Inhibitory effects of propiverine on rat and guinea-pig urinary bladder muscle

Summary In muscle strips isolated from guinea-pig and rat urinary bladder, propiverine (3–10 M) inhibited carbachol-induced contractions in the presence of verapamil and Ca²⁺-induced contractions in excess K⁺ medium containing atropine, suggesting it has both anticholinergic and Ca²⁺ channel blocking actions.The Ca²⁺ channel blocking action was also demonstrated by recording inward Ca ²⁺ currents in single cells dispersed from both species. The inhibition of inward currents by propiverine was three times stronger in the rat than the guinea-pig, ID₅₀ being 7 M for rat and 21 M for guinea-pig. The recovery of the current after washout was faster than that of mechanical inhibition. It is concluded that propiverine blocks not only muscarinic receptors, but also Ca²⁺ channels at similar concentrations.Correspondence to: T. Tomita at the above address     

Contribution of prostaglandins to the adenosine triphosphate-induced contraction of rabbit urinary bladder.

1 Adenosine 5'-triphosphate (ATP) produced an initial rapid, phasic contraction and a later, slowly developing tonic contraction in the isolated detrusor of the rabbit but mainly a rapid, phasic response in the guinea-pig bladder. 2 Electrical field stimulation elicited only a rapid, phasic contraction in both rabbit and guinea-pig bladders. 3 Prostaglandin synthesis inhibition by means of indomethacin and suprofen abolished the tonic response to ATP in the rabbit detrusor, leaving the phasic part of the contraction almost unaffected. The ATP-induced contraction in guinea-pig bladder was not influenced by indomethacin. 4 The contractile response of rabbit urinary bladder to prostaglandins F2 alpha and E2 and to carbachol were not significantly influenced by indomethacin. The contractions induced by the prostaglandins were similar to the tonic response to ATP. 5 Tetrodotoxin, atropine, phentolamine, and theophylline did not alter the ATP-induced contraction. However, the calcium antagonists, nifedipine and nimodipine, abolished the phasic ATP response and greatly reduced the tonic part of the contraction. 6 Tachyphylaxis occurred on repeated addition of ATP; the response to field stimulation was progressively reduced only after indomethacin pretreatment. 7 ATP and prostaglandins may contribute to the non-adrenergic, non-cholinergic component of the excitation of rabbit and guinea-pig bladder.     

Inhibitory effect of anticholinergics on the contraction of isolated caprine urinary bladder detrusor muscle

1. This study investigated whether four anticholinergics which are not clinically used for relaxing the urinary bladder detrusor muscle inhibit the contraction of isolated caprine (goat) detrusor muscle: cyclopentolate (100 nm ), homatropine (5 μm ), ipratropium (500 nm ) and valethamate (1 μm ). 2. The effects of these anticholinergics were compared with tolterodine (3 μm ), an anticholinergic clinically used for relaxing the detrusor muscle. The inhibitory effect of each of these five anticholinergics was studied on six strips of caprine detrusor muscle made to contract with 100 μm acetylcholine (ACh) by determining the percent inhibition of height of contraction and the area under the contractile curve (AUC). 3. It was found that all five anticholinergics inhibited the ACh‐induced contraction of the caprine detrusor and that this inhibition was reversed by raising the concentration of ACh. Hence, these four anticholinergics, like tolterodine, may be useful in managing clinical conditions that require relaxation of the detrusor muscle.     

Inhibitory effect of nicorandil on the contraction of isolated human urinary bladder detrusor muscle

This study was performed to determine whether the antianginal drug nicorandil relaxes isolated human detrusor muscle. Ten strips of detrusor muscle obtained from 10 pediatric patients who underwent surgery on the urinary bladder were contracted with 80 mM potassium chloride (KCl) before and after incubation with four concentrations of nicorandil (100, 200, 400 and 800 microM). The percent inhibition by nicorandil of the height and area under the curve (AUC) of KCl-induced contractions of the detrusor strips was calculated. The effect of glibenclamide (10 microM) on nicorandil (800 microM)-induced inhibition of KCl-induced detrusor contractions was also studied. Nicorandil caused a concentration-dependent inhibition of KClinduced contractions of the detrusor strips. The percent inhibition of the height of KCl-induced contractions of the detrusor by nicorandil was significant at concentrations of 200, 400 and 800 microM. The percent inhibition of the AUC for KCl-induced detrusor contractions was significant at all four concentrations of nicorandil used. Glibenclamide reversed the inhibitory effect of 800 microM nicorandil on KCl-induced detrusor contractions. These results suggest that nicorandil inhibits KCl-induced contractions of isolated human detrusor muscle and may therefore be useful in clinical conditions requiring detrusor muscle relaxation.     

