Urethral Relaxation Research Articles

Atypical relaxation by scorpion venom in the lamb urethral smooth muscle involves both NO-dependent and -independent responses.

The sustained depolarisation induced by alpha-toxins from scorpion venom (20 microg/ml(-1)) was used to test the hypothesis that an endogenous, photo-sensitive, nitrocompound could act as a stable nitrergic transmitter in the sheep (lamb) urethra. Scorpion venom-treatment effectively abolished neurogenic responses to electrical field stimulation, but it did not modify the spontaneous urethral photorelaxation. On the other hand, scorpion venom induced an atypical relaxation in noradrenaline-contracted preparations, which could be reverted, but not prevented, by tetrodotoxin (TTX, 1 microM). However, after TTX-pretreatment, relaxations elicited by scorpion venom were significantly delayed and slowed down, and similar responses were obtained in the presence of ouabain (10 microM), low sodium medium, or after the inhibition of the NO-cGMP pathway. Although the involvement of K(+) and Cl(-) channels can be ruled out since both charybdotoxin (300 nM) and chlorotoxin (50 nM) did not elicit any urethral relaxation nor modified the scorpion venom-induced one. However, a slow Ca(2+) channel seems to be involved. GVIA omega-conotoxin (1 microM), but not MVIIC omega-conotoxin (1 microM), significantly inhibited both EFS- and scorpion venom-induced relaxations and almost abolished the partial relaxation that was resistant to NO synthase inhibition. On the other hand, the presence of L-cis-diltiazem (0.3 mM), a selective inhibitor of cyclic nucleotide gated channels (CNGCs), also delayed and slowed down relaxation induced by scorpion venom, as well as abolish its reversal by TTX. L-cis-diltiazem pre-treatment induced a progressive decay in urethral relaxation brought about by electrical field stimulation only when repetitive, long duration stimulation protocols were used. Taken together, our results do not support the hypothesis of the endogenous, photo-sensitive, urethral nitrocompound as reflecting a stable nitrergic transmitter instead of NO. However, they suggest the involvement of both a NO-cGMP-dependent and TTX-sensitive component and a NO-independent response, mediated by GVIA omega-conotoxin-sensitive Ca(2+) channels, in the neurogenic relaxation of the urethral muscle. In addition, the likely involvement of CNGCs as an additional component of the cGMP signalling mechanism is suggested.

Age-related changes in urethrovesical coordination in male rats: relationship with bladder instability?

The micturition profile in conscious animals and the urethrovesical coordination in anesthetized conditions were investigated in 6- and 24-mo-old male Sprague-Dawley rats. The in vitro pharmacological responses to KCl, electrical field stimulation (EFS), carbachol, phenylephrine, and isoprenaline were determined in the isolated bladder body, the bladder neck, and urethra. A morphometric and immunohistological study has been included. During conscious cystomanometry, 63% of the aging rats but only 25% of the adult rats showed spontaneous contractions during the bladder-filling phase. In conscious aging rats, basal pressure, threshold pressure, and micturition pressure were also significantly increased. In anesthetized aging rats, a decrease in resting urethral pressure at micturition threshold and the occurrence of a significant delay in urethral relaxation during micturition were associated with an increased residual volume. In all isolated tissues, contractile response to KCl was not modified with aging, whereas age-related decreases in maximal responses to carbachol in the bladder body and to phenylephrine and carbachol in the urethra were observed. In the bladder neck only, we found a significant decrease in the amplitude of neurogenic contractions associated with fibrosis but without decrease in nerve density. These experiments show significant modifications in the voiding pattern of aging rats associated with urethral dysfunction and with regionally specific pharmacological and structural changes of the urinary tract. We propose that aging in rats is characterized by an impairment of the urethrovesical coordination, leading to bladder dysfunctions similar to those induced by bladder outlet obstruction.

Effect of the Bowman-Birk inhibitor (a soy protein) on in vitro bladder neck/urethral and penile corporal smooth muscle activity.

