Tachykinin antagonists and capsaicin-induced contraction of the rat isolated urinary bladder: evidence for tachykinin-mediated cotransmission

Immunohistochemical Expression of Neurokinin-A and Interleukin-8 in the Bronchial Epithelium of Horses with Severe Equine Asthma Syndrome during Asymptomatic, Exacerbation, and Remission Phase

Severe equine asthma (EA) syndrome is a chronic obstructive disease characterized by exaggerated contraction, inflammation, and structural alteration of the airways in adult horses, when exposed to airborne molds and particulate material. However, little is known about the relationship between the degree and type of inflammation on one hand, and the severity of the disease and the response to treatment on the other. Furthermore, to date, very few studies evaluate the diagnostic value of histology and immunohistochemical features of endoscopic biopsies on subjects with severe equine asthma. To investigate the expression of two inflammatory markers (NKA and IL-8) before, during, and after the exacerbation of severe EA, a histological and immunohistochemical study was carried out on a series of biopsy samples collected by bronchoscopy from six EA-affected horses subjected to process exacerbation through environmental stimuli and then to pharmacological treatment. The application of a histological biopsy scoring system revealed a significant difference between control cases and the EA-affected horses in all experimental phases (asymptomatic, early exacerbation phase, late exacerbation phase, and remission phase). For immunohistochemistry (IHC), only the intensity of NKA positivity increases significantly between control horses and the EA horses at late exacerbation and remission phases. In EA-affected horses, a difference was detected by comparing histology between asymptomatic and remission phase, meanwhile, NKA and IL-8 showed no differences between the experimental phases. Based on these results we can assert that: (1) The endoscopic biopsies generate reliable and homogeneous samples in the entire bronchial tree; (2) the clinical improvement associated with treatment is characterized by a significant worsening of the histological findings; and (3) the NKA immunopositivity seems to increase significantly rather than decrease, as one would have expected, after pharmacological treatment. Further studies are necessary both to implement the number of samples and to use other markers of inflammation to characterize the potential role of cytokines in the diagnosis and therapeutic approach of severe equine asthma.

Beyond Neuronal Heat Sensing: Diversity of TRPV1 Heat-Capsaicin Receptor-Channel Functions

Transient receptor potential vanilloid 1 (TRPV1) is a calcium-permeable ion channel best known for its ability to be gated by the pungent constituent of red chili pepper, capsaicin, and related chemicals from the group of vanilloids as well as by noxious heat. As such, it is mostly expressed in sensory neurons to act as a detector of painful stimuli produced by pungent chemicals and high temperatures. Its activation is also sensitized by the numerous endogenous inflammatory mediators and second messengers, making it an important determinant of nociceptive signaling. Except for such signaling, though, neuronal TRPV1 activation may influence various organ functions by promoting the release of bioactive neuropeptides from sensory fiber innervation organs. However, TRPV1 is also found outside the sensory nervous system in which its activation and function is not that straightforward. Thus, TRPV1 expression is detected in skeletal muscle; in some types of smooth muscle; in epithelial and immune cells; and in adipocytes, where it can be activated by the combination of dietary vanilloids, endovanilloids, and pro-inflammatory factors while the intracellular calcium signaling that this initiates can regulate processes as diverse as muscle constriction, cell differentiation, and carcinogenesis. The purpose of the present review is to provide a clear-cut distinction between neurogenic TRPV1 effects in various tissues consequent to its activation in sensory nerve endings and non-neurogenic TRPV1 effects due to its expression in cell types other than sensory neurons.

NK2 receptor-mediated detrusor muscle contraction involves Gq/11-dependent activation of voltage-dependent Ca2+ channels and the RhoA-Rho kinase pathway

Tachykinins (TKs) are involved in both the physiological regulation of urinary bladder functions and development of overactive bladder syndrome. The aim of the present study was to investigate the signal transduction pathways of TKs in the detrusor muscle to provide potential pharmacological targets for the treatment of bladder dysfunctions related to enhanced TK production. Contraction force, intracellular Ca²⁺ concentration, and RhoA activity were measured in the mouse urinary bladder smooth muscle (UBSM). TKs and the NK2 receptor (NK2R)-specific agonist [β-Ala⁸]-NKA(4-10) evoked contraction, which was inhibited by the NKR2 antagonist MEN10376. In Gα_q/11-deficient mice, [β-Ala⁸]-NKA(4-10)-induced contraction and the intracellular Ca²⁺ concentration increase were abolished. Although G_q/11 proteins are linked principally to phospholipase Cβ and inositol trisphosphate-mediated Ca²⁺ release from intracellular stores, we found that phospholipase Cβ inhibition and sarcoplasmic reticulum Ca²⁺ depletion failed to have any effect on contraction induced by [β-Ala⁸]-NKA(4-10). In contrast, lack of extracellular Ca²⁺ or blockade of voltage-dependent Ca²⁺ channels (VDCCs) suppressed contraction. Furthermore, [β-Ala⁸]-NKA(4-10) increased RhoA activity in the UBSM in a G_q/11-dependent manner and inhibition of Rho kinase with Y-27632 decreased contraction force, whereas the combination of Y-27632 with either VDCC blockade or depletion of extracellular Ca²⁺ resulted in complete inhibition of [β-Ala⁸]-NKA(4-10)-induced contractions. In summary, our results indicate that NK2Rs are linked exclusively to G_q/11 proteins in the UBSM and that the intracellular signaling involves the simultaneous activation of VDCC and the RhoA-Rho kinase pathway. These findings may help to identify potential therapeutic targets of bladder dysfunctions related to upregulation of TKs.

TRPA1 mediates the antinociceptive properties of the constituent of Crocus sativus L., safranal

Safranal, contained in Crocus sativus L., exerts anti‐inflammatory and analgesic effects. However, the underlying mechanisms for such effects are poorly understood. We explored whether safranal targets the transient receptor potential ankyrin 1 (TRPA1) channel, which in nociceptors mediates pain signals. Safranal by binding to specific cysteine/lysine residues, stimulates TRPA1, but not the TRP vanilloid 1 and 4 channels (TRPV1 and TRPV4), evoking calcium responses and currents in human cells and rat and mouse dorsal root ganglion (DRG) neurons. Genetic deletion or pharmacological blockade of TRPA1 attenuated safranal‐evoked release of calcitonin gene‐related peptide (CGRP) from rat and mouse dorsal spinal cord, and acute nociception in mice. Safranal contracted rat urinary bladder isolated strips in a TRPA1‐dependent manner, behaving as a partial agonist. After exposure to safranal the ability of allyl isothiocyanate (TRPA1 agonist), but not that of capsaicin (TRPV1 agonist) or GSK1016790A (TRPV4 agonist), to evoke currents in DRG neurons, contraction of urinary bladder strips and CGRP release from spinal cord slices in rats, and acute nociception in mice underwent desensitization. As previously shown for other herbal extracts, including petasites or parthenolide, safranal might exert analgesic properties by partial agonism and selective desensitization of the TRPA1 channel.

Hypoactivity of rat detrusor muscle in a model of cystitis: exacerbation by non-selective COX inhibitors and amelioration by a selective DP1 receptor antagonist

