The role of the hypogastric nerve in bladder and urethral activity of the dog

The Anatomy, Histology, and Function of the Major Pelvic Ganglion

This review provides a comprehensive analysis of the pelvic plexus and its regulation across various mammalian species, including rats, cats, dogs, and pigs. The pelvic and hypogastric nerves play crucial roles in regulating pelvic functions such as micturition, defecation, and erection. The anatomical organization of these nerves varies, forming either well-defined ganglia or complex plexuses. Despite these variations, the neurons within these structures are consistently regulated by key neurotransmitters, norepinephrine and acetylcholine. These neurons also possess receptors for testosterone and prolactin, particularly in rats, indicating the significant role of these hormones in neuronal function and development. Moreover, neuropeptides such as vasoactive intestinal peptide (VIP), substance P, neuropeptide Y (NPY), somatostatin (SOM), galanin (GAL), and calcitonin gene-related peptide (CGRP) are co-released with neurotransmitters to modulate pelvic functions. This review highlights the complex interplay between neurotransmitters, neuropeptides, and hormones in regulating pelvic physiology and emphasizes the importance of hormonal regulation in maintaining the functionality and health of the pelvic plexus across different species.

How important is the α1-adrenoceptor in primate and rodent proximal urethra? Sex differences in the contribution of α1-adrenoceptor to urethral contractility

Urethral smooth muscle (USM) contributes to urinary continence by contracting during the urine storage phase, which is mainly mediated by activation of postjunctional α₁-adrenoceptors. Males and females show differences in the functioning of the lower urinary tract and the most common urinary tract symptoms (LUTS). LUTS in men typically occur in association with bladder outlet obstruction, whereas in women urinary urge-incontinence symptoms are more common. Therefore, this study aimed to evaluate sex differences in α₁-adrenoceptor subtype expression and their importance in proximal urethra contraction in the mouse (C57BL6/J) and marmoset (Callithrix jacchus). Contractile responses to phenylephrine, norepinephrine, potassium chloride (KCl), and electrical-field stimulation (EFS) were evaluated. Phenylephrine, norepinephrine, KCl, and EFS produced markedly greater contractions in male mice and marmoset USM compared with females. The sex differences remained unchanged by N^ω-nitro-l-arginine (l-NAME; nitric oxide synthase inhibitor), atropine (muscarinic receptor antagonist), and PPADS (P2X1-purinoceptor antagonist). Additionally, selective α_1A (but not α_1B- and α_1D-)-adrenoceptor antagonists significantly reduced phenylephrine-induced USM contractions. qRT-PCR for α_1A-, _B-, and _D-adrenoceptor subtypes revealed a marked presence of the α_1A-adrenoceptor subtype in male USM, but not females. Male mouse urethra also exhibited a higher tyrosine hydroxylase mRNA expression. Histomorphometric analysis showed a greater USM area in male than female mice. In conclusion, male mouse and marmoset proximal USM shows strong α_1A- adrenoceptor-induced contractions and abundant α_1A-adrenoceptor expression, whereas α_1A-adrenoceptor-mediated mechanisms are much less important in females. The differential expression of α₁-adrenoceptors in the proximal urethra may contribute to the higher incidence of urinary incontinence in women and obstructed voiding in men.

Purinergic signalling in the urinary tract in health and disease

Purinergic signalling is involved in a number of physiological and pathophysiological activities in the lower urinary tract. In the bladder of laboratory animals there is parasympathetic excitatory cotransmission with the purinergic and cholinergic components being approximately equal, acting via P2X1 and muscarinic receptors, respectively. Purinergic mechanosensory transduction occurs where ATP, released from urothelial cells during distension of bladder and ureter, acts on P2X3 and P2X2/3 receptors on suburothelial sensory nerves to initiate the voiding reflex, via low threshold fibres, and nociception, via high threshold fibres. In human bladder the purinergic component of parasympathetic cotransmission is less than 3 %, but in pathological conditions, such as interstitial cystitis, obstructed and neuropathic bladder, the purinergic component is increased to 40 %. Other pathological conditions of the bladder have been shown to involve purinoceptor-mediated activities, including multiple sclerosis, ischaemia, diabetes, cancer and bacterial infections. In the ureter, P2X7 receptors have been implicated in inflammation and fibrosis. Purinergic therapeutic strategies are being explored that hopefully will be developed and bring benefit and relief to many patients with urinary tract disorders.

