Urethral response to sympathetic nerve stimulation in the cat]

The responses of the urethra to hypogastric nerve (HGN) and lumbosacral sympathetic chain (SC) stimulation were observed in 25 chloralose-anesthetized cats. Urethral perfusion pressure was monitored as an index of functional urethral responses. SC was stimulated at four points from L4 to S1. Urethral constrictive response induced by HGN stimulation (delta P:HGN) was significantly larger in male cats than in female cats. But there was no difference between male and female cats in urethral constrictive response induced by SC stimulation (delta P:SC). delta P:HGN was significantly larger than delta P:SC in both sexes, and the ratio of delta P:HGN to delta P:SC (L7-S1) was 2.7 to 1 in male cats and 1.7 to 1 in female cats. delta P:HGN was blocked by the alpha-adrenergic antagonist phentolamine (1-2 mg/kg) and reduced about 50% by autonomic ganglion blockade with hexamethonium bromide (2 mg/min, 25-50 mg). delta P:SC was blocked by both phenotolamine and hexamethonium bromide. In order to examine the pathways of projections of sympathetic fibers from the sacral SC to the urethra, HGN, pelvic nerve and pudendal nerve were transected serially. delta P:SC (L7-S1) was decreased 0%, 12% and 50% by transection of HGN, pelvic nerve and pudendal nerve, respectively. After severance of these three nerves, delta P:SC (L7-S1) was reduced 62%, but not abolished. These data suggest: 1) The effect of HGN to the feline urethra is more prominent than that of SC in both sexes and significantly larger response was noted in male cats with HGN stimulation but not with SC.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats

OBJECTIVE: To investigate the effects of anaesthesia on the nitrergic pathway during the micturition reflex in rats. MATERIALS AND METHODS: The effects of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, on bladder and urethral activities were evaluated by infusion cystometrography (CMG) and urethral perfusion pressure under isovolumetric conditions in awake or urethane-anaesthetized rats. L-NAME was administered intravenously (i.v.), intrathecally (i.t.), intracerebroventriculary (i.c.v.) or intravesically in normal rats or rats pre-treated with resiniferatoxin, a potent C-fibre afferent neurotoxin. RESULTS: L-NAME injected i.v. decreased the intercontraction interval (ICI) in the awake but increased it in the anaesthetized rats. L-NAME injected i.t. increased the ICI in both states and these effects were not apparent after pre-treatment with resiniferatoxin. L-NAME injected i.c.v. decreased the ICI in the awake but increased i.t. in the anaesthetized rats. Intravesical L-NAME decreased the ICI in the awake but not in the anaesthetized rats. L-NAME administered i.v., but not i.t. or i.c.v., increased bladder contraction during CMG. Under isovolumetric conditions, L-NAME administered i.v., but not i.t. or i.c.v., reduced the urethral relaxation without changing bladder contraction. CONCLUSIONS: These results indicate that spinal NO release facilitates the mechanoceptive C-fibres, and this facilitatory effect is masked by supraspinal (possibly forebrain) and local inhibitory effects of NO during the micturition reflex in awake rats. Urethane seems to inhibit the supraspinal and local inhibitory effects of NO, resulting in unmasking the facilitatory effect of NO in the spinal cord and brain stem. During the voiding phase, urethral relaxation depends on the peripheral but not the central NO system.     

Inhibitory roles of peripheral nitrergic mechanisms in capsaicin-induced detrusor overactivity in the rat