Various studies have confirmed that prostaglandins (PG) alter the bladder motor activity and micturition reflex in both human and animals. However, no sufficient data is reported about the effect of cyclooxygenase (COX) inhibitors neither in normal bladder physiology nor in pathological conditions. This study aims to compare the potential effects of some COX inhibitors with varying COX-1/COX-2 selectivities (indomethacin, ketoprofen, and diclofenac) with that of the selective COX-2 inhibitor (DFU) on bladder function. The role played by some PGs and their receptors in controlling detrusor muscle function in normal condition and in cystitis is also studied. Organ bath experiments were performed using isolated rat detrusor muscle. Direct and neurogenic contractions were induced using ACh and electric stimulation (EFS), respectively. A model of hemorrhagic cystitis was induced by single injection of cyclophosphamide (300 mg/kg) in rats, and confirmed by histophathological examination. Results are expressed as mean ± SEM of 5-9 rats. Alprostadil and iloprost (1 nM- 10 µM) concentration-dependently potentiated ACh (100 μM)- and EFS (4 Hz)-induced contraction, with maximum potentiation of 40.01 ± 5.29 and 27.59 ± 6.64%, respectively, in case of ACh contractions. In contrast, ONO-AE1-259 (selective EP₂ agonist, 1 nM-10 μM) inhibited muscle contraction. SC51322 (EP₁-antagonist, 10 μM) and RO1138452 (IP antagonist, 10 μM) inhibited both direct and neurogenic responses. Hemorrhagic cystitis reduced both ACh and EFS responses as well as the potentiatory effect of iloprost and the inhibitory effect of RO1138452 on ACh contractions. ONO-AE3-237 (DP₁ antagonist, 1 μM) significantly potentiated contractions in cystitis but showed no effect in normal bladder. A significant inhibition of contractile response was observed in presence of indomethacin, ketoprofen, and diclofenac at all tested concentrations (20, 50, and 100 μM). Highest effect was induced by diclofenac. The effect of these COX inhibitors on EFS contractions was intensified in case of cystitis, indomethacin being the most potent. Atropine (1 nM) significantly reduced indomethacin effect on ACh contraction only in normal rats. On the other hand, DFU (10^-6 M) significantly potentiated the contractile effect of ACh in case of cystitis although it showed no effect in normal rats. EP₁ receptors seem to play an important role in rat bladder contractility. DP₁ receptors as COX-2, on the other hand, gain an important role only in case of cystitis. The use of non-selective COX inhibitors in cystitis may be associated with bladder hypoactivity; selective COX-2 inhibitors may be a safer option.

Gene expression of muscarinic, tachykinin, and purinergic receptors in porcine bladder: comparison with cultured cells

Urothelial cells, myofibroblasts, and smooth muscle cells are important cell types contributing to bladder function. Multiple receptors including muscarinic (M₃/M₅), tachykinin (NK₁/NK₂), and purinergic (P2X₁/P2Y₆) receptors are involved in bladder motor and sensory actions. Using female pig bladder, our aim was to differentiate between various cell types in bladder by genetic markers. We compared the molecular expression pattern between the fresh tissue layers and their cultured cell counterparts. We also examined responses to agonists for these receptors in cultured cells. Urothelial, suburothelial (myofibroblasts), and smooth muscle cells isolated from pig bladder were cultured (10–14 days) and identified by marker antibodies. Gene (mRNA) expression level was demonstrated by real-time PCR. The receptor expression pattern was very similar between suburothelium and detrusor, and higher than urothelium. The gene expression of all receptors decreased in culture compared with the fresh tissue, although the reduction in cultured urothelial cells appeared less significant compared to suburothelial and detrusor cells. Cultured myofibroblasts and detrusor cells did not contract in response to the agonists acetylcholine, neurokinin A, and β,γ-MeATP, up to concentrations of 0.1 and 1 mM. The significant reduction of M₃, NK₂, and P2X₁ receptors under culture conditions may be associated with the unresponsiveness of cultured suburothelial and detrusor cells to their respective agonists. These results suggest that under culture conditions, bladder cells lose the receptors that are involved in contraction, as this function is no longer required. The study provides further evidence that cultured cells do not necessarily mimic the actions exerted by intact tissues.

Differential effects of botulinum neurotoxin A on bladder contractile responses to activation of efferent nerves, smooth muscles and afferent nerves in rats

PURPOSE

To determine the mechanisms of botulinum neurotoxin A (Metabiologics, Madison, Wisconsin) induced inhibition of bladder activity we examined the effect of botulinum neurotoxin A on detrusor contractile responses to the activation of L-type voltage-gated Ca(2+) channels, and efferent and afferent nerve terminals in the rat bladder.

MATERIALS AND METHODS

Rat bladder strips were incubated for 3 hours with different concentrations of botulinum neurotoxin A (0.3 to 100 nM). We examined the effect of botulinum neurotoxin A on detrusor contractility in response to activation of L-type voltage-gated Ca(2+) channels, and efferent and afferent nerve terminals induced by 70 mM KCl, electrical field stimulation and 1 μM capsaicin, respectively.

RESULTS

Botulinum neurotoxin A inhibited electrical field stimulation induced contractions at a concentration of 10 nM or higher. The maximal inhibition at 100 nM was 70% compared to that of control strips. KCl induced contractions, which were sensitive to nifedipine, were significantly inhibited by incubation with botulinum neurotoxin A at a concentration of 3 nM or higher. Maximal inhibition at 100 nM was 30% compared to that of control strips. Capsaicin induced contractions were not inhibited by 3-hour incubation but they were significantly inhibited by overnight incubation with 100 nM botulinum neurotoxin A (30% compared to control strips). Carbachol induced contractions were not altered by incubation with botulinum neurotoxin A.

CONCLUSIONS

The order of inhibitory potency of botulinum neurotoxin A was efferent nerve terminals >L-type voltage-gated Ca(2+) channels >afferent nerve terminals. Since the inhibitory effects on L-type voltage-gated Ca(2+) channels and efferent nerve terminals were observed at similar botulinum neurotoxin A concentrations, the inhibitory effect of botulinum neurotoxin A on L-type voltage-gated Ca(2+) channels may have an important role in regulating and stabilizing bladder activity.

Neurogenic inflammation of Guinea-pig bladder

Capsaicin, substance P, and ovalbumin, instilled into the bladders of naive and ovalbumin (OVA) sensitized guineapigs caused inflammation, as indicated by increased vascular permeability. Histological changes after exposure to these compounds progressed with time from intense vasodilatation to marginalization of granulocytes followed by interstitial migration of leukocytes. In vitro incubation of guinea-pig bladder tissue with substance P and ovalbumin stimulated release of prostaglandin D₂ and leukotrienes. In vitro incubation of bladder tissue with capsaicin, OVA, prostaglandin D₂, leukotriene C₄, histamine, or calcium ionophore A-23587 all stimulated substance P release. These data suggest that bladder inflammation initiated by a variety of stimuli could lead to a cyclic pattern of release of inflammatory mediators and neuropeptides, which could result in amplification and persistence of cystitis after the inciting cause has subsided.

Regulation of smooth muscle contraction by the epithelium: role of prostaglandins

As an analog to the endothelium situated next to the vascular smooth muscle, the epithelium is emerging as an important regulator of smooth muscle contraction in many vital organs/tissues by interacting with other cell types and releasing epithelium-derived factors, among which prostaglandins have been demonstrated to play a versatile role in governing smooth muscle contraction essential to the physiological and pathophysiological processes in a wide range of organ systems.

Models of inflammation of the lower urinary tract

Inflammation of the lower urinary tract occurs frequently in people. The causes remain obscure, with the exception of urinary tract infection. Animal models have proven useful for investigating and assessing mechanisms underlying symptoms associated with lower urinary tract inflammation and options for suppressing these symptoms. This review will discuss various animal models of lower urinary tract inflammation, including feline spontaneous (interstitial) cystitis, neurogenic cystitis, autoimmune cystitis, cystitis induced by intravesical instillation of chemicals or bacterial products (particularly lipopolysaccharide or LPS), and prostatic inflammation initiated by transurethral instillation of bacteria. Animal models will continue to be of significant value in identifying mechanisms resulting in bladder inflammation, but the relevance of some of these models to the causes underlying clinical disease is unclear. This is primarily because of the lack of understanding of causes of these disorders in people. Comparative and translational studies are required if the full potential of findings obtained with animal models to improve prevention and treatment of lower urinary tract inflammation in people is to be realized.

