The L-arginine/nitric oxide pathway in the rabbit urethral lamina propria

Functional nitrergic innervation of smooth muscle structures in the mucosa of pig lower urinary tract

Neurally released nitric oxide (NO) functions as an inhibitory neurotransmitter of urethral but not detrusor smooth muscles while relaxing bladder vasculature and muscularis mucosae (MM). Here, the distribution of nitrergic nerves was examined in the mucosa of pig lower urinary tract using immunohistochemistry, and their vasodilatory functions were studied by measuring arteriolar diameter changes. Properties of smooth muscle cells in the lamina propria (SMC-LP) of urethra and trigone were also investigated using florescence Ca²⁺ imaging. In the bladder mucosa, neuronal nitric oxide synthase (nNOS)-immunoreactive nitrergic fibres projected to suburothelial arterioles and venules. Perivascular nitrergic nerves were intermingled with but distinct from tyrosine hydroxylase (TH)-immunoreactive sympathetic or calcitonin gene-related peptide (CGRP)-immunoreactive afferent nerves. MM receive a nitrergic but not sympathetic or afferent innervation. In the mucosa of urethra and trigone, nitrergic nerves were in close apposition with sympathetic or afferent nerves around suburothelial vasculature but did not project to SMC-LP. In suburothelial arterioles of bladder and urethra, N ω-nitro-L-arginine (L-NA, 100 μM), an NOS inhibitor, enhanced electrical field stimulation (EFS)-induced sympathetic vasoconstrictions, while tadalafil (10 nM), a phosphodiesterase type 5 (PDE5) inhibitor, suppressed the vasoconstrictions. SMC-LP developed asynchronous spontaneous Ca²⁺ transients without responding to EFS. The spontaneous Ca²⁺ transients were enhanced by acetylcholine (1 μM) and diminished by noradrenaline (1 μM) but not SIN-1 (10 μM), an NO donor. In the lower urinary tract mucosa, perivascular nitrergic nerves appear to counteract the sympathetic vasoconstriction to maintain the mucosal circulation. Bladder MM but not SMC-LP receive an inhibitory nitrergic innervation.

Spontaneous photo-relaxation of urethral smooth muscle from sheep, pig and rat and its relationship with nitrergic neurotransmission

1. In the present work we have characterized the relaxant response induced by light stimulation (LS) in the lower urinary tract from sheep, pig and rat, establishing its relationship with nitrergic neurotransmission. 2. Urethral, but not detrusor, preparations showed pronounced photo-relaxation (PR) which declined progressively following repetitive LS. Sheep urethral PR was again restored either spontaneously or (to a greater extent) by exogenous nitric oxide (NO) addition and by electrical field stimulation (EFS) of intrinsic nitrergic nerves. 3. Greater NO generation was detected from sheep urethral than from detrusor homogenates following illumination. 4. Sheep urethral PR was inhibited by oxyhaemoglobin, but not by methaemoglobin, carboxy-PTIO, extracellular superoxide anion generators or superoxide dismutase. Guanylyl cyclase but not adenylyl cyclase activation mediates urethral relaxation to LS. 5. Urethral PR was more resistant to inhibition by L-thiocitrulline than EFS-induced responses, although this agent prevented PR restoration by high-frequency EFS. 6. Urethral PR was TTX insensitive and partially modified in high-K+ solutions. Cold storage for 24 h greatly impaired urethral PR, although it was restored by high-frequency EFS. 7. Repetitive exposure to LS, EFS or exogenous NO induced changes in the shape of the EFS-induced nitrergic relaxation, possibly by pre-synaptic mechanisms. 8. In conclusion, we suggest the presence of an endogenous, photo-labile, nitro-compound store in the urethra, which seems to be replenished by neural nitric oxide synthase activity, indicating a close functional relationship with the nitrergic neurotransmitter.

Presence of constitutive endothelial nitric oxide synthase immunoreactivity in urothelial cells of hamster proximal urethra

Electrical field stimulation caused frequency-dependent relaxations in precontracted strips of hamster proximal urethra, which were attenuated by L-N(G)-nitroarginine methyl ester (10(-4) M) and completely blocked by tetrodotoxin (10(-6) M). Strips of hamster urethra devoid of urothelium showed reduced relaxant responses to electrical field stimulation which were abolished by L-N(G)-nitroarginine methyl ester (10(-4) M). Western blot analysis showed the presence of a constitutive endothelial nitric oxide synthase in the urothelial layer, suggesting that urothelium may release nitric oxide in response to electrical field stimulation and that this release is blocked by tetrodotoxin. It is suggested that the urothelium may contribute to relaxations of the smooth muscle of hamster urethra produced by nerve stimulation.

