The effects of topical capsaicin on rat urinary bladder motility in vivo

The effects of topical capsaicin on urinary bladder motility were investigated following saline-induced distension of the bladder wall in urethane-anaesthetized rats and compared to the effects of topical substance P and acetylcholine. Capsaicin and substance P produced similar excitatory effects in both quiescent and rhythmically contracting bladders, i.e., a TTX resistant tonic contraction followed by a series of rhythmic, TTX sensitive, phasic contractions. Acetylcholine, in doses equieffective in producing TTX resistant contractions was less effective than capsaicin or substance P in triggering neurogenic rhythmic contractions of bladder muscle. Atropine pretreatment prevented the neurogenic component of the excitatory effect of both capsaicin and substance P. Repeated applications of capsaicin but not of substance P led to desensitization. Bladders of animals pretreated (4 days before) with a large dose of s.c. capsaicin developed insensitivity to topical capsaicin and a larger volume of saline was required to trigger neurogenic rhythmic contractions of the detrusor muscle. These results suggest that capsaicin acts by interfering with the mechanism(s) regulating the threshold for the micturition reflex to occur.     

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.     

Evidence that toluene diisocyanate activates the efferent function of capsaicin-sensitive primary afferents

Isocyanates are an important cause of occupational asthma. The mechanism of isocyanate-induced asthma is still unknown. To determine whether toluene diisocyanate stimulates the 'efferent' function of peripheral endings of capsaicin-sensitive sensory nerves, we investigated the effect of toluene diisocyanate in the rat isolated urinary bladder, a preparation in which the action of capsaicin has been well characterized. Toluene diisocyanate (0.03-3 mM) produced a concentration-dependent contraction of the bladder strips. Its maximal effect was about 50% of the response to capsaicin (1 microM). Previous exposure of the strips to capsaicin followed by washing out produced complete unresponsiveness, both to the first exposure to toluene diisocyanate and to a second exposure of capsaicin. Further, the response to both toluene diisocyanate and capsaicin was completely prevented by extrinsic bladder denervation, achieved by bilateral removal of pelvic ganglia (72 h before). Repeated exposure of the rat bladder to toluene diisocyanate reduced the capsaicin-evoked release of calcitonin gene-related peptide-like immunoreactivity (CGRP-LI), taken as biochemical marker of activation of these sensory nerves. These experiments provide the first evidence that toluene diisocyanate activates directly or indirectly the efferent function of capsaicin-sensitive primary sensory nerves.     

The contribution of capsaicin-sensitive sensory nerves to xylene-induced visceral pain in conscious,freely moving rats

1. Intravesical instillation of xylene (10-100%, dissolved in silicone oil) through a catheter implanted into the bladder of conscious, freely-moving rats produced behavioural effects (licking of lower abdomen or perineal region) suggestive of intense visceral pain, not mimicked by topical application of the irritant on the urethral outlet. 2. The xylene-induced visceral pain was prevented, to the same extent, by systemic desensitization to capsaicin (50 mg/kg s.c.) performed in either adult or newborn rats, as well as by extrinsic bladder denervation (pelvic ganglionectomy), thus indicating the involvement of primary afferents in the bladder wall. 3. Other behavioural responses induced by xylene instillation into the bladder (hind limb hyperextension, grooming) were not affected by systemic capsaicin desensitization in either adult or newborn rats, but were abolished by bladder denervation. 4. Systemic capsaicin desensitization produced an almost complete depletion of substance P-, neurokinin A-like and calcitonin gene-related peptide-like immunoreactivity in the rat urinary bladder. 5. These findings indicate that, in addition to their role in activating reflex micturition, the neuropeptides-containing capsaicin-sensitive sensory nerves of the rat bladder are involved in chemogenic visceral pain.     