Mechanisms of reflex bladder activation by pudendal afferents

Activation of pudendal afferents can evoke bladder contraction or relaxation dependent on the frequency of stimulation, but the mechanisms of reflex bladder excitation evoked by pudendal afferent stimulation are unknown. The objective of this study was to determine the contributions of sympathetic and parasympathetic mechanisms to bladder contractions evoked by stimulation of the dorsal nerve of the penis (DNP) in α-chloralose anesthetized adult male cats. Bladder contractions were evoked by DNP stimulation only above a bladder volume threshold equal to 73 ± 12% of the distension-evoked reflex contraction volume threshold. Bilateral hypogastric nerve transection (to eliminate sympathetic innervation of the bladder) or administration of propranolol (a β-adrenergic antagonist) decreased the stimulation-evoked and distension-evoked volume thresholds by -25% to -39%. Neither hypogastric nerve transection nor propranolol affected contraction magnitude, and robust bladder contractions were still evoked by stimulation at volume thresholds below the distension-evoked volume threshold. As well, inhibition of distention-evoked reflex bladder contractions by 10 Hz stimulation of the DNP was preserved following bilateral hypogastric nerve transection. Administration of phentolamine (an α-adrenergic antagonist) increased stimulation-evoked and distension-evoked volume thresholds by 18%, but again, robust contractions were still evoked by stimulation at volumes below the distension-evoked threshold. These results indicate that sympathetic mechanisms contribute to establishing the volume dependence of reflex contractions but are not critical to the excitatory pudendal to bladder reflex. A strong correlation between the magnitude of stimulation-evoked bladder contractions and bladder volume supports that convergence of pelvic afferents and pudendal afferents is responsible for bladder excitation evoked by pudendal afferents. Further, abolition of stimulation-evoked bladder contractions following administration of hexamethonium bromide confirmed that contractions were generated by pelvic efferent activation via the pelvic ganglion. These findings indicate that pudendal afferent stimulation evokes bladder contractions through convergence with pelvic afferents to increase pelvic efferent activity.

Regeneration of hypogastric nerve using a polyglycolic acid (PGA)-collagen nerve conduit filled with collagen sponge proved electrophysiologically in a canine model

The hypogastric nerve (HGN) is a sympathetic nerve in the peritoneal cavity and controls urinary and seminal functions. In this study, the regeneration of HGN was determined by using a new type of an artificial nerve conduit, polyglycolic acid (PGA)-collagen nerve conduit filled with collagen sponge in two dogs. A PGA-collagen nerve conduit (diameter=2 mm) was interposed in a 10 mm gap of the right HGN. The regeneration of the HGN was evaluated electrophysiologically 8 months after the operation. The intraluminal pressure of spermatic duct and the bladder neck were elevated 80 mmHg and 25 mmHg respectively by the stimulation across the regenerated HGN. The prostate contraction was also elicited. The responses diminished after the excision of the regenerated portion of HGN. These results proved the regeneration of HGN and this nerve conduit will be great help for patients who suffer from urinary and seminal disturbances.

Nitric oxide control of lower genitourinary tract functions: a review

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

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.

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.

Synchronized electrical stimulation of the sympathetic and parasympathetic innervation of the bladder: facilitation of the initiation of micturition in the dog

To improve the quality of bladder contractions induced by parasympathetic stimulation and to facilitate the initiation of voiding, we investigated the effect of sympathetic stimulation on the parasympathetic innervation of the bladder in 12 dogs. For the sympathetic system, the lumbar sympathetic trunks were electrically stimulated; for the parasympathetic system, either the pelvic nerve or the ventral root of S2 was stimulated. With voltages at or just above the threshold for achieving a measurable effect on bladder pressure, stimulation of the sympathetic system or the pelvic nerve alone did not lead to voiding, and sacral root stimulation alone elicited voiding in only 7.4 per cent of stimulations. However, when the same stimulus parameters were used for synchronous stimulation, the voiding process was facilitated when sympathetic stimulation was begun five to 10 seconds before parasympathetic stimulation. When the pelvic nerve was used, voiding resulted in 77.7 per cent of stimulations and the bladder was emptied by a mean of 68.7 per cent; with S2 ventral root stimulation, voiding resulted in 83.3 per cent of stimulations and the bladder was emptied by 59.7 per cent. The facilitory effect of sympathetic stimulation was not abolished when the sympathetic trunks were cut centrally to the point of stimulation, but was absent when the hypogastric nerves were transected. We feel that sympathetic stimulation modulates the parasympathetic innervation of the bladder.

