Endothelin-1-induced contractions of isolated pig detrusor and vesical arterial smooth muscle: calcium dependence and phosphoinositide hydrolysis

Neuropeptides in lower urinary tract function

Numerous neuropeptide/receptor systems including vasoactive intestinal polypeptide, pituitary adenylate cyclase-activating polypeptide, calcitonin gene-related peptide, substance P, neurokinin A, bradykinin, and endothelin-1 are expressed in the lower urinary tract (LUT) in both neural and nonneural (e.g., urothelium) components. LUT neuropeptide immunoreactivity is present in afferent and autonomic efferent neurons innervating the bladder and urethra and in the urothelium of the urinary bladder. Neuropeptides have tissue-specific distributions and functions in the LUT and exhibit neuroplastic changes in expression and function with LUT dysfunction following neural injury, inflammation, and disease. LUT dysfunction with abnormal voiding, including urinary urgency, increased voiding frequency, nocturia, urinary incontinence, and pain, may reflect a change in the balance of neuropeptides in bladder reflex pathways. LUT neuropeptide/receptor systems may represent potential targets for therapeutic intervention.

Participation of endogenous endothelin and ETA receptor in premicturition contractions in rats with bladder outlet obstruction

A relationship between endogenous endothelins and bladder overactivity has recently been suggested, but the related endothelin receptor subtype has not been identified. Here, to evaluate the involvement of endothelin-1 and its receptors in bladder overactivity, we investigated endothelin-1 levels and the expression of its receptors in the bladder of rats with bladder outlet obstruction (BOO), a model for bladder overactivity. We also investigated the effects of a selective endothelin ET(A) receptor antagonist, (E)-N-[6-methoxy-5-(2-methoxyphenoxy)[2,2'-bipyrimidin]-4-yl]-2-phenylethenesulfonamide monopotassium salt (YM598), on bladder functions in conscious BOO rats. Partial obstruction of the urethra led to a progressive increase in bladder weight from weeks 1 to 6. Binding assays performed using plasma membranes prepared from these bladders to estimate endothelin receptor density from the maximum [(125)I]endothelin-1 binding showed increased endothelin receptor density (about double) at 1, 2, and 6 weeks after the operation in the BOO bladder. The densities of endothelin ET(A) receptors in the bladder of sham-operated and BOO rats at 2 weeks after operation were about 3.5 and 5 times those of endothelin ET(B) receptors respectively. Furthermore, the endothelin-1 level was also increased in the BOO bladder. Two weeks after operation, BOO rats showed an increase in maximum bladder capacity and micturition volume and the generation of premicturition contractions. The frequency of premicturition contractions was dose-dependently reduced by YM598 (0.1-3 mg/kg, i.v.) without any effect on other voiding parameters in BOO rats. These data suggest that endothelin-1 and endothelin ET(A) receptors might be involved in the generation of premicturition contractions in BOO rats, and that endothelin ET(A) receptor antagonists such as YM598 may have ameliorating effects in patients with bladder overactivity associated with BOO.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Effect of endothelin on bladder contraction: potential role in bladder hyperactivity

In the present study, we demonstrate that the intravenous infusion of endothelin-1 (3 and 10 ng/kg/min) causes a decrease in the mean micturition volume of rats in addition to an increase in mean arterial pressure. These effects are blocked by both the ET(A)/ET(B)-non-selective and the ET(A)-selective endothelin antagonists SB 217242 and SB 247083 respectively (both 30 mg/kg). However, it was also observed that the ET(B)-selective agonist sarafotoxin 6c (3 and 10 ng/kg/min) had similar effects on both mean arterial pressure and micturition volume. Initial experiments indicated that spontaneously hypertensive rats have a much lower mean micturition volume than normal rats. Binding studies comparing the total number and ratio of ET(A)/ET(B) receptors in spontaneously hypertensive, Wister-Kyoto and Sprague-Dawley rats revealed no significant differences in receptor expression. However, the magnitude of the response to endothelin-1 was greater in spontaneously hypertensive versus normal rats.