Functional evidence for the existence of a capsaicin-sensitive innervation in the rat urinary bladder

Capsaicin (0.03-3 microM) induces contractions of the rat isolated bladder which are unaffected by either atropine (3 microM) or tetrodotoxin (0.5 microM). In the presence of capsaicin (0.1 microM) an enhancement of field stimulation-induced contractions was observed. Capsaicin-desensitization did not modify the height of these. The neurogenic nature of the capsaicin-induced contractions was proved by the observation that 'chronic' (48 h) denervation prevented, while 'acute' (2 h) denervation did not modify the effect of capsaicin. Denervated bladders maintained their responsiveness to acetylcholine but not to field stimulation. Isolated bladders from rat pups (1-2 days old) did not respond to capsaicin while strong contractile responses to acetylcholine or field stimulation were obtained in these preparations. In bladders from two week old animals, capsaicin produced similar contractions to those observed in preparations from adult animals. The bladders from rats receiving a high dose of capsaicin (50 mg kg-1 s.c.) at birth were heavier than those of their age-matched, vehicle-treated controls. Isolated bladders from 2 month old animals pretreated with capsaicin at birth were unresponsive to capsaicin while responsiveness to acetylcholine, substance P or field stimulation was unaffected compared with that of vehicle-treated controls. These experiments provide evidence that a capsaicin-sensitive innervation exists in the rat urinary bladder which undergoes a postnatal development at end organ level.     

The role of the capsaicin-sensitive innervation of the rat urinary bladder in the activation of micturition reflex

Capsaicin applied on the serosal surface of the urinary bladder in urethane-anaesthetized rats produces two distinct types of motor effects: a tetrodotoxin-, hexamethonium- and lidocaine-insensitive 'tonic' contraction and a series of tetrodotoxin-, hexamethonium- and lidocaine-sensitive rhythmic contractions. Both 'tonic' and rhythmic contractions are abolished by bladder denervation indicating their neurogenic origin. The rhythmic but not the 'tonic' component of the contractile effect of capsaicin is abolished by spinal cord transection indicating activation of a supraspinal micturition reflex. The motor effects of topical capsaicin are unaffected by pretreatment with indomethacin or diphenhydramine plus cimetidine. Pretreatment with a large dose of subcutaneous (SC) capsaicin increases both volume and pressure threshold for micturition while amplitude of micturition contraction is unaffected. Moreover the spinal somatovesical reflex elicited by pinching of the perineal skin is unaffected by capsaicin-desensitization. The intracerebroventricular (ICV) administration of capsaicin reproduces the effects of SC capsaicin on the bladder response to saline filling. Rats pretreated with ICV capsaicin are as sensitive as controls in reacting to noxious heat (hot plate test) while the wiping response to instillation of capsaicin into one eye was abolished. These findings provide functional evidence for the presence in the rat urinary bladder of a capsaicin-sensitive innervation which subserves a sensory function in relaying volume/pressure information from detrusor muscle to central nervous system. Information carried through these capsaicin-sensitive fibers appears to be relevant for initiation of a supraspinal vesico-vesical micturition reflex. Functional evidence indicates that these fibers may terminate at supraspinal level.     

Vesico-inhibitory responses and capsaicin-sensitive afferents in rats

Summary (1) The effect of perineal pinching and distension of a balloon inserted into the colon on motility of the urinary bladder has been investigated in adult urethane-anesthetized rats pretreated with capsaicin (50 mg/kg s.c.) or its vehicle 4 days before the experiments. (2) At bladder volumes which were sufficient to elicit reflex micturition, perineal pinching or colonic distension transiently inhibited the ongoing bladder voiding contraction. The somato-vesical inhibitory response was markedly reduced or even abolished by division of pudendal nerves. Neither the somato-vesical nor the colovesical inhibitory response were modified by desensitization with systemically administered capsaicin. (3) Intraurethral administration of capsaicin produced a transient inhibition of the reflexly-activated bladder contractions. A second administration of the drug was less effective, indicating desensitization. Intravenously administered capsaicin had a similar inhibitory effect on bladder motility. (4) The vesico-inhibitory response produced by intraurethral administration of capsaicin was not affected by phentolamine, propranolol, guanethidine, picrotoxin or naloxone, while it was greatly reduced or even abolished by bilateral section of the pudendal nerves. (5) These findings provide evidence that capsaicin-sensitive chemoreceptors in the rat urethra are involved in generating a vesico-inhibitory response via pudendal nerves. On the other hand, no evidence was found for the participation of capsaicin-sensitive nerves in the generation of the somato- or colo-vesical inhibitory response. Send offprint requests to C. A. Maggi at the above address     

