A comparison of the distribution of substance P and calcitonin gene-related peptide receptors in the rat bladder

Role of neurogenic inflammation in local communication in the visceral mucosa

Intense research has focused on the involvement of the nervous system in regard to cellular mechanisms underlying neurogenic inflammation in the pelvic viscera. Evidence supports the neural release of inflammatory factors, trophic factors, and neuropeptides in the initiation of inflammation. However, more recently, non-neuronal cells including epithelia, endothelial, mast cells, and paraneurons are likely important participants in nervous system functions. For example, the urinary bladder urothelial cells are emerging as key elements in the detection and transmission of both physiological and nociceptive stimuli in the lower urinary tract. There is mounting evidence that these cells are involved in sensory mechanisms and can release mediators. Further, localization of afferent nerves next to the urothelium suggests these cells may be targets for transmitters released from bladder nerves and that chemicals released by urothelial cells may alter afferent excitability. Modifications of this type of communication in a number of pathological conditions can result in altered release of epithelial-derived mediators, which can activate local sensory nerves. Taken together, these and other findings highlighted in this review suggest that neurogenic inflammation involves complex anatomical and physiological interactions among a number of cell types in the bladder wall. The specific factors and pathways that mediate inflammatory responses in both acute and chronic conditions are not well understood and need to be further examined. Elucidation of mechanisms impacting on these pathways may provide insights into the pathology of various types of disorders involving the pelvic viscera.

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.

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.

Increased expression of substance P receptor-encoding mRNA in bladder biopsies from patients with interstitial cystitis

OBJECTIVES

To determine whether substance P (SP, also known as neurokinin 1, NK1) receptors are differentially expressed in bladder biopsies from patients with interstitial cystitis (IC) compared with matched controls.

MATERIALS AND METHODS

Cold-cup biopsies were taken during routine diagnostic cystoscopy. NK1-receptor expression was assessed using a quantitative analysis of NK1-receptor-encoding mRNA in bladder biopsies from patients and controls using in situ hybridization histochemistry (ISHH) combined with autoradiographic image analysis.

RESULTS

Autoradiographic signal indicating the presence of NK1-encoding mRNA was localized to detrusor muscle, urothelium and vascular structures. In the bladder vasculature, the signal was predominantly associated with endothelial cells. NK1 receptor-encoding mRNA within the vascular endothelium was increased in the biopsies obtained from patients with IC.

CONCLUSION

Increased levels of NK1 receptor-encoding mRNA within the bladder vascular endothelium suggests the up-regulation of NK1 receptor as a putative factor in the pathogenesis of pain related to IC. Increased responsiveness to SP released from the perivascular sensory terminals may result in a local cascade of neurogenic inflammatory responses which trigger the pathophysiological changes, including pain, characteristic of IC.

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.

ATP is released from rabbit urinary bladder epithelial cells by hydrostatic pressure changes--a possible sensory mechanism?

1. The responses of rabbit urinary bladder to hydrostatic pressure changes and to electrical stimulation have been investigated using both the Ussing chamber and a superfusion apparatus. These experiments enabled us to monitor changes in both ionic transport across the tissue and cellular ATP release from it. 2. The urinary bladder of the rabbit maintains an electrical potential difference across its wall as a result largely of active sodium transport from the urinary (mucosal) to the serosal surface. 3. Small hydrostatic pressure differences produced by removal of bathing fluid from one side of the tissue caused reproducible changes in both potential difference and short-circuit current. The magnitude of these changes increases as the volume of fluid removed increases. 3. Amiloride on the mucosal (urinary), but not the serosal, surface of the membrane reduces the transepithelial potential difference and short-circuit current with an IC50 of 300 nM. Amiloride reduces the size of, but does not abolish, transepithelial potential changes caused by alterations in hydrostatic pressure. 4. Field electrical stimulation of strips of bladder tissue produces a reproducible release of ATP. Such release was demonstrated to occur largely from urothelial cells and is apparently non-vesicular as it increases in the absence of calcium and is not abolished by tetrodotoxin. 5. It is proposed that ATP is released from the urothelium as a sensory mediator for the degree of distension of the rabbit urinary bladder and other sensory modalities.

Effect of capsaicin on distribution of binding sites for tachykinins and calcitonin gene-related peptide in rat urinary bladder: a quantitative autoradiographic study

The autoradiographic localization of binding sites for [125I]BH-[Sar9,Met(O2)11]SP, [125I]NKA, and [125I]CGRP was investigated in adjacent sections of urinary bladder body, from adult rats pretreated 14 days before with capsaicin or vehicle. Location of silver grains was assessed both qualitatively and quantitatively using computerized densitometry. Dense labeling of smooth muscle was seen with both [125I]BH-[Sar9,Met(O2)11]SP ([125I]BHSar-SP) and [125I]NKA; in addition, [125I]BHSar-SP labeled submucosal blood vessels. For these radioligands, no differences were apparent between sections from capsaicin- and vehicle-pretreated rats. Specific binding of [125I]CGRP was observed over the epithelium and weakly over submucosal arterioles, but not over smooth muscle. The density of [125I]CGRP binding sites on the epithelium, but not blood vessels, was increased (p < 0.05) by 22% after chronic capsaicin pretreatment, suggesting receptor upregulation. This study demonstrates that although all three peptides are colocalized in primary afferent sensory fibers in rat urinary bladder, the receptors for these neuropeptides are located on different cell types and may be subject to different neural influences.

