Involvement of 5-hydroxytryptamine (HT)7 receptors in the 5-HT excitatory effects on the rat urinary bladder

Verification and Defined Dosage of Sodium Pentobarbital for a Urodynamic Study in the Possibility of Survival Experiments in Female Rat

Objectives

To evaluate the effects of pentobarbital dosages on lower urinary tract function and to define an appropriate dosage of sodium pentobarbital that would be suitable for urodynamic studies in which recovery from anesthesia and long term survive were needed for subsequent experiment.

Methods

Twenty-four 8-week-old, female, virgin, Sprague-Dawley rats (200-250 g) were used in this study. Rats in study groups received gradient doses of pentobarbital intraperitoneally, and those in the control group received urethane intraperitoneally. External urethral sphincter electromyography (EUS-EMG) was recorded simultaneously during cystometry and leak point pressure tests. The toe-pinch reflex was used to determine the level of anesthesia.

Results

Micturition was normally induced in both the urethane group and 32 mg/kg pentobarbital group. However, in groups of 40 mg/kg or 36 mg/kg pentobarbital, micturition failed to be induced; instead, nonvoiding contractions accompanied by EUS-EMG tonic activity were observed. There were no significant differences in leak point pressure or EUS-EMG amplitude or frequency between the urethane and 32 mg/kg pentobarbital groups.

Conclusions

This study confirmed significant dose-dependent effects of pentobarbital on lower urinary tract function and 32 mg/kg pentobarbital as an appropriate dosage for recovery urodynamic testing, which enable the achievement of expected essential micturition under satisfactory anesthesia in female rats.

Pharmacology and Therapeutic Potential of the 5-HT7 Receptor

It is well-documented that serotonin (5-HT) exerts its pharmacological effects through a series of 5-HT receptors. The most recently identified member of this family, 5-HT₇, was first identified in 1993. Over the course of the last 25 years, this receptor has been the subject of intense investigation, and it has been demonstrated that 5-HT₇ plays an important role in a wide range of pharmacological processes. As a result of these findings, modulation of 5-HT₇ activity has been the focus of numerous drug discovery and development programs. This review provides an overview of the roles of 5-HT₇ in normal physiology and the therapeutic potential of this interesting drug target.

Synthesis and Pharmacological Evaluation of Novel Silodosin-Based Arylsulfonamide Derivatives as α1A/α1D-Adrenergic Receptor Antagonist with Potential Uroselective Profile

Benign prostatic hyperplasia (BPH) is the most common male clinical problem impacting the quality of life of older men. Clinical studies have indicated that the inhibition of α_1A-/α_1D adrenoceptors might offer effective therapy in lower urinary tract symptoms. Herein, a limited series of arylsulfonamide derivatives of (aryloxy)ethyl alicyclic amines was designed, synthesized, and biologically evaluated as potent α₁-adrenoceptor antagonists with uroselective profile. Among them, compound 9 (3-chloro-2-fluoro-N-([1-(2-(2-(2,2,2-trifluoroethoxy)phenoxy]ethyl)piperidin-4-yl)methyl)benzenesulfonamide) behaved as an α_1A-/α_1D-adrenoceptor antagonist (K_i(α₁) = 50 nM, EC₅₀(α_1A) = 0.8 nM, EC₅₀(α_1D) = 1.1 nM), displayed selectivity over α₂-adrenoceptors (K_i(α₂) = 858 nM), and a 5-fold functional preference over the α_1B subtype. Compound 9 showed adequate metabolic stability in rat-liver microsome assay similar to the reference drug tamsulosin (Cl_int = 67 and 41 µL/min/mg, respectively). Compound 9 did not decrease systolic and diastolic blood pressure in normotensive anesthetized rats in the dose of 2 mg/kg, i.v. These data support development of uroselective agents in the group of arylsulfonamides of alicyclic amines with potential efficacy in the treatment of lower urinary tract symptoms associated to benign prostatic hyperplasia.

Expression of 5-Hydroxytryptamine Receptors in Human Urinary Bladders with Benign Prostatic Hyperplasia

INTRODUCTION

This study investigated the mRNA expression pattern and distribution of 5-hydroxytryptamine (5-HT) receptors 5-HT2A, 5-HT2B, 5-HT3A, 5-HT4, and 5-HT7 within the urothelium and detrusor of normal bladder tissue and in the urothelium of bladders from patients with benign prostatic hyperplasia (BPH).

METHODS

Normal urinary bladder specimens were obtained from 13 patients undergoing radical cystectomy due to bladder cancer (normal group) and BPH specimens were obtained from 27 benign prostatic obstruction patients receiving transurethral prostatectomy or retropubic prostatectomy. Receptor subtype mRNA expression was determined by real-time reverse transcription polymerase chain reaction on urothelium, detrusor, and whole mucosal preparations. Receptor distribution was determined by immunohistochemistry.

