Pharmacological analysis of the responses of the feline urethra to autonomic nerve stimulation

Innervation of bladder and bowel

The autonomic neuromuscular junction is described and neurotransmission, co-transmission and neuromodulation are defined, as well as the 'chemical coding' of sympathetic, parasympathetic, sensory-motor and intrinsic neurons in the wall of the bladder and bowel. A detailed description of the patterns of innervation of smooth muscle of the bowel, bladder and urethra and of the urethral and anal sphincters by intramural and extrinsic autonomic nerves is presented, and the functional and pharmacological features of this innervation are summarized. Finally, changes in the pattern of innervation and expression of co-transmitters and receptors in the bladder and bowel that occur during development and old age and following trauma, surgery and disease are discussed.

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.

Nitric oxide synthase-immunoreactive, adrenergic, cholinergic, and peptidergic nerves of the female rat urinary tract: a comparative study

The distribution and frequency of NO synthase (NOS)-immunoreactive (IR) nerves in relation to the general autonomic innervation, adrenergic, cholinergic and some peptidergic nerves, were investigated in the female rat urinary tract. NOS nerves were very frequent in the smooth musculature of the urethra together with cholinergic, adrenergic and neuropeptide Y (NPY)-IR nerves, whereas vasoactive intestinal peptide (VIP)-IR and calcitonin-gene-related peptide (CGRP)-IR nerves were much less abundant. NOS-IR, CGRP-IR and cholinergic nerves were also frequent in the longitudinal smooth musculature of the distal ureters and the ureteral orifices into the bladder, where no adrenergic, NPY-IR and VIP-IR nerves were found. In contrast, in the detrusor NOS-IR nerves were scarce. Bilateral pelvic ganglionectomy very pronouncedly decreased the number of any of the populations of nerves studied, whereas bilateral pelvic decentralization selectively reduced the number of CGRP-IR nerves in all structures and locations. Outflow obstruction very overtly reduced the number of NOS-IR nerves in parallel with the general autonomic innervation. Thus, in the rat female urinary tract, NOS-containing nerves particularly occur in regions with sphincteric functions such as urethra and ureteric orifices. In these regions NO may exert a transmitter role, both directly or by interaction with other transmitters/modulators.

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.

(R)-thionisoxetine, a potent and selective inhibitor of central and peripheral norepinephrine uptake

Inhibitors of neuronal norepinephrine (NE) uptake are useful for the treatment of a variety of diseases including depression and urinary incontinence. In the present study, we synthesized and evaluated a novel analog of the potent and selective NE uptake inhibitor, nisoxetine. Thionisoxetine more potently inhibited the uptake of [3H]-NE into hypothalamic synaptosomes and [3H]-nisoxetine binding to the NE transporter than (R)-nisoxetine. The (R) enantiomer of this compound was significantly more potent than the (S) enantiomer, having a Ki of 0.20 nM in [3H]-nisoxetine binding. The (R) enantiomer was approximately 70-fold more potent in inhibiting [3H]-NE uptake when compared to [3H]-5HT uptake. In rats, (R)-thionisoxetine prevented hypothalamic NE depletion by 6-hydroxydopamine with an ED50 of 0.21 mg/kg. Depletion of NE in peripheral nerves was accomplished by the administration of metaraminol to rats. In this paradigm, (R)-thionisoxetine prevented the depletion of heart NE with an ED50 of 3.4 mg/kg and urethral NE with an ED50 of 1.2 mg/kg. Thus, (R)-thionisoxetine is a potent and selective inhibitor of NE uptake in both central and peripheral tissues.