The Bowman-Birk inhibitor (BBI), is a serine protease inhibitor derived from soy beans, which is presently being evaluated in clinical trials for its ability to serve as a cancer preventive or anti-inflammatory agent. The form of BBI currently in clinical trials is known as Bowman-Birk inhibitor concentrate (BBIC). There have been anecdotal reports from patients of improved voiding and sexual functions in the ongoing BBIC trials. The objective of this study was to quantify the effect of BBI and BBIC on urethral and corporal smooth muscle activity. In vitro muscle strip studies of New Zealand White rabbit urethra/bladder neck and penile corpora in the presence or absence of BBI or BBIC incubation (5 mg/mL) were performed. In dose-response curves to alpha stimulation, BBI mediated a shift to the right (decreased receptor sensitivity in bladder/urethra as well as corpora with no change in the maximal response). Bladder base/ urethra contraction by field stimulation was significantly inhibited by BBI at higher frequencies (1-32 Hz) (12.2 + 0.8 g vs. 6.3 + 0.75 g, P < 0.05). BBI inhibited field stimulated relaxation of corporal muscle at lower frequencies. Muscarinic contraction of the bladder neck/urethra in alpha prestimulated tissue was significantly inhibited by BBI (5.3 + 0.2 g vs. 2.7 + 0.1 g, P < 0.05). BBI has an inhibitory effect on alpha adrenergic dose-response curves in bladder neck/urethral and corpora smooth muscle. BBI also significantly inhibited neurohumoral cholinergic release and in vitro muscarinic contraction of the urethra. The effects on corpora relaxation were less pronounced. The data suggest that the phytochemical BBI may promote physiologic effects of urethral relaxation and improved voiding by unique mechanisms and deserves further study as a pharmacologic agent for lower urinary tract symptoms.

An investigation of the effects of zaprinast, a PDE inhibitor, on the nitrergic control of the urethra in anaesthetized female rats

1. The effects of L-NAME and zaprinast were investigated (i.v.) on reflex-evoked changes in bladder and urethral pressures in urethane-anaesthetized female rats. 2. L-NAME attenuated reflex-evoked urethral relaxations (65+/-10%), while zaprinast potentiated these responses (68+/-24%). L-NAME and zaprinast also increased baseline urethral pressure and urethral striated muscle (EUS-EMG) activity. These drugs had little effect on the bladder. 3. Following pre-treatment with alpha-bungarotoxin (i.v.) to block urethral striated muscle, L-NAME and zaprinast failed to increase baseline urethral pressure. Further zaprinast failed to alter the size of reflex-evoked urethral relaxations. 4. Intra-urethral zaprinast caused a significant increase while sodium nitroprusside (SNP) and isoprenaline caused decreases in urethral pressure (+14+/-3%, -25+/-5%, -29+/-7%, respectively). These changes were associated with increases in EUS-EMG activity. After chlorisondamine (i.v.), zaprinast caused a significant fall in urethral pressure, while the decrease in urethral pressure caused by SNP and isoprenaline was potentiated. No changes in EUS-EMG activity occurred. 5. These results indicate that a nitrergic pathway mediates reflex-evoked urethral smooth muscle relaxations. The data also indicates that there is a background release of NO, which reduces sphincter skeletal muscle activity. Further, the ability of zaprinast to potentiate nitrergic evoked urethral relaxations involves an increase in striated muscle tone. This appears to be an indirect result of smooth muscle relaxation and is mediated, at least in part, by a chlorisondamine-sensitive mechanism.

The involvement of L-type Ca(2+) channels in the relaxant effects of the ATP-sensitive K(+) channel opener ZD6169 on pig urethral smooth muscle.