Urinary bladder and urethral responses to pelvic and hypogastric nerve stimulation and their relation to vasoactive intestinal polypeptide in the anaesthetized dog

The effects on the urinary bladder and urethra of pelvic and hypogastric nerve stimulation and their relation to vasoactive intestinal polypeptides (VIP) were investigated in the anaesthetized dog. Both pelvic and hypogastric nerve stimulation elicited a twofold increase in urinary bladder blood flow and a clear-cut increase in bladder venous effluent VIP concentration. Hypogastric nerve stimulation induced an initial, partly alpha-adrenergic and partly non-adrenergic, non-cholinergic, contraction of the urinary bladder followed by a relaxation. The urethra response was a maintained alpha-adrenergic contraction. Pelvic nerve stimulation elicited a bladder contraction with an initial non-cholinergic peak, whereafter the bladder pressure was maintained at a lower level, an effect which was mainly cholinergic in origin. The urethral response was an initial non-adrenergic, non-cholinergic contraction followed by a maintained cholinergic contractile response. Afferent pelvic nerve stimulation led to an efferent activity that seemed to be a combination of activity in pelvic and hypogastric pathways to the urinary bladder and the urethra. VIP (10 nmol) injected i.v. induced a relaxation of the urinary bladder and the urethra, together with a fall in systemic blood pressure. However, despite high plasma concentrations, no vasodilation was elicited in the urinary bladder. Thus, the main target for the VIP release during pelvic and hypogastric nerve stimulation is probably not the bladder vasculature, but instead perhaps the bladder smooth muscle proper.

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.

Influence of serotonin on lower urinary tract smooth muscle in vitro

The influence of serotonin (5-hydroxytryptamine) on human detrusor and on pig detrusor, trigone, bladder neck and urethral smooth muscle was explored in a series of in vitro experiments. Serotonin evoked a dose-dependent and reversible contraction of the detrusor. The reverse response was triggered in trigone, bladder neck and urethral smooth muscle--a dose-dependent and reversible relaxation. The maximum amplitude of this relaxation was 85 +/- 15% of the relaxation produced by electrical nerve stimulation. The effect of serotonin was unaltered by blockade of ganglia, alpha- and beta-adrenergic receptors, cholinergic receptors and prostaglandin synthesis. The serotonin antagonists ketanserin, methysergide and cyproheptadine partly inhibited the effect of serotonin. The antagonism differed in potency on strips of different origin. The antagonists were ineffective or minimally effective in blocking responses to nerve stimulation. The effect of serotonin was probably mediated by specific serotonin receptors different from the serotonin-S2-receptors predominating in vascular smooth muscle. Serotonin is a potential neurotransmitter in lower urinary tract smooth muscle, but its importance in micturition physiology and pathophysiology is unknown.

Intramural neurons of the guinea-pig urinary bladder: histochemical localization of putative neurotransmitters in cultures and newborn animals

