Electrical and mechanical properties of the capsular smooth muscles of the rabbit prostate in relation to the actions of the alpha 1-adrenoceptor blocker, YM-12617

New intraprostatic injectables and prostatic urethral lift for male LUTS

Treatment modalities for male lower urinary tract symptoms (LUTS) comprise a broad spectrum of medical and surgical options. Interest is growing in minimally invasive treatment options, which should ideally be performed in an outpatient setting and have a short recovery time, durable efficacy and a good safety profile. The preservation of all aspects of sexual function, including antegrade ejaculation, seems to be increasingly important for patients. Initial experimental data on new minimally invasive procedures-such as the intraprostatic injection of novel agents including botulinum neurotoxin A (BoNT-A), NX-1207 and PRX302-were promising, but clinical trials have not confirmed the findings. Trials of the mechanical prostatic urethral lift device-Urolift(®) (Neotract, Inc., USA)-have been positive, but further long-term results are needed to confirm its beneficial effects.

Relaxing effect of acetylcholine on phenylephrine-induced contraction of isolated rabbit prostate strips is mediated by neuronal nitric oxide synthase

Purpose

The location of acetylcholinesterase-containing nerve fibers suggests a role for acetylcholine in both contractility and secretion in the prostate gland. The colocalization of nitrergic nerves with cholinergic nerves, and the cotransmission of nitric oxide with acetylcholine in cholinergic nerves, has been demonstrated in the prostate glands of various species. Thus, we investigated the effects of acetylcholine on phenylephrine-induced contraction and the correlation between cholinergic transmission and nitric oxide synthase by using isolated prostate strips of rabbits.

Materials and Methods

Isolated prostate strips were contracted with phenylephrine and then treated with cumulative concentrations of acetylcholine. Changes in acetylcholine-induced relaxation after preincubation with NG-nitroarginine methyl ester, 7-nitroindazole, and aminoguanidine were measured. The effects of selective muscarinic receptor antagonists were also evaluated.

Results

In the longitudinal phenylephrine-contracted strip, the cumulative application of acetylcholine (10^-9 to 10^-4 M) elicited a concentration-dependent relaxation effect. Acetylcholine-induced relaxation was inhibited not only by nitric oxide synthase inhibitors (10 µM L-NAME or 10 µM 7-nitroindazole) but also by 10 µM atropine and some selective muscarinic receptor antagonists (10^-6 M 11-([2-[(diethylamino)methyl]-1-piperdinyl]acetyl)-5,11-dihydro-6H-pyrido[2,3-b][1,4]benzodiazepine-6-one and 10^-6 M 4-diphenylacetoxy-N-methyl-piperidine). In contrast, relaxation was significantly increased by pretreatment of the strips with 10 mM L-arginine.

Conclusions

Acetylcholine relaxed phenylephrine-induced contractions of isolated rabbit prostate strips. This relaxation may be mediated via both cholinergic and constitutive nitric oxide synthase with both the M2 and M3 receptors possibly playing key roles.

Effects of Botulinum Toxin A on the Contractile Function of Dog Prostate

OBJECTIVES

To study effects of botulinum toxin A (BoNT/A) on prostate contractile function in dogs.

METHODS

One hundred units (N=6) or 200 units (N=5) BoNT/A was injected into dog prostate. Sham control group (N=7) received normal saline injections. Before and 1 mo after injection, prostate urethral pressure response to electrostimulation and intravenous (IV) norepinephrine was measured. Contractile responses of prostate strips were tested in tissue bath. Structural changes were evaluated with conventional histology and smoothelin immunohistochemistry.

RESULTS

Injection of normal saline and 100 units BoNT/A did not significantly change prostate urethral pressure response to IV norepinephrine and electrostimulation. However, injection of 200 units BoNT/A significantly reduced prostate urethral pressure response to IV norepinephrine and electrostimulation. Contractile responses of prostate strips to potassium chloride, electrostimulation, and phenylephrine did not differ between sham control and 100U groups. In the 200U group, however, all responses were less than those of sham controls. Control and BoNT/A groups exhibited nitric oxide-related relaxation in prostate strips precontracted by phenylephrine. Injection of 100 units BoNT/A induced mild atrophy of prostate gland; injection of 200 units BoNT/A induced more pronounced atrophic changes in prostate gland and vacuoles formation in smooth muscle cells of stromal tissue.

