Calcitonin gene-related peptide in the regulation of urinary tract motility

Rat urinary bladder-derived relaxant factor: studies on its nature and release by coaxial bioassay system

The present study was designed to characterize the urinary bladder-derived relaxant factor that was demonstrated by acetylcholine-induced relaxation response in a coaxial bioassay system consisting of rat bladder as the donor organ and rat anococcygeus muscle as the assay tissue. The concentration-dependent relaxation to acetylcholine (10 nM-1 mM) was inhibited by atropine but was not altered by the antagonists of calcitonin gene-related peptide (CGRP 8-37), vasoactive intestinal peptide (VIP 6-28), tachykinin NK1 (L-732138), tachykinin NK2 (MEN-10376), tachykinin NK3 (SB-218795), purinergic P2 (PPADS) and adenosine (CGS 15943) receptors as well as alpha-chymotrypsin. Adenylate cyclase inhibitor SQ-22536 and protein kinase A inhibitor KT-5720 significantly inhibited the acetylcholine response while guanylate cyclase inhibitor ODQ, and protein kinase C inhibitor H-7 did not have any effect. The P2X agonist alpha,beta-methylene ATP (10 nM-0.1 mM) also produced concentration-dependent relaxation response that was inhibited by PPADS, SQ-22536 and KT-5720 in the coaxial bioassay system. In bladder strips, acetylcholine and alpha,beta-methylene ATP elicited concentration-dependent contractions that were not altered in the presence of SQ-22536 and KT-5720. In conclusion, the urinary bladder-derived relaxant factor that was recognized by the coaxial bioassay system is neither a peptide of the bladder neurons nor a purinergic mediator but adenylate cyclase and protein kinase A are involved in its release and/or relaxant effect. Furthermore, activation of purinergic P2X receptors besides the muscarinic receptors leads to the release of this factor.

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

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

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.

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.

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.

Characterization of small intestinal submucosa regenerated canine detrusor: assessment of reinnervation, in vitro compliance and contractility

PURPOSE

We characterized small intestinal submucosa regenerated canine bladder.

MATERIALS AND METHODS

We subjected 15-month small intestinal submucosa regenerated canine bladder strips to in vitro muscle bath compliance, contractility testing and immunohistochemical staining.

RESULTS

Compliance studies demonstrated no significant difference between small intestinal submucosa regenerated and control bladders, which were 30-fold more compliant than native small intestinal submucosal graft material. Contractility studies demonstrated contractile responses and innervation similar to those of normal canine bladder. Afferent nerves were demonstrated through immunohistochemical techniques.

CONCLUSIONS

These characteristics further support the regenerative capacity of small intestinal submucosa and its potential use as a bladder augmentation material.

Effect of exercise and 2-deoxyglucose on the K+ channel opener action of CGRP in the guinea pig ureter

1. In the guinea pig isolated ureter, a maximally effective concentration of calcitonin gene-related peptide (CGRP, 0.1 microM) produced a prompt and transient suppression of myogenic phasic contractions (twitches) evoked by direct excitation (electrical field stimulation, EFS) of the smooth muscle. This suppressant effect is prevented by glibenclamide (1 and 10 microM), indicating the importance of K+ channel activation in its genesis. In the presence of either 1 or 10 microM glibenclamide, CGRP produced a partial (about 30%) and delayed inhibition of the evoked response, but failed to produce a full suppression of twitches. 2. The intensity and duration of the early, glibenclamide-sensitive suppressant effect of CGRP were inversely related to the frequency at which the ureters were driven by EFS. The glibenclamide-resistant inhibitory effect of CGRP was unaffected by changes in the EFS driving frequency, and cromakalim (3 microM) suppressed twitches independently of the EFS driving frequency. 3. Replacement of 80% glucose in the Krebs solution with 2-deoxyglucose (2-DOG) reduced the amplitude of the EFS-evoked twitches. In the presence of 2-DOG the inhibitory effect of CGRP was enhanced and prolonged when tested in the absence, but not in the presence, of glibenclamide. 2-DOG counteracted the inhibitory effect produced by increasing the EFS driving frequency on the response to CGRP. 4. In sucrose gap, both CGRP (0.1 microM) and cromakalim (3 microM) produced prompt hyperpolarization of the membrane. During continued superfusion for 15 min in unstimulated preparations, the hyperpolarizing effect of cromakalim and CGRP was sustained. When tested within 3 min from the end of 'exercise', induced by application of EFS at intervals of 15 sec for 30 min, the hyperpolarization by CGRP was reduced and shortened but that produced by cromakalim was unaffected. 5. These findings demonstrate that exercise and metabolic inhibition selectively influence, in opposite directions, the K+ channel opener action of CGRP in the guinea pig ureter, indicating that the ability of this neuropeptide to suppress latent pacemakers in smooth muscle is markedly dependent upon degree/frequency of cell activation. These results suggest that the ability of endogenous CGRP to suppress ureteral motility may be inversely related to the frequency of ureteral peristalsis, the effect being reduced by, for example, increase in diuresis.