The differential contractile responses to capsaicin and anandamide in muscle strips isolated from the rat urinary bladder

The contractile responses to capsaicin and anandamide, exogenous and endogenous agonists for transient receptor potential vanilloid receptor 1 (TRPV1), respectively, were investigated in muscle strips isolated from the rat urinary bladder. Capsaicin and anandamide produced concentration-dependent contractions of the muscle strips. The contractile response induced by capsaicin disappeared within approximately 20 min. In contrast, anandamide produced contractile responses lasting at least for 30 min. Capsaicin produced additive contractile responses in anandamide-treated muscle strips. The contractile response to anandamide was attenuated, but not abolished in strips desensitized by capsaicin. The response to capsaicin was abolished in the presence of a TRPV1 antagonist, N-(4-tertiarybutylphenyl)-4-(3-chlorphyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC), but not altered in the presence of either tetrodotoxin, atropine or indomethacin. In the presence of SR140333, a tachykinin NK(1) receptor antagonist or SR48968, an NK(2) receptor antagonist, the response to capsaicin was attenuated. The response to anandamide was partially attenuated in the presence of ONO8130, a prostanoid EP(1) receptor antagonist, URB597, a fatty-acid amide hydrolase inhibitor, BCTC, SR140333 or SR48968, and almost completely abolished by indomethacin. Neither tetrodotoxin, atropine, a cannabinoid CB(1) receptor antagonist, AM251, nor a cannabinoid CB(2) receptor antagonist, AM630, had any effect on the response to anandamide. These results indicate that capsaicin produces muscle contractions by stimulating the TRPV1 receptor, followed by release of neuropeptides that can activate tachykinin NK(1) and/or NK(2) receptors in the bladder and that the contractile response to anandamide is mediated at least in part by activation of prostanoid EP(1) receptors due to production of prostaglandins in addition to TRPV1 receptor activation.

Role of capsaicin-sensitive sensory nerves in protease-activated receptor-2-mediated contraction of rat urinary bladder

The capsaicin receptor, transient receptor potential vanilloid receptor 1 (TRPV1), colocalizes with protease-activated receptors (PARs) in the urinary bladder, but functional interaction between TRPV1 and PARs remains to be clarified. In the present study, the role of capsaicin-sensitive sensory neurons in contraction induced by activation of PAR-2 was investigated in the rat urinary bladders. The contractile responses to trypsin and the PAR-2 agonist 2-furoyl-LIGRL-NH(2) were significantly attenuated by either desensitization of sensory neurons achieved by capsaicin (10 microM) or by the TRPV1 antagonist capsazepine (30 microM). These results suggest that stimulation of capsaicin-sensitive sensory fibers contributes, at least in part, to PAR-2-mediated bladder contractions in rats.

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.

Mechanisms of neurokinin A- and substance P-induced contractions in rat detrusor smooth musclein vitro

OBJECTIVE

To investigate the mechanisms of neurokinin A- and substance P-induced contractions of rat urinary bladder smooth muscle, and to compare them with those of the muscarinic agonist carbachol.

MATERIALS AND METHODS

Rat urinary bladder strips were suspended under 1 g of tension in a physiological buffer at 37 degrees C, gassed with 95% O(2)/5% CO(2). Mechanical activity was recorded isometrically during exposure to neurokinin A and substance P.

RESULTS

Both agents produced concentration-dependent contractions of smooth muscle strips which were unaffected by tetrodotoxin (1 micro mol/L), peptidase inhibitors (captopril, thiorphan and bestatin; 1 micro mol/L each) or piroxicam (10 micro mol/L). The rank order of potency of agonists was neurokinin A > substance P > carbachol. Contractile responses to neurokinin A and substance P, like the contractile responses to carbachol, were abolished in a nominally Ca(2+)-free medium and significantly reduced by nifedipine (1 micro mol/L). SKF-96365 (60 micro mol/L), an inhibitor of receptor-mediated Ca(2+) entry, abolished the nifedipine-resistant response to substance P and carbachol, and significantly attenuated the response to neurokinin A. Depleting intracellular Ca(2+) stores with thapsigargin (1 micro mol/L) significantly attenuated neurokinin A-induced contractions but had no effect on substance P- or carbachol- induced contractions. The Rho-kinase inhibitor, Y-27632 (10 micro mol/L), significantly reduced both phasic and tonic components of the contractile responses to neurokinin A, substance P and carbachol.

CONCLUSION

The contractile responses induced by tachykinins in rat urinary bladder smooth muscle strips involve a direct action on smooth muscle and are not modulated by peptidases or prostanoids. Neurokinin A and substance P, like carbachol-induced contractions, depend on extracellular Ca(2+) influx largely through voltage-operated and partly through receptor-operated Ca(2+) channels. Intracellular Ca(2+) release contributes to the contractile response to neurokinin A but appears to have no involvement in substance P- and carbachol-induced contractions. Rho-kinase activation contributes to contractions induced by substance P, neurokinin A and carbachol.

Effect of experimental diabetes on cholinergic, purinergic and peptidergic motor responses of the isolated rat bladder to electrical field stimulation or capsaicin

An attempt has been made to pharmacologically isolate cholinergic, P(2) purinoceptor-mediated and peptidergic (capsaicin-sensitive, tachykinin-mediated) contraction of the guanethidine-treated rat bladder detrusor preparation, in vitro. The effect of experimental diabetes was assessed on these types of contraction. Responses were evoked by electrical field stimulation (single shocks or 1 Hz for 30 s or 10 Hz for 40 s). Single shocks and 1-Hz stimulation were applied in the presence of (a). atropine (1 microM) or (b). P(2) purinoceptor antagonists (50 microM pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid) [PPADS] plus 100 microM suramin. Long-term electrical field stimulation (10 Hz for 40 s) (c). was applied with both atropine and the P(2) purinoceptor antagonists present in the organ bath. The effects of capsaicin (d). and ATP (e). were also studied. Three groups of experimental animals were used: streptozotocin-treated (50 mg.kg(-1) i.p., 8 weeks before the experiment), parallel solvent-treated and untreated rats. (a). Responses to electrical field stimulation in the presence of atropine were reduced by half by PPADS plus suramin, but were resistant to capsaicin tachyphylaxis. They were enhanced in preparations taken from diabetic rats. (b). Contractions to electrical field stimulation in the presence of PPADS plus suramin were reduced by 2/3 by atropine, but were left unchanged by capsaicin or diabetes. (c). Contractions to long-term stimulation had a quick and a sustained phase. Especially the latter was inhibited by capsaicin tachypyhlaxis; it was also strongly reduced in preparations taken from diabetic rats. (d). Contractions to capsaicin (30 nM and 1 microM) were resistant to tetrodotoxin, strongly reduced by a combination of tachykinin NK(1) and NK(2) receptor antagonists, and slightly reduced in preparations from diabetic animals. Capsaicin (1 microM) had no acute inhibitory action on cholinergic or purinergic responses, nor did it cause relaxation in precontracted preparations treated with tachykinin receptor antagonists. (e) ATP-induced contractions were strongly reduced by PPADS plus suramin (50 plus 100 microM) and to a similar degree by 100 plus 200 microM, respectively. It is concluded that experimental diabetes selectively impairs peptidergic, capsaicin-sensitive responses (especially those that involve impulse conduction) in the rat detrusor preparation. The contractile response to electrical field stimulation that remains after atropine plus the P(2) purinoceptor antagonists has a yet unknown transmitter background.

Hydrogen sulfide (H2S) stimulates capsaicin-sensitive primary afferent neurons in the rat urinary bladder

In the rat isolated urinary bladder, NaHS (30 microm-3 mm) and capsaicin (10 nm-3 microm) produced concentration-dependent contractile responses (pEC(50)=3.5+/-0.02 and 7.1+/-0.02, respectively) undergoing dramatic tachyphylaxis. In preparations in which sensory nerves were rendered desensitized (defunctionalized) by high-capsaicin (10 microm for 15 min) pretreatment, neither capsaicin itself nor NaHS produced any motor effect. NaHS-induced contractile effects were totally prevented by the simultaneous incubation with tachykinin NK(1) (GR 82334; 10 microm) and NK(2) (nepadutant; 0.3 microm) receptor-selective antagonists. Tetrodotoxin (1 microm) only partially reduced the response to NaHS. These results provide pharmacological evidence that H(2)S stimulates capsaicin-sensitive primary afferent nerve terminals, from which tachykinins are released to produce the observed contraction by activating NK(1) and NK(2) receptors. While the molecular site of action of H(2)S remains to be investigated, our discovery may have important physiological significance since H(2)S concentrations capable of stimulating sensory nerves overlap those occurring in mammalian tissues under normal conditions.