The role of nitric oxide in the acetylcholine-induced relaxation of the feline internal anal sphincter, in vitro

BACKGROUND

The relaxatory effect of acetylcholine was investigated on the feline internal anal sphincter (IAS), in vitro.

RESULTS

Acetylcholine (10, 30, 100, and 1000 microM) caused a concentration-dependent relaxation of the same magnitude in strips from the proximal and distal IAS. The antagonist of nitric oxide synthase, N omega-nitro-L-arginine (L-NNA; 1, 10, and 100 microM), in a concentration-dependent and stereospecific manner, blocked the acetylcholine-induced relaxation, leaving a residual response of 10-30%. The blocking effect of L-NNA (100 microM) could not be shown in tissues that had been incubated with the substrate for nitric oxide synthase, L-arginine (1 mM).

CONCLUSIONS

The present results suggest that the acetylcholine-induced relaxation of the IAS to a major extent is due to an activation of nitrergic, inhibitory motor neurons to the IAS.

A pharmacological and histochemical study of hamster urethra and the role of urothelium

1. Electrical field stimulation (EFS) of circular strips of hamster proximal urethra caused frequency-dependent relaxations at raised tone. Phentolamine (10(-6) M), propranolol (10(-6) M) and atropine (10(-6) M) were present throughout the experiment. Neurogenic relaxation was attenuated by L-NG-nitroarginine methyl ester (L-NAME) (10(-4) M), was restored by L-arginine (3 x 10(-3) M) but not by D-arginine (3 x 10(-3) M) and completely blocked by tetrodotoxin (10(-6) M). Neurogenic relaxation was also reduced by suramin (10(-4) M) and totally blocked by suramin together with L-NAME. Strips of hamster urethra devoid of urothelium showed little, if any, relaxant response to EFS. 2. An immunohistochemical study showed nitric oxide synthase-immunoreactive nerves in the smooth muscle layers and in the lamina propria, just beneath the urothelium, but no nitric oxide synthase (NOS) staining in the urothelial layer. 3. Noradrenaline elicited a significantly greater contraction in strips without urothelium than in control strips. L-NAME (10(-4) M) did not affect noradrenaline-induced contraction in both control and urothelium-free strips. The contractile response to acetylcholine was not dependent on the presence or absence of urothelium. Nevertheless the response induced by exogenous acetylcholine (10(-3) M) was increased by L-NAME (10(-4) M), both in intact and in urothelium-free strips. 4. Prostaglandin E2 (10(-8)-5 x 10(-6) M) and 2-methyl-thio-ATP (10(-9)-10(-5) M) relaxed proximal urethra. Suramin (10(-4) M) significantly inhibited the relaxation induced by 2-methyl-thio-ATP. The amplitude of these responses was not significantly different between intact and urothelium-free strips and was not blocked by L-NAME (10(-4) M). 5. These results suggest that nitric oxide (NO) is the principal transmitter involved in the non-adrenergic, non-cholinergic (NANC) relaxation of hamster proximal urethra possibly together with another inhibitory transmitter released from nerves. NO can be released from nerves located in the circular smooth muscle layer and in the lamina propria rather than in the urothelium. The reduced neurogenic relaxation in urothelium-free preparations suggests that a NO-dependent inhibitory factor is released from the urothelium. In addition, ATP and prostaglandin E2 may be involved, together with NO, in the urethra during micturition.

Nitric oxide synthase in rat nasal mucosa; immunohistochemical and histochemical localization