RESULTS

In normal tissues, expressions of 5-HT2B and 5-HT7 receptor mRNAs in the urothelium, detrusor, and whole mucosa were greater than the average expression for all receptor subtype mRNAs. 5-HT2B receptor protein was distributed in the apical urothelium and among the detrusor smooth muscle layers. In contrast, the 5-HT7 receptors were within the urothelium middle cell layers and detrusor smooth muscle cells. The expression pattern of each 5-HT receptor subtype mRNA within the BPH urothelium was similar to that in the normal urothelium. The expression level of 5-HT2A receptor mRNA in the BPH group was significantly lower than the normal group; however, the expressions of both 5-HT3A and 5-HT7 mRNAs were significantly higher. The expressions of both 5-HT2B and 5-HT4 mRNAs were not significantly different between the normal and BPH groups.

CONCLUSION

In normal urinary bladders, the expressions of both 5-HT2B and 5-HT7 mRNAs were higher compared to the 5-HT2A, 5-HT3A, and 5-HT4 mRNAs. The distributions of 5-HT2B and 5-HT7 receptors were different in the urothelium and detrusor layers. The 5-HT3A and 5-HT7 receptor mRNAs in the BPH group were significantly higher compared to the normal urothelium, while the 5-HT2A mRNA was significantly lower.

FUNDING

Asahi Kasei Pharma Corporation.

The effect of 5-HT and electrical field stimulation on the contractility of the whole isolated urinary bladder of Suncus murinus

The present study used the whole isolated urinary bladder of Suncus murinus, to investigate the effect of exogenously added serotonin (5-HT) and electrical field stimulation (EFS) in the absence and presence of methysergide, a 5-HT1/2/7 receptor antagonist or the selective 5-HT7 receptor antagonist, SB269970. Further experiments investigated the involvement of potassium channel, cholinergic and purinergic systems in mediating the contractile response to EFS. Pre-treatment with methysergide reduced and increased the contractile responses to 5-HT and EFS, respectively. Pre-treatment with SB269970 increased the responses to 5-HT without modifying the EFS-induced contractions. EFS-induced contractions were not modified by pre-treatment with atropine (10μM), α-β-methylene ATP or glibenclamide. EFS-induced contractions were attenuated by cromakalim (10µM) or atropine (0.1 µM). In conclusion, the 5-HT2 receptors are likely to play a role in mediating the contractile response to 5-HT in detrusor muscle. Furthermore, EFS-induced contractions are mediated through cholinergic and an unknown neurotransmitter which is modulated by K(ATP) channels in the detrusor muscle of Suncus murinus.

The effect of the 5-HT7 serotonin receptor agonist, LP44, on micturition in rats with chronic spinal cord injury

AIMS

To better understand the effects of the selective 5-HT7 receptor agonist 4-[2-(Methylthio)phenyl]-N-(1,2,3,4-tetrahydro-1-naphthalenyl)-1-piperazinehexanamide hydrochloride (LP44) on micturition in spinal cord injury (SCI) rats.

METHODS

Female Sprague-Dawley rats weighing 200-275 g were used. SCI was produced in 8 of the 16 rats by transection at the T10 level; cystometric study occurred 8-12 weeks post-transection. Intravesical pressure was monitored in urethane-anesthetized animals via a transvesical catheter. The selective 5-HT7 antagonist (R)-3-[2-[2-(4-Methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl] phenol hydrochloride (SB-269970) was administered after each LP44 dose-response curve (all drugs were administered intravenously, i.v).

RESULTS

Compared to controls, SCI rats had a higher bladder capacity and residual volume, and a lower voiding efficiency. In SCI rats, LP44 (0.003-0.3 mg/kg, i.v) induced significant dose-dependent increases in micturition volume, significant dose-dependent decreases in residual volume, resulting in significant increases in voiding efficiency. CMG measurements showed a dose-dependent increase of the high-frequency oscillation (HFO) activity, including the number of small oscillation per voiding. This was correlated with the improved voiding efficiency. SB-269970 (0.1 mg/kg, i.v) partially or completely reversed all LP44-induced changes.

CONCLUSIONS

HFOs seems to be correlated with external urethral sphincter (EUS) bursting activity during voiding. Both the bladder voiding efficiency and the periodic EUS activity were decreased in SCI rats. 5-HT7 receptor agonist can enhance HFO activity, thereby improving voiding efficiency. Whether or not these results may have implications for the future treatment of voiding dysfunction in SCI patients remains to be studied.

The distribution of muscles fibers and their types in the female rat urethra: cytoarchitecture and three-dimensional reconstruction

An attempt to explore urethral cytoarchitecture including the distribution of smooth muscles and fast and slow striated muscles of adult female Sprague Dawley rat--a popular model in studying lower urinary tract function. Histological and immunohistochemical stainings were carried out to investigate the distribution of urethral muscle fibers and motor end plates. The urethral sphincter was furthermore three-dimensionally reconstructed from serial histological sections. The mucosa at the distal urethra was significantly thicker than that of other segments. A prominent inner longitudinal and outer circular layer of smooth muscles covered the proximal end of urethra. Thick circular smooth muscles of the bladder neck region (urethral portion) decreased significantly distalward and longitudinal smooth muscles became 2- to 3-fold thicker in the rest of the urethra. An additional layer of striated muscles appeared externally after neck region (urethra) and in association with motor end plates ran throughout the remaining urethra as the striated sphincter layer. Most striated muscles were fast fibers while relatively fewer slow fibers often concentrated at the periphery. A pair of extraneous striated muscles, resembling the human urethrovaginal sphincter muscles, connected both sides of mainly the distal vagina to the dorsal striated muscles in the wall of the middle urethra. The tension provided by this pair of muscles, and in conjunction with the striated sphincter of the urethral wall, was likely to function to suspend the middle urethra and facilitates its closure. Comprehensive morphological data of urethral sphincter offers solid basis for researchers conducting studies on dysfunction of bladder outlet.

