Bladder Detrusor Smooth Muscle Research Articles

Vascular response of the rabbit bladder to chronic partial outlet obstruction.

Partial outlet obstruction of the rabbit urinary bladder results, initially, in a rapid increase in bladder mass and remodeling of the bladder wall. Previously, it was shown that this response was characterized by serosal growth (thickening) which was apparent after 1 day of obstruction, before any visible vascularization was observed. After 1 week of obstruction, significant microvessel formation was seen in the transition region between the detrusor smooth muscle and the thickening serosa; after 2 weeks the entire serosa was vascularized. In this study we investigated the effect of chronic (4 week) partial outlet obstruction on microvessel density and distribution in the bladder wall immunohistochemically using CD31 as a marker for vascular endothelium. Transverse sections of bladder wall were examined after 4 weeks of no surgery, sham surgery or partial obstruction. The microvessel density of the obstructed rabbit bladder mucosa and detrusor smooth muscle increased relative to augmentation of these compartments while new vessels appeared in the thickening serosa. Although vessel density did not change with obstruction a significant shift in mean vessel circumference to the left occurred indicating a significant increase in the number of microvessels and small vessels consistent with angiogenesis.

Vascular response of the rabbit bladder to short term partial outlet obstruction.

Partial bladder outlet obstruction of the rabbit bladder results in a rapid increase in mass characterized by remodeling of the bladder wall. In this study we investigated the effect of partial outlet obstruction on microvessel density and distribution in the bladder wall immunohistochemically using CD31 as a marker for vascular endothelium, and on blood flow using a fluorescent microsphere technique. Transverse sections of bladder wall were examined after 0 (unobstructed), 1, 3, 5, 7, and 14 days of obstruction. The microvasculature of obstructed rabbit bladder mucosa and detrusor smooth muscle apparently increased relative to augmentation of these compartments, while new vessels appeared in the thickening serosa. These vascular changes correlated with results showing that, at 1 week after obstruction, blood flow (ml/min/g tissue) to the mucosa and detrusor was unchanged. Thickening of the serosa, apparent after 1 day of obstruction, began before its vascularization. Then, 1 week post-obstruction, there was significant microvessel formation in the transition region between the detrusor smooth muscle and the increasing serosa; after 2 weeks, the entire serosa was vascularized. The vascularization of the muscle-serosal transition region and then the remaining serosa apparently precedes fibroblast differentiation, providing blood supply and thus metabolic support for this process. All obstructed rabbit bladders in this study were in a state of compensated function based on their weights. Our working hypothesis is that blood flow per unit tissue mass is normal in compensated obstructed bladders, thus allowing for normal contractile function and cellular metabolism. The results of this study indicate the presence of an augmented microvasculature in compensated obstructed rabbit bladders that provides adequate blood perfusion for normal function.

OVERACTIVITY AND STRUCTURAL CHANGES IN THE CHRONICALLY ISCHEMIC BLADDER

Our aim was to study the effect of chronic ischemia on bladder contraction and detrusor smooth muscle reactivity. The relationship between structural damage and functional changes in the chronically ischemic bladder was also investigated. Male New Zealand White rabbits were divided into arterial injury (AI), hypercholesterolemia (Hch) and control groups. The AI group (n = 18) underwent balloon endothelial injury of the iliac arteries and received a 0.5% cholesterol diet. The Hch group (n = 8) received a 0.5% cholesterol diet alone. The control group (n = 8) received a regular diet. After 16 weeks, iliac artery and bladder wall blood flows were recorded. Cystometrograms and arteriography were obtained and bladder tissues were processed for isometric tension measurement in the organ bath and for histological evaluation. At 16 weeks, blood flow through the iliac arteries was significantly reduced in the AI group compared with the Hch and control groups. In the AI group, 8 animals developed severe bladder ischemia (SBI) defined as greater than 60% decrease in bladder blood flow, 7 animals developed moderate bladder ischemia (MBI) defined as 40 to 60% decrease in bladder blood flow, and 3 animals failed to develop significant bladder ischemia (<40% decrease in bladder blood flow). In the control animals, bladder blood flow increased prior to contraction, decreased during contraction and rebounded to baseline levels after contraction. In animals with MBI and SBI, the increase in bladder blood flow prior to contraction and the rebound of blood flow after contraction, both seen in control animals, were diminished. Detrusor overactivity (significant increase in the frequency of spontaneous bladder contractions) was observed in the MBI group and impaired bladder contraction in the SBI group. In the organ bath, bladder strips from the MBI group demonstrated increased contractile response to carbachol and electrical field stimulation (EFS) while bladder strips from the SBI group showed impaired contractility. Hch alone produced only short-lived ischemia during bladder contraction and caused significantly lesser functional changes compared with those seen in MBI. Histological examination showed atherosclerotic occlusion in the iliac arteries and bladder microcirculation and marked disruption of urothelium in the MBI and SBI groups. Severe fibrosis was seen in bladder tissue from the SBI group, moderate fibrosis in tissue from the MBI group and mild fibrosis in tissue from the Hch group. Our studies show that chronic MBI is associated with detrusor overactivity and increased smooth muscle contractility to carbachol and EFS while chronic SBI is associated with impaired detrusor contraction. The mechanism of chronic ischemia-induced bladder dysfunction is not known and may involve multiple physiologic and structural changes in the bladder nerves, receptors and contractile components. Our studies suggest that ischemia-induced structural damage in the urothelium and possible chronic exposure of the underlying tissue and nerves to the urine may also play a role in MBI-induced detrusor overactivity. SBI-induced impairment of bladder contraction may involve, in part, extensive fibrosis and loss of bladder smooth muscle. Histopathophysiologic changes in bladder tissue from our MBI model are similar to those seen in patients with detrusor instability, suggesting that chronic ischemia may play a role in the development of idiopathic detrusor instability.