1. The effects of ZD6169, a novel ATP-sensitive K(+) channel (K(ATP) channel) opener, were investigated on membrane currents in isolated myocytes using patch-clamp techniques. Tension measurement was also performed to study the effects of ZD6169 on the resting tone of pig urethral smooth muscle. 2. Levcromakalim was more potent than ZD6169 in lowering the resting urethral tone. Relaxation induced by low concentrations of ZD6169 (< or =3 microM) was completely suppressed by additional application of glibenclamide (1 microM). In contrast, glibenclamide (1-10 microM) only partially inhibited the relaxation induced by higher concentrations of ZD6169 (> or = microM). 3. Bay K8644 (1 microM) reduced the maximum relaxation produced by ZD6169 (> or =10 microM). 4. In whole-cell configuration, ZD6169 suppressed the peak amplitude of voltage-dependent Ba(2+) currents in a concentration- and voltage-dependent manner, and at 100 microM, shifted the steady-state inactivation curve of the voltage-dependent Ba(2+) currents to the left at a holding potential of -90 mV. 5. In cell-attached configuration, open probability of unitary voltage-dependent Ba(2+) channels (27 pS, 90 mM Ba(2+)) was inhibited by 100 microM ZD6169 and by 10 microM nifedipine. 6. Reverse transcriptase-polymerase chain reaction (RT - PCR) analysis revealed the presence of the transcript of the alpha(1C) subunit of L-type Ca(2+) channels in pig urethra. 7. These results demonstrate that ZD6169 causes urethral relaxation through two distinct mechanisms, activation of K(ATP) channels at lower concentrations and inhibition of voltage-dependent Ca(2+) channels at higher concentrations (about 10 microM).

Tension-Free vaginal tape (TVT) in women with mixed urinary incontinence--a long-term follow-up.

In a prospective long-term study we evaluated the effect of TVT surgery in 80 women suffering from mixed urinary incontinence. Their mean age was 59 +/- 11 years with a mean parity of 2 (range 0-6). Mean follow-up was 4 years (range 3-5). The preoperative evaluation included a 24-hour pad test, quality of life evaluation, gynecologic examination and urodynamic investigations, including simultaneous urethrocystometry. From the patient history 96 patients were initially tentative candidates for TVT operation. Sixteen of these had only minor symptoms and signs of stress incontinence but significant symptoms and signs of detrusor instability, and were not considered suitable for TVT surgery. In the remaining 80 women the urodynamic investigation with filling urethrocystometry demonstrated stress incontinence and urge incontinence concomitant with urethral relaxation and/or 'premature micturition' reflex. At the postoperative long-term follow-up 85% of the patients were completely cured. Another 4% were significantly improved. In 11% of the patients the operation failed. Few intra- or postoperative complications occurred. Based on these results, we conclude that TVT surgery can be used for treatment of female mixed urinary incontinence. A proper urodynamic assessment is recommended before surgery is performed.

Involvement of accumulated endogenous NOS inhibitors and decreased NOS activity in the impaired neurogenic relaxation of the rabbit proximal urethra with ischaemia.

1. We examined the effect of ischaemia on the neurogenic and nitric oxide (NO)-mediated urethral relaxation. 2. Rabbits were divided into control and urethral ischaemia (UI) groups, which was prepared by the partial occlusion of bilateral iliac arteries using blood vessel occluders. 3. Neurogenic and NO-mediated proximal urethral relaxation induced by electrical field stimulation (EFS) was greatly impaired in the UI group, while relaxation by sodium nitroprusside (SNP) as a NO donor showed no difference between the two groups. Pretreatment with L-arginine significantly improved but did not normalize the impaired relaxation in the UI group. Not only basal level, but also stimulated production of cyclic GMP with EFS, were significantly decreased in the UI group. 4. The tissue contents of N(G)-methyl-L-arginine (L-NMA) and asymmetric N(G), N(G)-dimethyl-L-arginine (ADMA) in the proximal urethra were increased following ischaemia. While L-arginine and symmetric N(G), N'(G)-dimethyl-L-arginine (SDMA) contents remained unchanged. Exogenously applied authentic L-NMA and ADMA (1 -- 100 microM) concentration-dependently inhibited the EFS-induced urethral relaxation in the control group. The inhibition with L-NMA and ADMA was undetectable in the presence of 3 mM L-arginine. 5. The Ca(2+)-dependent NOS activity in the urethra from the UI group was significantly lower than that from the control group and was not restored by an addition of 3 mM L-arginine. 6. These results suggest that the impaired neurogenic and NO-mediated urethral relaxation with ischaemia is closely related to the increased accumulation of L-NMA and ADMA and decreased NOS activity, which would result in an accelerated reduction in NO production/release.