CGRP inhibition of electromechanical coupling in the guinea-pig isolated renal pelvis

We aimed at studying the mechanism(s) of the inhibitory effect exerted by calcitonin gene-related peptide (CGRP) on the spontaneous activity of the guinea-pig isolated renal pelvis. In organ bath experiments, CGRP (1-100 nM) produced a concentration-dependent (EC50 8 nM) partial inhibition (Emax about 35% inhibition of motility index) of spontaneous contractions. The potassium (K) channel opener, cromakalim (3-10 microM) promptly suppressed the spontaneous contractions in a glibenclamide-(10 microM) sensitive manner. Glibenclamide (10 microM) did not affect the inhibitory action of CGRP. The calcium (Ca) channel agonist, Bay K 8644 (1 microM), markedly enhanced the spontaneous activity of the renal pelvis and reduced the inhibitory effect of CGRP. The protein kinase A inhibitors Rp-cAMPS (300 microM), H8 (100 microM) and H89 (10 microM), and the blockers of intracellular Ca handling by sarcoplasmic reticulum, ryanodine (100 microM) and thapsigargin (1 microM) did not affect the response to CGRP. The response to CGRP was likewise unaffected by the nitric oxide synthase inhibitor, L-nitroarginine (30 microM) and by the protein kinase G inhibitor, KT5823 (3 microM). Furthermore, the inhibitory action of CGRP was not modified by lowering the extracellular concentration of K (from 5.9 to 1.2 mM) nor by increasing (from 2.5 to 3.75 mM) or decreasing (from 2.5 to 0.25 mM) the extracellular Ca concentration. Replacement of 80% glucose with 2-deoxyglucose (2-DOG) reduced the amplitude of spontaneous contractions, both in the absence and presence of 10 microM glibenclamide. In the presence of 2-DOG, the inhibitory action of CGRP was enhanced at a similar extent, either in the absence or presence of glibenclamide. In sucrose gap, the effect of CGRP (0.1 microM for 5 min) was separately analyzed in the proximal (close to the kidney) and distal (close to the ureter) regions of the renal pelvis. Both preparations discharged spontaneous (pacemaker) action potentials having different shape, duration and frequently. CGRP had no effect on pacemaker potentials in the proximal renal pelvis while producing about 30% reduction of the frequency of pacemaker potentials and motility index in the distal renal pelvis. Cromakalim (3 microM) abolished pacemaker potentials in both regions of the renal pelvis. In conjunction with the results of previous studies in the guinea-pig ureter, the present findings document the existence of remarkable regional differences in the effector mechanisms initiated by CGRP receptor occupancy in the guinea-pig pyeloureteral tract. CGRP appears to be inherently unable to activate glibenclamide-sensitive K channels in the guinea-pig renal pelvis, a mechanism which is central for its ability to suppress latent pacemakers in the ureter. Within the renal pelvis, the sensitivity to the inhibitory effect of CGRP appears in the more distal region, from which an 'ureter-like' action potential is recorded.

Role of cyclic AMP and protein kinase A in K+ channel activation by calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

1. The aim of this study was to assess whether agents that interfere with the intracellular actions of cAMP and activation of protein kinase A (PKA) prevent the inhibitory action of human alpha-calcitonin gene-related peptide (CGRP) in the guinea-pig ureter smooth muscle. The action of CGRP was compared to that of the K+ channel opener, cromakalim, and the adenylyl cyclase activator, forskolin, toward electrical field stimulation- (EFS) induced myogenic twitch contractions of the ureter. To further verify the role of cAMP in the action of CGRP, we also studied the effect of stable cAMP analogues and of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). 2. Maximally effective concentrations of CGRP (0.1 microM) or forskolin (10 microM) produced a transient suppression of twitches. Cromakalim (3 microM) likewise produced a prompt suppression of twitches that in most cases exceeded 15 min. The early suppressant effect of CGRP or forskolin was inhibited by 1 or 10 microM glibenclamide; about 30% of the effect of CGRP was glibenclamide-resistant. The effect of cromakalim was totally suppressed by glibenclamide. 3. The inhibitory effect of CGRP was concentration-dependently reduced by low concentrations of barium chloride (IC50 63 microM), which blocked with similar potency the inhibitory action of cromakalim (IC50 60 microM). Glibenclamide (10 nM-10 microM) concentration-dependently inhibited the effect of CGRP and cromakalim with IC50S of 0.13 and 0.72 microM, respectively. 4. The cAMP analogues dibutyrye-cAMP (1-3 mM), 8-(4-chlorophenylthio)cAMP (0.3-1 mM) and Sp-cAMP monophosphothioate (0.1-0.3 mM) were either ineffective or poorly effective in inhibiting twitches. The cGMP analog, 8Br-cGMP (100-300 microM) produced a slowly developing, glibenclamide (1 microM)-resistant partial inhibition (25-30%) of twitches. 5. IBMX (1-300 microM) produced a concentration-dependent inhibition of twitches (EC50 16 microM). IBMX (100 microM) produced a large (peak 91%) and transient inhibition: glibenclamide (1 microM) blocked the early peak of the inhibitory action of IBMX, similar to the effect observed toward CGRP and forskolin.