Hydrogen sulfide (H2S) stimulates capsaicin-sensitive primary afferent neurons in the rat urinary bladder

In the rat isolated urinary bladder, NaHS (30 microm-3 mm) and capsaicin (10 nm-3 microm) produced concentration-dependent contractile responses (pEC(50)=3.5+/-0.02 and 7.1+/-0.02, respectively) undergoing dramatic tachyphylaxis. In preparations in which sensory nerves were rendered desensitized (defunctionalized) by high-capsaicin (10 microm for 15 min) pretreatment, neither capsaicin itself nor NaHS produced any motor effect. NaHS-induced contractile effects were totally prevented by the simultaneous incubation with tachykinin NK(1) (GR 82334; 10 microm) and NK(2) (nepadutant; 0.3 microm) receptor-selective antagonists. Tetrodotoxin (1 microm) only partially reduced the response to NaHS. These results provide pharmacological evidence that H(2)S stimulates capsaicin-sensitive primary afferent nerve terminals, from which tachykinins are released to produce the observed contraction by activating NK(1) and NK(2) receptors. While the molecular site of action of H(2)S remains to be investigated, our discovery may have important physiological significance since H(2)S concentrations capable of stimulating sensory nerves overlap those occurring in mammalian tissues under normal conditions.

Biologic activity of the tachykinins on lamb and sheep gallbladder

In this study, we examined the activity of the tachykinins (TKs) on lamb and sheep isolated gallbladder and whether the TKs are involved in the capsaicin-induced activity in these tissues. Substance P (SP) and physalaemin (PHYS) contracted lamb gallbladder, PHYS-induced striking tachyphylaxis. This tissue was nearly insensitive to neurokinin A (NKA), neurokinin B (NKB), septide, and capsaicin. As in lamb tissues, SP and PHYS both contracted sheep gallbladder although PHYS induced no tachyphylaxis. At doses that had no effect on lamb tissue, NKA, NKB, septide, and capsaicin contracted sheep gallbladder. Our findings indicate that TK receptors differ in adult and young ovine gallbladder. The activity of PHYS on lamb gallbladder could depend on the existence of an unusual binding site, carrying one or more residues critical for the N-terminal sequence present in PHYS but not in SP.

Expression and functional role of Rho-kinase in rat urinary bladder smooth muscle

(1) The involvement of Rho-kinase (ROCK) in the contractile mechanisms mediating smooth muscle contraction of the rat urinary bladder was investigated using expression studies and the ROCK inhibitor Y-27632. (2) Both isoforms of ROCK (ROCK I and ROCK II) were detected in high levels in rat urinary bladder. (3) Y-27632 (10 micro M) significantly attenuated contractions of rat urinary bladder strips evoked by the G-protein coupled receptor agonists carbachol (58.1+/-10.5% at 0.3 micro M) and neurokinin A (68.6+/-12.7% at 1 micro M) without affecting contractions to potassium chloride (10-100 mM). In addition, basal tone was reduced by 47.8+/-2.0% by 10 micro M Y-27632 in the absence of stimulation. (4) Contractions of urinary bladder strips evoked by the P2X receptor agonist alpha,beta-methylene ATP (alpha,beta-mATP; 10 micro M) were also attenuated by Y-27632 (30.0+/-7.2% at 10 micro M). (5) Y-27632 (10 micro M) significantly attenuated contractions evoked by electrical field stimulation (2-16 Hz). The effect of Y-27632 on the tonic portion of the neurogenic response (4-16 Hz) was not significantly different from the effect of atropine (1 micro M) alone. (6) While the mechanism underlying the ability of Y-27632 to inhibit alpha,beta-mATP-evoked contractions remains undetermined, the results of the present study clearly demonstrate a role for ROCK in the regulation of rat urinary bladder smooth muscle contraction and tone.

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.

Tachykinin-independent activity of capsaicin on in-vitro lamb detrusor

The capsicum alkaloid capsaicin is an afferent fibre exciter. In the vesical bladder, capsaicin acts by releasing peptides stored in afferent fibres. The aim of this work was to verify the activity of capsaicin on in-vitro lamb urinary bladder and to ascertain whether this alkaloid evokes peptide release. Capsaicin relaxed about 80% of the lamb detrusor muscle preparations tested and contracted about 20%. Whereas neurokinin A and substance P antagonists, administered alone or together, left the contractile responses to capsaicin unchanged, atropine and tetrodotoxin totally inhibited contraction. Ruthenium red and indometacin abolished contractions and relaxation. The substance P and neurokinin A antagonists and the NO-synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) left relaxation unchanged; conversely, the calcitonin gene-related peptide antagonist alpha h-CGRP (8-37) abolished this response. These results suggest that capsaicin relaxes lamb detrusor muscle not through tachykinins but by releasing CGRP from afferent fibres. Our observation that indometacin blocks the capsaicin response in in-vitro lamb urinary bladder also suggests a role of prostanoids.

Calcitonin Gene-related Peptide Causes Intraspinal Spreading of Substance P Released by Peripheral Stimulation

Experiments were performed in barbiturate-anaesthetized, spinalized cats to investigate the effect of calcitonin gene-related peptide (CGRP) on the spatial distribution of immunoreactive substance P (ir-SP) in the spinal cord released by electrical nerve stimulation and noxious mechanical stimuli. The presence of ir-SP was assessed with microprobes bearing C-terminus-directed antibodies to SP. CGRP was microinjected into the grey matter of the spinal cord near microprobe insertion sites at depths of 2500, 2000, 1500 and 1000 microm using minute amounts (in total 0.2 - 0.5 microl) of Ringer solution containing CGRP at a concentration of 10-5 or 10-3 M. In the untreated cord electrical stimulation of the tibial nerve (suprathreshold for all C fibres) elicited release of ir-SP which was centred in and around the lamina II. After microinjection of CGRP, stimulation-associated ir-SP was detected in a region extending from the cord surface down to the ventral horn. This pattern was similar to that observed after the microinjection of synthetic peptidase inhibitors (Duggan et al., Brain Res., 579, 261 - 269, 1992). The large expansion of sites accessed by ir-SP was time-dependent, reaching a maximal effect within 10 - 40 min after microinjection of CGRP, and reversal was observed in subsequent probes. A similar expansion of the regions accessed by ir-SP after microinjection of CGRP was also observed when release of ir-SP was evoked by noxious mechanical stimulation of the toes. These results indicate that one important function of CGRP in the spinal cord may be the control of the intraspinal sites and neuronal circuits accessed by released substance P, possibly by inhibition of endopeptidases responsible for peptide degradation.

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.

Principles of tachykininergic co-transmission in the peripheral and enteric nervous system

The tachykinins substance P (SP) and neurokinin A (NKA) are synthesized and released from nerves in the peripheral and enteric nervous system (PNS and ENS). They act as nonadrenergic noncholinergic (NANC) excitatory transmitters in mammalian airways, and the genitourinary and gastrointestinal tract. At the postjunctional level, both NK(1) (SP-preferring) and NK(2) (NKA-preferring) receptors are often co-expressed by target cells innervated by TKergic nerves. Thus an issue of duplication seems to exists with regard to peripheral tachykininergic co-transmission, the duplication involving both messengers (the peptides) and effectors (the receptors). By using receptor selective antagonists it has been possible to dissect the relative contribution of different receptors to TKergic co-transmission: the available results indicate that multiple arrangements exist involving both summation, cooperation and specialization of different messengers/effectors in producing the overall response.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Expression of neuropeptides and nitric oxide synthase in neurones innervating the inflamed rat urinary bladder