Pharmacological and molecular biological evidence for ETA endothelin receptor subtype mediating mechanical responses in the detrusor smooth muscle of the human urinary bladder

The aim of this study was to characterize endothelin receptor subtypes of the detrusor muscle of the human urinary bladder. The receptor subtypes mediating endothelin (ET)-1-induced activity in the human detrusor smooth muscles have been characterized using isometric contraction and reverse transcription-polymerase chain reaction (RT-PCR). ET-1 (a non-selective ET receptor agonist; 10(-10) M to 10(-6) M) exhibited concentration-dependent contractions in human urinary bladder with a plateau at concentrations above 3x10(-7) M. Neither IRL1620 nor sarafotoxin S6c (both ETB-selective agonists; 10(-10) M to 10(-6) M) elicited contractile activity in the human urinary bladder detrusor smooth muscle. FR139317 (an ETA-selective antagonist; 10(-7) M to 10(-5) M) produced a marked shift to the right of the ET-1 concentration-response curve in human urinary bladder detrusor smooth muscle (from the Schild plot TpA2=7.96; slope=0.95). In contrast, RES701-1 (an ETB-selective antagonist; 10(-7) M to 10(-5) M) had no effect on the ET-1 concentration-response curve. RT-PCR revealed positive amplification of ETA receptor mRNA fragment, but not ETB. These results indicate that the ET-1-induced contractile effects of urinary bladder detrusor smooth muscle seem to be mediated mainly by the ETA receptor, not by the ETB receptor.

Bladder instability and detrusor smooth muscle function.

Bladder, or detrusor, instability is a symptomatic condition which is characterized by uncontrollable rises in pressure within the bladder lumen leading to a feeling of urgency of micturition and, if severe enough, urinary incontinence. The rises in pressure are brought about by contraction of the detrusor smooth muscle which forms the major tissue component of the urinary bladder wall. This abnormality can be associated with a number of clinical conditions and when there is evidence of associated neurological deficits it is termed detrusor hyper-reflexia. An increase in bladder outflow resistance is also associated with detrusor instability and this is especially prevalent in men due to the age-related hypertrophy of the prostate gland which surrounds the urethra. However, in the majority of cases the cause is idiopathic and probably multifactorial. No matter what the cause, detrusor instability is one the largest causes of morbidity in the community; in the UK its prevalence increases from about 2 % in men and 9 % in women aged 15-64 years to 7 % and 12 %, respectively, in the over 65 years age group (Thomas et al. 1980; Brocklehurst, 1993).

Functional pharmacological characterization of the muscarinic cholinoceptor-mediated inhibition of adenylyl cyclase in primary cultured human bladder detrusor smooth muscle cells

Functional pharmacological characterization of the muscarinic cholinoceptor-mediated inhibition of adenylyl cyclase in primary cultured human bladder detrusor smooth muscle cells

Effect of calcium and calcium chelator on the response of the bladder to in vitro ischaemia.