CONCLUSIONS

Injecting BoNT/A into dog prostate reduces contractile function while maintaining relaxation response of the prostate. These effects make BoNT/A a viable option in managing prostate-related symptoms. However, large, randomized clinical studies to determine long-term effects and safety of BoNT/A application in human prostates are required.

Ligand design and synthesis of new imidazo[5,1-b]quinazoline derivatives as α1-adrenoceptor agonists and antagonists

A series of new imidazo[5,1-b]quinazoline derivatives (VII-IX) was designed, synthesized, and biologically evaluated for their in vivo hypotensive or hypertensive activities. The design of these compounds was based upon the molecular modeling simulation of the fitting values and conformational energy values of the best-fitted conformers to both the alpha(1)-adrenoceptor (alpha(1)-AR) agonist and alpha(1)-adrenoceptor (alpha(1)-AR) antagonist hypotheses. These hypotheses were generated from their corresponding lead compounds using CATALYST software. The simulation studies predicted that compounds IXa and IXe would have probable affinity for the alpha(1)-AR antagonist hypothesis, while compounds IXb, IXc, and IXg predicted a higher affinity for the alpha(1)-AR agonist hypothesis. In vivo biological evaluation of these compounds for their effects on the blood pressure of normotensive cats was consistent with the results of molecular modeling studies, where compounds IXa and IXe exhibited hypotensive activity, while compounds IXb, IXc, and IXg resulted in increasing the blood pressure of the experimental animals at different doses.

Cholinergic innervation and function in the prostate gland

The mammalian prostate is densely innervated by hypogastric and pelvic nerves that play an important role in regulating the growth and function of the gland. While there has been much interest in the role of the noradrenergic innervation and adrenoceptors in prostate function, the role of cholinergic neurones in prostate physiology and pathophysiology is not well understood. This review focuses on the role of acetylcholine and cholinoceptors in prostate function. Nitric oxide, vasoactive intestinal polypeptide, and/or neuropeptide Y are co-localised with cholinesterase and/or acetylcholine transporter in some of the nerve fibres supplying the prostate. Their roles are also briefly discussed in this review. A dense network of cholinesterase-staining fibres supplies both prostate epithelium and stroma, suggesting a role of acetylcholine and/or co-localised neuropeptides in the modulation of prostatic secretions, as well as smooth muscle tone. A predominantly epithelial location for prostate muscarinic receptors indicated a major secretomotor role for acetylcholine. The muscarinic receptor subtype mediating muscarinic agonist-induced smooth muscle contraction or enhancement of contractions evoked by nerve stimulation differs in different species. In the human, there is evidence for M(1) receptors on the epithelium, M(2) receptors on the stroma, and both M(1) and M(3) receptors in some prostate cancer cell lines. Several recent investigations indicate that muscarinic receptors may also mediate or modulate normal, benign, and malignant prostate growth. The role of muscarinic agonists and their receptors and the influences of age, testicular, and other steroids in regulating the effects are reviewed.

Tamsulosin: assessment of affinity of 3H-prazosin bindings to two alpha1-adrenoceptor subtypes (alpha1H and alpha1L) in bovine prostate and rat heart and brain

1. The present study was designed to assess the displacement potencies of tamsulosin to 3H-prazosin bindings in two alpha1-adrenoceptor (AR) subtypes (alpha1H and alpha1L) in bovine prostate, rat heart and brain compared with those of amosulalol, labetalol, ketanserin, clonidine and propranolol. 2. The pKi values of tamsulosin to alpha1H and alpha1L subtypes in bovine prostate were 9.13 and 8.99 and these values were almost the same as those of prazosin. On the other hand, low pKi binding values of amosulalol, labetalol, ketanserin, clonidine and propranolol to these subtypes were observed. 3. Low pKi values of tamsulosin to alpha2- and beta-ARs and muscarinic and 5HT2 receptors in the rat brain were observed. 4. These results suggest that tamsulosin has high affinities to alpha1L-AR subtypes in bovine prostate and rat hearts as well as alpha1H-AR subtypes, implying an inhibitory effect of this drug on the contraction of the prostate.