Histochemical methods have been used to study the distribution of putative neurotransmitters in the urinary bladder of newborn guinea-pigs and in cultures of intramural ganglia. Following the nicotinamide adenine dinucleotide (NADH)-diaphorase reaction which specifically labels nerve cell bodies, up to 66 ganglia were observed in stretch preparations of the newborn urinary bladder. Each ganglion contained 2-50 nerve cell bodies. Vasoactive intestinal polypeptide was localized in a few nerve cell bodies of intramural ganglia both in in situ and culture preparations. In the in situ preparations it was widely distributed in nerve fibres to the muscle, being most dense at the base of the bladder, and in some mucosal epithelial cells. Somatostatin was contained in numerous neuronal cell bodies in the detrusor muscle both in situ and in culture. Extensively distributed varicose fibres were found in culture and in the muscle, submucous and mucosal layers in situ. Substance P immunofluorescence was demonstrated in a few neuronal cell bodies in ganglia both in situ and in vitro, particularly in those of the mucosa at the base of the bladder. In the in situ preparations varicose nerve fibres containing substance P were seen in the muscle coats with greatest density in the bladder base. Met-enkephalin-immunoreactive nerve cell bodies were not seen either in situ or in culture. Nerve fibres in in situ preparations were found largely enveloping neuronal cell bodies within the ganglia. Neither serotonin-immunoreactive nor catecholamine-containing neuronal cell bodies were seen in the in situ bladder preparation. However, some nerve cell bodies in culture showed positive staining, possibly as a result of selective uptake of serotonin and catecholamine known to be contained in foetal calf serum in the culture medium or possibly as the result of increased synthetic activity in certain neurones in the culture situation. In whole-mount stretch preparations, no serotonin-immunoreactive nerve fibres were seen, but catecholamine-containing small intensely fluorescent cells and nerve fibres were observed. Acetylcholinesterase-positive nerve cell bodies and nerve fibres were observed both in in situ and culture preparations of the bladder. Quinacrine-positive nerve cell bodies (as an indicator of purinergic neurones) were found in numerous intramural neurones examined. in situ; however, under the culture conditions used, non-selective staining of all cell types occurred.

The neural and non-neural mechanisms involved in urethral activity in rabbits

The effects of electrical and chemical stimulation on the mechanical or electrical properties of the circular smooth muscle cells of the bladder neck, and proximal urethra of the male rabbit were investigated by means of micro-electrode, double-sucrose-gap and tension-recording methods. In the bladder neck, application of short current pulses (50 microseconds) produced an initial excitatory junction potential (e.j.p.) with a superimposed spike, followed by a late depolarization, and these electrical events evoked contraction. The initial e.j.p. was unaffected by guanethidine, phentolamine, methysergide or mepyramine, indicating the initial e.j.p. is not mediated by activation of adrenergic, tryptaminergic or histaminergic receptors. The late depolarization was enhanced by pre-treatment with neostigmine (10(-7) M) and abolished by atropine (10(-6) M). In the proximal urethra, electrical-field stimulation evoked phasic contraction which was followed by relaxation, associated with initial e.j.p.s, late depolarization and inhibitory junction potentials (i.j.p.s). Guanethidine (10(-5) M) or phentolamine (10(-6) M) reduced the size of the initial e.j.p. to 40-50% of the control value and combined application of guanethidine and atropine further reduced the amplitude of the e.j.p. to 20-30%. There was a parallel reduction in the mechanical response. The late depolarization was enhanced by neostigmine and abolished by atropine. The i.j.p. and muscle relaxation were not affected by propranolol, phentolamine, guanethidine or atropine. These results indicate that the proximal urethral smooth muscle cells are innervated by adrenergic and cholinergic excitatory, and by non-cholinergic non-adrenergic inhibitory nerve fibres. In the prostatic urethra, field stimulations also evoked twitch contractions with or without following phasic contraction and relaxation. The twitch contractions were abolished by d-tubocurarine (10(-6) M), suggesting that they arise from striated muscle. Exogenously applied prostaglandin (PG) E1, PGE2 or PGF2 alpha (greater than 10(-10) M) evoked sustained increase in the muscle tone in the presence or absence of indomethacin, and enhanced the amplitude of muscle relaxation evoked by the field stimulation without affecting the resting membrane potential. Indomethacin (10(-6)-10(-5) M) gradually reduced the muscle tone of the proximal urethra with no change in the resting membrane potential. At the reduced muscle tone, electrical-field stimulation did not evoke muscle relaxation. Thus, the amplitude of muscle relaxation evoked by field stimulation was dependent on the level of muscle tone of the circular muscle strips.(ABSTRACT TRUNCATED AT 400 WORDS)

Cyclic AMP response to vasoactive intestinal peptide and beta-adrenergic or cholinergic agonists in isolated epithelial cells of rat ventral prostate

Vasoactive intestinal peptide (VIP) and the beta-adrenergic agonist isoproterenol stimulated cyclic AMP formation through independent receptors in isolated epithelial cells of rat ventral prostate. The specific beta-adrenergic antagonist propranolol inhibited the stimulatory effect of isoproterenol but not that of VIP. Besides small differences in the efficiency of both agents, results indicated that isoproterenol was 500 times less potent than VIP. Acetylcholine did not modify the basal cyclic AMP levels but inhibited the accumulation of the cyclic nucleotide in the presence of either VIP or isoproterenol. The inhibitory action of muscarinic receptors was calcium-dependent. The coexistence of receptors for cholinergic, adrenergic and peptidergic agents which can regulate cyclic AMP suggests that the functions of prostatic epithelium may be interdependently controlled by multiple neural effectors.