Micturition reflexes become hyperexcitable with the development of a cystitis. In the present study the question is addressed, whether alterations in the expression of neuropeptides and nitric oxide synthase (NOS) in the neuronal pathways to the bladder may be involved in the hyperexcitability. Primary sensory neurones in the dorsal root ganglia (DRG) L1, L2, L6 and S1 as well as postganglionic efferent neurones in the major pelvic ganglia (MPG) that innervate the rat urinary bladder were labeled with retrogradely transported Fast Blue (FB). Immunocytochemical techniques were used to determine alterations in the expression of calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL) and NOS in these neurones following mustard oil-induced inflammation of the urinary bladder. Instillation of 2.5% mustard oil into the bladder led to a massive leukocyte infiltration of the vesical tissues, partial damage of the mucosal layer and a marked hyperreflexia of the detrusor muscle. 48 h after induction of the cystitis the proportion of FB-labeled bladder afferent neurones that expressed CGRP and SP were significantly increased in both the rostral lumbar DRGs (L1, L2) and the lumbosacral DRGs (L6, S1) (CGRP, +15-38%; SP, +47-158%) as compared to control animals. However, there was a differential effect of the inflammation on the expression of GAL and NOS in bladder afferents at the two segmental levels examined. Significant alterations in the number of FB-labeled afferents exhibiting GAL immunoreactivity were mainly restricted to the lumbosacral DRGs L6 (+169%) and S1 (+60%). On the contrary, the proportion of NOS-immunoreactive bladder afferents significantly increased only in the rostral lumbar DRGs L1 (+144%) and L2 (+193%), while the level of NOS-expression was unaffected at the lumbosacral levels. Inflammation furthermore induced a significant increase (+275%) in the number of FB-labeled neurones in the MPGs that exhibited NOS immunoreactivity. These results indicate that an upregulation of CGRP-, SP-, GAL- and NOS-synthesis in sensory and efferent neurones is involved in the response to an acute cystitis. Because of the differences in the segmental pattern and degree of upregulation of these substances in bladder afferents that project to the rostral lumbar and lumbosacral spinal cord a different regulation of the sympathetic and parasympathetic efferent outflow to the urinary bladder is suggested. The involvement of CGRP, SP, GAL and NOS in the modulation of both excitatory and inhibitory mechanisms that control the cystitis-induced detrusor hyperreflexia is discussed.

Effect of octreotide, a somatostatin analogue, on release of inflammatory mediators from isolated guinea pig bladder

OBJECTIVE

Somatostatin has been demonstrated to inhibit inflammation under certain circumstances. We hypothesized that in vivo treatment with octreotide, a long-acting analogue of somatostatin analogue, would diminish the capacity of inflammatory peptides to stimulate in vitro release of inflammatory mediators by the bladder.

METHODS

Female guinea pigs were injected with octreotide (20 mg./kg. i.m.) prior to euthanasia. Control guinea pigs received no treatment prior to euthanasia. Urinary bladders were removed and incubated with substance P (SP, 10 microM), neurokinin A (NKA, 10 microM), or bradykinin (BK, 10 microM) in the presence or absence of indomethacin (50 microM), and release of histamine, prostaglandins (PGE2 and PGF2 alpha), and leukotriene (LTB4) was determined.

RESULTS

Sensory peptides and BK induced time-dependent release of histamine and eicosanoids from isolated urinary bladder. Blockade of cyclooxygenase with indomethacin (50 microM) abolished peptide-induced prostaglandin release but enhanced LTB4 release. In vivo octreotide pretreatment decreased peptide-induced histamine release, had no effect on PGE2 or PGF2 alpha release, and LTB4 release. However, octreotide prevented the increase in LTB4 release in tissues incubated with indomethacin.

CONCLUSIONS

These results indicate that somatostatin has the capacity to suppress the release of histamine and prevents potentiation of LTB4 release by indomethacin by the guinea pig bladder in response to pro-inflammatory peptides, indicating that somatostatin may be useful in preventing or treating some forms of cystitis.

Functional, biochemical and anatomical changes in the rat urinary bladder induced by perigangliar injection of colchicine

The aim of this study was to assess the effect of blocking the axonal transport of sensory neuropeptides, by local injection of colchicine at pelvic ganglia level, on the sensory and efferent functions mediated by capsaicin-sensitive primary afferent neurons innervating the rat urinary bladder. Bilateral injection of colchicine in the prostatic tissue underneath the pelvic ganglia of male rats induced a time-dependent reduction (maximal at 72 h, 100% reduction) of the in vitro contraction of the bladder strips induced by capsaicin (1 microM). The response to electrical field stimulation was also reduced, although to a lesser extent. The direct contractions induced by substance P (100 nM) or KCl (80 mM) were not affected by colchicine pretreatment. In vivo, perigangliar injection of colchicine (72 h before) greatly increased bladder capacity, and reduced the amplitude of micturition contractions and micturition frequency. Capsaicin-induced plasma protein extravasation was abolished in the urinary bladder and reduced in the distal, but not the proximal ureter of colchicine-treated rats. Topical application of capsaicin onto the urinary bladder or onto the stomach induced a cardiovascular pressor reflex in urethane-anaesthetized, spinalized rats. Colchicine pretreatment reduced (by about 50%) the pressor response elicited by chemonociceptive stimulation of the bladder but not that arising from the stomach. Colchicine pretreatment did not produce overt changes of nerve profiles immunoreactive for calcitonin gene-related peptide- or tachykinin-like material in the rat urinary bladder. A more intense staining of nerve fibres positive for calcitonin-gene related peptide-like immunoreactivity and tachykinin-like immunoreactivity was observed in pelvic ganglia of colchicine-pretreated rats. No changes were detected in the dorsal horns of spinal cord segments where pelvic bladder afferents project (L6-S1). Colchicine pretreatment reduced, but did not abolish, bladder levels of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity. However, vasoactive intestinal peptide-like immunoreactivity levels were not changed. The capsaicin-evoked (1 microM) release of calcitonin gene-related peptide was abolished in capsaicin as well as in colchicine-pretreated animals. The present findings demonstrate that local treatment of pelvic ganglia with colchicine totally eliminates the "efferent" functions of capsaicin-sensitive afferent nerves in the urinary bladder. Although reduced, tissue levels of sensory neuropeptides are not completely depleted, thus indicating the existence of a releasable versus non-releasable pool. The chemically induced blockade of axoplasmic transport also induces a limited impairment of the sensory function of capsaicin-sensitive afferents, and of the parasympathetic efferent system.

The mammalian tachykinin receptors

The tachykinins (TKs) are a family of small peptides which share the common C-terminal sequence Phe-X-Gly-Leu-MetNH2. Three peptides of this family, substance P, neurokinin A and neurokinin B, have an established role as neurotransmitters in mammals. 2. Three receptors for TKs have been cloned: they are G-protein coupled receptors with seven putative transmembrane spanning segments and have been termed NK1 (substance P-preferring), NK2 (neurokinin A-preferring) and NK3 (neurokinin B-preferring). 3. Synthetic agonists are available to selectively stimulate only one receptor, while natural TKs can act as full agonist at each one of the three receptors, albeit at different concentrations. 4. A number of potent and selective antagonists, both peptide and nonpeptide in nature, have recently been developed. 5. The introduction of these ligands has revealed an unforeseen pharmacological heterogeneity of NK1, NK2 and NK3 receptors which appears largely, if not exclusively, linked to the existence of species homologues of the three receptors.

Activation of the micturition reflex by NK2 receptor stimulation in the anaesthetized guinea-pig

1. The mechanisms underlying stimulation of bladder contractions and bronchoconstriction by the selective NK2 receptor agonist, [beta-Ala8]NKA(4-10), were examined in the anaesthetized guinea-pig. 2. Atropine, alpha,beta-methylene-ATP and ganglion blocking agents were used to examine the contribution of reflex arc activation and/or potentiation of efferent mechanisms to the NK2 receptor-mediated responses seen in these two tissues. 3. [beta-Ala8]NKA(4-10)-induced bronchoconstriction was immediate, dose-dependent and was unaffected by pretreatment with ganglion blockers (hexamethonium or chlorisondamine), blockade of muscarinic receptors by atropine, or desensitization of P2 purinoceptors by alpha,beta-methylene-ATP. 4. At does of 5 micrograms kg-1 and above, [beta-Ala8]NKA(4-10) induced bladder contractions that appeared to be of an 'all-or-nothing' nature. These contractions occurred after a delay of 10 to 30 s and were often biphasic, comprised of an initial rapid component followed by a slower tonic component. 5. Pretreatment of the animals with either atropine or the desensitizing purinoceptor agonist alpha,beta-methylene-ATP, resulted in partial inhibition of bladder contractile responses to [beta-Ala8]NKA(4-10). The combination of atropine and alpha,beta-methylene-ATP pretreatment resulted in additive inhibition leading to complete blockade of the response. 6. The bladder responses to [beta-Ala8]NKA(4-10) (5 micrograms kg-1) were inhibited by pretreatment with the ganglion blockers, hexamethonium and chlorisondamine, indicating a preganglionic mechanism of action. 7. These findings demonstrate the indirect nature of the bladder contractions induced by activation of NK2 receptors in the anaesthetized guinea-pig. Contractions occur secondary to the release of endogenous cholinergic and NANC transmitters by activation of neuronal NK2 receptors located at apreganglionic site, possibly on capsaicin-sensitive sensory afferent nerves, where NK2 sites have been demonstrated autoradiographically. In contrast, [beta-Ala8]NKA(4- 10)-induced bronchoconstriction in the anaesthetized guinea-pig is a direct smooth muscle contractile response that is unaffected by ganglionblockade or blockade of muscarinic receptors.