Doxazosin effects on cholinergic and adrenergic responses in rat isolated detrusor smooth muscle preparations from obstructed bladder

We investigated the effect of doxazosin on cholinergic and adrenergic agonists responses in detrusor smooth muscle preparations from sham-operated and 2-week partially obstructed rat bladders. Male Wistar albino rats, 200-250 g, were randomly allocated to 4 experimental groups consisting of 12 animals each: sham-operated bladder, sham-operated bladder treated with doxazosin, partially obstructed bladder, and partially obstructed bladder treated with doxazosin. Partial outlet obstruction of the rat was surgically induced. The response to carbachol (10(-7)-10(-4) M), isoproterenol (10(-6)-10(-3) M), and 80 mM KCl were recorded. Carbachol caused concentration-dependent contractile responses in the detrusor smooth muscles from sham-operated and partially obstructed bladder. Isoproterenol produced concentration-dependent relaxation responses in the detrusor strips from all groups. Dose-response curves for carbachol and isoproterenol showed a shift to the left in rat detrusor smooth muscles from partially obstructed bladder when compared with the results obtained in detrusor muscles from sham-operated bladder. These responses were reversed to normal by doxazosin treatment in rat detrusor smooth muscles from partially obstructed bladder. KCl produced contractile responses in rat detrusor smooth muscles from all groups. The contractile responses to KCl were not significantly changed in all groups. We have shown that carbachol and isoproterenol responses were shifted to the left in rat detrusor smooth muscles from partially obstructed bladder and these responses were reversed by doxazosin treatment.     

Muscarinic receptors of the urinary bladder: detrusor,urothelial and prejunctional

1. The parasympathetic nervous system is responsible for maintaining normal bladder function, contracting the bladder smooth muscle (detrusor) and relaxing the bladder outlet during micturition. 2. Contraction of the bladder involves direct contraction via M3 receptors and an indirect 're-contraction' via M2-receptors whereby a reduction in adenylate cyclase activity reverses the relaxation induced by beta-adrenoceptor stimulation. 3. Muscarinic receptors are also located on the epithelial lining of the bladder (urothelium) where they induce the release of a diffusible factor responsible for inhibiting contraction of the underlying detrusor smooth muscle. The factor remains unidentified but is not nitric oxide, a cyclooxygenase product or adenosine triphosphate. 4. Finally, muscarinic receptors are also located prejunctionally in the bladder on cholinergic and adrenergic nerve terminals, where M1-receptors facilitate transmitter release and M2 or M4-receptors inhibit transmitter release. 5. In pathological states, changes may occur in these receptor systems resulting in bladder dysfunction. Muscarinic receptor antagonists are the main therapeutic agents available for treatment of the overactive bladder, but whether their therapeutic effect involves actions at all three locations (detrusor, prejunctional, urothelial) has yet to be established.     

The effects of adenosine triphosphate and adenosine diphosphate on transmission at the rat and frog neuromuscular junctions

1 The effects of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) were investigated on evoked end-plate potentials (e.p.ps) and on miniature end-plate potentials (min. e.p.ps) recorded from muscle fibres of the rat diaphragm and the frog sartorius.

2 ATP and ADP decreased the quantum content of the e.p.ps and the frequency of the min. e.p.ps. The maximum effects produced by the two substances were similar.

3 The potency of ATP was found to be similar to that of adenosine. In the presence of adenosine, in a concentration producing its maximum effect, the addition of ATP had no further effect. This is compatible with the idea that ATP acts in the same way as adenosine.