Studies on quinazolines and 1,2,4-benzothiadiazine 1,1-dioxides. 8.1, 2 synthesis and pharmacological evaluation of tricyclic fused quinazolines and 1,2,4-benzothiadiazine 1,1-dioxides as potential alpha1-adrenoceptor antagonists

A series of 2-substituted methyl 2,3-dihydroimidazo[1, 2-c]quinazolin-5(6H)-ones (4), 3-substituted methyl 2, 3-dihydroimidazo[1,2-c]quinazolin-5(6H)-ones (5), 3-substituted methyl 2,3-dihydro-5H-thiazolo[2,3-b]quinazolin-5-ones (15a,b), 3-substituted methyl 2,3-dihydroimidazo[2,1-b]quinazolin-5(1H)-ones (16a,b), 3-substituted methyl 2,3-dihydro-1H-imidazo[1,2-b][1,2, 4]benzothiadiazine 5,5-dioxides (33a,b), 2-substituted methyl imidazo[1,2-c]quinazolin-5(6H)-ones (42-45a,b), 3-substituted methyl imidazo[1,2-c]quinazolin-5(6H)-ones (50-53a,b), 3-substituted methyl 5H-thiazolo[2,3-b]quinazolin-5-ones (55-56a,b), and 3-substituted methyl 5-(methylthio)-2,3-dihydroimidazo[1,2-c]quinazoline (57) were synthesized as compound 1conformational rigid congeners for pharmacological evaluation as potential alpha1-adrenoceptor antagonists. Compounds 4, 5, 33a,b, 44a,b, 45a,b, 52a,b, 53a,b, and 57 were found to possess high affinity for the alpha1-adrenoceptor. Compounds 5 and 57 were the most highly selective and potent alpha1 antagonists with Ki = 0.21 +/- 0.02 and 0.90 +/- 0.08 nM, respectively. The S-enantiomers of these two compounds (Ki = 0.13 +/- 0.01 nM for (S)-(-)-5; Ki = 1.0 +/- 0.2 nM for (S)-(+)-57) were 144-200-fold more potent than the R-enantiomers (Ki = 26 +/- 8 nM for (R)-(+)-5; Ki = 144 +/- 23 nM for (R)-(-)-57). Compound 4 showed 8-fold higher affinity to alpha1A-AR better than alpha1B-AR. These compounds possessed weak to no activity against the 5-HT1A receptor.

Effect of orchiectomy on the alpha adrenergic contractile response of dog prostate

PURPOSE

To investigate the effect of androgen deprivation on the alpha-adrenergic contractile response of the dog prostate using both in vitro and in vivo methods.

MATERIALS AND METHODS

In vitro muscle bath study: One month after surgery, responses to KCl (120 mM.) and norepinephrine (10(-8) to 10(-3)M.) of prostatic tissue strips (of the same size) from castrated (n = 6) and sham-operated (n = 6) adult mongrel dogs were determined. In vivo study: Before and 1 month after surgery, the intraprostatic urethral pressure response to intravenous norepinephrine administration of 6 castrated and 5 sham-operated adult dogs was examined.

RESULTS

(1) Before castration the serum level of testosterone was 1.24 +/- 0.2 ng./ml.; 1 month after castration, it had dropped to an undetectable level. (2) Histological examination of the prostates from castrated animals revealed profound atrophy of glandular tissue with a relatively increased stromal tissue component in each section. (3) In vitro study: The contractile responses to KCl and norepinephrine of individual prostate strips (same size) from castrated animals were significantly higher than control. However, if the response to norepinephrine was normalized to the response to KCl, there was no significant difference in response to norepinephrine between the 2 groups. In addition, the ED50 of the norepinephrine-stimulated contractile response was not changed by castration. (4) In vivo study: There was no significant change in intraprostatic urethral pressure response to intravenous norepinephrine administration after orchiectomy.

CONCLUSIONS

The results of this study show that the sensitivity of the alpha-adrenergic contractile response of the dog prostate is not affected by androgen deprivation, nor is alpha-adrenergic contractile activity of the dog prostate regulated by androgen.