OBJECTIVES: To investigate the peripheral role of nitric oxide (NO) in capsaicin-induced detrusor overactivity (DO), as exogenously applied vanilloids can evoke NO release in urothelial cells but its functional role has not yet been reported. MATERIALS AND METHODS: The effects of N(G)-nitro-l-arginine methyl ester (L-NAME), an inhibitor of NO synthase (NOS), on bladder activity during intravesical capsaicin (30 microm) instillation were examined by using continuous infusion cystometry in urethane-anaesthetized rats. L-NAME was administered intravenously (i.v., 20 mg/kg), intrathecally (i.t., 270 microg/rat), intracerebroventricularly (i.c.v., 270 microg/rat) or intravesically (10 mg/mL) before or during capsaicin instillation. RESULTS: During cystometry with intravesical saline infusion, L-NAME injected i.v., i.t. and i.c.v., but not intravesically, significantly increased the intercontraction intervals (ICI) and L-NAME injected i.v., but not i.t., i.c.v. or intravesically, increased the maximum voiding pressure (MVP) without affecting the baseline pressure. Capsaicin instillation induced DO evidenced by a significant reduction in the ICI. L-NAME administered i.v. further decreased the ICI and increased the MVP and the baseline pressure during capsaicin instillation. Co-intravesical application of capsaicin and L-NAME also similarly enhanced capsaicin-induced DO. However, L-NAME injected i.t. or i.c.v. had no effect on capsaicin-induced DO. The excitatory effects of i.v and intravesical L-NAME on the ICI, MVP and baseline pressure during capsaicin infusion were significantly suppressed by desensitization of C-fibre afferent pathways by capsaicin pretreatment (125 mg/kg s.c., 4 days before cystometry). CONCLUSION: These results indicate that locally released NO can suppress DO induced by capsaicin-mediated C-fibre activation and that central NO pathways are not involved in capsaicin-induced DO.     

Sex difference in urethral response to electrical stimulation of efferent nerves in the pudendal sensory branch of rats

BACKGROUND: We reported sex difference in the urethral pressure (UP) response to electrical stimulation (ES) of the hypogastric nerve in rats. The purpose of the present study was to report on sex difference in the UP response to ES of the pudendal nerves (PN) in rats before and after injection of d-tubocurarine (d-tc). METHODS: Wistar rats were anesthetized with urethane and alpha-chloralose. The L6-S1 trunk was exposed on the left side and resected. After resection of the motor branch of the PN the peripheral end of the L6-S1 trunk was stimulated. Fluid was infused into the urethra through a catheter inserted into the bladder neck at a constant rate (0.5 mL/10 min) and the infusion resistance was measured as the UP. When d-tc was injected, the rats were ventilated with an artificial respirator. RESULTS: Though ES of the L6-S1 trunk caused fibrillation of the muscles near the tail and steep reduction of the UP, it caused elevation and reduction of UP in male and female rats, respectively, after intravenous injection of d-tc (0.3 mg/kg). ES of the sensory branch of the PN caused the elevation in male rats and reduction of the UP without injection of d-tc, and prazosin inhibited the UP elevation but the reduction was not inhibited by Nomega-nitro-L-arginine methyl ester. CONCLUSION: In the sensory branch of the PN, the nerves innervating the smooth muscles in the urethral sphincter were contained. In male rats norepinephrine mediates the UP elevation, but the neurotransmitter that mediates the UP reduction in female rats is not known.     

Urethral sensitivity to α-adrenoceptor stimulation and blockade in patients with parasympathetically decentralized lower urinary tract and in healthy volunteers

The urethral pressure responses to i.v. infusion of increasing doses of noradrenaline (NA) and to i.v. injection of a single dose of phentolamine were compared in male and female patients with parasympathetically decentralized lower urinary tract and in normal volunteers of both sexes. Maximum urethral pressure (MUP) was significantly lower in the patients than in the volunteers. NA caused a dose-dependent increase in MUP in all subjects; the absolute increase was greater in the patients. However, even at the highest rates of NA infusion, the MUP of the patients did not reach the resting pressure of the normal volunteers', and the dose-response relations for the NA effect did not differ between patients and normal subjects. Phentolamine reduced the urethral pressure significantly less in male volunteers than in the other subjects. It is concluded that patients with parasympathetically decentralized lower urinary tract have no urethral smooth muscle supersensitivity to NA, and that it cannot be excluded that the pelvic, parasympathetic innervation contributes to the regulation of pressure in both the male and female urethra.     