ROLE OF A CENTRAL MUSCARINIC CHOLINERGIC PATHWAY FOR RELAXATION OF THE PROXIMAL URETHRA DURING THE VOIDING PHASE IN RATS

We examined the role of a central muscarinic cholinergic pathway in proximal urethral function during the voiding phase. During isovolumetric bladder contraction we independently recorded proximal urethral pressure, external urethral sphincter activity, and hypogastric and pelvic nerve discharge in urethane anesthetized rats. We administered intravenous, intrathecal or intracerebral ventricular atropine sulfate and atropine methyl nitrate. Atropine sulfate crosses the blood-brain barrier, while atropine methyl nitrate does not. Filling the bladder with 0.5 ml saline induced rhythmic urethral relaxation accompanied by efferent burst discharges from the pelvic nerve. When administered intravenously, only atropine sulfate caused the dose dependent inhibition of urethral relaxation and efferent pelvic nerve discharge. Neither atropine sulfate nor atropine methyl nitrate affected the maximum firing rate of the external urethral sphincter or hypogastric efferent discharge. Intrathecal and intracerebral ventricular atropine sulfate and atropine methyl nitrate similarly inhibited urethral relaxation. These results suggest that excitation of the central muscarinic cholinergic pathway at a supraspinal or spinal site promotes proximal urethral relaxation during the voiding phase through the activation of efferent pathways in the pelvic nerves.

Effect of TAK-637, a Tachykinin NKrReceptor Antagonist, on Lower Urinary Tract Function in Cats

The effect of TAK-637 ((aR,9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10,11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H[1,4]diazocino[2,1g][1,7]naphthyridine-6,13-dione), a tachykinin NK1-receptor antagonist, on lower urinary tract function was investigated in cats. TAK-637 (0.1, 0.3, 1 and 3 mg/kg, i.v.) produced a dose-dependent increase in bladder capacity without any significant reduction in voiding efficiency in decerebrate cats. The maximal increase in bladder capacity was 94%. By contrast, oxybutynin at 1 and 3 mg/kg (i.v.) produced a 18% and 35% increase in bladder capacity, respectively, with a 47% and 45% reduction in voiding efficiency. TAK-637 (3 mg/kg, i.v.) did not inhibit the micturition reflex induced by electrical stimulation of the rostral brainstem near the locus coeruleus, indicating that it does not impair the well-organized micturition reflex (bladder contraction and urethral relaxation). These results suggest that TAK-637 increases bladder storage capability without inhibiting the voiding function of the lower urinary tract, presumably by inhibiting the afferent pathway of the micturition reflex, rather than the efferent pathway.

Prejunctional α-adrenoceptors regulate nitrergic neurotransmission in the rabbit urethra

We evaluated the effects of prejunctional α-adrenoceptors on nitric oxide (NO)-mediated urethral relaxation in rabbits using a muscle bath technique and high-performance liquid chromatography coupled with a microdialysis procedure. The amount of NO 2 −/NO 3 − released during electrical field stimulation was measured by an NO 2 −/NO 3 − analyzer based on the Griess method. Pretreatment with phenylephrine (0.01 μM) and yohimbine (0.1–10 μM) significantly reduced the relaxation responses induced by electrical field stimulation. In contrast, pretreatment with clonidine (0.01 μM) and prazosin (0.01–1 μM) enhanced the relaxation responses. Cys-NO-induced relaxations of rabbit urethral smooth muscle were not affected by pretreatment with α-adrenoceptor agonists and antagonists. The amount of NO 2 −/NO 3 − released by electrical field stimulation increased after pretreatment with clonidine (0.01 μM) and prazosin (0.01–1 μM), but decreased after pretreatment with phenylephrine (0.01 μM) and yohimbine (0.1–10 μM). The results suggest that the release of NO from nitrergic nerves in the rabbit urethra is reduced and increased by stimulation of prejunctional α 1- and α 2-adrenoceptors, respectively.