To examine the effect of different concentrations of calcium on the contractile responses of isolated strips of rabbit bladder detrusor to various forms of stimulation after 2 h incubation in the presence of substrate and oxygen depletion (in vitro ischaemia), followed by 1 h of recovery. The resultant contractile responses were correlated with the level of lipid peroxidation as determined by malonedialdehyde (MDA) concentration. Isolated strips of rabbit bladder detrusor smooth muscle were incubated in Tyrode's solution containing different concentrations of calcium (0-5.4 mmol/L). The effect of 2 h of incubation in oxygen- and substrate-free medium (in vitro ischaemia), followed by a 1-h incubation in the presence of oxygen and substrate, on the contractile responses to field stimulation, carbachol and KCl were determined. The effects of repetitive stimulation (15 s of stimulation at 32 Hz applied every 5 min during the 2-h experimental period) were also assessed. The contractile responses to all stimuli increased as the extracellular calcium concentration was increased from 0.6 to 5.4 mmol/L. A 2 h exposure to in vitro ischaemia, followed by a return to normal solution, resulted in a diminished response to all stimuli. This contractile dysfunction was least in the presence of calcium chelator (EGTA) and greatest in the presence of 5.4 mmol/L calcium. Repetitive stimulation during in vitro ischaemia also exacerbated the contractile dysfunction. Lipid peroxidation increased during in vitro ischaemia in proportion to the calcium concentration and was enhanced by repetitive stimulation during this period. Regardless of the incubation conditions, the reduction in the contractile response was significantly greater for field-stimulated tissues than for those stimulated with carbachol or KCl. These results show that the magnitude of contractile dysfunction induced by incubation in the presence of substrate and oxygen depletion is reduced in the presence of low calcium concentrations, increased in the presence of high calcium levels and increased in the presence of repetitive stimulation. In addition, the level of lipid peroxidation after the recovery period was proportional to the magnitude of contractile dysfunction present.

IN VITRO FUNCTIONAL PROPERTIES OF THE RAT BLADDER REGENERATED BY THE BLADDER ACELLULAR MATRIX GRAFT

Purpose To assess the response of rat urinary bladder regenerated by the homologous bladder acellular matrix graft (BAMG) to in vitro electrical and pharmacologic stimuli. Materials and Methods In Sprague-Dawley rats, partial cystectomy (>50%) was performed, followed by BAMG augmentation cystoplasty. After 4 months, organ bath studies of tissue strips in 10 were used to compare the contractility of the BAMG regenerates and the corresponding host detrusor smooth muscle. Results The BAMG regenerates exhibited contractile activity to electrical field stimulation and a qualitatively identical pattern of response to muscarinic, purinergic, alpha- and beta-adrenergic drug administration and nitric oxide. At 4 months after surgery, the maximum forces of contraction of the BAMG regenerates to carbachol stimulation amounted to close to 80% of the host bladder response. With electrical field stimulation, they equaled 44% and 62% of the host bladder response after 2.5 and 4 months, respectively. Histological and immunohistochemical studies confirmed the presence of receptors for neurotransmitters that these functional in vitro studies implied. Conclusions The present study provides further evidence that augmentation cystoplasty with the BAMG leads to functional regeneration of the rat bladder detrusor smooth muscle.

Purinergic Modulation of Rat Urinary Bladder Detrusor Smooth Muscle

1. Rat detrusor muscle was responsive to both ATP and adenosine; ATP elicited an excitatory response, whereas adenosine had an inhibitory effect. 2. ATP and adenosine had an inhibitory modulatory action on responses to acetylcholine, potassium depolarization and field stimulation. 3. Quinidine inhibited the ATP response and blocked the inhibitory effect of ATP on acetylcholine, potassium-depolarization and field-stimulation responses. The effect of adenosine remained unaltered in the presence of quinidine. 4. Caffeine and theophylline blocked the adenosine inhibition of responses to field stimulation. 5. It is concluded that excitatory P 2-type purinoreceptors mediated by ATP and inhibitory P 1-type purinoreceptors mediated by adenosine exist in rat urinary bladder detrusor smooth muscle and that both ATP and adenosine exhibit a modulatory action on detrusor muscle agonist-induced responses.

Age-related differential susceptibility to calcium channel blocker and low calcium medium in rat detrusor muscle: response to field stimulation.