URETHRAL AFFERENT NERVE ACTIVITY AFFECTS THE MICTURITION REFLEX; IMPLICATION FOR THE RELATIONSHIP BETWEEN STRESS INCONTINENCE AND DETRUSOR INSTABILITY

PURPOSE: A causative relationship between stress urinary incontinence (SUI) and detrusor instability has been suspected but never proven. Many women with mixed incontinence have resolution of detrusor instability after surgical correction of SUI. We sought experimental support that stimulation of urethral afferent nerves can induce or change reflex detrusor contractions. MATERIALS AND METHODS: Urethral perfusion pressure and isovolumetric bladder pressure were measured with catheters inserted through the bladder dome in urethane anesthetized female S.D. rats (250 to 300 grams; n = 12). The catheter assembly was seated securely in the bladder neck to block passage of fluid between the bladder and urethra without affecting the nerve supply to the organs. The external urethra was not catheterized. Responses were examined in the control state at a urethral saline perfusion speed of 0.075 ml. per minute. Intraurethral drugs were administered following blockade of striated sphincter activity with intravenous alpha-bungarotoxin (0.1 mg./kg.). RESULTS: Stopping the urethral saline infusion caused a significant decrease in micturition frequency in approximately 50% of the animals studied (n = 12). Intraurethral lidocaine (1%) infused at 0.075 ml. per minute caused a slight decrease in urethral perfusion pressure but no change in detrusor contraction amplitude. However, intraurethral lidocaine caused a significant (45%) decrease in the bladder contraction frequency (n = 5). The micturition frequency returned to baseline 30 minutes after stopping lidocaine infusion. Intraurethral infusion of nitric oxide (NO) donors (S-nitroso-N-acetylpenicillamine [SNAP] (2 mM) or nitroprusside (1 mM) immediately decreased urethral perfusion pressure by 30 to 37% (n = 5). A 45 to 75% decrease (n = 5) in bladder contraction frequency was also seen, which was similar to that observed following lidocaine. Neither NO donor changed the amplitude of bladder contractions. CONCLUSIONS: These results indicate that in the anesthetized rat activation of urethral afferents by urethral perfusion can modulate the micturition reflex. Thus in patients with stress urinary incontinence, leakage of urine into the proximal urethra may stimulate urethral afferents and facilitate voiding reflexes. This implies that stress incontinence can induce and/or increase detrusor instability. These findings have significant implications for the treatment of patients with mixed urge and stress incontinence. Correction of stress incontinence by surgery or pelvic floor exercise in patients with mixed incontinence may resolve the detrusor instability.     

Clinical, Hormonal and Pathological Findings in a Comparative Study of Adrenocortical Neoplasms in Childhood and Adulthood

The present study investigated the role of nitric oxide (NO) in the reflex changes in urethral outlet activity during micturition. Isovolumetric bladder contractions, urethral pressure and external urethral sphincter electromyogram (EUS EMG) activity were recorded independently in urethane-anesthetized rats. During reflex bladder contractions, the urethra exhibited reflex responses characterized by an initial decrease in urethral pressure in conjunction with a rise in bladder pressure. This was followed by a period of high frequency oscillations (HFOs) associated with maximal urethral relaxation and burst type EUS EMG activity. Administration of N-nitro-L-arginine (L-NOARG) 10 mg./kg. intravenously, a nitric oxide synthase inhibitor, reversibly decreased the magnitude (62 percent, p less than 0.05) and duration (40 percent, p less than 0.05) of reflex urethral relaxation (N = 7). In 4 additional experiments, L-NOARG (10 to 15 mg./kg. intravenously) completely eliminated reflex urethral relaxation during micturition, and this effect was reversed in all animals by the administration of L-arginine (100 to 150 mg./kg. intravenously). Administration of N-nitro-D-arginine (D-NOARG) (10 to 30 mg./kg. intravenously) had no effect on reflex urethral relaxation. Neuromuscular blockade (vecuronium bromide 5 mg./kg. intravenously) reversibly decreased resting urethral pressure and eliminated the HFOs. The urethral smooth muscle relaxation that remained after neuromuscular blockade was eliminated following administration of L-NOARG (10 mg./kg. intravenously) in 2 of 3 animals. These results suggest that reflex urethral responses during micturition involve changes in both smooth and striated muscle activity, and that the predominant neurotransmitter mechanisms that mediate reflex urethral smooth muscle relaxation involve NO.     