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)

Facilitatory and inhibitory effects of selective norepinephrine reuptake inhibitors on hypogastric nerve-evoked urethral contractions in the cat: a prominent role of urethral beta-adrenergic receptors

Tricyclic antidepressants (TCA), such as imipramine, are well-accepted for the treatment of urinary incontinence and enuresis, but their mechanism of action remains undefined due to their multiple pharmacological actions. To explore only the contribution imparted by sympathomimetic effects on the urethra by norepinephrine (NE) reuptake inhibition, two selective NE reuptake inhibitors (nisoxetine and tomoxetine) that possess no antimuscarinic or serotonergic properties were examined for their effects on sympathetic hypogastric nerve (HgN) evoked urethral contractions in chloralose anesthetized cats. Under control conditions, HgN stimulation produced a biphasic response composed of a consistent initial contraction that was prazosin- (alpha adrenergic antagonist) sensitive, followed by a more variable relaxation that was propranolol- (beta adrenergic antagonist) sensitive. Unexpectedly, nisoxetine (0.03 to 1.0 mg./kg. intravenously, n = 6) and tomoxetine (0.3 to 3 mg./kg. intravenously, n = 3) produced decreases (about 50% to 60% of control) in HgN-evoked contractions. These inhibitory effects of the reuptake inhibitors were reversed by propranolol. In cats that were pretreated with propranolol, nisoxetine produced a significant increase in HgN-evoked contractions. In conclusion, these results indicate that inhibition of NE reuptake into the sympathetic nerve terminal produces a relative increase in the activation of beta adrenergic receptors compared with alpha adrenergic receptors in the urethra. This increased beta receptor stimulation might be due to a greater diffusion of NE away from the neuro-effector junction to extrajunctional sites following blockade of junctional reuptake. These findings should highlight the importance of urethral beta adrenergic receptors, which is not well-recognized in the literature.

An electromyographic study on the urethral rhabdosphincter in normal and chronically rhizotomized cats: analysis of electrical potentials evoked by sympathetic nerve stimulation

To investigate functional aspects of sympathetic nerve influence on the urethral rhabdosphincter, we examined electrical potentials of the male feline rhabdosphincter evoked by hypogastric nerve (HGN) stimulation using electromyography. Hypogastric nerve stimulation (1 Hz) elicited electrical potentials of the rhabdosphincter in both normal and chronically rhizotomized cats. In normal cats, the evoked potentials were not affected by transection of the bilateral pudendal nerves. The amplitudes of the evoked potentials were significantly larger in rhizotomized cats (p < 0.001), while the threshold stimuli and latency periods were not. These evoked potentials were prazosin- and atropine-resistant, but were abolished by hexamethonium and pancuronium in both groups. In normal cats, high frequency stimulation (10 to 20 Hz) of the HGN increased the activity of the rhabdosphincter when the bladder was empty, but not when the bladder was full enough to trigger the vesicourethral relaxation reflex. This excitatory effect of HGN stimulation was blocked by prazosin. These data suggest that the potential of the rhabdosphincter evoked by HGN stimulation (1 Hz) is produced through synapse from sympathetic preganglionic to cholinergic postganglionic neurons, and that, after sacral rhizotomy, cholinergic postganglionic terminals form more effective functional connections to somatically denervated motor end-plates of the rhabdosphincter. The sympathetic nerve is also believed to play a role in modulating urethral afferent activities through action on urethral smooth muscle.

Control of detrusor stiffness in the chronic decentralized feline bladder

The neuropharmacology of increased bladder stiffness, which may contribute to upper tract damage and incontinence, was investigated in 76 cats. beta-blockade increased but combined alpha 1-adrenergic with muscarinic blockade decreased filling phase stiffness in normal cats. Bladder wall stiffness during the early filling phase was unaffected by chronic S2 ventrodorsal rhizotomy or L7-S3 ventral rhizotomy, but was decreased when L7-S3 dorsal rhizotomy or total sympathectomy was combined with the ventral root lesion, implying that sacral dorsal roots and sympathetic efferents maintain normal detrusor stiffness. Acute sympathectomy increased stiffness in all the former 3 chronic groups, implying that a tonic or reflex sympathetic inhibition operates independently of the L7-S3 dorsal roots. Stiffness during early filling phase decreased with acute ventral rhizotomy. This change persisted with chronic sympathectomy but returned to normal if sympathetic nerves were left intact. These results suggest that bladder stiffness is modulated by tonic or reflexic sympathetic activity, which is influenced by L7-S3 afferents. Detrusor stiffness during the later stages of filling, which was decreased by acute sympathectomy in chronic groups but increased by chronic sympathectomy, was reduced by interference with adrenergic or muscarinic mechanisms after either lesion. Therefore, a peripheral pathway with facilitatory alpha 1-adrenergic and muscarinic receptors is involved in the production of increased late stage stiffness after chronic sympathetic damage. We propose that the increased bladder stiffness seen in congenital sacral lesions may be analogous to the stiffness during late stages of filling reported here. Our results also imply that the presence of this increased stiffness is closely associated with chronic sympathetic damage. Whether the increased stiffness in congenital and traumatic neural lesions in humans arises from sympathetic damage remains to be determined.