The influences of aging on the response of urinary bladder detrusor smooth muscle in response to neurogenic stimulation (electric field stimulation) were investigated in rats aged 3-4 months (young) and 18-20 months (old). In addition, age-associated changes in calcium homeostasis were evaluated by comparing the basal intracellular free calcium concentration ([Ca2+]i), the change of [Ca2+]i in response to field stimulation, the contractile response at different extracellular calcium concentrations (Ca2+ = 1.8, 0.6, and 0 mM), and the sensitivity to the L-type calcium channel blocker. In both groups, the frequency-response curve in response to field stimulation (1-32 Hz) was similar. The contractile response to field stimulation was biphasic (phasic and tonic). The phasic/tonic ratio at different frequencies was similar between the two groups. The contractile responses were equally inhibited by atropine (1 microM) and preincubation with alpha, beta-methylene ATP (50 microM). Tetrodotoxin (1 microM) virtually abolished the responses to field stimulation in both groups. The biphasic components showed different sensitivities to diltiazem and low calcium. The tonic component was more readily inhibited by diltiazem, whereas the phasic component was more sensitive to low calcium medium. In general, the response to lower frequency stimulations was more sensitive to both diltiazem and low calcium. The aged group was more sensitive to the inhibitory effects of both low calcium and diltiazem. In Ca2(+)-free medium, the contractile response to higher frequency (e.g., 32 Hz) was temporarily preserved in most of the preparations. This response disappeared after repeated stimulation. The magnitude of this Ca2(+)-free response to 32 Hz stimulation was significantly lower in the aged group than in the young group (18.1 +/- 1.4 vs.29.1 +/- 3.2% of the control response in normal Tyrode medium, P < 0.05). The basal [Ca2+]i levels were similar in the two groups (young: 131 +/- 12 nM, n = 5; old: 118 +/- 10 nM, n = 4, P > 0.05). The magnitude and time course of the [Ca2+]i response to field stimulation were also similar in the two groups. It is concluded that aging seems to have little effect on the neuromuscular activities of rat urinary bladder. However, the calcium homeostasis may be altered as evidenced by the increased sensitivity to diltiazem and low extracellular calcium.

Characterization of a fibroblast cell from the urinary bladder wall

For the first time we report on the growth, culture, and matrix production characteristics of a cell type isolated from the lamina propria of the urinary bladder wall. A fibroblastlike cell was identified as distinct from bladder detrusor smooth muscle cells and urothelium based on morphology, growth characteristics, and immunohistochemical staining. Characterization of extracellular matrix synthesis by this cell type using 35S-methionine metabolic labeling demonstrated that these cells are capable of secreting components of the surrounding connective tissue, including several fibrillar collagens, a basement membrane collagen, and fibronectin.

Flash photolysis studies of relaxation and cross-bridge detachment: higher sensitivity of tonic than phasic smooth muscle to MgADP

The effects of MgADP and inorganic phosphate (Pi) on cross-bridge detachment were determined in tonic (rabbit femoral artery) and phasic (rabbit bladder and guinea pig portal vein) smooth muscles permeabilized with staphylococcal alpha-toxin. Relaxation from rigor was induced by photolysis of ATP (1.2-1.5 mM) from caged ATP. The initial one second of relaxation from rigor was resolved into two exponential components: a rapid component with normalized amplitudes, Af, of 8, 15 and 26% and rate constants, kf (in s-1) of 26, 36 and 30 in rabbit femoral artery, guinea pig portal vein, and rabbit bladder; the respective rate constants of the second, slower component, ks, were 0.07, 0.2 and 0.1. Removal of residual endogenous ADP with apyrase treatment increased the amplitude Af and accelerated ks; addition of MgADP reduced Af. The combination of these effects (increases in Af and ks) decreased the t1/2 of relaxation from control values by factors of 2.6 (femoral artery), 6.7 (portal vein) and 10 (bladder). Pi (30 mM) further increased the amplitudes Af. The affinity of MgADP for myosin cross-bridges, estimated as the reduction of the relative amplitude of the rapid component, Af, was significantly higher in tonic than in phasic smooth muscle: the KD of MgADP was 1.1 +/- 0.3 microM in rabbit femoral artery and 4.9 +/- 1.0 microM in rabbit bladder. The higher affinity of tonic smooth muscle myosin for MgADP correlated with its relatively high LC17b isoform content (58 +/- 4.2%) in contrast to the lower affinity of the phasic, bladder detrusor smooth muscle that contained only the LC17a isoform.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of tiropramide on the activity of lower urinary tract in dogs and its interpretation

The rhythmic contractions of urinary bladder under constant volume condition were evoked in decerebrate and de-anesthetized dogs, while various myogenic and nerve-mediated electrical and mechanical activities of smooth muscles were recorded from in vivo pelvic viscera. The vesical rhythmic contractions were transiently and partially blocked by intravenous application of tiropromide. This 'partial' block showed a good contrast to the 'complete' block of identical contractions, which was observed after application of oxybutynin, known as a potent anti-muscarinic drug. The bladder voiding cycles were observed in other decerebrate dogs, while the warmed Ringer solution was infused at a steady rate into the dome of the bladder until principal voiding contraction occurred in cystometric recordings. The initiation of voiding contraction was markedly delayed after intravenous injection of tiropramide. The delay of principal contraction was found to be due to successive appearance of falling waves in cystometric recordings. As a evident contrast, terodiline caused a significant reduction of voiding contraction height and shortening of clonic discharge phase of external urethral sphincters during voiding cycle. It is concluded that tiropramide does not reveal anti-muscarinic action which oxybutynin or terodiline does really show, instead tiropramide acts principally on bladder detrusor itself, especially on its relaxation phase of premature contraction to be prolonged. The evidences were also presented for electrophysiological identification of bladder detrusor and urethral smooth muscle.