The components of the hypogastric nerve in male and female guinea pigs

A quantitative study has been made of the neural components of the hypogastric nerves of male and female guinea pigs using retrograde transport of horseradish peroxidase (HRP) to identify the population of neurones projecting in the nerve trunk, and electronmicroscopic analysis of the myelinated and unmyelinated axons present. Application of HRP to the transected axons of the hypogastric nerve labelled the cell bodies of sensory neurones in lumbar and sacral dorsal root ganglia, preganglionic neurones in the lumbar and sacral spinal cord, and postganglionic neurones in the inferior mesenteric ganglion and in the lumbar paravertebral chain; some ganglion cells of the pelvic plexus were also labelled. The number and distribution of each type of neurone with axons in the hypogastric nerve differed between the sexes: in particular, about twice as many preganglionic axons were present in the male as in the female.

Studies on the integrated extrinsic nervous control of rectal motility in the cat

The effect of sympathetic nervous activity on rectal motility induced by pelvic nerve stimulation (PNS) was studied in anaesthetized cats. Division of the sympathetic lumbar colonic and hypogastric nerves or alpha-adrenoreceptor blockade, both of which reduced rectal tone, also reversed a predominantly relaxatory pelvic nerve response into a pure contraction. Contractions to pelvic nerve stimulation were reduced by simultaneous lumbar colonic nerve stimulation. This lumbar colonic nerve-induced inhibition was augmented by alpha-adrenoceptor blockade and abolished by beta-blockade. Close intra-arterial injection of a beta-adrenergic agonist reduced contractions to PNS, while an alpha-adrenergic agonist had no effect. Stimulation of the hypogastric nerves enhanced rectal contractions to simultaneous PNS. The apparent similarity with the arrangement of extrinsic nervous control of the internal anal sphincter suggests that the rectum is functionally involved in continence mechanisms.

The effects of nicotine on spontaneous contractions of cat urinary bladder in situ

Nicotine and dimethyl-phenylpiperazinium (DMPP) increased intravesicular pressure and then transiently depressed the spontaneous activity of the urinary bladder in chloralose anaesthetized cats. Adrenaline (5-10 micrograms kg-1), noradrenaline (5-20 micrograms kg-1) and isoprenaline (40-50 micrograms kg-1) which depressed spontaneous urinary bladder activity, were antagonized by the beta-receptor blocking agent propranolol (1 mg kg-1). Phenylephrine (10-30 micrograms kg-1) was ineffective on the urinary bladder though it increased the systemic blood pressure. This latter effect was blocked by the alpha-receptor blocking agent phentolamine (2 mg kg-1). Acetylcholine (2-8 micrograms kg-1) caused a marked fall in systemic blood pressure, which was potentiated by physostigmine, but failed to produce any response on the intravesicular pressure even after physostigmine (50-100 micrograms kg-1) treatment. ATP (2 mg kg-1) produced an increase in intravesicular pressure accompanied by a fall in systemic blood pressure. The increased intravesicular pressure was antagonized by quinidine (20 mg kg-1); however, the fall in blood pressure remained unaltered. The increased intravesicular pressure induced by nicotine (20-40 micrograms kg-1) or DMPP (50-100 micrograms kg-1) was not affected by phentolamine (2 mg kg-1), propranolol (1 mg kg-1) or guanethidine (15-20 mg kg-1). Physostigmine (50-100 micrograms kg-1), hemicholinium 3 (2 mg kg-1) or atropine (1 mg kg-1) were also unable to affect the response to nicotine. Hexamethonium (1 mg kg-1), reduced the amplitude of spontaneous bladder contractions and quinidine (20 mg kg-1) abolished the effect of nicotine. 7 Bilateral sectioning of the cervical sympathetic or hypogastric nerves did not alter the effect of nicotine or DMPP. Higher spinal cord transection (Cl-C2) blocked the spontaneous, as well as the nicotine- and DMPP-induced, contractions of the bladder. 8 It is concluded that the increase in intravesicular pressure induced by nicotine is atropineresistant and is not mediated either through adrenergic or cholinergic mechanisms. It is probable that a purinergic mechanism is involved, via the activation of P2-receptors present in the urinary bladder.