Effects of the alpha 1-adrenoceptor antagonist R-(-)-YM12617 on isolated human penile erectile tissue and vas deferens

The effects of the selective alpha 1-adrenoceptor antagonist, R-(-)-YM12617 (5-[2-[[2-(0-ethoxyphenoxy)ethyl]amino] propyl]-2-methoxybenzenesulphonamide HCl), were investigated in isolated human corpus spongiosum, corpus cavernosum, and vas deferens. R-(-)-YM12617 concentration dependently and competitively inhibited contractions induced by noradrenaline in human penile erectile tissue (pA2 value in corpus spongiosum = 9.92), and the drug was approximately 12 times more potent than prazosin (pA2 value = 8.83). In the vas deferens, R-(-)-YM12617 and prazosin inhibited electrically induced contractions concentration dependently, and abolished the contractions at 10(-6) and 10(-5) M, respectively. The -log IC50 values for R-(-)-YM1261 and prazosin were 8.46 and 7.50, respectively. It is concluded that R-(-)-YM12617 is a potent inhibitor of alpha 1-adrenoceptors in human penile erectile tissues and vas deferens, and that the drug, if injected intracavernosally, may be useful for the treatment of penile erectile dysfunction.

Electrical and mechanical activity of rabbit prostate smooth muscles in response to nerve stimulation

1. The rabbit prostate contains two smooth muscle bundles: one forms the capsule of the prostate and the other runs longitudinally in the outermost layer of the prostate. The former was contracted by exogenously applied noradrenaline (NA) and the latter by acetylcholine (ACh), and were therefore identified as NA-sensitive and ACh-sensitive muscles, respectively. 2. In the NA-sensitive muscle, exogenously applied NA, but not ACh, depolarized the smooth muscle membrane, and this action of NA was antagonized by prazosin but not by yohimbine. The membrane of the ACh-sensitive muscle was depolarized by ACh and hyperpolarized by NA. The former was antagonized by atropine and the latter by phentolamine. 3. In both bundles, electrical stimulation of intramural nerves elicited a biphasic junction potential: an excitatory junction potential (EJP) followed by an inhibitory junction potential (IJP). In the NA-sensitive muscle, the EJP was resistant to alpha-adrenoreceptor antagonists and sensitive to guanethidine, while the IJP was sensitive to apamin and resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. The EJP and IJP elicited in the ACh-sensitive muscle were inhibited by atropine and apamin, respectively, but both potentials were resistant to alpha- or beta-adrenoreceptor antagonists or guanethidine. 4. Transmural nerve stimulation elicited a twitch contraction in both muscle bundles, and the contractions in the NA-sensitive muscle were partially inhibited by prazosin and blocked completely by guanethidine. The contraction of the ACh-sensitive muscle was blocked by atropine. Contractions produced by exogenously applied NA and ACh were antagonized by prazosin and atropine, respectively. 5. It is concluded that in the rabbit prostate there are two smooth muscles bundles which are respectively contracted with associated depolarization by NA or ACh. The NA-sensitive muscle receives adrenergic excitatory and non-adrenergic non-cholinergic inhibitory innervation. The ACh-sensitive muscle receives cholinergic excitatory and non-adrenergic non-cholinergic inhibitory innervation.

Infravesical outflow obstruction in rats: a comparison of two models

1. A new model of infravesical outflow obstruction was developed in male rats by the repeated s.c. administration of testosterone for 5-15 days (3 mg/kg die). The effects of this treatment which produced a 65% increase of prostate weight (10 days) on bladder voiding was evaluated in urethane anesthetized rats by the transvesical infusion of saline and compared to the cystometric alterations produced by application of a silk ligature at urethral level in female rats (4-8 weeks before) as described by Malmgren et al. (1987a, b). 2. Testosterone-pretreatment for 10 days produced little changes in bladder weight, bladder capacity or amplitude of micturition contraction but determined a marked increase in residual volume, indicating that infravesical outflow obstruction impaired significantly bladder voiding. Furthermore, detrusor instability was observed in the majority of testosterone-treated rats. 3. The participation of an active component to voiding impairment in testosterone-treated rats was suggested by the effect of intravenous prazosin which improved voiding efficiency. 4. In urethra-ligated female rats there was a marked increase in bladder weight which was paralleled by a dramatic alteration in micturition reflex that is marked increase in bladder capacity and residual volume. 5. It is concluded that these two models of infravesical outflow obstruction produce cystometric patterns simulating the urodynamic alterations observed in patients with benign prostatic hyperplasia and are potentially suitable for development of drugs in this field.