Species-related variations in the effects of capsaicin on urinary bladder functions: relation to bladder content of substance P-like immunoreactivity

Summary 1. The effect of capsaicin on bladder motility in vivo (urethane anaesthesia) and in vitro, plasma extravasation (Evans blue leakage technique) and content of substance P-like immunoreactivity (SP-LI) of the urinary bladder was investigated in various mammalian species. 2. Systemic capsaicin desensitization (rat and hamster, 50 mg/kg s.c. 4 days before; guinea-pig 55 mg/kg s. c. 4–7 days before) increased bladder capacity in rats and guinea-pigs and reduced voiding efficiency in guinea-pigs. All other urodynamic parameters were unaffected in both rats, guinea-pigs and hamsters. 3. Reflex bladder voiding was abolished by spinal cord transection in anaesthetized rats and hamsters. On the other hand, hexamethonium-(20 mg/kg i.v.)sensitive voiding contractions were obtained in response to saline filling 45 min from cord transection in guinea-pigs, indicating a profound interspecies variation in the basic organization of micturition. 4. Exposure to capsaicin (1 M) produced a contraction of the isolated bladder from rats, guinea-pigs (dome) and mice. Capsaicin produced only a slight contractile response in the guinea-pig bladder base. The motor response to capsaicin of the rat, guinea-pig and mouse bladder exhibited marked desensitization, suggesting a specific effect on sensory nerves. On the other hand, capsaicin (1 M) produced a slight relaxation of the hamster isolated bladder but this effect was reproducible at 1–2 h intervals, suggesting an unspecific effect. Capsaicin (1–10 M) did not affect motility of strips from the dome or the base of the rabbit bladder. 5. Intravenously administered capsaicin produced a marked plasma extravasation (Evans blue leakage) in the lower urinary tract of rats, mice and guinea pigs. In rats but not guinea-pigs the reaction in the bladder base was greater than in the dome. In hamsters intravenous capsaicin failed to induce any significant Evans blue leakage in the lower urinary tract. 6. SP-LI was detected in the lower urinary tract of rats, guinea-pigs, rabbits and mice but not hamsters. Bladder SP-LI was depleted by systemic capsaicin desensitization in rats, guinea-pigs and mice. Reverse phase HPLC indicated that all the immunoreactive material co-eluted with authentic substance P or its oxidized form. 7. These findings indicate that noticeable species-related differences exist with regard to the functions mediated by the Capsaicin-sensitive neurons in the urinary bladder. Send offprint requests to C. A. Maggi     

Evidence for the involvement of bradykinin in chemically-evoked cystitis in anaesthetized rats

Summary The effect of Hoe 140, a potent bradykinin B2 receptor antagonist, on the micturition reflex and detrusor hyperreflexia induced by chemical cystitis has been investigated in anaesthetized rats. Hoe 140 (1–100 nmol/kg i. v.) produced a dose-dependent blockade of the contraction of the rat urinary bladder induced by i. v. administration of bradykinin (100 nmol/kg) without affecting the response produced by the selective tachykinin NK-1 receptor agonist, [Sar⁹] substance P (SP) sulfone (1 nmol/kg i. v.). At doses which produce selective and long-lasting blockade of bradykinin receptors in the urinary bladder, Hoe 140 did not modify urodynamic parameters in normal rats.Intravesical instillation of xylene in female rats decreased bladder capacity and increased micturition frequency. These effects also occurred in rats pretreated with capsaicin as adults. Hoe 140 did not modify xylene-induced cystitis. Intraperitoneal administration of cyclophosphamide (150 mg/kg, 48 h before) decreased bladder capacity and increased micturition frequency. These effects of cyclophosphamide were abolished in rats pretreated with capsaicin as adults. Hoe 140 increased bladder capacity and decreased micturition frequency in rats pretreated with cyclophosphamide.Addition of bradykinin (10 µmol/l) to the medium in the superfused rat urinary bladder preparation evoked a prompt increase in the outflow of calcitonin gene-related peptide like immunoreactivity (CGRP-LI). Hoe 140 (3 µmol/l) inhibited (by about 50%) the CGRP-LI outflow stimulated by bradykinin.These findings demonstrate the participation of bradykinin, through 132 receptors, in the genesis of detrusor hyperreflexia during cyclophosphamide-induced cystitis. Capsaicin-sensitive primary afferent neurons are a likely target for Hoe 140 action in this model of experimental cystitis, as exemplified by its ability to prevent CGRP-LI outflow by bradykinin.Correspondence to C. A. Maggi at the above address     