Developmental changes in the functional, biochemical and molecular properties of rat bladder endothelin receptors

The effect of aging on functional, biochemical, anatomical and molecular properties of endothelin (ET) receptors in bladder smooth muscle of the 3-week-, 3-month- and 22-month-old rats was examined using isolated muscle bath techniques, radioligand binding on membrane particulates and slide mounted tissue sections, and real-time reverse transcription polymerase chain reaction (RT-PCR). ET-1 induced significantly larger contractile responses in bladder dome muscle strips from 3-week- than from 3-month- and 22-month-old rats. The expression level of total ET receptors, determined by saturation binding experiments with [(125)I]ET-1, was higher in detrusor from 3-week- than 22-month-old rats. Inhibition studies with BQ123, a selective ET(A) receptor antagonist, indicated the predominance of the ET(A) receptor subtype and a similar proportion of ET(A) to ET(B) receptor subtypes in the rat detrusor at all ages studied. Autoradiographic data support the age-dependent decrease in the density of ET receptors and also indicate that the ET(A) receptor subtype is primarily located in the smooth muscle layer, whereas the ET(B) receptor subtype is located in both the urothelial and smooth muscle layers. Determined by real-time RT-PCR, ET 1, ET-3, ECE-1 and ET receptor subtype (ET(A) and ET(B)) mRNAs were shown to be higher in bladders of 3-week- compared to 3-month- or 22-month-old rats. This study indicates age-dependent alterations in the ET receptor system at both gene transcript and protein levels in the Fischer rat detrusor.

Physiology of female micturition

Micturition is a dynamic physiologic process consisting of alternating storage and expulsion phases and is accomplished by complex interactions among innervation, smooth muscle, connective tissue, urothelium and supportive structures. Although our current understanding of the anatomy and physiology of the lower urinary tract is far from complete, intensive research over the last decade has dramatically improved our appreciation of the neural, biomechanical, biochemical, and morphologic properties of the bladder and urethra, as well as the hormonal influences and unique pelvic and perineal anatomy of women. Continued research related to the physiology of female micturition promises to offer new insights into the complex bladder-urethral interactions and to provide a basis for developing better management strategies for a variety of voiding dysfunctions in women.

Pharmacology of the lower urinary tract

The functions of the lower urinary tract, to store and periodically release urine, are dependent on the activity of smooth and striated muscles in the urinary bladder, urethra, and external urethral sphincter. This activity is in turn controlled by neural circuits in the brain, spinal cord, and peripheral ganglia. Various neurotransmitters, including acetylcholine, norepinephrine, dopamine, serotonin, excitatory and inhibitory amino acids, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in the neural regulation of the lower urinary tract. Injuries or diseases of the nervous system, as well as drugs and disorders of the peripheral organs, can produce voiding dysfunctions such as urinary frequency, urgency, and incontinence or inefficient voiding and urinary retention. This chapter will review recent advances in our understanding of the pathophysiology of voiding disorders and the targets for drug therapy.

Expression of the ET(A) and ET(B) endothelin receptor subtype mRNA in human detrusor cultured smooth muscle cells

The aim of this study was to determine the expression of the endothelin receptor subtype mRNAs in human detrusor cultured smooth muscle cells using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization (ISH). First strand cDNA was made from human detrusor cultured smooth muscle cells total RNA and used for PCR with primers designed to amplify fragments of the ET(A) and ET(B) endothelin receptor subtype cDNA sequences. Subcloned fragments of the ET(A) and ET(B) endothelin receptor cDNAs were used to synthesize digoxigenin-labeled cRNA probes by in vitro transcription. COS-7 cells transfected with the ET(A) and ET(B) receptor cDNAs were used as positive control and to confirm the absence of cross-hybridization due to sequence homology. Both ET(A) and ET(B) receptor mRNAs were detected by RT-PCR analysis. By ISH, both ET(A) and ET(B) receptor subtype mRNAs were detected. However, ET(A) signal was much more intense than ET(B) signal. These results indicate that mRNAs for both ET(A) and ET(B) receptors are expressed in detrusor smooth muscle cells of human urinary bladder. The ET(A) receptor is the predominant detrusor ET receptor.

Age-related changes in contractile responses of rabbit lower urinary tract to endothelin

PURPOSE

As there are significant amounts of endothelin (ET) receptors in the mammalian urinary tract, we investigated the pharmacological properties and localization of ET receptors in the rabbit lower urinary tract as a function of age.