Physiological effects in vitro of calcitonin gene-related peptide on gubernacular contractility with or without denervation

The gubernaculum in neonatal rats has been shown previously by direct observation to contract rhythmically in response to exogenous calcitonin gene-related peptide (CGRP), but the physiological properties of these contractions were unknown. In the first study the authors investigated gubernacular contractility in vitro using a strain gauge to see if there were characteristics of skeletal or smooth muscle. Both the frequency and the amplitude of contractions were significantly enhanced by CGRP, and isotonic tension of the gubernaculum and the duration of contractions were also increased after CGRP. The effect of CGRP on gubernacular contractions appeared several minutes after adding CGRP, and it was independent of the acetylcholine action, which induced only a single twitch response of the gubernaculum. In the second study the authors investigated the effect on gubernacular contractility of prior transection of the genitofemoral nerve (GFN), which contains CGRP. Vigorous contractions occurred in 85% of denervated gubernacular compared with 46% of controls (P < .01). These data provide the first quantitative evidence of rhythmic gubernacular contractions, and suggest that CGRP enhances gubernacular contractility by a direct effect independent of acetylcholine. Further, the contractile properties resemble those of differentiated cardiac muscle or primitive embryonic skeletal muscle. GFN transection enhances the gubernacular contractile response to exogenous CGRP, which is consistent with the GFN being the normal source of CGRP for the gubernaculum in vivo.

A pharmacological analysis of calcium channels involved in phasic and tonic responses of the guinea-pig ureter to high potassium

1. Previous studies have established a marked difference in sensitivity to organic calcium channel blockers of the phasic compared with tonic component of the contraction to potassium chloride (KCl) in the guinea-pig ureter. The mechanisms responsible for this difference have remained unsettled. In particular, the possible involvement of non-L-type calcium channels in contractility of the ureter has not been determined. In this study we have re-addressed this problem and, to eliminate any possible contribution of sensory neuropeptides released by KCl from peripheral endings of afferent nerves, all experiments were performed in ureters pre-exposed to the sensory neurone blocking agent, capsaicin (10 microM for 15 min). 2. Increasing concentrations of KCl (10-160 mM) produced phasic and tonic contractions of the guinea-pig isolated ureter: the L-type calcium channel agonist, Bay K 8644 (1 microM), enhanced both components of the contraction to KCl. 3. Nifedipine (1 microM) abolished all responses to increasing concentrations of KCl after 60 min contact time; after a shorter incubation period (15 min), the phasic contractions to low KCl concentrations were still observed, while the tonic responses were abolished. 4. The effects of nifedipine (0.1 nM-1 microM) on the phasic and tonic components of the response to 80 nM KCl were assessed after 15-120 min contact time. Nifedipine was equipotent in inhibiting the tonic response at all times tested, while a marked time-dependency of inhibition toward phasic responses was observed. After 15 min contact time, nifedipine was 181 times more potent in inhibiting tonic than phasic response to KCl, while after 120 min contact time the difference between EC50 values was only 5.4 times. 5. Cadmium chloride (3-30 microM) was equi-effective in inhibiting the phasic and tonic responses to KCl while nickel chloride was ineffective at 10-fold higher concentrations. omega-Conotoxin (0.1 microM) and tetrodotoxin (0.3 microM) were ineffective. 6. The present findings indicate that L-type voltage-dependent calcium channels mediate both phasic and tonic components of the response of the guinea-pig ureter to KCl while neither T-type nor N-type voltage-dependent calcium channels are involved. The marked time-dependency of inhibitory action of nifedipine suggests that L-type voltage-dependent calcium channels which are responsible for the generation of phasic contraction of the ureter are in a low affinity state for interaction with nifedipine.