Neural Control of Urethral Outlet Activity in Vivo: Role of Nitric Oxide

The present study investigated the role of nitric oxide (NO) in the reflex changes in urethral outlet activity during micturition. Isovolumetric bladder contractions, urethral pressure and external urethral sphincter electromyogram (EUS EMG) activity were recorded independently in urethane-anesthetized rats. During reflex bladder contractions, the urethra exhibited reflex responses characterized by an initial decrease in urethral pressure in conjunction with a rise in bladder pressure. This was followed by a period of high frequency oscillations (HFOs) associated with maximal urethral relaxation and burst type EUS EMG activity. Administration of N-nitro-L-arginine (L-NOARG) 10 mg./kg. intravenously, a nitric oxide synthase inhibitor, reversibly decreased the magnitude (62 percent, p less than 0.05) and duration (40 percent, p less than 0.05) of reflex urethral relaxation (N = 7). In 4 additional experiments, L-NOARG (10 to 15 mg./kg. intravenously) completely eliminated reflex urethral relaxation during micturition, and this effect was reversed in all animals by the administration of L-arginine (100 to 150 mg./kg. intravenously). Administration of N-nitro-D-arginine (D-NOARG) (10 to 30 mg./kg. intravenously) had no effect on reflex urethral relaxation. Neuromuscular blockade (vecuronium bromide 5 mg./kg. intravenously) reversibly decreased resting urethral pressure and eliminated the HFOs. The urethral smooth muscle relaxation that remained after neuromuscular blockade was eliminated following administration of L-NOARG (10 mg./kg. intravenously) in 2 of 3 animals. These results suggest that reflex urethral responses during micturition involve changes in both smooth and striated muscle activity, and that the predominant neurotransmitter mechanisms that mediate reflex urethral smooth muscle relaxation involve NO.     

Renal and cardiovascular effects of renal denervation in conscious rats after adenosine administration and nitric oxide synthase inhibition

The role of renal nerves on renal and cardiovascular responses to adenosine administration and/or acute NO synthase inhibition was investigated. Conscious male Wistar rats with implanted catheters in femoral artery for blood pressure registration, femoral vein for drug infusion and bladder for urine collection were used. Adenosine was applied i.v. (1.0 mg/kg BW bolus) followed by infusion of 0.1 mg/kg.min, and/or nitric oxide synthase inhibition (NOSI) was performed by i.v. administration of 10 mg/kg BW N-Omega-nitro-L-arginine methyl ester (L-NAME) before and 1 week after bilateral renal denervation (BRD). NOSI decreased HR and increased SAP, MAP and DAP both in intact and BRD rats. Baroreflex sensitivity increased in intact and BRD rats. Adenosine did not change HR, blood pressure or baroreflex sensitivity in intact as well as BRD rats. NOSI increased V, VU(Na) and VU(CI) in intact rats but decreased V and did not alter VU(Na) and VU(CI) in BRD rats. Adenosine increased V, VU(CI) and C(cr) in intact rats but did not change renal excretory function in BRD rats. Combined application of adenosine and L-NAME led to a dramatic increase of V, VU(Na), VU(Cl) and C(cr) in intact rats. However, VU(Na) and VU(CI) in BRD rats were lower as compared to intact rats. Therefore, changes in renal excretory function seen after NOSI are not exclusively the result of pressure diuresis and natriuresis but in some way are dependent on renal nerves. Renal denervation attenuates the renal excretory response to adenosine. Sympathetic nervous system is important in mediating the effects of adenosine and/or NO on renal excretory function. Renal denervation did not change the pattern of baroreflex sensitivity after adenosine and/or L-NAME administration.     