Essential role for nitric oxide in neurogenic inflammation in rat cutaneous microcirculation. Evidence for an endothelium-independent mechanism

The possible modulatory role of nitric oxide (NO) in neurogenic edema formation in rat paw skin, induced by electrical stimulation of the saphenous nerve, was investigated by using two NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI). Both L-NAME (100 mg/kg IV, P < .05) and 7-NI (10 mg/kg IV, P < .05) caused an L-arginine (100 mg/kg IV, P < .01)-reversible inhibition of neurogenic edema as measured by 125I-albumin accumulation, whereas D-NAME (inactive enantiomer of L-NAME) and 6-aminoindazole (structurally similar to 7-NI) were without inhibitory effect. L-NAME produced the predicted vasopressor effect (before, 115 +/- 18 mm Hg; 5 minutes after, 174 +/- 18 mm Hg; n = 6; P < .05), whereas 7-NI showed no significant increase in blood pressure (before, 96 +/- 9 mm Hg; 5 minutes after, 102 +/- 10 mm Hg; n = 6), and neither L-NAME nor 7-NI had any effect on basal or vasodilator calcitonin gene-related peptide (CGRP, 10 pmol per site)-stimulated local blood flow in rat skin, as measured by laser Doppler flowmetry. Furthermore, systemic and local 7-NI had no effect on edema formation induced by local administration of substance P (with or without CGRP) and histamine (with or without CGRP) in rat skin. Since 7-NI blocks edema produced by stimulation of the saphenous nerve, it is suggested that release of NO is involved in neurogenic edema formation, but the vasodilator action of NO is unimportant in this context.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of substance P and capsaicin on urinary bladder of diabetic rats and the role of the epithelium

The in vitro responses of rat urinary bladder, to substance P and capsaicin were studied at 1, 4, 16, and 26 weeks of diabetes induction by streptozotocin. We also studied the role of epithelium in these responses. The results were compared with those obtained in age-matched control rats. The bladder contractile response to exogenous substance P was similar in both groups at all stages (1-26 weeks) studied, whereas the bladder response to capsaicin gradually decreased with the progression of diabetes. Atropine did not inhibit these responses whereas indomethacin slightly reduced substance P- but not capsaicin-induced responses in control and diabetic rats. The removal of epithelium slightly increased the substance P- and capsaicin-induced responses in control tissue; these responses were significantly reduced in tissue excised from diabetic rats. Our results indicate that, in rat urinary bladder, diabetes (1) provokes an impairment of capsaicin-sensitive sensory fibers but not of the cholinergic system even at an early stage (4 weeks) of the disease, (2) has no effect on the sensitivity of smooth muscle cells to substance P, (3) stimulates the release of epithelial contracting factors, partially non-prostanoic. Furthermore epithelium removal impairs acetylcholine-induced contraction in bladder excised from diabetic rats but not in controls.

Non-adrenergic, non-cholinergic control of the urinary bladder

In the urinary, bladder, ATP is an excitatory neuromuscular transmitter, possibly a cotransmitter with acetylcholine from postganglionic parasympathetic nerves, which activates P2X-purinoceptors. The synthesis of prostaglandins is closely linked to the activation of P2X-purinoceptors, and these compounds make a significant contribution to non-cholinergic neurogenic responses. Many neuropeptides, such as NPY, VIP, somatostatin, SP and CGRP, are found in nerves innervating the lower urinary tract, but it is unlikely that any is a neuromuscular transmitter in the detrusor; rather, they may act as potent modulators of sympathetic and parasympathetic transmission. Modulatory actions are shown by GABA par excellence; this compound is also well represented in vesicular neurons and, via activation of GABAA- or GABAB-receptors, can potentiate or inhibit parasympathetic transmission. Although not discussed in depth in this review, the urinary bladder shows extraordinary plasticity in expression of nerves and of their transmitters and receptors under pathophysiological conditions, including pregnancy and ageing as well as disease states. Finally, the accessibility of the urinary bladder and the enormous range of chemoreceptors that it possesses has led to its being used extensively for pharmacological investigations of transmitter and drug receptors and their subclasses.

Intraspinal release of immunoreactive calcitonin gene-related peptide during development of inflammation in the joint in vivo--a study with antibody microprobes in cat and rat

This study addressed the intraspinal release of immunoreactive calcitonin gene-related peptide in vivo during mechanical stimulation of the normal joint and during the development of an acute experimental inflammation in the knee joint in the anaesthetized cat (spinalized) and rat (not spinalized). Release was assessed using microprobes coated with antibody to calcitonin gene-related peptide; inhibition of binding of [125I]calcitonin gene-related peptide to these probes following insertion into the spinal cord is equated with intraspinal release of the endogenous (unlabelled) peptide. Probes inserted prior to inflammation showed marked basal release of immunoreactive calcitonin gene-related peptide in the dorsal horn with a maximum in the superficial dorsal horn in the absence of intentional stimulation. The pattern of binding of [125I]calcitonin gene-related peptide was not or only minimally changed by innocuous mechanical stimuli (flexion of and innocuous pressure to the knee in the cat and innocuous pressure to the knee of the rat) but was significantly altered by electrical stimulation of the tibial nerve in the cat (sufficient to excite unmyelinated afferent fibres), indicating release of the peptide by the latter stimulus. During the first hours of the development of an experimental inflammation in the knee joint induced by intra-articular injections of kaolin and carrageenan, the pattern of binding of [125I]calcitonin gene-related peptide changed. In the cat, the level of immunoreactive calcitonin gene-related peptide showed a persistent increase in the gray matter and up to the surface of the cord and release was slightly increased by innocuous stimuli. In the rat, increased levels of immunoreactive calcitonin gene-related peptide were mainly seen in the superficial and deep dorsal horn during innocuous pressure (this stimulus did not evoke release of the peptide prior to inflammation) and noxious pressure applied to the injected knee, whereas increased basal levels were only observed at later stages. These data show that the development of an acute experimental inflammation in the joint is associated with an enhancement of the intraspinal release of immunoreactive calcitonin gene-related peptide. Since the changes in the release were noted at an early stage, within the first hours, they could contribute to the generation of inflammation-evoked changes of the responsiveness of spinal cord neurons and hence to the mechanisms inducing inflammatory pain.

Role of intrathecal tachykinins for micturition in unanaesthetized rats with and without bladder outlet obstruction

1. The effects on micturition of RP 67,580, a selective NK1 receptor antagonist, and SR 48,968, a highly, potent antagonist at NK2 receptor sites, given intrathecally (i.t.) or intra-arterially (i.a.) near the bladder, were investigated in unanaesthetized rats with and without bladder outlet obstruction. 2. In normal rats, RP 67,580, given i.t. in doses of 2 and 20 nmol per rat, decreased micturition pressure, but did not change other cystometric parameters. After 20 nmol of RP 67,580, dribbling incontinence due to retention was observed in 1 out of 7 animals. This effect was reversible. I.t. RP 67,580 in a dose of 2 nmol, had no effect on hyperactivity induced by intravesically instilled capsaicin. 3. In animals with bladder hypertrophy secondary to outflow obstruction, RP 67,580, given i.t. in a dose of 2 nmol per rat, decreased the micturition pressure, but had no effect on other cystometric parameters. After 20 nmol, dribbling incontinence due to retention was observed in 5 out of 7 animals. 4. RP 67,580, given i.a. in a dose of 4 nmol, had little effect on the cystometric parameters investigated, both in normal animals and rats with bladder hypertrophy. 5. SR 48,968, given i.t. in doses of 2 and 20 nmol per rat, had no clear-cut effects on the micturition pattern in normal rats, or rats with bladder hypertrophy. However, the drug reduced capsaicin-induced bladder hyperactivity. When given i.a. in a dose of 4 nmol, SR 48,968 had no effect on cystometric parameters in normal rats or rats with bladder hypertrophy. 6. The effects of both RP 67,580 and SR 48,968 were stereoselective, their enantiomers (RP 68,651 and SR 48,965) being inactive.7. These results thus suggest that at the spinal level there is a tachykinin involvement (via NK,receptors) in the micturition reflex induced by bladder filling, both in normal rats, and, more clearly, in animals with bladder hypertrophy secondary to outflow obstruction. The bladder response to filling was not influenced by blockade of vesical NKI and NK2 receptors. On the other hand, the bladder hyperactivity evoked by intravesical capsaicin seems to involve NK2 receptors both at the bladder and spinal levels.