MATERIALS AND METHODS

The characteristics of ET receptors in bladder dome, trigone and urethra of 6 weeks and 6 months old male rabbits were determined using muscle bath and autoradiographic techniques.

RESULTS

ET-1 produces significant contractile responses in smooth muscle strips from bladder dome, trigone, and urethra in both 6 weeks and 6 months old rabbits. Although there was no significant difference in the maximum contractile response of urethral muscle strips to ET-1 between 6 weeks and 6 months old rabbits, the maximum responses to ET-1 were higher in both bladder dome and trigone of 6 weeks than 6 months old rabbits. A selective ETA receptor antagonist, BQ 610, shifted the concentration response curve to ET-1 to the right without decreasing maximal contractile responses in all regions from both age groups, whereas a selective ETB receptor antagonist, IRL 1038, had no significant effect on the contractile response in these tissues. Autoradiographic studies indicate that both ET receptor subtypes are expressed in bladder dome, trigone, and urethra with the ETA subtype being located only in the smooth muscle layers and the ETB subtype being located in both the urothelial and smooth muscle layers.

CONCLUSION

Our data indicate the presence of region- and age-dependent differences in the contractile properties of ET receptors in the male rabbit lower urinary tract. Although both ETA and ETB receptor subtypes are present in the smooth muscle layers, the ETA receptor is the sub-type that is primarily involved in the mediation of contractions.

Gene expression, localization, and pharmacological characterization of endothelin receptors in diabetic rat bladder dome

As there are significant amounts of functional endothelin receptors in the mammalian urinary tract, we examined the effect of experimental diabetes on the expression of endothelin receptors and their mRNAs in the rat bladder dome. The density of endothelin receptors in the rat bladder dome was higher (8 and 16 weeks following the onset of diabetes) than in age-matched controls. Insulin treatment, started 8 weeks after the induction of diabetes, partially reversed the endothelin receptor alterations. The pharmacological profile of the endothelin receptors in the bladder dome was similar in all groups and was consistent with the predominance of the endothelin ET(A) receptor subtype (ET(A):ET(B)=approximately 4:1). Autoradiographic studies demonstrated that the endothelin receptors were located in all tissue components of the bladder, including epithelial and muscular layers. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) data indicated that diabetes increased the expression level of gene transcripts for both endothelin receptor subtypes and that insulin treatment reversed the mRNA upregulation.

Developmental aspects of endothelin receptors in rabbit lower urinary tract

Since evidence of development/age-related alterations of endothelin receptors in circulation and respiration systems has been increasing, we attempted to investigate the pharmacological characterization of endothelin receptors in neonatal, premature, and mature male rabbit lower urinary tract. The biochemical properties of ET receptors were examined in the lower urinary tracts of 1-day (neonatal)-, 6-week (premature)-, and 1-year(mature)-old male rabbits with binding technique utilizing [(125)I]ET-1. The rank orders of the densities (B(max) values) of endothelin receptors in the bladder dome, bladder base, and urethra of different aged rabbits were bladder dome, 1 day > 6 week &vbar;Ls 1 year, bladder base, 1 day > 6 week &vbar;Ls 1 year, and urethra, 1 day > 6 week > 1 year. The pharmacological profiles of these binding sites inhibited by various kinds of endothelin receptor compounds showed similar K(i) values and similar proportions of endothelin receptor subtypes in the same regions of 1-day-, 6-week-, and 1-year-old animals. Our data clearly demonstrated the presence of regional difference and development-related changes in the density and subtype specificity of endothelin receptors in the lower urinary tract of the male rabbit. Neurourol. Urodynam. 19:71-85, 2000.

Effects of insulin treatment on diabetes-induced alterations in endothelin receptors in rat ureter

BACKGROUND

The present investigation was undertaken to examine the effect of insulin treatment on diabetes-induced alterations in endothelin (ET) receptors in rat ureters.

METHODS

The biochemical properties of ET receptors were examined in rat ureters from the following groups: 8 weeks diabetic (D8); 8 weeks age-matched control (C8); 16 weeks diabetic (D16); 16 weeks diabetic-insulin treated (insulin started 8 weeks after the onset of diabetes) (DI16); and 16 weeks age-matched control (C16). Diabetes was induced by the i.v. injection of 65 mg/kg streptozotocin (STZ).