The localization of nitric oxide synthase (NOS) and its cofactor, nicotinamide-adenine dinucleotide hydrogen phosphate (NADPH)-diaphorase, was examined in the nasal mucosa of the rat by immunohistochemical and histochemical methods. In addition to cryostat sections, whole mount preparations were used to examine the distribution of nerves. Both in the nasal mucosa and in associated ganglia, the distribution of NOS-immunoreactive nervous structures essentially corresponded to that of NADPH-diaphorase-positive ones. The NOS-immunopositive nerve fibers in the respiratory area of the nasal mucosa were distributed around blood vessels and in submucosal glands. Part of the respiratory area was supplied with intraepithelial arborizations of the immunopositive fibers. The epithelial cells in the respiratory area were NADPH-diaphorase positive but NOS immunoreactivity negative. In the olfactory area, the NADPH-diaphorase- and NOS-positive nerve fibers were restricted to blood vessels located deep in the submucosa. Throughout the nasal mucosa, arterial endothelium was NADPH-diaphorase positive but NOS immunoreactivity negative. Both NOS immunoreactivity and NADPH-diaphorase activity were found in major populations of neuronal somata in the sphenopalatine ganglion. The present study provides the direct evidence supporting the notion that nitric oxide is richly produced in autonomic nerves of the nasal mucosa derived from the sphenopalatine ganglion.

NANC neurotransmission in lamina propria of the rabbit urethra: regulation by different subsets of calcium channels

1. Electrical field stimulation (EFS) of the rabbit urethral lamina propria elicited a frequency-dependent non-adrenergic, non-cholinergic (NANC) relaxation, which was abolished by N omega-nitro-L-arginine (L-NOARG). 2. omega-Conotoxin GVIA, a selective blocker of N-type voltage-operated calcium channels (VOCCs), and omega-conotoxin MVIIC (blocker of N- and Q-type VOCCs) inhibited the NANC relaxation, and the inhibition was inversely related to the frequency of stimulation. Combined, the two toxins were more effective than omega-contoxin GVIA alone. 3. The relaxation induced by the nitric oxide (NO) donor, 3-morpholino-sydnonimine (SIN-1) was not affected by omega-conotoxin MVIIC. 4. omega-Agatoxin IVA (blocker of P-type VOCCs) did not attenuate the NANC relaxation. 5. Reduction of the calcium concentration from 1.5 to 0.5 mM reduced the NANC relaxation at low but not at high frequencies of stimulation; the relaxation induced by SIN-1 was not affected. 6. EFS (20 Hz, 30 s) increased the cyclic GMP level 3 fold in normal Krebs solutions, but was unable to enhance significantly the cyclic GMP level after calcium omission. L-NOARG reduced the cyclic GMP content in 'calcium-free' medium, indicating an ongoing NO synthesis that was independent of extracellular calcium. 7. Caffeine, ryanodine and thapsigargin (inhibitors of sarcoplasmic calcium release), and CGP 37157 (inhibitor of mitochondrial sodium/calcium exchange) had no effect on the NANC relaxation. 8. It is suggested that nitrergic nerve activation in the rabbit urethral lamina propria is mediated in partby N-type (omega-conotoxin GVIA-sensitive) and in part by Q-type (omega-conotoxin MVIIC-sensitive) VOCCs.With high frequences of stimulation, another mechanism, possibly calcium-independent, appears to become operational.

Nitric oxide control of lower genitourinary tract functions: a review

It is apparent that evolving concepts of the regulatory basis for functions in the pelvis must take into account the role exerted by nitric oxide. A recently characterized messenger molecule, nitric oxide has been associated with numerous physiologic processes. Intense investigations of this molecule have extended its importance to several genitourinary functions. Penile erection, micturition, peristalsis of the male excurrent duct system, contractile properties of the prostate, and lumbosacral spinal cord neurotransmission are all functions that may transpire under some degree of control by nitric oxide. Impotence, urinary obstruction, or ejaculatory problems, in turn, may represent alterations of nitric oxide production or action. The strategic manipulation of nitric oxide or its mechanism of action, possibly by pharmacologic means, may restore or produce desired functional effects. These possibilities, therefore, suggest that the advancing knowledge of nitric oxide in the genitourinary tract may be of enormous clinical value in the future.

Co-existence of nitrergic, peptidergic and acetylcholine esterase-positive nerves in the pig lower urinary tract