Capsaicin-induced bladder hyperactivity in normal conscious rats

Capsaicin, instilled intravesically in normal, unanesthetized rats induced a concentration-dependent bladder hyperactivity, which could be abolished by hexamethonium, given intra-arterially near the bladder, or by morphine administered intrathecally. The effect was reversible and could be repeated. The NK-2 receptor selective antagonist SR 48,968 and the nonselective NK receptor antagonist spantide, given intra-arterially near the bladder, which by themselves, in the concentrations used, did not affect cystometric parameters, both counteracted the capsaicin-induced hyperactivity, whereas the NK-1 receptor selective antagonist RP 67,580 failed to do so. Blockade of tachykinin receptors in the urinary bladder does not seem to produce changes of the micturition reflex associated with bladder filling in the conscious rat. However, tachykinins released from capsaicin-sensitive nerves by various stimuli may, through stimulation of NK-2 receptors, lower the threshold for initiation of the micturition reflex. In the rat, intravesical capsaicin may be a suitable model for studies of afferent activity caused by stimuli releasing peptides from sensory nerves in the bladder, thereby provoking bladder hyperactivity.

Evidence for a capsaicin-sensitive, tachykinin-mediated, component in the NANC contraction of the rat urinary bladder to nerve stimulation

1. In the presence of atropine (1 microM) and guanethidine (3 microM), electrical field stimulation (EFS) of the rat isolated urinary bladder for 30 s induced a frequency-dependent (1-30 Hz) nonadrenergic non-cholinergic (NANC) triphasic contraction characterized by a peak response (within 10 s from onset of stimulation), a late response (determined as the tension developed at the end of the stimulation period) and a prolonged post-stimulus 'off' response. The latter peaked at 2-6 min from the end of the stimulation period. At 10 Hz, the amplitude of the three responses averaged 89 +/- 6, 76 +/- 6 and 18 +/- 3% of the response to 40 mM KCl, respectively. Tetrodotoxin (1 microM) abolished all contractile responses to EFS. 2. In capsaicin-pretreated bladder strips (10 microM for 15 min) the amplitude of the peak response to EFS (1-30 Hz for 30 s) was unchanged, the 'late' response to EFS was significantly reduced as compared to controls, and the post-stimulus response was absent, being replaced by a transient relaxation. 3. When varying train duration from 1 to 120 s at a frequency of 10 Hz, the differences between control and capsaicin-treated strips became evident for periods of stimulation > 10 s. 4. The tachykinin NK1 receptor antagonist, SR 140,333 (0.1-1 microM) had no effect on the peak response to EFS (10 Hz for 30 s) while it decreased significantly the late response at both concentrations tested (16 +/- 3 and 33 +/- 3% inhibition). At 1 micro M, SR 140,333 also significantly reduced (29 +/- 9% inhibition)the peak of the post-stimulus contraction. The tachykinin NK2 receptor antagonist, MEN 10,627(0. 1-1 9 MicroM) had no significant effect on the peak response to EFS (10 Hz for 30 s), and decreased the late response at 1 MicroM only (32 +/- 4% inhibition). MEN 10,627 inhibited the post-stimulus response at both concentrations tested and almost abolished it at 1 MicroM.5. The combined administration of SR 140,333 and MEN 10,627 (1 MicroM each) produced a small reduction(22 +/- 3% inhibition) of the peak response to EFS, a marked reduction (48 +/- 3% inhibition) of the late response and the abolition of the post-stimulus response which was replaced by a post-stimulus relaxation as observed in capsaicin-pretreated strips.6. SR 140,333 (0.1 and 1.0 MicroM) produced a large rightward shift in the concentration-response curve tothe NKI receptor agonist, [Sar9]substance P sulphone (apparent pKB 8.97 +/- 0.14), without affecting the response to the NK2 receptor-selective agonist, [Beta Ala8]neurokinin A (4-10). MEN 10,627 (0.1 and 1 MicroM)produced a large rightward shift of the concentration-response curve to [Beta Ala8]neurokinin A (4-10)(apparent pKB 8.95 +/- 0.16) without affecting the response to [Sarl substance P sulphone. SR 140,333 and MEN 10,627 (1.0 MicroM each) did not affect the contraction produced by exogenous ATP (1 mM).7. These findings provide evidence that the NANC contraction of the rat isolated urinary bladder to transmural nerve stimulation has two components, which are sharply differentiated by blockade of the efferent function of sensory nerves following in vitro capsaicin administration. The first component,probably mediated by endogenous ATP, is fully activated during short periods of nerve activity (< 10 s)and does not involve capsaicin-sensitive nerve afferents. The second component, which is capsaicin sensitive and tachykinin-mediated, is evident as a late 'on' response during nerve stimulation and as a post-stimulus 'off response for periods of stimulation >lOs. Activation of both NK1 and NK2receptors contributes to the capsaicin-sensitive responses.

Characterization of the capsaicin-sensitive component of cyclophosphamide-induced inflammation in the rat urinary bladder

1. Cyclophosphamide (CYP) (150 mg kg-1, i.p. 0.5-48 h before) caused a time-dependent plasma protein extravasation in the rat urinary bladder with the maximal extravasation occurring at between 2 and 4 h after administration of the drug. 2. Prior capsaicin desensitization of capsaicin-sensitive primary afferent neurones (CSPANs) (50 mg kg-1, s.c., 4 days before) resulted in approximately 50% inhibition of the magnitude of the extravasation response at the 2 h time-point. 3. Intraperitoneal (i.p.) pretreatment with the tachykinin NK1 receptor antagonist, RP 67,580 (0.44 mg kg-1) or the bradykinin B2 receptor antagonist, Hoe 140 (0.13 mg kg-1) had significant inhibitory effects, giving responses of 56 +/- 6% and 39 +/- 4% of the control extravasation response to CYP treatment after 2 h. Pretreatment with the tachykinin NK2 receptor antagonist, SR 48,968 (0.3 mg kg-1, i.p.), the histamine H1 receptor blocker, chlorpheniramine (10 mg kg-1, i.p.), the 5-HT receptor blocker, methysergide (6 mg kg-1, i.p.) or the cyclo-oxygenase inhibitor indomethacin (5 mg kg-1, i.p.) had no significant effect upon the development of the extravasation response at this same time-point. 4. In rat isolated urinary bladder strips, the active metabolite of CYP, acrolein (1-300 microM) produced a concentration-dependent contraction that was significantly reduced by in vitro capsaicin desensitization (10 microM for 15 min) indicating direct stimulation of CSPANs. CYP was without appreciable effect. 5. The effect of acrolein in vitro was significantly reduced by pretreatment of the bladder with a combination of tachykinin NK1 and NK2 receptor antagonists, RP 67,580 (3 microM) and SR 48,968 (1 microM). The dose-response curve to acrolein was also significantly inhibited by treatment with indomethacin (10 microM) and slightly affected by Hoe 140 (1 microM). 6. These findings demonstrate the contribution of CSPANs to the development of CYP-induced cystitis.Plasma protein extravasation involves activation of tachykinin NKI and bradykinin B2 receptors.Activation of CSPANs in the urinary bladder is likely to be due to the conversion of CYP into its active metabolite, acrolein, and not to a direct effect of CYP upon these nerve-endings.