Visceromotor responses to calcitonin gene-related peptide (CGRP) in the rat lower urinary tract: evidence for a transmitter role in the capsaicin-sensitive nerves of the ureter

Either intra-arterial or topical administration of calcitonin gene-related peptide (CGRP) had little effect on motility of the urinary bladder in urethane-anaesthetized rats. Only a high concentration (50 microM) of topical CGRP activated the micturition reflex and potentiated the response to exogenous substance P (SP). In the isolated rat bladder CGRP had inconsistent effects on spontaneous or field-stimulated contractions. CGRP neither produced any significant plasma extravasation (Evans blue leakage) in the rat lower urinary tract, nor potentiated the response to exogenous SP. CGRP inhibited motility in the rat isolated proximal urethra and ureters and counteracted the contractile response to neurokinins. An inhibitory effect of capsaicin on stimulated motility of the urethra was observed in all preparations and a small contractile response was evident in about 40% of cases. Lack of desensitization to the action of CGRP prevented the study of its interaction with capsaicin. The inhibitory effect of CGRP in the ureter exhibited a specific desensitization: if the preparations were pre-exposed to exogenous CGRP, the inhibition of motility produced by antidromic activation of the capsaicin-sensitive nerve terminals (field stimulation) as well as the response to capsaicin (1 microM) was prevented but the inhibitory response to isoprenaline was unaffected. These findings indicate that CGRP is able to influence markedly the motility of the rat lower urinary tract, but exhibits marked regional differences in its action. Endogenous CGRP could be the inhibitory transmitter which, when released from capsaicin-sensitive fibers, participate in the control of ureteral motility.     

Effect of ruthenium red on responses mediated by activation of capsaicin-sensitive nerves of the rat urinary bladder

Summary (1) Topical administration of Ruthenium Red (10–100 M in saline) to the serosal surface of the urinary bladder in urethane-anesthetized rats prevented the motor response of the urinary bladder to topical administration of capsaicin and protected the sensory fibers from capsaicin desensitization, but had no effect on the volume-evoked contractions (micturition reflex). At 1 mM increased bladder capacity and decreased amplitude of micturition contraction were observed. (2) At 100 M, topical Ruthenium Red prevented the blood pressure rise produced by topical administration of capsaicin onto the bladder but did not affect the blood pressure rise produced by sudden bladder distension in spinal rats. (3) After intrathecal administration, Ruthenium Red (80–800 ng/rat) produced a long lasting inhibition of the micturition reflex in urethane-anesthetized rats, this effect being evident in both vehicleor capsaicin- (50 mg/kg s. c. 4 days before) pretreated rats. At 800 ng/rat, intrathecal Ruthenium Red did not affect the blood pressure rise produced by topical administration of capsaicin onto the rat bladder nor that produced by bladder distension. (4) These findings provide further evidence that Ruthenium Red acts quite selectively as a capsaicin antagonist preventing both reflex and efferent responses activated by peripherally administered capsaicin. By contrast, sensory impulse generation by a natural stimulus such as bladder distension is apparently unaffected by Ruthenium Red. The marked inhibition of the micturition reflex observed after intrathecal administration of Ruthenium Red does probably not involve an interaction with primary afferents in the spinal cord.     