The distribution of NO synthase (NOS) immunoreactive nerves and the possible co-existence with other neurotransmitters were investigated in the pig lower urinary tract. NOS immunoreactive nerves were found in the muscle layer, in the lamina propria and around blood vessels. The density of NOS immunoreactive nerves was more prominent in the trigone and urethra than in the detrusor. All parts of the lower urinary tract were supplied by numerous acetylcholine esterase (AChE) positive nerves. The number of adrenergic nerves in the trigone and urethra was moderate to rich, whereas only very few adrenergic nerves were demonstrated in the detrusor. A low to moderate number of nerve fibres containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) were observed in the trigone and urethra, while very few were found in the detrusor. A small number of nerves, confined to the trigone and urethra, were stained for calcitonin-gene-related peptide, somatostatin and leu-enkephalin. Nerve fibres exhibiting immunoreactivity to bombesin/gastrin releasing peptide, gastrin/cholecystokinin, substance P or neurokinin A were virtually absent. Co-localization studies revealed that some NOS-immunoreactive nerves also stained for NPY, VIP or AChE. The present study shows that nitrergic nerves are present in the pig lower urinary tract in a density lower than the cholinergic, but higher than any of the studied peptidergic nerves. Coinciding localization of NOS-positive nerves with nerves expressing AChE, VIP and NPY suggests that NO may have a role as a messenger in the lower urinary tract directly and by interaction with other transmitters.

Extensive distribution of NADPH diaphorase activity in the nerve supply of the cat lower urinary tract

Nitric oxide is a neurotransmitter which causes smooth muscle relaxation and may contribute to this response in some regions of the lower urinary tract. In the present study the distributions of neurons and their axons which contain the synthetic enzyme for nitric oxide, nitric oxide synthase, were mapped by staining for NADPH diaphorase in sections of proximal urethra, bladder trigone and detrusor and whole mounts of vesical ganglia from cats. Stained axons were present in the smooth muscle of all regions of bladder and proximal urethra, but were most common in the urethra and least prevalent in the detrusor. Stained axons were also present in the mucosa; most of these were associated with blood vessels, but some travelled close to the epithelium. Stained mucosal axons were much more numerous in the proximal urethra than in any bladder region. Darkly stained neuronal somata were found throughout the vesical ganglia, where they appeared to comprise the majority of neurons. Small ganglia containing stained neurons were also found in sections of various urinary tract regions, where they were located in the serosa, between muscle layers and, in the urethra, also in the mucosa. These studies have shown an extensive distribution of neurons and axons that stain for NADPH diaphorase (and are predicted to synthesize nitric oxide) throughout all tissues of the cat lower urinary tract. It is hypothesized that nitric oxide is an inhibitory transmitter in the cat bladder and proximal urethra and may also have a role as a sensory transmitter in the mucosa of these regions.

Nitric oxide synthase and nitric oxide-mediated effects in lower urinary tract smooth muscles

In the lower urinary tract smooth muscles, both excitatory and inhibitory non-adrenergic, non-cholinergic (NANC) nerves and neurotransmission can be demonstrated. An inhibitory, relaxation-mediating system may serve not only the detrusor, the trigone, and the bladder neck/urethra, but may also be of importance for their integrated function. Available data suggest that nitric oxide synthase (NOS) is localized in nerve fibres of the lower urinary tract, preferably in the outflow region, and evidence has accumulated that L-arginine-derived nitric oxide (NO) is responsible for the main part of the inhibitory NANC response. Coinciding localization of NOS positive nerves with nerves expressing acetylcholine esterase, vasoactive intestinal peptide, and neuropeptide Y, suggests that NO may have a role both as a directly acting transmitter and as a modulator of efferent neurotransmission. In addition, NO may be involved in afferent neurotransmission. Theoretically, NO released from nerves in the detrusor, could be one factor keeping the bladder relaxed during filling. However, the detrusor has a low sensitivity to NO and agents acting via cyclic GMP, which makes it less likely that NO has a role as a relaxant neurotransmitter. This does not exclude that NO may modulate the effects of other transmitters, or that it has an afferent function. NO effectively relaxes isolated smooth muscle preparations from the outflow region, suggesting that it may be involved in the decrease in intraurethral pressure associated with normal micturition, and with the excessive urethral pressure variations ("unstable urethra"), which may be associated with certain voiding disturbances in women.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-adrenergic, non-cholinergic relaxation and levels of cyclic nucleotides in rabbit lower urinary tract