Pressure–flow study as an evaluating method of neurogenic urethral relaxation failure

Voiding difficulty is a common feature in neurological diseases, which can be attributed to dysfunction of the urethral sphincter and the detrusor. Electromyography (EMG)–cystometry can reveal the presence of detrusor–external sphincter dyssynergia (DESD), however, internal sphincter function on voiding is not easily evaluated. Pressure–flow study is widely used to diagnose benign outlet obstruction due to prostatic hypertrophy. We applied pressure–flow study in neurological patients in order to evaluate neurogenic urethral relaxation failure. We recruited 71 patients with neurological diseases. All were men under 60 years, with mean age of 44 years, ranging from 18 to 59 years. None had abnormal finding of digital examination or ultrasound echography of the prostate. Standard cystometry showed detrusor hyperreflexia in 33 patients and residual urine was noted in 36. DESD was noted in seven of 43 patients. Pressure–flow relation curve and a detrusor pressure ( P det) at the point of maximum flow rate ( Q max) (i.e., P det Q max) were obtained by urodynamic computers. The Abram–Griffiths (AG) number ( P det Q max−2 Q max), showing outlet obstruction particularly over 40, was also obtained. The points of P det Q max of the patients fell into three categories of the AG nomogram, showing obstruction in 19.7%, equivocal in 52.1% and unobstructed in 28.2%. Patients with DESD had AG number over 40 more commonly (57.1%) than those without DESD (8.4%) ( p<0.05). The mean AG number was 46.4 in patients with DESD, which was larger than 17.1 in patients without DESD ( p<0.01). Patients with detrusor hyperreflexia had AG number over 40 more commonly (42.4%) than those with normal cystometric curve (0%) ( p<0.01). The mean AG number was 30.6 in patients with detrusor hyperreflexia, which was larger than 13.6 in patients with normal cystometric curve ( p<0.01). The results showed that 19.7% of patients with neurological diseases had obstructive pattern (high pressure voiding), evidence of urethral relaxation failure with relatively preserved detrusor contraction. DESD is a factor contributing to the urethral relaxation failure of the patients. The results also indicated a relationship between detrusor hyperreflexia and obstructed pattern, probably reflecting co-occurrence of detrusor hyperreflexia with DESD or detrusor–internal sphincter dyssynergia.

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.

Stress urinary incontinence at rest.

We retrospectively identified 37 cases in which urinary incontinence occurred at rest during urodynamic testing in the absence of a coincident detrusor contraction or urethral relaxation. This phenomenon, genuine stress incontinence at rest, was observed during 9.6% of multichannel cystometrograms performed at our institution. The observed urine loss occurred at bladder volumes between 145 ml and 800 ml. Loss occurred with bladder overdistension (overflow incontinence) in only 3 subjects (8%). Decreased bladder compliance was observed in 11 (30%) and decreased outlet resistance was demonstrated in 24 (65%). Our findings suggest that genuine stress incontinence at rest is relatively common in a referred population of incontinent women. This phenomenon is associated with impaired urethral function and/or decreased bladder compliance.

Pudendal nerve stimulation induces urethral contraction and relaxation.

In this study we measured urethral pressure changes in response to efferent pudendal nerve stimulation in rats. All other neural pathways to the urethra were transected, and the urethra was continuously perfused. We found fast twitch-like contractions, superimposed on a slow relaxation. The amplitude of the twitches was independent of the stimulation frequency below 26 Hz, whereas the relaxation depended highly on this frequency. The twitches were caused by striated urethral muscles, and the relaxation was caused by smooth muscles. Both were mediated by acetylcholine. We calculated the effective urethral relaxation as the absolute relaxation multiplied by the time fraction between the twitches. Maximum effective relaxation occurred at 8-10 Hz, exactly the frequency of spontaneous oscillations during bladder voiding in rats. Although the oscillatory sphincter contractions in rats during voiding may be needed in other mechanisms for efficient voiding, our data suggest that they may be a side effect of the actual purpose: urethral relaxation.