Nitric oxide synthase in the external urethral sphincter of the sheep: immunohistochemical and functional study

PURPOSE: We studied the distribution of neuronal nitric oxide synthase (nNOS) and the effects of nitric oxide (NO) modulating drugs on contractile function of the external urethral sphincter of lambs. Gender differences were evaluated. MATERIALS AND METHODS: Longitudinal and transverse sections of the external urethral sphincter from 10 female and 10 male lambs were studied using reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry and nNOS immunocytochemistry. Isometric contractile responses to electrical field stimulation were recorded from external urethral sphincter preparations from 47 female and 45 male lambs and the effects of NO modulating drugs were evaluated. RESULTS: We detected nNOS in the sarcolemma of some but not all striated fibers, where nNOS seems to be concentrated at the neuromuscular junction. In addition, nNOS was present in nerve fibers and intramural ganglia. The density of innervation decreased toward the distal part of the external urethral sphincter and was higher in male preparations. No significant functional effects of the NOS inhibitor NG-nitro-L-arginine (10 mM.) or the NO donors diethylamine and spermine NONOate (Sigma Chemical Co., St. Louis, Missouri) (5 mM. each) on external urethral sphincter isometric contractility were found in either gender. CONCLUSIONS: Despite the evidence for nNOS at the sarcolemma and nerve fibers of the external urethral sphincter the physiological relevance of these immunohistochemical findings remains to be determined.     

Roles of nitric oxide and oxidative stress in the regulation of blood pressure and renal function in prehypertensive Ren-2 transgenic rats

AIMS: The present study was performed to evaluate the role of nitric oxide (NO) and its interaction with superoxide anion (O2-) in the regulation of blood pressure (BP) and renal function during the developmental phase of hypertension in Ren-2 transgenic rats (TGR). The first aim was to compare BP and renal functional responses to acute NO synthase (NOS) inhibition achieved by intravenous (i.v.) infusion of Nomega-nitro-L-arginine-methyl ester (L-NAME) in prehypertensive heterozygous TGR and in transgene-negative Hannover Sprague-Dawley (HanSD) rats. The second aim was to evaluate whether scavenging of O2- by infusion of the superoxide dismutase mimetic tempol increases NO bioavailability which therefore should augment BP and renal functional responses to L-NAME. Methods: Rats were anesthetized, prepared for clearance experiments and BP and renal functional responses were evaluated in response to i.v. L-NAME administration (20 microg.100 g(-1).min(-1)) without or with tempol pretreatment (i.v., 300 microg.100 g(-1).min(-1)). In renal cortical tissue, nitrotyrosine protein expression was assessed by immunoblotting as marker of O2- production and urinary 8-epi-PGF(2alpha) excretion as marker of intrarenal oxidative stress was assessed by enzyme immunoassay. Results: BP, glomerular filtration rate (GFR), renal plasma flow (RPF) and sodium excretion were similar in TGR and HanSD. L-NAME infusion induced greater increases in BP in TGR than in HanSD (+42 +/- 4 vs. +25 +/- 3 mmHg, p < 0.05). In the absence of a significant change in GFR, L-NAME caused similar decreases in RPF (-32 +/- 6 and -25 +/- 4%, p < 0.05) in TGR and HanSD. Despite significantly higher renocortical expression of nitrotyrosine and urinary 8-epi-PGF2alpha excretion in TGR than in HanSD, pretreatment with tempol did not augment the rise in BP and the decrease in RPF induced by L-NAME. CONCLUSIONS: The greater BP response to L-NAME in TGR suggests that prehypertensive TGR exhibit an enhanced NO activity in the systemic vasculature as compared with HanSD. Despite increased intrarenal oxidative stress in TGR, the dependency of the intrarenal vascular tone on NO appears to be similar in TGR and HanSD. The lack of a compensatory increase in renal NO activity may partially account for the enhanced renal vascular response to ANG II present in TGR.     