Electrical field stimulation at 12 Hz produced urethral relaxation and increased the tissue cyclic GMP content by 111 +/- 36% (n = 6, P < 0.05). Pretreatment with zaprinast (10 microM) increased the tissue cyclic GMP content in response to electrical stimulation by 160 +/- 56% (n = 7, P < 0.05). The nitric oxide synthase inhibitor NG-nitro-L-arginine (0.1 mM) and methylene blue (50 microM) inhibited electrically-induced cyclic GMP accumulation. Methylene blue only partially inhibited urethral relaxation, whereas NG-nitro-L-arginine caused complete inhibition. Electrical stimulation of urethral preparations did not affect the tissue levels of cyclic AMP. Administration of sodium nitroprusside increased the cyclic GMP content in the urethra and detrusor. Administration of isoprenaline increased the detrusor cyclic AMP content, but no change in urethral cyclic AMP levels could be detected. Cyclic GMP related drugs (sodium nitroprusside, 8-bromo-cyclic GMP) reduced urethral tone by 67-75% and detrusor tone by 13-39%. These results suggest that nerve-induced relaxation of the rabbit urethra is associated with an increase in cyclic GMP, but not cyclic AMP content. Synthesis of NO is essential for both nerve-mediated relaxation and cyclic GMP accumulation. The urethral smooth muscle tissue is more sensitive to cyclic GMP-activating drugs than the detrusor smooth muscle.

Localization of NADPH-diaphorase reactivity in the chick and mouse thyroid gland

In the present study, nicotinamide adenine dinucleotide hydrogen phosphate-diaphorase (NADPH-d) histochemistry has been used as a marker for nitric oxide synthase (NOS). The colored reaction product, formazan, was localized in neuronal cell bodies, nerve fibers, and vascular endothelium in the thyroid of chick and mouse. In these two animal species, most of the NADPH-d-labeled neuronal cell bodies were found in the thyroid capsule and interfollicular connective tissue while some were associated with blood vessels. Most nerve fibers travelled with blood vessels supplying the thyroid gland, while a few of them were intimately associated with the thyroid follicular cells. Control sections not incubated with beta-NADPH failed to show labeling of the above structures. It is concluded that nitric oxide may play an important role in endocrine secretion by controlling the regional blood flow in the thyroid gland and by directly acting on the thyroid follicular cells.

Effects of omega-conotoxin on adrenergic, cholinergic and NANC neurotransmission in the rabbit urethra and detrusor

1. The effects of omega-conotoxin GVIA (an inhibitor of N-type voltage-operated calcium channels; VOCCs) were compared on adrenergic, cholinergic and non-adrenergic, non-cholinergic (NANC) responses induced by electrical field stimulation (EFS) in the rabbit urethra and detrusor. 2. EFS induced a relaxation in urethral smooth muscle and lamina propria precontracted by arginine vasopressin (AVP). The relaxation was abolished by tetrodotoxin (TTX) or the nitric oxide (NO) synthase inhibitor N omega-nitro-L-arginine. omega-Conotoxin inhibited the relaxation induced by EFS, but not that elicited by the NO donor 3-morpholino-sydnonimin. The inhibition, however, decreased with increasing frequencies of stimulation. Nimodipine, tetramethrin and nickel did not affect the omega-contoxin-resistant relaxation in lamina propria, suggesting that neuronal L or T VOCCs were not involved in the response. 3. EFS contracted urethral smooth muscle at resting tension. The contractions were virtually abolished by TTX or prazosin. omega-Conotoxin effectively inhibited the contractile responses to EFS, but not those to exogenous noradrenaline. An omega-conotoxin-resistant contraction was, however, observed at high frequencies of stimulation. 4. The detrusor responded with frequency-dependent contractions upon EFS. A TTX-resistant contraction less than 10% of controls remained at 30 Hz stimulation. At a stimulation frequency of 10 Hz, scopolamine reduced the EFS-induced contraction by 71%. omega-Conotoxin inhibited the responses in both the absence and presence of scopolamine. The inhibition decreased with increasing frequencies of stimulation (examined in the absence of scopolamine). omega-Conotoxin did not affect the contractile responses to carbachol or adenosine 5'-triphosphate. 5. The adrenergic contraction (25 Hz) and NANC relaxation (10 Hz) in the urethra, and cholinergic and NANC contractions (10 Hz) in the detrusor were inhibited concentration-dependently by omega-conotoxin.The adrenergic contraction in the urethra was 10 times and the cholinergic contraction in the detrusor was three times more sensitive to omega-conotoxin than the NANC responses.6. These results suggest that NANC neurotransmission is less inhibited by omega-conotoxin than transmission mediated by adrenergic and cholinergic nerves in the rabbit lower urinary tract. In the urethra a marked omega-conotoxin-resistant component of the NANC relaxation was observed which increased with increasing stimulation frequencies and was unaffected by inhibitors of L and T type VOCCs. This raises the question whether VOCCs of a type other than L, T, and N is involved in the mediation of this response.