Plasma extravasation induced by dynorphin-(1-13) in rat skin

The plasma extravasation response to dynorphin-(1-13) was investigated using the Evans blue dye leakage technique. Dynorphin induced plasma extravasation in rat and guinea-pig abdominal skin with a similar potency to substance P. In rat skin dynorphin, unlike substance P, produced its action entirely by release of histamine and 5-hydroxytryptamine since the response was abolished by pretreatment of rats with mepyramine and methysergide. Pretreatment of rats with capsaicin or the tachykinin antagonist, spantide, reduced but did not abolish the response to dynorphin, indicating that its action was not mediated primarily by a neurogenic mechanism. Since the response was not significantly reduced by naloxone it was concluded that the plasma extravasation response to dynorphin was mediated by receptors other than mu opiate receptors. Thus dynorphin, if released from sensory nerves, might play a role in neurogenic inflammation.     

Noladin ether, a putative endocannabinoid, attenuates sensory neurotransmission in the rat isolated mesenteric arterial bed via a non-CB1/CB2 G(i/o) linked receptor

1 Noladin ether has recently been reported to be an endocannabinoid, with selectivity for the cannabinoid (CB) CB1 receptor. In the present study, we investigated the effects of noladin ether in the rat isolated mesenteric arterial bed, cultured dorsal root ganglia (DRG) cells and human vanilloid (TRPV1)-receptor-expressing HEK293 cells (TRPV1-HEK293 cells). 2 Electrical field stimulation of the mesenteric bed evoked frequency-dependent vasorelaxation due to the action of calcitonin gene-related peptide (CGRP) released from sensory nerves. Noladin ether (0.1-3 microm) attenuated sensory neurogenic relaxation in a concentration-dependent manner. Noladin ether (1 microm) reduced vasorelaxation at a submaximal frequency (8 Hz), from 57.3+/-6.8 to 23.3+/-3.8% (P<0.05, n=4). 3 The inhibitory effects of noladin ether were unaffected by the CB1 antagonists SR141716A and LY320135, and the CB2 antagonist SR144528 (1 microm). 4 Noladin ether had no effect on vasorelaxation elicited by exogenous CGRP or capsaicin. These data suggest that noladin ether is acting at a prejunctional site and no interaction with TRPV1 is involved. 5 In mesenteric beds from pertussis toxin (PTX)-pretreated rats, the inhibitory actions of noladin ether on sensory neurotransmission were abolished, indicating the involvement of G(i/o) protein-coupled receptors. 6 Noladin ether evoked a concentration-dependent increase in intracellular Ca2+ concentration in TRPV1-HEK293 cells at 10 microm (36.5+/-3.2% of maximal capsaicin-induced response), but it was a less potent agonist than both capsaicin and anandamide and at 1 microm it was essentially inactive. Noladin ether (1 microm) had no effect on capsaicin-evoked Ca2+ responses in DRG cells, and produced no response alone, indicating it neither modulates nor acts directly on TRPV1 receptors. 7 These data demonstrate that noladin ether attenuates sensory neurotransmission in rat mesenteric arteries via a non-CB1 non-CB2 PTX-sensitive prejunctional site, independently of TRPV1 receptors.     

Evidence for the involvement of endogenous substance P in the motor effects of capsaicin on the rat urinary bladder

[pro4,trp7,9,Leu11]SP-(4-11), a substance P (SP) antagonist, selectively antagonized contractions produced by either capsaicin or SP on the rat isolated urinary bladder. These experiments provide direct evidence indicating that the motor effects of capsaicin on rat urinary bladder are attributable, at least in part, to the release of endogenous SP.     

The effect of calcium free medium and nifedipine on the release of substance P-like immunoreactivity and contractions induced by capsaicin in the isolated guinea-pig and rat bladder