Neurogenic responses of urethra isolated from the dog

Electrical transmural stimulation evoked contraction and relaxation in isolated urethral circular muscle of the dog. The responses were abolished by tetrodotoxin, indicating their neurogenic origin. The contractile force in the middle urethra was greater than that in the proximal and distal urethra. The contractions were not affected by atropine and propranolol, but were completely inhibited by phenoxybenzamine, prazosin and guanethidine. In preparations contracted with prostaglandin F2 alpha, electrical stimulation induced frequency-dependent relaxation in all urethral portions. Atropine, phenoxybenzamine, prazosin and guanethidine had no effect on the relaxation, while propranolol slightly attenuated the relaxation induced at the highest frequency used (5 Hz). The non-adrenergic, non-cholinergic relaxation was also not affected by ketanserin, methysergide, diphenhydramine, alpha,beta-methylene ATP or capsaicin. Exogenously applied phenylephrine and clonidine both produced contractions but the maximal response to clonidine was much smaller than that to phenylephrine. Acetylcholine produced no or feeble contractions. In the preparations contracted with prostaglandin F2 alpha, isoproterenol and vasoactive intestinal polypeptide (VIP) produced relaxation. These results suggest that the circular muscle of dog urethra is reciprocally innervated by sympathetic adrenergic and non-adrenergic, non-cholinergic nerves, and that the neurogenic responses are markedly affected by muscle tension and the portion of the urethra examined.

Sympathetic innervation of the male feline urethral rhabdosphincter

Sympathetic innervation of the male feline urethral rhabdosphincter was investigated by means of electromyography (EMG). Hypogastric nerve stimulation elicited responses in the rhabdosphincter, the latencies and amplitudes ranged from 40 to 107 ms and 6 to 40 microV, respectively. These hypogastric nerve-evoked responses in the rhabdosphincter were not affected by whether the urinary bladder was empty or full. The results suggest that hypogastric nerve-evoked responses in the rhabdosphincter are not dependent on somatic nerve, but are produced through a rather direct effect of sympathetic nerve on the rhabdosphincter.

Functional responses of different muscle types of the female rat urethra in vitro

The influence of muscle type on functional responses of the female rat urethra was investigated using morphological and functional in-vitro techniques. The urethral submucosa was found to contain longitudinally or obliquely oriented smooth muscle cells. The muscularis layer is composed of circularly oriented muscle cells. Near the bladder orifice smooth muscle fibres dominate, but in the mid-urethra the vast majority is circularly oriented striated muscle cells. Circular preparations responded to electrical field stimulation in vitro with a rapid contraction. Stimulation with single impulses resulted in a twitch response; frequencies exceeding 5-10 Hz induced a summation and tetanus. The response was unaffected by phenoxybenzamine, propranolol and scopolamine and had a low sensitivity to calcium-free solution but was sensitive to suxamethonium and tetrodotoxin. Using longer impulse trains stimulation evoked also a slow contraction, sensitive to calcium-free solution. In longitudinal preparations stimulation induced a relaxation followed by a contraction, responses much smaller than those seen in the circular preparations. Both preparations relaxed on addition of calcitonin gene-related peptide or capsaicin. The relaxation to calcitonin gene-related peptide was larger than that to capsaicin in longitudinal preparations but equally large in the circular ones. Substance P and 5-hydroxytryptamine contracted both preparations. The longitudinal urethra showed a larger contraction to 5-hydroxytryptamine than to substance P, whereas both substances induced similar responses in the circular preparations. The study shows a similar muscle arrangement in the female rat urethra as described in humans and further points to a functional differentiation between the different types of muscle.