Effects of five alpha-blockers on the hypogastric nerve stimulation of the canine lower urinary tract

Electrical stimulation of the hypogastric nerve increased both urethral and bladder pressures of anaesthetized male dogs, without affecting cardiovascular parameters. Intravenous injections of prazosin, phentolamine, thymoxamine, phenoxybenzamine and yohimbine inhibited the urethral pressure increase in a dose-dependent manner, but the increase in bladder pressure was not modified by these alpha-blockers.     

An electromyographic study of the feline urethral rhabdosphincter in the normal state and after sacral rhizotomy. Part 2. Responses of the rhabdosphincter to hypogastric nerve stimulation]

To investigate functional aspect of sympathetic innervation of the urethral rhabdosphincter, responses of the male feline rhabdosphincter to hypogastric nerve (HGN) stimulation were examined by means of electromyography using fine electrodes. Experiments were performed on 28 normal (N group) and 13 rhizotomized cats under chloralose anesthesia, the latter being further divided into two groups: 4 cats of 1-3 weeks (SR group) and 9 cats of 10-24 weeks (LR groups) after complete sacral rhizotomy. HGN stimulation (1 Hz, 0.3 ms pulse duration, 2-30 V) elicited responses of the rhabdosphincter in N and LR groups. In N group, HGN stimulation still elicited responses of the rhabdosphincter even after pudendal nerve was transected in advance, indicating that these evoked potentials were independent of somatic nerve inflow. The threshold stimuli and latencies of the evoked responses in N group (3.0 +/- 0.2 V, 81.7 +/- 5.7 ms, respectively) were not significantly different from those in LR group (2.9 +/- 0.3 V, 71.5 +/- 10.5 ms), but the amplitudes of the evoked responses were significantly larger in LR group than in N group (110 +/- 12 vs 18 +/- 2 microV, p less than 0.001). These evoked responses of the rhabdosphincter were resistive to prazosin (0.2 mg/kg) and atropine (0.5 mg/kg), but were abolished by hexamethonium (2 mg/min, 10-25 mg) and pancuronium (0.1-0.3 mg/kg) in both groups. In N group, repetitive stimulation (10-20 Hz) of HGN increased activities of the rhabdosphincter when the bladder was empty, but not when the bladder was full enough to trigger the vesicourethral relaxation reflex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urinary Bladder Response to Hypogastric Nerve Stimulation After Bilateral Resection of the Pelvic Nerve or Spinal Cord Injury in Rats

Background: We examined the mechanism of urinary bladder motility return after bladder areflexia induced by interruption of the sacral parasympathetic outflow to the urinary bladder following damage to the sacral cord or pelvic nerves in the rat.
Methods: The L6 and SI nerve bundles were resected near the vertebrae, and bilateral pelvic nerve resections (PNR) performed. Spinal cord injury (SCI) was performed by means of a legion generator at the T12 vertebra. Thirty days after PNR and SCI, cystometrograms were recorded under anesthesia.
Results: In all rats subjected to PNR or SCI, overflow incontinence continued, yet some rats subjected to SCI recovered within 2 weeks after the operation. Cystometrograms showed that repetitive bladder contractions appeared in rats subjected to SCI irrespective of hypogastric nerve (HCN) innervation, while bladder contractions did not appear in rats subjected to PNR. Electrical stimulation of the HGN induced higher bladder pressure elevation in rats who underwent PNR than in rats subjected to SCI.
Conclusions: These results suggest that the generation of repetitive bladder contractions induced by bladder distention after bladder areflexia requires the presence of intact pelvic nerves that transmit sacral cord-originating excitatory information to the bladder. However, the HGN system and functioning pelvic nerve ganglia are not involved in this process. Also, the connection from the preganglionic HGN to the postganglionic parasympathetic nerves in the pelvic plexus did not form after PNR.     