1. Capsaicin produced a prompt release of substance P-like immunoreactivity (SP-LI) from superfused mucosa-free muscle strips excised from the guinea-pig urinary bladder. A second application of capsaicin had no further effect, indicating desensitization. 2. Neither tetrodotoxin (1 microM) or nifedipine (10 microM) had any inhibitory effect on SP-LI release by capsaicin nor influenced the establishment of the desensitized state. Nifedipine produced per se some SP-LI release. 3. SP-LI release by capsaicin was abolished by incubation in a Calcium(Ca)-free medium containing EDTA (1.0 mM) which also afforded a partial protection toward desensitization. A lower EDTA concentration (0.1 mM) did not suppress SP-LI release by capsaicin but still inhibited desensitization. 4. When the concentration of CaCl2 in the medium was lowered to 1/10-1/100 of that present in normal Krebs solution, capsaicin still evoked a marked SP-LI release and desensitization occurred. In a nominally Ca free medium (maximal Ca concentration due to impurities was 6.7 microM) SP-LI release was still observed and desensitization was incomplete. 5. In a nominally Ca free medium, removal of Mg ions enhanced the SP-LI release induced by capsaicin and enhanced desensitization. 6. In functional studies, nifedipine greatly reduced or abolished the capsaicin- or SP-induced contraction of the rat or guinea-pig isolated bladder but did not prevent desensitization. Likewise, SP-LI depletion in the rat bladder following systemic capsaicin desensitization was not prevented by nifedipine pretreatment. On the other hand, the protective action of Ca free media (containing EDTA) was confirmed in organ bath studies (guinea-pig bladder). 7. These findings indicate that: (a) the requirements of extracellular calcium for activation of neuropeptide release from sensory nerves by capsaicin are very low; (b) both excitation of sensory fibers (SP-LI release) and desensitization are dependent upon the presence of extracellular calcium and (c) L-type voltage-sensitive Ca channels are not likely to be involved in the actions of capsaicin on sensory nerve terminals.     

Capsaicin-sensitive afferents in the rat urinary bladder activate a spinal sympathetic cardiovascular reflex

Summary In urethane-anesthetized rats with an intact spinal cord, application of capsaicin on the outer surface of the urinary bladder produced a transient bradycardia, hypotension and negative cardiac inotropism which were neither prevented by i. v. atropine (0.5 mg/kg) nor by cervical vagotomy. In acute spinal rats (C2-C3) application of capsaicin (0.2 and 2 pg in 25 pl) on the urinary bladder induced a transient hypertension, tachycardia and positive cardiac inotropism. A second application (30 min later) induced minor cardiovascular effects, expecially with the higher dose, indicating desensitization. All cardiovascular responses to topical capsaicin were abolished by systemic capsaicin desensitization (50 mg/kg s. c., 4 days before). The excitatory cardiovascular response to capsaicin in acute spinal rats was markedly reduced by bilateral section of pelvic but not hypogastric nerves. Further, it was abolished by pretreatment with hexamethonium (20 mg/kg i.v.) or reserpine (5 mg/kg i. p., 2 days before) and reduced, at various extent for the different components, by phentolamine (0.5 mg/kg i. v.) or propranolol (1 mg/kg). In rats with pelvic and hypogastric nerves intact, section of the cord at a level (T12-L1), just above the medullary segments which receive primary afferent input from the bladder (L6-S1), abolished the excitatory cardiovascular response to application of capsaicin on the bladder. In spinal rats (C2-C3) rapid distension of the urinary bladder with saline produced transient tachycardia, hypertension and positive cardiac inotropism similar to that evoked by capsaicin. These responses were not observed in rats systemically pretreated with capsaicin. These findings indicate that certain bladder afferents which are susceptible to capsaicin desensitization in adult rats activate a spinal reflex having excitatory influence on cardiovascular function. This response is apparently mediated by spinal centers located above the site of entry of bladder pelvic afferents into the cord and most likely involves excitation of preganglionic sympathetic neurons in the spinal cord.Send offprint requests to S. Giuliani at the above address     

Pharmacological modulation of the contractile response to toluene diisocyanate in the rat isolated urinary bladder.

