. CTX (0.1 microM) failed to affect contraction produced by ATP or acetylcholine at concentrations (0.3 mM and 0.5 microM) which produced a response similar to that to EFS. 3. The effect of physostigmine was more intense for the late than the early response and was abolished by atropine. In the presence of CTX, physostigmine enhanced both the early and the late components of the mechanical response to EFS. 4. Nifedipine (0.1-1 microM) reduced to a similar extent both the early and late responses. Bay K 8644 (1 microM) produced a marked enhancement of the response to EFS, which, however, did not have a distinct late peak. In the presence of Bay K 8644, either atropine (3 microM) or tetrodotoxin (1 microM) had minor inhibitory effects indicating the myogenic origin of the response. 5. Neurokinin A (0.1-1 nM) enhanced both the early and late responses to EFS without affecting the contraction produced by exogenous acetylcholine or ATP. A consistent potentiation was evident also in the presence of CTX and for the early response, in the presence of atropine. Clonidine (3 microM) inhibited the response to EFS either in the absence or the presence of physostigmine. The inhibitory effect of clonidine, shown previously to depend upon activation of prejunctional alpha 2-adrenoceptors, was still observed in presence of CTX or atropine. 6. It is concluded that CTX-sensitive voltage dependent calcium channels play a more important role in determining the cholinergic rather than the non-cholinergic, putatively purinergic, component of the biphasic response of the rat bladder to single pulse EFS. The action of CTX is likely to be exerted on N-type rather than L-type (dihydropyridine-sensitive) calcium channels. Prejunctional modulation (enhancement by neurokinin A, inhibition by clonidine) occurs even in the presence of CTX-sensitive channels blockade.

Difference in the actions of calcitonin gene-related peptide on pig detrusor and vesical arterial smooth muscle

Calcitonin gene-related peptide has been demonstrated in urinary bladder nerves, and suggested to play a role in local control of bladder motility. In isolated strips of pig detrusor muscle, calcitonin gene-related peptide did not affect spontaneous contractile activity, or contractions induced by high K+, carbachol, substance P, and electrical field stimulation. In contrast, calcitonin gene-related peptide elicited a concentration-dependent and pronounced (78-99%) relaxation of vesical arteries precontracted with endothelin-1, noradrenaline or prostaglandin F2 alpha. As a vasodilator, CGRP was approximately 50 times more potent than acetylcholine. Removal of the endothelium abolished acetylcholine-induced relaxation, but did not affect the relaxation produced by calcitonin gene-related peptide. Pretreatment with methylene blue, glibenclamide or indomethacin had no influence on CGRP's ability to relax the vessels. The inhibitor of NO-synthesis, NG-nitro-L-arginine, had no effect on the maximum vascular relaxation induced by calcitonin gene-relate peptide. It is concluded that in the pig, calcitonin gene-related peptide has no functionally important mechanical effects on isolated detrusor muscle strips, but is a potent dilator of vesical arteries. The vascular effects of the peptide are endothelium-independent, and seem to be exerted directly on the vascular smooth muscle.

Facilitation of reflex micturition by intravesical administration of [beta Ala8]-neurokinin A (4-10), a selective NK-2 tachykinin receptor agonist

We have determined the ability of [beta Ala8]-NKA(4-10), a selective agonist for NK-2 tachykinin receptors to stimulate micturition in anesthetized rats and guinea-pigs. In both species, the intravesical instillation of the peptide at microM concentrations reduced bladder capacity and residual volume, indicating a facilitatory effect on reflex micturition. At these concentrations, no plasma extravasation was produced as determined by the Evans blue content of the organ. In experiments on the isolated rat or guinea-pig bladder strips, the NK-2 receptor agonist induced powerful contractions. In a in vitro model of the guinea-pig whole bladder the intravesical instillation of the NK-2 agonist facilitated the occurrence of rhythmic contractile activity. It is concluded from these studies that intravenous administration of [beta Ala8]-NKA(4-10) exerts a facilitatory effect on the micturition reflex, presumably involving the ability of the NK-2 receptor agonist to cross the urothelium and stimulate smooth muscle contraction.