Substance P and calcitonin gene-related peptide in the ureter of chicken and guinea-pig: distribution, binding sites and possible functions

To elucidate the possible functional significance of sensory neuropeptides in visceral organs of mammals and birds the distribution, binding sites and the effects on ureteric peristalsis of substance P and calcitonin gene-related peptide (CGRP) were investigated in the ureter of guinea-pigs and chickens. In the guinea-pig numerous substance P and CGRP-immunoreactive fibres were located in the adventitia, smooth muscle layer, submucosa and occasionally in the epithelium. Varicose peptidergic fibres were often found on blood vessels. Binding sites for substance P were associated with blood vessels and epithelium in the following density order: venules greater than epithelium greater than arterioles. The highest density of CGRP binding sites was detected on the smooth muscle; venules and arterioles expressed moderate binding. The peristalsis frequency of the isolated ureter of the guinea-pig was increased by neurokinin A and substance P, whereas CGRP inhibited ureteric motility. In the chicken the immunoreactivity to substance P and CGRP was less pronounced. Immunoreactive fibres were found in the submucosa close to the epithelium and around ureteric ganglion cells. Correspondingly, substance P binding sites were located in the epithelium and in ureteric ganglia; however, specific CGRP binding was restricted to large blood vessels. In the chicken none of the sensory neuropeptides affected ureteric motility. Only high doses of the sensory neurotoxin capsaicin (greater than 10 microM) repeatedly produced a non-specific inhibitory effect, similar to that found in a capsaicin-desensitized guinea-pig ureter preparation. The data suggest that in the guinea-pig ureter sensory neuropeptides play a modulatory role in the regulation of ureteric motility and might have vascular and epithelial functions. In the chicken, substance P might be involved in the regulation of epithelial function and modulation of ganglionic transmission. The physiological or pathophysiological role of sensory neuropeptides and the efferent functions of afferent fibres appears to be much better developed in the guinea-pig than in the chicken.

Therapeutic potential of capsaicin-like molecules: studies in animals and humans

Capsaicin-sensitive primary afferent neurons in the peripheral nervous system are widely distributed to both the somatic and visceral territories: their inactivation following capsaicin "desensitization" is expected to produce analgesia and to be useful for a number of human diseases such as asthma, urinary incontinence, inflammatory diseases of the gut, arthritis and psoriasis. The present communication reviews the therapeutic potential of capsaicin-like drugs in the pathophysiology of the mammalian urinary bladder.

Binding sites of calcitonin gene related peptide (CGRP) to trout tissues

We localized specific binding sites for human calcitonin gene related peptide (hCGRP) in different organs of the trout using labelled human CGRP. Maximal binding was observed in gill and spleen membranes. The binding of 125I-hCGRP was time and temperature dependent. Scatchard analysis of binding data for the spleen and the gills disclosed two binding sites. The constants for the site of high affinity and low capacity (KAM-1 and Bmax (fmol/mg of proteins] were 2.9 x 10(9) for the spleen and 70 and 3.5 x 10(9) for the gill. Salmon calcitonin (sCT) inhibited the binding of 125I-hCGRP to spleen membranes with the same order of potency as hCGRP. In contrast sCT was less effective than hCGRP in suppressing the specific binding of 125I-hCGRP to gill membranes.

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

1. The possible involvement of tachykinins (TKs) in the contraction produced by capsaicin in the rat isolated urinary bladder was addressed on the hypothesis that co-release of substance P (SP) and neurokinin A (NKA) occurs from sensory nerve terminals. 2. A low concentration of SP (30 nM) produced a rapid contraction which faded to baseline within 10 min. A low concentration of NKA (10 nM) produced a slowly developing contraction which was still evident at 10 min. Capsaicin (1 microM) produced a rapid phasic response and a tonic response (late response to capsaicin). Co-administration of SP and NKA mimicked the response to capsaicin more than each TK alone. 3. Fading of the response to SP was not caused by receptor desensitization and was partially prevented by peptidase inhibitors. 4. Spantide (3 microM) selectively antagonized the SP-induced contraction while L-659,877 (3-10 microM) or MEN 10,376 (10-30 microM) which are NK2 receptor selective antagonists selectively blocked the response to NKA. Co-administration of spantide and L-659,877 inhibited the response to both SP and NKA by an amount not greater than that produced by each antagonist alone. 5. Spantide selectively reduced the peak response to capsaicin, while leaving the late response unaffected. L-659,877 (3 microM) and MEN 10,376 (10 microM) selectively inhibited the late response to capsaicin while, at higher concentrations, also reduced the peak response to capsaicin. Co-administration of spantide and L-659,877 reduced the peak response to capsaicin more than that produced by each antagonist alone. 6. Bombesin (10 nM) produced a tonic contraction similar to that induced by NKA. The response to bombesin was not affected by spantide, L-659,877 or MEN 10,376. 7 P2. purinoceptor desensitization by repeated administration of alpha,betal-methylene ATP depressed the twitch response to electrical stimulation of postganglionic nerves but did not affect the peak or the late response to capsaicin. 8. We conclude that multiple TKs are coreleased by capsaicin in the rat bladder and mediate the capsaicin-induced contraction by activating both NKI and NK2 receptors. Endogenous TK with preferential affinity for the NK, receptor (putatively SP) are selectively involved in the peak response to capsaicin while endogenous TK with preferential affinity for the NK2 receptor (putatively NKA) are selectively involved in the late response to capsaicin and partly contribute to the peak response. These findings provide pharmacological evidence for tachykinin-mediated cotransmission in the rat urinary bladder. ATP is unlikely to be involved in the efferent function of capsaicin-sensitive sensory nerves in the rat bladder.