Functional studies on the cholinergic and sympathetic innervation of the rat proximal urethra: effect of pelvic ganglionectomy or experimental diabetes

1. Isolated rings of rat proximal urethra contracted in response to acetylcholine, noradrenaline, phenylephrine, tachykinins or field stimulation. In the presence of field stimulation-induced contractions, isoprenaline or CGRP produced an inhibitory effect on evoked contractions. 2. Electrical field stimulation produced frequency-related contractions which, when using trains of stimuli, consisted of a phasic and a tonic response. These contractions were abolished by tetrodotoxin (1 microM) but unaffected by hexamethonium (10 microM). 3. Atropine (3 microM) produced a partial inhibition of these nerve-mediated contractions, slightly more evident on the tonic than the phasic response. In the presence of atropine (3 microM), phentolamine (3 microM) or prazosin (1-10 nM) produced an almost complete inhibition of the response to field stimulation. 4. After bilateral removal of the pelvic ganglia, electrical field stimulation was still able to induce tetrodotoxin-sensitive contractions of the rat proximal urethra. However, the inhibitory effect of atropine was much reduced as compared to controls, while the phentolamine-sensitive portion of the response was increased. 5. DMPP (0.1 mM) a nicotinic receptor agonist, produced a contraction (phasic and tonic components) which was strongly inhibited by hexamethonium (10 microM), abolished by prazosin (1 microM) and reduced by tetrodotoxin (3 microM). 6. In urethral rings from diabetic rats (i.v. streptozotocin 7-9 weeks before) the contractile response to acetylcholine or noradrenaline as well as the response to field stimulation were unchanged as compared to controls. 7. Capsaicin (1 microM) produced an inhibitory effect on the nerve-mediated contractions of the rat proximal urethra. This response was abolished by pelvic ganglionectomy but was unaffected in streptozotocin-treated rats. 8. These findings provide functional evidence that both cholinergic and noradrenergic nerves mediate the contractions of the rat proximal urethra. In addition, capsaicin-sensitive sensory nerves can produce certain local motor responses through release of endogenous neuropeptides. In vivo studies are needed to examine the interplay between these differents sets of motor nerves in the regulation of proximal urethra motility.

Infravesical outflow obstruction in rats: a comparison of two models

1. A new model of infravesical outflow obstruction was developed in male rats by the repeated s.c. administration of testosterone for 5-15 days (3 mg/kg die). The effects of this treatment which produced a 65% increase of prostate weight (10 days) on bladder voiding was evaluated in urethane anesthetized rats by the transvesical infusion of saline and compared to the cystometric alterations produced by application of a silk ligature at urethral level in female rats (4-8 weeks before) as described by Malmgren et al. (1987a, b). 2. Testosterone-pretreatment for 10 days produced little changes in bladder weight, bladder capacity or amplitude of micturition contraction but determined a marked increase in residual volume, indicating that infravesical outflow obstruction impaired significantly bladder voiding. Furthermore, detrusor instability was observed in the majority of testosterone-treated rats. 3. The participation of an active component to voiding impairment in testosterone-treated rats was suggested by the effect of intravenous prazosin which improved voiding efficiency. 4. In urethra-ligated female rats there was a marked increase in bladder weight which was paralleled by a dramatic alteration in micturition reflex that is marked increase in bladder capacity and residual volume. 5. It is concluded that these two models of infravesical outflow obstruction produce cystometric patterns simulating the urodynamic alterations observed in patients with benign prostatic hyperplasia and are potentially suitable for development of drugs in this field.

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.