A Computer Model for Describing the Effect of Urethral Afferents on Simulated Lower Urinary Tract Function

A computer model of mechanical properties of the bladder, the urethra and the rhabdosphincter, as well as their neural control is presented in this paper. The model has a rather simple design and processes sensory information from both the bladder wall tension and urethral stretch. It is assumed that afferent signals from the urethra are involved in a sacral excitatory reflex and a supraspinal inhibitory reflex. Pressure and flow signals that resemble experimentally measured normal human behaviour could be simulated with this model. From these simulations the relation between the neural control mechanisms used in the model and the neural control mechanism in vivo cannot be judged entirely because similar behaviour could be simulated with models that are bas ed on different neural control mechanisms. Also behaviour that resembles detrusor overactivity was simulated with our model after an externally induced rise in detrusor pressure was added. Detrusor overactivity, sometimes in combination with urethral relaxation, can occur during a urodynamic investigation. A possible explanation for this detrusor overactivity might be that the micturition reflex is triggered by unknown disturbances and is inhibited immediately after by the same mechanism that normally ceases voiding. The described model provides such a mechanism. Based on these simulations, therefore, it is concluded that urethral afferent signals might be important in lower urinary tract control.

The role of ATP-receptor in controlling the urinary bladder and urethral function in rats

The detrusor contraction involves an atropine resistant, nonadrenergic noncholinergic (NANC), component. Since adenosine triphosphate (ATP) has been proposed as a NANC transmitter, the role of ATP-receptors in the lower urinary tract was examined. The isovolumetric bladder contractions and the urethral pressure were monitored after intra-arterial administration of ATP analogues and other drugs in 52 female SD rats under intraperitoneal urethane anesthesia. alpha beta metATP induced a rapid, phasic increase of the maximal bladder pressure immediately after the drug administration, which was followed by a decrease during the P 2 X-purinoceptor desensitization period, but it did not affect the resting bladder pressure. RB-2 did not affect both the maximal bladder pressure and the resting bladder pressure. As for the urethral functions, alpha beta metATP induced a decrease of the resting urethral pressure during the P 2 X-purinoceptors desensitization period, while RB-2 induced a increase of the resting urethral pressure in contrast. ATP, alpha beta metATP and RB-2 did not changed the maximal urethral relaxation. The results will indicate that ATP produces detrusor contractions through the P 2 X-purinoceptor. Although ATP dose not affect urethral relaxation during voiding phase, it controls the urethral tone during collecting phase by both the excitation of P 2 X-purinoceptor and the inhibition of P 2 Y-purinoceptor.

Inhibitory innervation of the guinea-pig urethra; roles of CO, NO and VIP

The inhibitory innervation of guinea-pig urethral smooth muscle was investigated histochemically and functionally. The distribution of immunoreactivities to haem oxygenases (HO), neuronal NO synthase (nNOS), and vasoactive intestinal polypeptide (VIP) was studied, and the functional effects of the corresponding putative transmitters, CO, NO, and VIP, were assessed. HO-2 immunoreactivity was found in all nerve cell bodies of intramural ganglia, localized between smooth muscle bundles in the detrusor, bladder base and proximal urethra. About 70% of the ganglionic cell bodies were also NOS-immunoreactive (IR), whereas a minor part was VIP-IR. Some ganglion cells exhibiting tyrosine hydroxylase (TH) activity were demonstrated. Rich numbers of NOS-IR varicose nerve terminals could be found innervating the smooth muscle of the urethra, whereas VIP-IR terminals were less numerous. A rich number of TH-IR terminals were observed. The bladder showed a similar distribution of nerves, although only a few number of TH-IR nerves could be found. In bladder preparations exposed to sodium nitroprusside, cGMP-IR cells could be seen, forming an interconnecting network with long spindle-shaped processes. The cGMP-IR cells were especially abundant in the outer smooth muscle layers of the bladder, but less numerous in the urethra. In urethral strip preparations, electrical field stimulation evoked long-lasting frequency-dependent relaxations. The relaxations were not inhibited by the NO-synthesis inhibitor, l-NOARG, or enhanced by the NO-precursor, l-arginine. The haem precursor, 5-aminolevulinic acid (5-ALA), or the inhibitor of guanylate cyclase, ODQ, did not affect the urethral relaxations. Exogenously applied NO, SIN-1, and VIP relaxed the preparations by approximately 50%, whereas the relaxation evoked by exogenous CO was minor. These results suggest that CO probably is not involved in non-adrenergic, non-cholinergic inhibitory control of the guinea-pig urethra, where a non-NO/cGMP mediated relaxation seems to be predominant.