1. Toluene diisocyanate produced concentration-dependent contractions of the rat isolated urinary bladder. 2. The contractions were tetrodotoxin-resistant and were abolished by previous exposure of the strips to capsaicin. 3. Indomethacin (5 microM) and ruthenium red (30 microM) inhibited toluene diisocyanate-induced contractions. Responses expressed as a percentage of the response obtained with substance P, 30 nM, were respectively 141.6 +/- 24.8% and 20.1 +/- 5.1% in control and indomethacin-treated strips (P less than 0.005); 123.0 +/- 30.2% and 14.0 +/- 6.5% in control and ruthenium red-treated strips (0.01 less than P less than 0.05). 4. These results suggest that toluene diisocyanate-induced contractions of the rat isolated bladder are the result of the release of cyclo-oxygenase products which may act by activating the capsaicin receptor.     

Excitatory and inhibitory urinary bladder reflexes induced by stimulation of cervicovaginal capsaicin-sensitive sensory fibers in rats

We have investigated the effect of intravaginal application of capsaicin on micturition reflex in female rats. Urinary bladder contractility was measured by transurethral pressure recording at isovolumetric and subthreshold conditions in anaesthetized rats. The intravaginal application of capsaicin (15 mug/50 mul rat) induced reproducible bladder phasic contractions, without desensitization upon repeated applications, that were blocked by intravenous atropine (1 mg/kg) or hexamethonium (5 mg/kg) and prevented by removal of paracervical ganglia or systemic capsaicin pretreatment (125 mg/kg, s.c.). The inhibition of sympathetic transmission by guanethidine (30 mg/kg, s.c.) produced significant increase of the bladder reflex contractions activated by intravaginal capsaicin. Intravenous administration of the TRPV1 antagonist, capsazepine (3 mg/kg), significantly reduced the excitatory reflex response to capsaicin. Intravaginal administration of capsaicin (15 mug/50 mul), during distension-induced reflex bladder contractions, produced a transient block of reflexes, unaffected by guanethidine pretreatment. In conclusion, the stimulation of capsaicin-sensitive sensory nerve endings in the rat cervix-vagina induced a dual excitatory or inhibitory bladder response in anaesthetized female rats depending on the degree of bladder distension.     

Regional differences in the effects of capsaicin and tachykinins on motor activity and vascular permeability of the rat lower urinary tract

Summary 1. The effects of capsaicin, substance P (SP) and neurokinin A (NKA) on motor activity and vascular permeability was investigated in the rat lower urinary tract (bladder dome and neck, proximal urethra and ureters). 2. Capsaicin produced contractions of the rat bladder dome and neck and of the proximal urethra in vitro, which were unaffected by tetrodotoxin and abolished by ganglionectomy. SP and NKA were almost equipotent in producing a contraction of the rat isolated bladder dome or neck and urethra. However, the maximal response to NKA was about twice that of SP on the urethra and bladder neck. 3. Capsaicin did not affect motility of the unstimulated rat isolated ureter, while NKA or SP activated rhythmic contractions, NKA being about 850 times more potent than SP. Either capsaicin or field stimulation produced a transient inhibition of the NKA-activated rhythmic contractions of the rat isolated ureter which was prevented by capsaicin-desensitization. 4. The capsaicin-(1 M) or field stimulation-induced inhibition of NKA-activated rhythmic contractions of the rat isolated ureter were unaffected by removal of pelvic ganglia but abolished by cold storage (72 h at 4°C). 5. Intravenous capsaicin induced an inflammatory response (Evans blue leakage) in the bladder, proximal urethra and ureters in vivo. Plasma extravasation was greater in the ureters, urethra and bladder neck than in the dome. SP, NKA and histamine produced a dose-dependent dye leakage in all segments of the rat urinary tract, the response being slightly greater in the bladder neck than in the dome. 6. The capsaicin-induced inflammatory response was abolished by systemic capsaicin-desensitization and reduced, to a variable extent, by pelvic ganglionectomy, in the various tissues examined. Topical application of tetrodotoxin on the bladder dome failed to affect the capsaicin-induced plasma extravasation in the urinary bladder. 7. These findings indicate that chemoceptive, capsaicin-sensitive nerves are present throughout the whole rat lower urinary tract and their activation determines a variety of visceromotor responses and an increase of vascular permeability. In various instances the response to capsaicin may be explained by the action of tachykinins but some effects may involve other sensory neuropeptides. Send offprint requests to C. A. Maggi at the above address