Efferent sympathetic nervous control of rectal motility in the cat

The sympathetic nervous control of rectal motility was studied in anesthetized cats. Division of the sympathetic nerves, i.e. the hypogastric nerves and the lumbar colonic nerves and alpha-adrenergic blockade reduced rectal tone indicating that these nerves are tonically active. Efferent electrical stimulation of the nerves at high intensities caused an immediate and sustained contraction which was inhibited after phentolamine but unaffected by hexamethonium suggesting a direct alpha-adrenergic effect on the rectal smooth muscle. However when prevailing rectal tone was high beta-adrenergic inhibitory responses unaffected by hexamethonium were observed. In addition the hypogastric nerves seem to convey cholinergic excitatory fibres to the rectum. The results imply that the sympathetic nerves are integrated in the nervous regulation of rectal motility in a fashion similar to the nervous control of the internal anal sphincter.

Reserpine-induced detrusor hyperreflexia: an in vivo model for studying smooth muscle relaxants at urinary bladder level

A new in vivo model for studying the effects of smooth muscle relaxant drugs at urinary bladder level has been developed. This involves the determination of a cystometrogram at a physiological filling rate in urethane anesthetized rats. The amount of infused saline required to elicit TTX-sensitive rhythmic contractions (micturition reflex) of urinary bladder was choosen as end point to evaluate the effect of test substances. Reserpine pretreatment significantly reduced the volume of saline required to elicit the micturition reflex. The effect of reserpine can be reproduced by intravenous prazosin, but not by propranolol or yohimbine, in control rats. Intravenous, but not topical, hexamethonium reversed the effects of reserpine pretreatment on the amount of infused saline required to elicit rhythmic contractions. The nature of rhythmic contractions produced by saline filling of the urinary bladder in these experimental conditions, as well as the potential mechanism(s) involved in the effects of reserpine, are discussed in view of the existing literature on the physiology and pharmacology of the micturition reflex. The effects of various drugs commonly used to produce a relaxation of bladder muscle suggest that this model might be useful for detecting substances of potential therapeutic usefulness in the treatment of bladder hypermotility disorders.

The effects of clonidine on electrically-induced contractions of rat detrusor strips in vitro

Clonidine (10(-9)-3 X 10(-6) M) produced a concentration dependent inhibition of field stimulation-induced contractions of rat detrusor muscle strip at 0.1 and 1 Hz which were completely abolished by tetrodotoxin (5 X 10(-7) M) but were unaffected by hexamethonium (10(-5) M). Pretreatment with yohimbine (10(-8)-10(-7) M) did not modify the amplitude of contractions but produced a rightward parallel shift of clonidine's cumulative response curve without a depression of the maximal response. The corresponding pA2 value for yohimbine was 8.44 +/- 0.1. Atropine (3 X 10(-6) M) produced a partial inhibition of contractions at both frequencies. In the presence of atropine the cumulative response curve of clonidine was significantly reduced at 1 but not at 0.1 Hz. Indomethacin (5 X 10(-5) M) and theophylline (2 X 10(-4) M) produced a partial inhibition of amplitude of contractions at both frequencies without any interference with the effect of a supramaximal concentration of clonidine. Prazosin (10(-6) M), propranolol (10(-6) M), chlorpheniramine (10(-6) M), ranitidine (10(-6) M), haloperidol (10(-7) M), pizotifen (10(-6) M), naloxone (10(-6) M), quinidine (10(-6) M), strychnine (10(-5) M) or picrotoxin (10(-5) M) neither affected the amplitude of contractions at either frequency nor antagonized clonidine effects. The contractile response of non stimulated strips to acetylcholine (10(-5) M), carbachol (3 X 10(-6) M) and ATP (10(-3) M) were not significantly influenced by pretreatment with clonidine (3 X 10(-6) M). These results suggest that stimulation of prejunctional alpha 2-adrenoreceptors located on postganglionic nerve endings might reduce the output of excitatory neurotransmitter(s) in rat urinary bladder.