The contractile effect of tachykinins on human prostatic urethra: involvement of NK-2 receptors

The contractile response to natural tachykinins [substance P (SP), neurokinin A (NKA), arginin-neurokinin B (ArgNKB)] and to synthetic peptide [Pro9]SP sulfone, [beta Ala8]NKA(4-10) and [MePhe7]NKB, were investigated in the isolated smooth muscle from the human prostatic urethra. Natural tachykinins evoked concentration-related responses with the following order of potency: NKA----NKB--------SP. Among selective agonists [beta Ala8]NKA(4-10) produced concentration-related contractions, while [Pro9]SP sulfone and [MePhe7]NKB were inactive. These data indicate the presence of NK-2 receptors in the smooth muscle of the human prostatic urethra.

Competitive antagonists discriminate between NK2 tachykinin receptor subtypes

1. We have compared the ability of various tachykinins and selective tachykinin receptor agonists to induce contraction of the endothelium-denuded rabbit pulmonary artery (RPA) and hamster trachea (HT) and have estimated the affinity of some newly developed NK2 selective antagonists in the same tissues. 2. In confirmation of previous findings, experiments with the agonists indicated that NK2 receptors are the main if not the sole mediators of the response to tachykinins in both RPA and HT. No evidence for significant degradation of neurokinin A (NKA) was found in either tissue when experiments were repeated in the presence of a mixture of peptidase inhibitors (thiorphan, captopril and bestatin, 1 microM each). 3. The peptide antagonists tested were: Peptide I = [Tyr5, D-Trp6,8,9, Arg10]-NKA(4-10); Peptide II = [Tyr5, D-Trp6,8,9, Arg10]-NKA(3-10); Peptide III = Ac-Leu-Asp-Gln-Trp-Phe-Gly-NH2. The three peptides produced a concentration-dependent rightward shift of the concentration-response curve to NKA in both RPA and HT with no significant depression of the maximal response attainable. The slopes of the Schild plots were not significantly different from unity, indicating a competitive antagonism. Peptides I and II were about 100 times more potent in the RPA than in the HT, while Peptide III was about 100 times more potent in the HT than RPA. 4. The pA2 values obtained in these two tissues with the three antagonists were not significantly different when tested in the absence or presence of peptidase inhibitors, or when a selective NK2 receptor agonist, [beta Ala8]-NKA(4-10) was used instead of NKA. Similar pA2 values were obtained after 15 or 90min of incubation with the antagonists. Peptides I, II and III had no inhibitory effect on contractions produced by noradrenaline in the RPA or by carbachol in the HT. 5. Peptides I, II and III showed weak or no antagonistic activity toward the vasodilatator effect of substance P in the dog carotid artery (NK, receptor-mediated) or toward the contractile effect of neurokinin B in the rat portal vein (NK3 receptor-mediated). 6. These results provide pharmacological evidence for heterogeneity of NK2 receptors in the RPA and HT. The NK2 receptors present in these tissues are not discriminated by natural tachykinins or selective agonists, but are recognized with very different affinity by NK2 receptor antagonists.

In vivo pharmacology of [beta Ala8]neurokinin A-(4-10), a selective NK-2 tachykinin receptor agonist

We studied the effect of [beta Ala8]neurokinin A-(4-10), a newly developed selective NK-2 tachykinin receptor agonist, on various parameters in anaesthetized rats (blood pressure, urinary bladder motility, plasma extravasation) and guinea-pigs (salivation, increase of pulmonary insufflation pressure) as compared to the response produced by tachykinins. [beta Ala8]Neurokinin A-(4-10) was as active as, or more active than, neurokinin A (NKA) or NKA-(4-10) in producing rat bladder contraction or bronchospasm in guinea-pigs, two effects known to involve activation of NK-2 receptors. On the other hand, the synthetic peptide was weakly active, if active at all, in producing hypotension or plasma extravasation in the rat bladder as well as salivation in guinea-pigs, effects known to involve activation of NK-1 receptors. These findings provide evidence that [beta Ala8]NKA-(4-10) acts as a selective NK-2 agonist in vivo and that it can be used to explore the distribution and function of NK-2 receptors.