     

Beta-adrenoceptor subtypes in the detrusor of guinea-pig urinary bladder.

beta-Adrenoceptors have been demonstrated in the urinary bladders of many animals including the guinea pig. However, there is little information on the subtypes involved in the antispasmodic activity of beta-adrenoceptor activation in the guinea-pig detrusor. The present study uses the non-selective beta-agonist isoproterenol, the antagonist nadolol, the beta 2-selective agonists salbutamol and terbutaline, the antagonist ICI 118551, and the beta 1-selective antagonist metoprolol, to demonstrate functionally the subtypes existing in the guinea-pig detrusor. Isoproterenol dose-dependently reduces the myogenic activity in the guinea-pig detrusor induced by mild depolarization with 20 mM potassium in the tissue bath. At the supramaximal concentration of 30 microM, isoproterenol achieves 73 +/- 2% of the reference maximal response. This activity of isoproterenol is reduced to 9 +/- 5, 24 +/- 6 and 54 +/- 1% in the total blockade of beta, beta 1 and beta 2 with nadolol, metoprolol and ICI 118551, respectively. Consistently, salbutamol and terbutaline at the same concentration produce only 35 +/- 1 and 38 +/- 4% of the response, respectively. Thus, both beta 1- and beta 2-adrenoceptors are present in the detrusor of the guinea-pig urinary bladder. Although activation of either subtype results in antispasmodic action, the larger portion of the antispasmodic activity appears to be associated with the activation of the beta 1-subtype.     

Ionic basis for the regulation of spontaneous excitation in detrusor smooth muscle cells of the guinea-pig urinary bladder

(1) The regulatory mechanisms of spontaneous excitation in detrusor smooth muscles of the guinea-pig urinary bladder were investigated using intracellular microelectrode and muscle tension recording techniques. (2) Detrusor smooth muscle cells exhibited nifedipine-sensitive spontaneous action potentials. Their frequency was highly sensitive to membrane polarization and was reduced by lowering the temperature. Lowering the temperature also reduced the frequency of spontaneous contractions and increased their amplitude. (3) Charybdotoxin (50 nm) and iberiotoxin (0.1 microm) increased the amplitude and duration of action potentials, and abolished after hyperpolarizations (AHPs). Both agents also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. Apamin (0.1 microm) did not change the shape of action potentials but often converted individual action potentials into bursts. It also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. 4-aminopyrideine (4-AP, 1 mm) increased the frequency of action potentials without affecting their shape, and increased the amplitude and frequency of spontaneous contractions. (4) Cyclopiazonic acid (CPA, 10 microm) and ryanodine (50 microm) increased the amplitude of action potentials, and suppressed AHPs. Both agents also increased the amplitude and duration of spontaneous contractions, and reduced their frequency. 1,2-(Bis (2-aminophenoxy) ethane-N,N,N', N'-tetraacetic acid tetrakis (acetoxymethyl ester) (50 microm) dramatically increased the amplitude and duration of the action potential, and abolished AHPs. (5) Spontaneous action potentials in detrusor smooth muscles cells result from the opening of L-type Ca2+ channels, and their frequency is regulated by voltage-dependent mechanisms and by some metabolic process. Both the activation of large conductance Ca2+-activated K+ (BK) channels and Ca2+-mediated inactivation of the Ca2+ channels are involved in the repolarizing phase of action potentials. The Ca2+ influx through L-type Ca2+ channels triggers calcium-induced calcium release via ryanodine receptors and activates BK channels to generate AHPs. Both small conductance Ca2+-activated K+ channels and voltage-sensitive K+ channels may contribute to the resting membrane potential and regulate the frequency of action potentials. The regulatory mechanisms of action potentials are closely related to the regulation of spontaneous contractions.     

Expression and functional role of Rho-kinase in rat urinary bladder smooth muscle

(1) The involvement of Rho-kinase (ROCK) in the contractile mechanisms mediating smooth muscle contraction of the rat urinary bladder was investigated using expression studies and the ROCK inhibitor Y-27632. (2) Both isoforms of ROCK (ROCK I and ROCK II) were detected in high levels in rat urinary bladder. (3) Y-27632 (10 micro M) significantly attenuated contractions of rat urinary bladder strips evoked by the G-protein coupled receptor agonists carbachol (58.1+/-10.5% at 0.3 micro M) and neurokinin A (68.6+/-12.7% at 1 micro M) without affecting contractions to potassium chloride (10-100 mM). In addition, basal tone was reduced by 47.8+/-2.0% by 10 micro M Y-27632 in the absence of stimulation. (4) Contractions of urinary bladder strips evoked by the P2X receptor agonist alpha,beta-methylene ATP (alpha,beta-mATP; 10 micro M) were also attenuated by Y-27632 (30.0+/-7.2% at 10 micro M). (5) Y-27632 (10 micro M) significantly attenuated contractions evoked by electrical field stimulation (2-16 Hz). The effect of Y-27632 on the tonic portion of the neurogenic response (4-16 Hz) was not significantly different from the effect of atropine (1 micro M) alone. (6) While the mechanism underlying the ability of Y-27632 to inhibit alpha,beta-mATP-evoked contractions remains undetermined, the results of the present study clearly demonstrate a role for ROCK in the regulation of rat urinary bladder smooth muscle contraction and tone.     