Bladder and urethral function and supersensitivity to subcutaneously administered bethanechol in cats with chronic cauda equina lesions

The failure of bethanechol chloride to induce voiding in patients with neurogenic bladder, despite a positive bethanechol test, is being reported more frequently. An experimental model was designed in the cat to study the response of the bladder and urethra to subcutaneous and intraarterial bethanechol after complete and partial sacral decentralization. Complete sacral rhizotomy abolished the micturition reflex. Basal urethral perfusion pressure was not affected by complete sacral rhizotomy and a significant part of this basal urethral pressure remained sympathetically mediated. However, the urethral constriction response to bladder filling was lost in half the cats with complete lesions. Bladder and urethral supersensitivity to bethanechol chloride in cats with complete lesions was characterized by a shift to the left of the i.a. dose-response curve, and by the presence of responses to doses of s.c. bethanechol chloride which are subthreshold in normal cats. The urethra also showed exaggerated constriction responses to i.a. and s.c. bethanechol. After complete lesions a part of the bladder and urethral responses to s.c. bethanechol was adrenergically mediated and exerted through the vesicourethral short neuron system. The rest of the response was due to stimulation of urethral muscarinic receptors. Partial sacral lesions were compatible with a micturition reflex and the urethra retained its reflex response to bladder distension. After partial decentralization the bladder and urethra also showed responses to subthreshold doses of s.c. bethanechol. While the bladder response to s.c. bethanechol did not show a significant adrenergic component in cats with partial lesions, most of the urethral response was sympathetically mediated. In conclusion, complete cauda equina lesions result in an areflexic detrusor with frequent loss of the urethral responsiveness to bladder filling. Urethral supersensitivity to s.c. bethanechol might be responsible for a non-voiding outcome after bethanechol injection in patients with complete cauda equina lesions, despite a positive bethanechol test. Because the detrusor reflex is preserved and the urethra is less supersensitive to bethanechol after partial cauda equina lesions, these may represent a better indication for bethanechol therapy than do complete ones.

Adrenergic and non-adrenergic contraction of isolated urethral muscle from rabbit and man

Isolated urethral muscle from rabbit and man was subjected to electrical field stimulation and the components of the resulting contraction were analyzed. Contraction usually consisted of 2 main components. One was rapidly developing, non-adrenergic and atropine-resistant. The other developed more slowly and was sensitive to alpha-adrenoceptor blockade and to chemical sympathectomy with 6-hydroxydopamine. By lowering the temperature from 37C to 20C, these contraction components could be separated from each other. Both could be blocked by tetrodotoxin but the effects of this drug were not consistent in human tissue. Characteristic for the initial contraction component was its dependence on the tension of the preparation; it increased with increasing tension. The adrenergic part of the contraction could be effectively blocked by phentolamine and prazosin, whereas rauwolscine was less effective. Atropine and scopolamine also inhibited the adrenergic part of the contraction, whereas acetylcholine caused a transient increase. The non-adrenergic contraction component was less sensitive to deprivation of extracellular Ca2+ than the adrenergic; almost 40 per cent remained after exposure to Ca2+ free solution for 40 min., whereas the adrenergic component disappeared after 20 min. exposure. Light and electron microscopic investigation revealed 3 distinct layers of the rabbit urethral wall, 1 outer consisting of smooth and striated muscle, 1 middle consisting of smooth muscle only, and a submucosal layer where vessels and smooth muscle cells were found. Removal of the longitudinal muscle layer did not change the responses to electrical stimulation. The results suggest that the electrically induced adrenergic activation of urethral muscle of both rabbit and man was mediated mainly via alpha-adrenoceptors and that this muscle is innervated not only by sympathetic, adrenergic nerves but also by a type of nerve able to release a non-cholinergic, contraction-mediating transmitter.