Laboratory comparison of urethral profilometry techniques

A comparison of urethral pressure profiles performed with the air infusion, water infusion, membrane catheter, and transducer tip catheter techniques was made in a canine model. The gas and water infusion methods gave statistically identical results if the gas studies were performed at flow rates of 100 ml./min. and pull rates of 5 cm./min. The transducer tip catheter and the gas and water infusion techniques gave accurate recordings of peak urethral pressure but were incapable of detecting multiple areas of urethral compression. The transducer tip catheter measurements often were difficult to interpret because of rotation and flexion artifact. The membrane catheter was capable of recording multiple areas of urethral compression but gave spuriously high recordings of peak urethral pressure. We conclude that none of the methods tested will give accurate recordings of urethral pressure in all clinical situations.     

Protection from diaphragmatic fatigue by nitric oxide synthase inhibitor in dogs

The role of endogenous nitric oxide (NO) in producing diaphragmatic fatigue was examined in 26 anaesthetized, mechanically ventilated dogs divided into four groups. In Group Ia (n = 5), dogs without fatigue received only Ringer's lactate solution. In Group Ib (n = 5), dogs without fatigue were given i.v. L-arginine analog N omega-nitro-L-arginine methyl ester (L-NAME) 10 mg.kg-1 to inhibit NO synthase (NOS). Groups IIa and IIb (n = 8 of each) received the same doses of i.v. lactate and L-NAME as Groups Ia and Ib effectively. Following administration of the i.v. solution, diaphragmatic fatigue was induced by intermittent supramaximal bilateral electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. Diaphragmatic contractility was assessed in each group by measuring transdiaphragmatic pressure (Pdi). No difference in Pdi was observed between Groups Ia and Ib. After the fatigue-producing period, in Group IIa, Pdi at low-frequency (20 Hz) stimulation decreased from the pre-fatigued values (P < 0.05), whereas Pdi at high-frequency (100 Hz) stimulation did not change. In Group IIb, given L-NAME before producing fatigue, Pdi at both stimuli did not change. In conclusion, L-NAME inhibits the production of diaphragmatic fatigue. This finding suggests that endogenous NO plays an important role in producing diaphragmatic fatigue.     

Urethral dysfunction in diabetic rats

PURPOSE: We investigated the effects of diabetes mellitus (DM) on urethral relaxation mechanisms during reflex bladder contractions in rats. MATERIALS AND METHODS: Five weeks after streptozotocin injection (65 mg/kg intraperitoneally) the effects of DM on urethral relaxation mechanisms were evaluated by simultaneous recordings of intravesical pressure under isovolumetric conditions and urethral perfusion pressure (UPP) using urethane anesthesia. RESULTS: In diabetic rats the UPP nadir during urethral relaxation and intravesical pressure thresholds for inducing urethral relaxation were significantly higher (199% and 92%, respectively) than in normal rats, while baseline UPPs were not significantly different. The mean rate and amplitude of high frequency oscillations of urethral striated muscle in diabetic rats were also significantly lower (17% and 64%, respectively) compared with normal rats. Following alpha-bungarotoxin treatment to eliminate striated muscle sphincter contractions intravenous administration of L-arginine (200 mg/kg) [corrected] , the substrate of nitric oxide (NO) synthase, decreased the UPP nadir (36% and 22%, in diabetic and normal rats) as well as intravesical pressure thresholds (49% and 22%, respectively). The effect was greater (61% to 126%) in diabetic rats than in normal rats. In each group of rats the effect of L-arginine was inhibited by Nomega-nitro-L-arginine (100 mg/kg intravenously) [corrected], a NO synthase inhibitor. CONCLUSIONS: During reflex bladder contractions streptozotocin induced diabetic rats exhibited smooth and striated muscle dysfunctions of the urethral outlet. L-arginine therapy, which could augment urethral smooth muscle relaxation by increasing NO production, may be useful for partially restoring the urethral relaxation mechanism in DM.     