Rabbit versus rat urinary bladder: effects of in vitro hypoxia.

PURPOSE: Studies indicate that bladder hypoxia may be an etiological factor for lower urinary tract dysfunction. Rat and rabbit are two species of experimental animals used frequently to study lower urinary tract function and dysfunction. The objective of this study was to compare directly effects of in vitro hypoxia on contractile responses of rat and rabbit urinary bladder to different forms of stimulation. METHODS: Sexually mature male New Zealand White rabbits and Sprague-Dawley rats were compared. Each bladder was excised while the animal was anesthetized, and longitudinal bladder strips were cut, then mounted in organ baths. A tension of 2 g was placed on all strips. Effects of 1, 2, 3 and 4 h hypoxia followed by 1 h of reoxygenation on contractile responses of bladder strips to field stimulation (FS), carbachol (100 micromol/l), ATP (1 mmol/l) and KCl (120 mmol/l) were determined. RESULTS: Contractility, per unit tissue mass, of rat bladder strips was significantly greater than that of rabbit bladder strips in response to FS (all frequencies), carbachol, KCl and ATP. Hypoxia (followed by reoxygenation) resulted in time-dependent progressive reduction in contractile responses of bladder strips to all stimuli. Rat bladder was significantly more sensitive to hypoxia than rabbit bladder in response to FS and carbachol. Hypoxia induced similar effects on rat and rabbit bladder responses to ATP and KCl. CONCLUSION: Rat bladder neurogenic and cholinergic responses are significantly more sensitive to hypoxia than are those of rabbit bladder, which may be due to the rat bladder's greater contractile force generation and previously reported higher Ca2+-ATPase activity.     

腺苷及腺苷三磷酸对大鼠离体结肠平滑肌的作用

目的 比较腺苷和腺苷三磷酸对大鼠离体近端结肠纵行平滑肌活动的调节作用.方法 四导生理记录仪记录大鼠近端结肠纵行肌的等长舒张和收缩反应.结果 对于静息状态下的大鼠离体近端结肠纵行肌标本,腺苷无明显影响(P＞0.05).但是,腺苷三磷酸使静息状态下的大鼠离体近端结肠纵行肌产生微弱的舒张反应后续浓度依赖性收缩反应;腺苷三磷酸的上述作用不受神经阻断剂河豚毒素的影响.大鼠离体近端结肠纵行肌标本在五羟色胺或乙酰胆碱预收缩条件下,腺苷和腺苷三磷酸均可产生浓度依赖性舒张反应,但是腺苷引起的舒张反应明显弱于腺苷三磷酸(P＜0.01).结论 在大鼠离体近端结肠纵行肌,腺苷三磷酸可产生舒张反应和收缩反应,而腺苷仅产生舒张反应.     

Phentolamine-induced rhythmic contractions in bladder detrusor muscle of guinea-pig.

Phentolamine caused a rhythmic contraction concentration-dependently without affecting resting tone in the detrusor muscle. Prazosin, yohimbine, propranolol, noradrenaline, clonidine or isoprenaline failed to cause the rhythmic contraction. These agents did not modify the response to phentolamine suggesting no involvement of alpha- or beta-adrenoceptors in the response to phentolamine. Chlorpheniramine, cimetidine, methysergide, SK&F 83566, atropine, bretylium, hemicholinium or tetrodotoxin failed to inhibit the response to phentolamine. These results suggest that the effect of phentolamine is not mediated through histaminergic, 5-hydroxytryptaminergic, dopaminergic or cholinergic systems, or through transmitter release from nerve endings. Prostaglandin F2 alpha (PGF2 alpha), arachidonic acid but not ATP caused rhythmic contractions which resembled the response to phentolamine. Potassium also caused a contraction with increasing resting tone. Following treatment with nifedipine, or incubation in a Ca2+-free medium, the responses to phentolamine, PGF2 alpha, arachidonic acid and potassium were markedly inhibited or abolished. Cyclo-oxygenase inhibitors such as indomethacin, aspirin and corticosterone inhibited or abolished the responses to phentolamine and arachidonic acid but did not inhibit the response to PGF2 alpha. The results suggest that the phentolamine-induced rhythmic contraction may, at least in part, result from the cyclo-oxygenase metabolite of arachidonic acid in guinea-pig detrusor muscles and a consequent increase in the transmembrane Ca2+-influx.     