Propagation of impulses in the guinea-pig ureter and its blockade by calcitonin gene-related peptide (CGRP)

The guinea-pig ureter was placed in a three-compartment organ bath to enable the application of electrical stimuli or drugs to its renal end (R-site), the middle region (M-site) or the bladder end (B-site) while recording mechanical activity at the R- and B-sites. All experiments were performed in ureters pre-exposed to capsaicin (10 microM for 15 min) to prevent the release of sensory neuropeptides from afferent nerves. Electrical field stimulation (EFS, 5-25 ms pulse width, 20 V) produced a phasic contraction at the site of stimulation ('direct' response to EFS) which propagated to the other end of the ureter. Section of the ureter at the M-site abolished the propagated response to EFS; after section, EFS applied at the M-site induced a phasic contraction at both the R- and B-sites. Likewise, the application of KCl at the M-site produced phasic contractions at both the R- and B-sites. Tetrodotoxin (1 microM), nifedipine (1 microM) or Bay K 8644 (1 microM) applied at the M-site had no influence on the direct or propagated responses to EFS; nifedipine (10 microM) applied at the M-site abolished the propagated responses without affecting the direct responses to EFS. Bay K 8644 (1 microM) applied at the R-site produced a marked enhancement of the direct response (EFS applied at R-site) while having no effect on the amplitude of the propagated response to EFS.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory transmitter action of calcitonin gene-related peptide in guinea-pig ureter via activation of glibenclamide-sensitive K channels

1. In single sucrose gap, electrical field stimulation (EFS, 1-5 Hz) produced graded hyperpolarization of the membrane of the guinea-pig ureter smooth muscle, which was blocked by tetrodotoxin (0.3 microM) or in vitro capsaicin desensitization (3 microM for 15 min). Capsaicin itself produced a transient hyperpolarization of the membrane on its first application. 2. Superfusion with human alpha calcitonin gene-related peptide (CGRP, 30-300 mM) likewise produced a transient hyperpolarization of the membrane, mimicking the neurogenic inhibitory junction potential (i.j.p.). The hyperpolarization by CGRP was unaffected by tetrodotoxin, indicating a postjunctional site of action. 3. Both the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization were inhibited by the CGRP receptor antagonist, CGRP(8-37) (0.3-3 microM) which did not affect the hyperpolarization produced by the KATP channel opener, cromakalim (0.3 microM). 4. The KATP channel blocker, glibenclamide (1 microM) blocked both the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization. 5. When evoked in a low K medium (1.2 mM, KCl being replaced by an equimolar amount of NaCl), the EFS-evoked i.j.p. and the CGRP-induced hyperpolarization were both markedly enhanced, consistent with the idea that opening of K channels underlies both responses. 6. The present findings provide direct electrophysiological evidence for a neurotransmitter role of CGRP, released from the peripheral endings of capsaicin-sensitive primary afferent neurones, in the guinea-pig ureter. The action of both exogenous and endogenous CGRP involves the activation of glibenclamide-sensitive (KATP) potassium channels.

Calcitonin gene-related peptide (CGRP) regulates excitability and refractory period of the guinea pig ureter

Previous studies have indicated that calcitonin gene-related peptide (CGRP), released from the peripheral endings of capsaicin-sensitive primary afferent neurons, may play a role as an inhibitory transmitter in the guinea pig ureter. The aim of this study was to compare the effect of capsaicin desensitization and administration of a CGRP receptor antagonist on the excitability and refractory period of the guinea pig ureter to electrical field stimulation. Electrical field stimulation using a long (5 msec.) pulse width produced phasic contractions of the ureter which were unaffected by tetrodotoxin, that is, were produced through direct excitation of ureteral smooth muscle. Human alpha CGRP (1 to 10 nM.) produced a concentration-dependent transient suppression of the evoked contractions, and its effect was prevented by the CGRP receptor antagonist human alpha CGRP(8-37) (1 microM.). In vitro capsaicin pretreatment (10 microM. for 15 minutes) to block neuropeptide release from peripheral endings of sensory nerves or administration of the CGRP receptor antagonist enhanced the responsiveness of the guinea pig ureter to electrical stimulation. In control ureters, the application of two trains of electrical stimuli failed to produce a second contraction at intertrain intervals greater than 20 seconds. The intertrain interval required to obtain a second contraction averaging 50% of the amplitude of the first response (ITI50) of control ureters was about 50 seconds. In vitro capsaicin pretreatment or administration of the CGRP receptor antagonist reduced the refractory period of the ureter to electrical field stimulation: ITI50 averaged 8.8 and 9.1 seconds after capsaicin or CGRP antagonist pretreatment, respectively. These findings demonstrate that capsaicin pretreatment or blockade of CGRP receptors produced qualitatively and quantitatively similar excitatory effects on ureteral excitability and refractory period and are in general agreement with the idea that CGRP is a primary inhibitory transmitter in guinea pig ureter. Inhibition of motility by CGRP could be important for setting the frequency of ureteral peristalsis and suppression of latent pacemakers to prevent the occurrence of antiperistaltic waves.