Urethral function after cystectomy: a canine in vivo experiment

Summary To study the function of the pelvic floor and the isolated urethra after removal of the bladder, 5 male and 5 female mongrel dogs were used in an acute in vivo experiment. Urethral pressure changes secondary to unilateral stimulation of the pelvic and pudendal nerves were recorded. After baseline data of the intact system were documented, the following procedures were carried out: separation of the urethra from the bladder neck (prostate), nerve-sparing cystectomy (cystoprostatectomy), and cold-knife incision through the entire length of the proximal urethra. Pressure recordings were repeated after each step of surgery. Pudendal nerve stimulation resulted in rapid and large pressure rises in the distal urethra (reaction typical of striated muscle). This response remained unchanged after all three surgical steps. Pelvic nerve stimulation provoked pressure rises within the urethra of a pattern typical of smooth muscle. The findings persisted after separation of the urethra from the bladder neck (prostate) and after cystectomy, but were not observed after urethrotomy. Contractions secondary to pudendal nerve stimulation were inhibited by curare, which did not affect the reaction to pelvic nerve stimulation. Our experiments demonstrate that in the dog the continuity of bladder and urethra is not required for the function of urethral closure mechanisms. The contractile potency of the urethral smooth muscles remains intact after nerve-sparing cystectomy. We believe that problems with the baseline continence of surrogate bladders should mainly be ascribed to a lack of surgical caution in preserving the autonomic nerves of cystectomy. A poor response to stress conditions cannot be explained by damage to the neural pathway of the striated sphincter, as the pudendal nerve is not at risk during nerve-sparing cystectomy. In our opinion mechanical malfunction of the striated muscle components secondary to scarring at the site of the anastomosis is the main reason for stress incontinence after orthotopic bladder replacement.     

Functional conditions of micturition induced by selective sacral anterior root stimulation: experimental results in a canine animal model

Electrical stimulation of the sacral anterior roots using conventional rectangular current pulses results in a simultaneous contraction of the urinary bladder and the striated urethral sphincter. Using a tripolar nerve cuff electrode with quasitrapezoidal current pulses and appropriate stimulation parameters, hyperpolarization of the nerve-fiber cell membrane under the anode of the stimulating electrode can reversibly arrest action potential propagation in large myelinated nerve fibers, innervating the striated urethral sphincter, while leaving action potential propagation unaffected in small non-myelinated nerve fibers innervating the urinary bladder smooth muscle (anodal arrest). Using this technique in 19 female mongrel dogs, we studied the effect of bladder filling, level of anesthesia, and sacral deafferentation on bladder pressure, urethral pressure, and urinary flow. Effective micturition could be induced only after complete dorsal rhizotomy, abolishing reflex contraction of the striated urethral sphincter, when blocking quasitrapezoidal current pulses were used for stimulation. Stimulation with rectangular current pulses directly induced a rise in distal urethral pressure, preventing micturition during stimulation.     

Pharmacological Effect of Amezinium on Urethra and Bladder of Rabbits

The pharmacological effect of amezinium on the urethra and bladder of rabbits was investigated. Amezinium produced concentration-dependent contractions in isolated urethral strips. The maximum response was approximately 30% of that caused by norepinephrine (NE). The concentration–response curve of NE was shifted to the left by amezinium. Moreover, amezinium enhanced the relaxative effect of NE on carbachol-induced contractions in isolated bladder strips. In anesthetized rabbits, amezinium significantly increased the intraurethral pressure (IUP) but produced only slight increases in mean blood pressure (MBP). Pre-treatment with amezinium ehhanced NE-induced increases in IUP index and MBP. The enhancing effect on the IUP index lasted much longer than that on MBP. In a stress incontinence model amezinium significantly inhibited the incontinence after an i.v. infusion of a low dose of NE. This effect was antagonized by pre-treatment with prazosin. These results suggest that amezinium may produce an excellent effect for stress incontinence, especially mixed, without severe adverse events such as sudden hypertension.