5-hydroxytryptamine induced relaxation in the pig urinary bladder neck

BACKGROUND AND PURPOSE

5-Hydroxytryptamine (5-HT) is one of the inhibitory mediators in the urinary bladder outlet region. Here we investigated mechanisms involved in 5-HT-induced relaxations of the pig bladder neck.

EXPERIMENTAL APPROACH

Urothelium-denuded strips of pig bladder were mounted in organ baths for isometric force recordings of responses to 5-HT and electrical field stimulation (EFS).

KEY RESULTS

After phenylephrine-induced contraction, 5-HT and 5-HT receptor agonists concentration-dependently relaxed the preparations, with the potency order: 5-carboxamidotryptamine (5-CT) > 5-HT = RS67333 > (+/-)-8-hydroxy-2-dipropylaminotetralinhydrobromide > m-chlorophenylbiguanide > alpha-methyl-5-HT > ergotamine. 5-HT and 5-CT relaxations were reduced by the 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulphonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride and potentiated by (S)-N-tert-butyl-3-(4-(2-methoxyphenyl)-piperazin-1-yl)-2-phenylpropanamide dihydrochloride (WAY 100135) and cyanopindolol, 5-HT(1A) and 5-HT(1A/1B) receptor antagonists respectively. Inhibitors of 5-HT(1B/1D), 5-HT(2), 5-HT(2B/2C), 5-HT(3), 5-HT(4), 5-HT(5A) and 5-HT(6) receptors failed to modify 5-HT responses. Blockade of monoamine oxidase A/B, noradrenergic neurotransmission, alpha-adrenoceptors, muscarinic and purinergic receptors, nitric oxide synthase, guanylate cyclase and prostanoid synthesis did not alter relaxations to 5-HT. Inhibitors of Ca(2+)-activated K(+) and ATP-dependent K(+) channels failed to modify 5-HT responses but blockade of neuronal voltage-gated Na(+)-, Ca(2+)- and voltage-gated K(+) (K(v))-channels potentiated these relaxations. Adenylyl cyclase activation and cAMP-dependent protein kinase (PKA) inhibition potentiated and reduced, respectively, 5-HT-induced responses. Under non-adrenergic, non-cholinergic, non-nitrergic conditions, EFS induced neurogenic, frequency-dependent, relaxations which were resistant to WAY 100135 and cyanopindolol.

CONCLUSIONS AND IMPLICATIONS

5-HT relaxed the pig urinary bladder neck through muscle 5-HT(7) receptors linked to the cAMP-PKA pathway. Prejunctional 5-HT(1A) receptors and K(v) channels modulated 5-HT-induced relaxations whereas postjunctional K(+) channels were not involved in such responses. 5-HT(7) receptor antagonists could be useful in the therapy of urinary incontinence produced by intrinsic sphincter deficiency.

Comparison of the urethral properties of the female guinea pig and rat

AIMS

The main focus of this study was to profile and compare urethral function in the female guinea pig and rat, and to characterize urodynamically distinctive patterns in the micturition cycle of the two species. This exercise aimed to investigate potential species-related differences and determine a suitable animal model for the human urethra.

MATERIALS & METHODS

Female Dunkin-Hartley guinea pigs (400-500 g) and Sprague-Dawley rats (200-300 g) were used throughout the study. For in vitro experiments urethral rings were suspended vertically for isometric tension recording in 5 ml organ baths and drugs (phenylephrine 10(-4) M and carbachol 10(-4) M) were applied directly to the bathing solution. In vivo urethral pull-through and urodynamic studies were performed under urethane anesthesia, and phenylephrine (200 microg/kg) was administered during urethral pull-through experiments via the intravenous (i.v.) route. Urethral, bladder and arterial pressures, and external urethral sphincter electromyographic (EMG) spike activity were recorded simultaneously throughout.

RESULTS

Organ bath studies coupled with in vivo pull-through experiments produced urethral profiles with distinct regional variations for both species. Urodynamic studies with the urethral probe fixed in the high pressure zones of the proximal urethra produced similar recordings in both species during bladder filling and marked differences during micturition. The guinea pig showed complete sphincteric inhibition immediately prior and during micturition as also seen in the human, whereas the rat exhibited high frequency bursts in EMG activity at this stage in the cycle.

CONCLUSIONS

The EMG activity seen in the rat during micturition is presumably necessary for efficient voiding, thus the guinea pig is a more suitable comparative model for the human in relation to urethral properties during micturition.