A thiorphan-sensitive mechanism regulates the action of both exogenous and endogenous calcitonin gene-related peptide (CGRP) in the guinea-pig ureter

The aim of this study was to assess the existence of mechanisms regulating the intensity and duration of action of calcitonin gene-related peptide (CGRP), the main candidate inhibitory transmitter released from capsaicin-sensitive afferents in the guinea-pig ureter. In a first series of experiments, performed in capsaicin-pretreated ureters, exogenously administered human alpha CGRP (h alpha CGRP) produced inhibition of contractions of the guinea-pig isolated ureter evoked by direct electrical stimulation of smooth muscle. The intensity and duration of the inhibitory effect of h alpha CGRP were potentiated by the inhibitor of neutral endopeptidase, thiorphan, while captopril and bestatin were without effect. In a second series of experiments, background motility of the guinea-pig ureter was evoked by administration of endothelin-1 (ET-1): electrical stimulation of intramural nerves produced a transient suppression of the ET-1-evoked contractions, ascribable to release of endogenous CGRP. Thiorphan enhanced the inhibitory effect produced by endogenous CGRP, while bestatin and captopril were without effect. These findings demonstrate that a thiorphan-sensitive mechanism, presumably neutral endopeptidase, regulates the intensity and duration of the inhibitory activity of both exogenous and endogenous CGRP in the guinea-pig ureter. The existence of a mechanisms for inactivation of the released peptide is consistent with the proposed role of CGRP as inhibitory neurotransmitter in this preparation.

Effect of bradykinin and tachykinin receptor antagonist on xylene-induced cystitis in rats

The effects of the bradykinin receptor selective antagonist, Hoe 140, and of the tachykinin NK-1 receptor antagonist (+/-)CP 96,345 were investigated in a rat model of chemically-induced cystitis (intravesical instillation of xylene in female rats). Intravenous injection of bradykinin (1 mumol./kg.) or substance P (3 nmol./kg.) produced plasma protein extravasation (PPE) in the rat urinary bladder. Bradykinin response was prevented by Hoe 140 (100 nmol./kg. intravenously) and unaffected by (+/-)CP 96,345 (10 mumol./kg. intravenously). Plasma protein extravasation produced by substance P was inhibited by (+/-)CP 96,345 but unchanged by Hoe 140. Catheterization required for intravesical xylene instillation into the female rat bladder produced per se an inflammatory response which was abolished by either Hoe 140 or (+/-)CP 96,345. Intravesical instillation of xylene produced a large PPE response which was reduced by about 65% by Hoe 140 or (+/-)CP 96,345. Combined administration of the two antagonists produced an additive effect on the PPE response to xylene. We conclude that both bradykinin and tachykinins are involved in the inflammatory reaction of the rat urinary bladder to catheterization and xylene irritation.

Cyclophosphamide-induced cystitis in rats: involvement of capsaicin-sensitive primary afferents

The involvement of capsaicin-sensitive primary afferent neurons has been investigated in a rat model of cyclophosphamide (CYP)-induced cystitis. CYP (150 mg/kg i.p., 48 h before) was administered in both vehicle- and capsaicin-(50 mg/kg s.c., 4 days before)-treated rats. Some experiments were performed 96 h after bilateral removal of pelvic ganglia (bladder denervation). CYP produced a marked detrusor hyperreflexia which was abolished by capsaicin pretreatment. CYP produced a marked increase in bladder weight and plasma protein extravasation (PPE, measured by Evans blue leakage technique): CYP-induced PPE was reduced by bladder denervation and was aggravated by capsaicin pretreatment. PPE aggravation by capsaicin was abolished by ganglionectomy. The bladder content of calcitonin gene-related peptide, was unaffected CYP. We conclude that CYP-induced decrease in bladder capacity is entirely mediated through stimulation of capsaicin-sensitive bladder afferents. At the time chosen as end point in these experiments, capsaicin-sensitive afferents exert an antiinflammatory influence on CYP-induced cystitis.