RESULTS

The densities of ET receptors (Bmax values), as determined by saturation experiments with [125I]-ET-1, in the ureteral plasma membranes of D8, C8, D16, DI16 and C16 were 91.7 +/- 10.1, 42.1 +/- 7.2, 71.1 +/- 2.4, 51.5 +/- 6.3 and 45.1 +/- 3.3 fmol/mg of protein, respectively. [125I]-ET-1 binding to the ET receptors in rat ureteral membrane particulates was inhibited by ET-1 (non-selective), ET-3 (ET(B/C selective), BQ610 (ET(A) selective) and IRL 1620 (ET(B) selective) with the following rank order of Ki values: ET-1 < BQ 610 < ET-3 << IRL 1620. The pharmacological profile of the ET receptors was similar in all groups examined and was consistent with the predominance of the ET(A) receptor subtype in the ureteral membrane particulates. The subtype specificity of ET receptors in the ureteral tissues is confirmed with inhibition data obtained from similar binding studies in cloned human ET(A) and ET(B) receptors.

CONCLUSION

The data indicate that diabetes results in an up-regulation of ET receptors in the rat ureter, which is normalized by insulin treatment.

Role of nitric oxide in fetal lower urinary tract function

We studied the role of nitric oxide (NO) in normal function of the lower urinary tract in fetal lambs. Fetal surgery was performed in pregnant ewes at 118 days' gestation (term 145-days) to place arterial, venous, and double-lumen urachal catheters. Five animals had a catheter secured in the distal urethra (to measure voided volume), and six underwent ligation of the urethra. Urodynamic studies were performed via the urachal catheter under baseline conditions, during systemic blockade of NO synthesis with N omega-nitro-L-arginine, and with systemic NO stimulation by L-arginine 48 hours postoperatively. Nitric oxide blockade caused an 88% mean increase in bladder capacity (volume to initiation of voiding) (p < 0.001) and a 5.8-fold increase in mean postvoid residual volume (p < 0.0001) despite normal maximal bladder pressures, suggesting inadequate sphincteric relaxation. Qualitatively, NO inhibition increased the presence of low-level bladder contractions and caused a trend toward decreased bladder compliance. Increase of NO substrate by L-arginine infusion restored baseline findings if performed after N omega-nitro-L-arginine. Stimulation of NO by L-arginine infusion caused continuous efflux of the infusate secondary to a persistently open sphincter. In conclusion, NO is active in the function of the lower urinary tract in the fetal lamb and appears to influence both sphincter and detrusor activity.

Endothelin-1-induced phosphoinositide hydrolysis and contraction in isolated rabbit detrusor and urethral smooth muscle

1. Endothelin-1 (ET-1) caused a concentration-dependent increase in the formation of inositol phosphates (IPs) in isolated rabbit detrusor and urethral smooth muscle preparations prelabelled with myo-[3H]inositol. 2. The increase in accumulation of IPs was slow in onset in both detrusor and urethra, with no significant accumulation demonstrable during the first 30 min. The increase in IPs accumulation found after exposure of detrusor tissue to ET-1 (10(-7) M) for 2 hr (250 +/- 38%, n = 7) was not significantly different from that found in the urethra (279 +/- 40%, n = 6), when expressed as per cent of corresponding control values. 3. Pretreatment with nifedipine (10(-6) M) did not reduce IPs formation. In contrast, no increase in IPs formation was demonstrated in Ca(2+)-free medium. 4. ET-1 (10(-11)-10(-7) M) produced concentration-dependent, slowly developing contractions in both detrusor and urethral preparations. Pretreatment with H-7 (3 x 10(-5) M) for 30 min before ET-1 application resulted in a non-parallel shift of the ET-1 concentration-response curve with significant reductions in maximal responses in both tissues. 5. ET-1-induced contractions in urethral preparations were markedly inhibited by Ni2+ (3 x 10(-4) M), whereas the effect of Ni2+ in the detrusor was less pronounced. 6. The results suggest that ET-1 stimulates phosphoinositide hydrolysis in the rabbit detrusor and urethra. Both IPs formation and contractile activation evoked by ET-1 are dependent on extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)