In vivo and in vitro pharmacology of SR 48,968, a non-peptide tachykinin NK2 receptor antagonist

The activity of SR 48,968, a novel non-peptide antagonist of tachykinin NK2 receptors was evaluated in vitro in several bioassays for the NK2 receptor (rabbit pulmonary artery, rabbit bronchus, hamster trachea, rat vas deferens) and compared to that of the peptide antagonists, MEN 10,376, L 659,877 and MDL 29,913. SR 48,968 behaved as a potent and competitive antagonist in the four isolated preparations (pA2 values between 8.3 and 9.6 in different preparations), being more potent (about 10 times) in the rabbit pulmonary artery and rabbit bronchus than in the hamster trachea or rat vas deferens. The antagonistic profile of SR 48,968 resembled that of MEN 10,376, and contrasted with those of L 659,877 and MDL 29,913 which were distinctly more potent on the hamster trachea and rat vas deferens. In vivo, SR 48,968 (0.1 mumol/kg i.v.) blocked the contraction of rat urinary bladder stimulated by [beta Ala8]neurokinin A-(4-10) (NK2 receptor agonist) without affecting that produced by [Sar9]substance P sulfone (NK1 receptor agonist). The hypotension and salivary secretion produced by the latter agonist were not modified by SR 48,968. In contrast, (+/-)-CP 96,345 (10 mumol/kg i.v.) blocked bladder contraction, salivary secretion and hypotensive responses elicited by the NK1 receptor agonist while leaving unaffected the bladder contraction produced by the NK2 receptor agonist. SR 48,968 is a potent and competitive antagonist of the tachykinin NK2 receptor with a limited but distinct ability to discriminate between putative subtypes/species variants of the NK2 receptor. The high potency and selectivity of SR 48,968 make this novel compound an important tool for studying the distribution and function of tachykinin NK2 receptors.

A comparison of capsazepine and ruthenium red as capsaicin antagonists in the rat isolated urinary bladder and vas deferens

1. The ability of capsazepine, a recently developed capsaicin receptor antagonist, to prevent the effects of capsaicin on the rat isolated urinary bladder (contraction) and vas deferens (inhibition of electrically-evoked twitches) was compared to that of ruthenium red, a dye which behaves as a functional antagonist of capsaicin. 2. In the rat bladder, capsazepine (3-30 microM) produced a concentration-dependent rightward shift of the curve to capsaicin without any significant depression of the maximal response to the agonist. By contrast, ruthenium red (10-30 microM) produced a non-competitive type of antagonism, characterized by marked depression of the maximal response attainable. Similar findings were obtained in the rat isolated vas deferens in which capsazepine (10 microM) produced a rightward shift of the curve to capsaicin while ruthenium red (3 microM) depressed the maximal response to the agonist. 3. At the concentrations used to block the effect of capsaicin, neither capsazepine nor ruthenium red affected the contractile response of the rat urinary bladder produced by either neurokinin A or electrical field stimulation or the twitch inhibition produced by rat alpha-calcitonin gene-related peptide (alpha CGRP) in the vas deferens. 4. These findings provide additional evidence that both capsazepine and ruthenium red are valuable tools for exploration of the function of capsaicin-sensitive primary afferent neurones. The antagonism of the action of capsaicin by capsazepine is entirely consistent with the proposed interaction of this substance with a vanilloid receptor located on primary afferents, while the action of ruthenium red apparently involves a more complex, non-competitive antagonism.

A pharmacological study of NK1 and NK2 tachykinin receptor characteristics in the rat isolated urinary bladder

1. We have estimated potencies of tachykinin receptor agonist and antagonist analogues in order to determine the recognition characteristics of tachykinin receptors mediating phasic contractile responses of the rat isolated urinary bladder in vitro. 2. The NK1-selective synthetic agonists, substance P methyl ester and GR73632, the synthetic NK2-selective agonists [beta-Ala8]-NKA(4-10) and GR64349, and the mammalian tachykinins, neurokinin A and neurokinin B, were assayed relative to substance P and were found to be approximately equipotent. The NK3-selective agonist, senktide, was inactive (10 microM). 3. Potencies of all these agonists were not significantly different (P > 0.05) when experiments were carried out in the presence of the neutral endopeptidase inhibitor, phosphoramidon, and the kininase II inhibitor, enalaprilat (both 1 microM). 4. The NK1-selective antagonist, GR82334, inhibited responses to substance P methyl ester in a competitive manner in the rat urinary bladder and the rat ileum, and also in the guinea-pig ileum. Markedly different pKB estimates were obtained in the rat bladder (6.38) and rat ileum (6.56) compared to the guinea-pig ileum (7.42). GR82334 (3 microM) was inactive against responses of the rat bladder to [beta-Ala8]-NKA(4-10). 5. The NK1-selective antagonist (+/-)-CP-96,345 also inhibited responses of the rat bladder and guinea-pig ileum to substance P methyl ester; however, in the rat bladder at 1 microM, this antagonist reversibly inhibited responses both to the NK2-selective agonist [beta-Ala8]-NKA(4-10) and to the muscarinic agonist carbachol (P < or = 0.01), thus showing evidence of some non-selective depressant actions. 6. The NK2-selective antagonists, MEN10207 and L-659,874, competitively inhibited responses of the rat bladder to the NK2-selective agonist [P-Ala5]-NKA(4-10) giving pKB estimates of 5.75 and 6.68,respectively. Both antagonists (1O microM) were inactive against responses to the NKI-selective agonist substance P methyl ester.7. These results support the proposal of a mixed population of NKI and NK2 receptors mediating contraction of the rat isolated urinary bladder. The NK2 receptor is characterized by a relatively low affinity for the NK2-selective antagonist MEN10207 but a high affinity for L-659,874. The NKImediated responses are inhibited by (+/-)-CP-96,345: this compound however, has non-specific depressant effects in the rat bladder at high concentration (1 microM). In contrast, the NK,-receptor peptide antagonist GR82334, did not have non-specific depressant effects and competitively inhibited NK, responses in the rat bladder and rat ileum with an affinity significantly lower than at the NK,-receptors in the guinea-pigileum.

Tachykininergic transmission to the circular muscle of the guinea-pig ileum: evidence for the involvement of NK2 receptors

1. The effect of newly developed, receptor-selective tachykinin antagonists (GR 71,251 for NK1 receptors, MEN 10,376 and L 659,877 for NK2 receptors) on noncholinergic transmission to the circular muscle of the guinea-pig ileum has been investigated. 2. In circular muscle strips of the ileum, electrical field stimulation in the presence of atropine (2 microM) and apamin (0.1 microM) evoked a complex motor response. The tonic primary contraction in this response was reduced by GR 71,251 (10 microM) and MEN 10,376 (3-10 microM) but not by L 659,877 (up to 10 microM). The presence of apamin was necessary in this experimental arrangement to unmask an atropine-resistant primary contraction, sensitive to tachykinin antagonists. The motor response was abolished by tetrodotoxin. 3. In circular strips of the ileum GR 71,251 (10 microM) inhibited the tonic contraction produced by [Sar9] substance P sulphone, a selective NK1 receptor agonist but not that produced by [beta Ala8] neurokinin A (4-10), a selective NK2 receptor agonist. By contrast, MEN 10,376 antagonized the effect of the NK2 agonist while leaving the response to the NK1 agonist unaffected. 4. In whole segments of the ileum, distension of the gut wall by an intraluminal balloon placed at about 1 cm from the point of recording of mechanical activity of the circular muscle produced atropine-sensitive phasic contractions (ascending enteric reflex). In the presence of atropine (2 microM), a noncholinergic response was elicited, which required larger volumes of distension that the cholinergic one. The atropine-resistant ascending enteric reflex was enhanced by apamin (0.1 microM) and abolished by tetrodotoxin, either in the presence or absence of apamin.5. MEN 10,376 (3-lOmicroM) inhibited the atropine-resistant ascending enteric reflex in the presence of apamin while GR 71,251 or L 659,877 (10 microM each) were ineffective. MEN 10,376 inhibited the atropine-resistant ascending enteric reflex to a larger extent in the absence than in the presence of apamin and also slightly inhibited the ascending enteric reflex in the absence of atropine.6. These findings provide evidence for an involvement of NK2 tachykinin receptors in excitatory transmission to the circular muscle of the guinea-pig ileum. NK2 receptors are also involved in the physiological-like circular muscle activation produced by stimulation of intramural neuronal pathways which subserve the atropine-resistant ascending enteric reflex.