Effect of estrogen on nitric oxide-induced relaxation of the rabbit urethra

We evaluated the effect of estrogen on nitric oxide (NO)-mediated urethral relaxation in rabbits. Female New Zealand white rabbits, 4–5 weeks old, were treated with 5 mg/kg estradiol dipropionate (estrogen group) or saline (control group) injected intramuscularly weekly for 2 weeks. Electrical field stimulation (supramaximum voltage, 2 ms pulse duration, 0.3–15 Hz and 3 s train) caused frequency-dependent relaxation of urethral strips in both groups, which was inhibited by N ω -nitro- l-arginine ( l-NNA). This inhibition was overcome by addition of l-arginine. The relaxation induced by nitrergic nerve stimulation was significantly lower in the estrogen group than in the control group. There was no significant difference in sodium nitroprusside-induced urethral relaxation between the two groups. The production of NO in urethral strips during nitrergic nerve stimulation was evaluated by measuring nitrite/nitrate (NO 2 −/NO 3 −) levels in both groups, using microdialysis. The NO 2 −/NO 3 − production during electrical field stimulation in the estrogen group was significantly less than that in the control group. The NADPH diaphorase-positive reaction in the control group was greater than that in the estrogen group. The results suggest that estrogen treatment may reduce NO synthase activity, and inhibit the relaxation induced by nitrergic nerve stimulation in rabbit urethral smooth muscle.

REORGANIZATION OF SOMATO-URETHRAL REFLEXES FOLLOWING SPINAL CORD INJURY IN THE RAT

It is known that reflex activity of the urinary bladder can be inhibited or facilitated by perineal cutaneous stimulation. This study was undertaken to examine the urethral striated (EUS) and smooth muscle responses evoked by perineal cutaneous stimulation in the rat. Urethral perfusion pressure and EUS-EMG were monitored in urethane-anesthetized normal and chronic spinal rats (4-5 weeks after T(8-9) spinalization) of either sex. Somatic perineal stimulation was performed by tactile or pinch stimulation to the perineum. In both normal and chronic spinal rats, perineal stimulation elicited a transient increase in EUS-EMG activity which was abolished following neuromuscular blockade with alpha-bungarotoxin i.v. In normal rats treated with alpha-bungarotoxin perineal stimulation did not elicit a detectable urethral smooth muscle response. However, in chronic spinal rats perineal stimulation increased urethral pressure by smooth muscle contraction in males and decreased urethral pressure by smooth muscle relaxation in females. The evoked urethral smooth muscle contraction in males was significantly reduced or abolished by atropine i.v., but not by sympathetic nerve transection or prazosin i.v., whereas the relaxation in females was significantly reduced or abolished by N-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor, i.v.). These data indicate that spinal cord injury unmasks somato-urethral smooth muscle reflexes mediated by lumbosacral parasympathetic efferent pathways. The reflexes consist of a nitric oxide-mediated urethral relaxation in females and an atropine-sensitive urethral contraction in male rats.

Effects of ethanol on responses of isolated rabbit urinary bladder and urethra.

Acute ethanol ingestion increases the risk of urinary retention in patients with benign prostatic hyperplasia (BPH). To elucidate the mechanism of this effect, we investigated the in vitro effects of ethanol on lower urinary tract function in rabbits. The responses to various stimuli of muscle strips isolated from male rabbit bladder and urethra were determined in the presence of 0%, 0.5%, 1.0%, and 3.0% ethanol. Basal tension of tissue strips taken from the bladder and the urethra was reduced by ethanol in a dose-dependent manner, as were bladder contractions induced by field stimulation, bethanechol, and ATP. Ethanol also reduced phenylephrine-induced contractions of the prostatic urethra. A high (3%) concentration of ethanol significantly reduced KCl-induced contraction of both the bladder and urethra, as well as urethral relaxation induced by field stimulation following contraction with 200 mumol/L phenylephrine. Responsiveness of the rabbit lower urinary tract was significantly reduced by exposure to ethanol. A similar decrease in tonus and contractility of the detrusor and inhibition of relaxation in the prostatic urethra may lead to urinary retention in men following acute ingestion of ethanol.