Comparative pharmacological response of an in vitro whole bladder preparation (rabbit) with response of isolated smooth muscle strips

Although much of our knowledge of the pharmacological response of the urinary bladder comes from in vitro muscle strip studies, it is not clear if these studies can be directly correlated with bladder function. We have compared the pharmacological response of an in vitro whole bladder model with the response of the standard muscle strip technique. The whole bladder model has the advantage of being able to measure both the isometric contractile response to drugs as well as a functional response in which the bladder can empty in the presence of a constant resistance. The results of these studies may be summarized as follows: 1) bethanechol was equipotent in contracting the muscle strips and in the closed whole bladder model; 2) at low and intermediate bladder volumes, the bladder fully emptied at concentrations of bethanechol significantly below the concentration required for maximal contraction; 3) isoproterenol, a potent beta-adrenergic agonist, stimulated a strong relaxation in muscle strips, whereas the whole bladder responded very poorly to isoproterenol; 4) in muscle strips isoproterenol strongly antagonized bethanechol contraction, whereas, in the whole bladder system, isoproterenol did not significantly antagonize bethanechol contraction; 5) methoxamine and adenosine triphosphate produced a moderate, equipotent contraction in both models.

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

The effects of sympathetic and parasympathetic nerve stimulation on resistance to flow in the proximal urethra was examined in male, chloralose-anesthetized cats. Hypogastric (sympathetic) nerve stimulation increased urethral resistance, an effect that was blocked by the alpha-adrenergic antagonist prazosin (0.1 mg/kg), reduced 50% by ganglionic blockade with hexamethonium (0.4 to 0.6 mg/min) and potentiated by the beta-adrenergic antagonist sotalol (5 mg/kg). In the presence of phenylephrine-induced constrictions of the urethra, hypogastric nerve stimulation decreased resistance by a sotalol-sensitive, hexamethonium-resistant mechanism. The results imply that sympathetic stimulation can either raise or lower urethral resistance under different conditions, and that the organization of the nerves mediating the two types of response differs. Because pelvic nerve stimulation produced small and inconsistent responses, the parasympathetic input was instead activated by sacral ventral root stimulation. Sacral stimulation produced an atropine-sensitive constriction when basal urethral resistance was low, and dilatation when resistance was high. The latter response was reduced by atropine, but was resistant to sotalol. However, the decrease in resistance produced by acetylcholine in the presence of PE was not reduced by atropine, implying that acetylcholine-induced dilatation of the urethra is not due to activation of muscarinic receptors on smooth muscle. It is hypothesized that parasympathetic dilatation of the urethra may be mediated by a non-cholinergic, non-adrenergic inhibitory transmitter released from post-ganglionic neurons. A muscarinic mechanism may be involved in this response either to potentiate the action of the unknown transmitter or to facilitate the ganglionic excitation of these neurons. Parasympathetic constrictor responses can be attributed to activation of postganglionic cholinergic neurons.

Electrical and mechanical activity recorded from rabbit urinary bladder in response to nerve stimulation

Responses of the smooth muscle membrane of the rabbit bladder to intramuscular nerve stimulation were investigated by the micro-electrode and double sucrose-gap methods. The cell generated regular spontaneous action potentials. Acetylcholine produced a maintained increase in the frequency and ATP a transient increase. Noradrenaline only increased the frequency at very high concentrations. Application of short current pulses (50 microseconds) produced an initial excitatory junction potential (e.j.p.) with a superimposed spike, followed by a late depolarization. On some occasions, hyperpolarization of the membrane appeared between initial e.j.p. and the late depolarization. All these responses were abolished by tetrodotoxin. The late depolarization was enhanced by pre-treatment with neostigmine and abolished by atropine. This means that the delayed depolarization is due to activation of the muscarinic receptor. When the late depolarization was abolished, the amplitude of hyperpolarization was enhanced. The e.j.p. and contraction were unaffected by guanethidine, phentolamine, methysergide, mepyramine, quinidine or theophylline. This means that the e.j.p. is not mediated by activation of adrenergic, tryptaminergic, histaminergic or purinergic receptors. ATP reduced the amplitude of the e.j.p. due to depolarization of the membrane and reduction in the membrane resistance. The amplitude of the e.j.p. was gradually reduced by repetitive stimulation (0.5-2.0 Hz). However, the rate of depression was unchanged in the presence of ATP. Dipyridamole did not change the electrical and mechanical responses to field stimulation. These results do not support the proposal that ATP is the non-cholinergic excitatory transmitter. Apamine and tetraethylammonium (TEA) suppressed the hyperpolarization produced by field stimulation but guanethidine did not inhibit the hyperpolarization. Therefore, the hyperpolarization is due to increased K conductance of the membrane but it is not possible to conclude whether this component is due to the inhibitory action of a neurotransmitter or solely to after hyperpolarization of the spike. It was concluded that the rabbit bladder receives both cholinergic and noncholinergic excitatory neurones.