The effects of pH changes on human and ferret detrusor muscle function.

1. The effects of altering extracellular pH on the electrically evoked contractions of ferret and human bladder (detrusor) smooth muscle have been investigated. pH was varied by changing superfusate PCO2 or NaHCO3 concentration. Acidosis increased force when superfusate PCO2 was raised but decreased force when the NaHCO3 concentration was reduced. 2. Intracellular pH (pHi) in isolated ferret detrusor cells was measured separately by epifluorescence microscopy. Extracellular pH changes caused by altering superfusate PCO2 were accompanied by similar changes of pHi, whereas variation of the NaHCO3 concentration had smaller effects on pHi. 3. It was proposed that intracellular acidosis increased contraction but extracellular acidosis depressed contraction. 4. Other interventions, such as addition and removal of NH4Cl, Cl- replacement, and NaHCO3 replacement with HEPES, changed pHi and had predictable effects on force. It was possible to describe unique relationships between tension and either intracellular or extracellular pH regardless of the means whereby pH changes were brought about. 5. Resting tension was reduced whether brought about by either intracellular or extracellular acidosis. K+ contractures were similarly affected by acidosis. Ferret preparations showed low levels of spontaneous activity, which was reduced by acidosis and enhanced by alkalosis.

A possible role for abscisic acid analogues as calcium channel blockers in mammalian smooth muscle

1. 1. The abscisic acid (ABA) analogue SD217595 at 10 μM caused inhibition of K +-induced phasic and tonic contractions of rat bladder detrusor smooth muscle strips. 2. 2. This attenuation of contraction was a dual effect: the inhibition of phasic contractions was irreversible whereas that of the tonic contractions was readily reversed. 3. 3. The dual inhibition is possibly due to blockade of two subtypes of voltage-operated calcium channels with T- and L-type characteristics. 4. 4. The inhibition of contraction induced by SD217595 is in stark contrast to the potentiation of smooth muscle contraction reported previously with the parent molecule ABA. 5. 5. Two other ABA analogues studied (WL019376 and WL019377) showed neither inhibitory or excitatory effects upon K +-induced smooth muscle contraction after short exposures of 10 min.

Field stimulation responses of rat urinary bladder detrusor smooth-muscle. Dependence upon slow calcium channel activity determined by K + depolarization and calcium antagonists

1. 1. Field stimulation responses of rat urinary bladder detrusor smooth muscle were unaffected by atropine, phentolamine, propranolol, caffeine and theophylline. After caffeine or theophylline treatment, previously quiescent detrusor preparations developed pronounced spontaneous contractile activity. 2. 2. Both natural spontaneous contractile activity and field stimulation responses were eliminated in Ca-free EGTA media. After washout, both kinds of activity returned but over quite different time scales. 3. 3. At moderate levels of K +-induced depolarization which inactivate fast Ca-channels, field stimulation responses persisted and additively superimposed upon the K +-induced tension, suggesting that field stimulation-induced depolarization had activated slow voltage-dependent Ca-channels. 4. 4. Amost 61% of detrusor muscle preparations examined showed some spontaneous contractile activity. Such preparations were more sensitive to K +-induced depolarization than quiescent preparations and K +-depolarization greatly accelerated the spontaneous activity of these muscle strips. 5. 5. The slow Ca-channel blockers nifedipine and verapamil eliminated field stimulation responses in the 10 −6–10 −5M range, but octylonium bromide was far less effective even at 10 −4 M. 6. 6. The inorganic Ca-channel blocker Mn 2+ inhibited field stimulation responses at 0.5–1.0 mM but La 3+ was surprisingly far less effective than Mn 2+ in this concentration range, requiring a 1 mM level to achieve a 50% inhibition of response. 7. 7. It is concluded that field stimulation induced a depolarization of rat urinary bladder detrusor muscle which activates slow voltage-dependent Ca-channels. Field stimulation responses and natural spontaneous activity appear to strongly depend upon a sustained Ca influx through these channels for the sustained release of intracellular calcium and the maintenance of contractile force.