The effects of oestrogens on spontaneous activity and responses to phenylephrine of the mammalian urethra

The electrical and mechanical activity of strips of urethral smooth muscle from female ovariectomized rabbits were studied. Results were compared with strips from guinea-pigs, dogs and Tammar wallabies and with anaesthetized rabbits. From pressure recordings in intact animals and contractile responses of strips it was concluded that in the urethra of the rabbit both cholinergic and alpha-adrenergic receptors were excitatory. Urethral strips from rabbits and wallabies had continuous spontaneous mechanical activity that was reduced by pre-treatment with oestrogen. In dogs spontaneous activity was transient and in guinea-pigs was usually absent. The alpha-adrenergic agonist, phenylephrine, produced a dose-related contraction of urethral strips from all species. Pre-treatment with oestrogen produced no significant change in the rabbit and guinea-pig but increased sensitivity in the dog and wallaby. Electrical activity was recorded with micro-electrodes from smooth muscle cells of rabbit and guinea-pig urethra. In both species pre-treatment with oestrogen produced slight depolarization. In rabbits regular spike activity was recorded from all animals but there was a tendency for double spikes and reduced amplitude following oestrogen treatment. In guinea-pigs bursts of spikes occurred in control animals; after hormone treatment there was often incomplete recovery of spikes within the burst. The results indicate that oestrogens can influence the smooth muscle of the urethra by modifying both spontaneous activity and the responses to stimulation of alpha-adrenoceptors.

Experimental evidence for a central nervous system site of action in the effect of alpha-adrenergic blockers on the external urinary sphincter

The present study was done to test the hypothesis that alpha-adrenoceptor blocking drugs (phentolamine and prazosin) could interfere with somatic control of the external sphincter through an action in the central nervous system. Stimulation of the hypogastric nerve in the chloralose-anesthetized cat caused a urethral constriction which could be antagonized by alpha-receptor blockers. However, the constriction produced by stimulation of the S1 or S2 ventral root was completely resistant to alpha blockade. The drugs therefore had the expected action against sympathetic stimulation of the urethra but had no peripheral effect on the somatic component. The central effect of these drugs was investigated by recording urethral perfusion pressure responses, or compound action potentials on the central cut end of the pudendal nerve, evoked by stimulation of the contralateral pudendal or pelvic nerve. The urethral constriction produced by stimulation of the central cut end of 1 pudendal nerve was antagonized by both prazosin and phentolamine. Action potentials evoked on the pudendal nerve by stimulation of the central cut end of the contralateral pudendal or pelvic nerve were substantially inhibited by prazosin. Phentolamine produced a more variable blockade of the pudendal-pudendal reflex. The results strongly indicate that these alpha-adrenoceptor antagonists and especially prazosin can influence pudendal nerve-dependent urethral responses through a central nervous system action and not through a peripheral mechanism.

Urethral response during bladder contraction induced by subcutaneous bethanechol chloride: elicitation of a sympathetic reflex urethral constriction

The responses of the urethra to bladder filling and to subcutaneous bethanechol were studied in a surgically separated bladder-urethra preparation in chloralose anesthetized cats. With the pudendal nerves cut or the neuromuscular junction blocked with gallamine, urethral closure pressure increased during bladder filling and the initial phase of the micturition contraction. It then fell spontaneously or in response to bladder emptying through a vent. With the bladder volume held constant subcutaneous bethanechol induced an increase in basal bladder pressure which culminated in a sustained (reflex) contraction. The urethral constrictor response resembled that seen during the cystometrogram; an increase during the rise in detrusor pressure and a fall during the latter part of the sustained (reflex) contraction. In both cases the urethral response was substantially depressed by hypogastric nerve transection or by intravenous prazosin, implying that the urethral responses were reflexly mediated through the sympathetic system. Intra-arterial bethanechol also produced a urethral constriction, but this response was abolished by atropine and not affected by hypogastric nerve section or prazosin. It is therefore concluded that although bethanechol can produce urethral constriction through a direct muscarinic action on the urethra, it does not do so after subcutaneous administration in a neurally intact cat. The urethral response seen after subcutaneous bethanechol administration is part of the micturition reflex complex and is sympathetically mediated.