Modulation by beta-adrenoreceptors of spontaneous contractions of rat urinary bladder

1 Propranolol (0.1 mg/kg i.v.) but not metoprolol (0.2 mg/kg i.v.) pretreatment increased the spontaneous motility triggered by progressive filling of rat urinary bladder without a concomitant effect on bladder capacity, except at high filling volumes. Compared to controls, the spontaneous motility of urinary bladder in propranolol pretreated rats displayed a higher frequency, indicating the existence of a tonic sympathetic inhibition. 2 beta-adrenoreceptor stimulation by isoprenaline (0.1-10 microgram/kg i.v.) or terbutaline (0.1-1 mg/kg i.v.) in vivo produced a dose dependent inhibition of bladder spontaneous motility which was antagonized by propranolol (0.1 mg/kg i.v.) but not by metoprolol (0.2 mg/kg i.v.). Propranolol (0.2 mg/kg i.v.) pretreatment did not antagonize the inhibition of bladder motility produced by intravenous papaverine (0.5 mg/kg). 3 Propranolol (0.1 mg/kg i.v.) significantly antagonized the isoprenaline-induced tachycardia (beta 1 mediated) and fall in diastolic blood pressure (beta 2 mediated) while metoprolol (0.2 mg/kg i.v.) antagonism was confined to beta 1 mediated responses. 4 Isoprenaline (0.25-1.5 microM) inhibited in a concentration dependent manner field stimulation induced contractions of rat detrusor muscle strips as did tetrodotoxin (0.5 microM). Hexamethonium (50 microM) had no inhibitory effect. 5 Our in vivo findings support the view that beta 2-adrenoreceptors are responsible for modulating bladder motility mainly by suppressing the onset of spontaneous contractions.

Electrical and mechanical activity of the isolated lower urinary tract of the guinea-pig

1 Strips of urethra taken from guinea-pigs contracted in response to acetylcholine, noradrenaline (via alpha-adrenoceptors) and 5-hydroxytryptamine, and were relaxed by adenosine triphosphate (ATP) if the tone was raised. Isoprenaline produced relaxation of bladder strips (via beta-adrenoceptors) whereas ATP caused contraction. 2 Atropine completely blocked all responses to acetylcholine; quinidine failed to block ATP responses selectively; methysergide blocked responses of the urethra but not the bladder to 5-hydroxytryptamine. 3 Spontaneous electrical activity was recorded with intracellular microelectrodes from all regions: in the urethra infrequent bursts of spikes occurred at 1-7 min intervals; regular spikes at 6-30/min were recorded from the detrusor muscle. In the bladder base, bursts of spikes were superimposed on the regular pattern. 4 Bursts of spikes in the urethra were initiated by noradrenaline, phenylephrine or acetylcholine and inhibited by ATP; regular spikes in the bladder were accelerated by acetylcholine or ATP and slowed by noradrenaline or isoprenaline. 5 The intrinsic electrical activity and pharmacological properties of the urethra therefore differ from those of the bladder. This may account for the different responses of the two regions in normal function.

A comparison between propantheline and imipramine on bladder and salivary gland function

The effects of propantheline and imipramine on detrusor function and salivary gland secretion were studied in the dog. Both drugs caused a decrease in the rise of intravesical pressure following pelvic nerve stimulation in the anaesthetised dog. Propantheline had a profound effect on the salivary gland, whereas imipramine had very little effect on the volume of saliva produced after electrical stimulation of the chorda tympani. This suggests that the action of imipramine on the bladder is not anticholinergic. The significance for treatment of detrusor dysfunction is discussed.