Energy cost of contraction in rat urinary bladder smooth muscle during anoxia

1. The aim of the present study was to investigate the effects of hypoxia on energy metabolism and contraction of rat urinary bladder smooth muscle, thereby gaining insight into the capacity of this smooth muscle to maintain contractile function when rendered hypoxic. 2. Isometric force, oxygen consumption, lactate production, heat production and unloaded shortening velocity were measured in isolated muscle strips under both aerobic and anaerobic conditions. Muscle strips were bathed in physiological saline solution with the anaerobic condition being created by replacing the oxygen bubbling the solution with nitrogen. 3. During contraction under anaerobic conditions, the rate of lactate production was increased 2.5-fold above that observed under aerobic conditions. This, however, only provided for a rate of ATP production of approximately 30% of that measured under aerobic conditions. Despite this, force maintenance was only slightly depressed, indicating that the metabolic cost of contraction was reduced in hypoxia. In support of this, the rate of heat production during contractions in anoxia was only approximately half of that under aerobic conditions, whereas, again, force was only slightly lower. Unloaded shortening velocity was significantly lower in anoxia, suggesting a slower cross-bridge turnover rate. 4. The results indicate that the economy of force maintenance is increased in bladder smooth muscle under hypoxic conditions and that this is due, at least in part, to a reduced rate of cross-bridge cycling. This may help to preserve bladder contractile function during periods of ischaemia that may be associated with bladder filling and emptying.     

Motor effects of loperamide on rat urinary bladder: an in vitro study

Motility recordings in muscle strips from rat urinary bladder were performed and the effect of the opiate agonist loperamide on motor activity was studied. Loperamide induced a concentration-dependent (10(-7)-10(-3) M) inhibition of the contractile response of the detrusor strip of the same order of magnitude after activation of intramural nerves, stimulation of cholinergic receptors with acetylcholine and after direct depolarisation of the cell with potassium. Pretreatment with the opiate-antagonist naloxone (10(-5) M) did not antagonise the inhibitory action of loperamide on bladder motility regardless of the type of activation. Naloxone per se, however, facilitated the nerve-mediated motor response. The inhibitory action of loperamide on the potassium-induced contraction could partly be counteracted by elevation of the calcium concentration in the medium. It is suggested that the demonstrated inhibitory effect of loperamide on bladder motility is a calcium-dependent direct smooth muscle action, without any significant opiate-receptor-mediated action in the present in vitro preparation.     

Electrical properties of detrusor smooth muscles from the pig and human urinary bladder

(1) The electrophysiological properties of detrusor smooth muscles have been studied almost exclusively in small mammals and the relevance of the information to the human bladder has been questioned. In the present study, electrical properties of detrusor smooth muscles of the pig and human were investigated using intracellular recording techniques. (2) Bladder smooth muscles of the pig and human exhibited nifedipine (10 microm)-sensitive spontaneous action potentials, and their frequency was highly sensitive to membrane polarization. (3) During bursts of action potentials, each action potential was followed by a fast after-hyperpolarization (fast AHP). Charybdotoxin (CTX, 50 nm) increased the amplitude and duration of action potentials but failed to inhibit the fast AHPs, while apamin (0.1 microm) blocked the fast AHPs and induced action potential complexes, which were followed by slow AHPs. 4-Aminopyridine (4-AP, 1 mm) suppressed the slow AHP and increased action potential frequency. (4) In the human bladder, transmural stimuli initiated inhibitory junction potential-like hyperpolarizations, which were followed by action potential discharges. The hyperpolarizations were blocked by atropine (1 microm) and by apamin (0.1 microm) but not by CTX (50 nm). In the pig bladder, transmural stimuli evoked excitatory junction potentials (EJPs), which triggered action potentials. After desensitizing P2x receptors with alpha,beta methylene-ATP (10 microm), nerve-evoked responses were similar to those of human bladder. (5) These results indicate that detrusor smooth muscles of the pig share many features of electrical properties with those of the human. In addition to large conductance (BK) and small conductance (SK) Ca2+-activated K+ channels, voltage-dependent K+ (VK) channels may play an important role in the regulation of electrical activity of detrusor smooth muscles.