Characterization of in vitro relaxant mechanisms in erectile tissue from rabbits of different ages

Diet, herbs and erectile function: A good friendship!

Plants and plant materials have been used for thousands of years to treat and control erectile dysfunction in men. This practice has spanned many cultures and traditions around the world, with the therapeutic effects of many plants attributed to their phytochemical constituents. This review explains how polyphenols (including phenolic acids, flavonoids, terpenoids, carotenoids, alkaloids and polyunsaturated fatty acids) in plants and plant food products interact with key enzymes (phosphodiesterase-5 [PDE-5], angiotensin-converting enzyme [ACE], acetylcholinesterase [AChE], adenosine deaminase [ADA] and arginase) associated with erectile dysfunction. By modulating or altering the activity of these physiologically important enzymes, various bioactive compounds from plants or plant products can synergistically or additively provide tremendous protection against male erectile problems.

Changes in nerve- and endothelium-mediated contractile tone of the corpus cavernosum in a mouse model of pre-mature ageing

Erectile dysfunction (ED) is very prevalent in the older population, although the ageing-related mechanisms involved in the development of ED are poorly understood. We propose that age-induced differences in nerve- and endothelium-mediated smooth muscle contractility in the corpus cavernosum (CC) could be found between a senescent-accelerated mouse prone (SAMP8) and senescent-accelerated mouse resistant (SAMR1) strains. We analysed the changes in muscle tension induced by electrical field stimulation (EFS) or agonist addition 'in vitro', assessing nerve density (adrenergic, cholinergic and nitrergic), the expression of endothelial nitric oxide synthase (eNOS), cGMP accumulation and the distribution of interstitial cells (ICs) by immunofluorescence. We observed no change in both the nerve-dependent adrenergic excitatory contractility at physiological levels of stimulation and in the nitrergic inhibitory response in SAMP8 animals. Unlike cholinergic innervation, the density of adrenergic and nitrergic nerves increased in SAMP8 mice. In contrast, smooth muscle sensitivity to exogenous noradrenaline (NA) was slightly reduced, whereas cGMP accumulation in response to EFS and DEA/NO, and relaxations to DEA/NO and sildenafil, were not modified. No changes in the expression of eNOS and in the distribution of vimentin-positive ICs were detected in the aged animals. The ACh induced atropine-sensitive biphasic endothelium-dependent responses involved relaxation at low concentrations that turned into contractions at the highest doses. CC relaxation was mainly because of the production of NO together with some relaxant prostanoid, which did not change in SAMP8 animals. In contrast, the contractile component was considerably higher in the aged animals and it was completely inhibited by indomethacin. In conclusion, a clear imbalance towards enhanced production of contractile prostanoids from the endothelium may contribute to ED in the elderly. On the basis of these data, we propose the senescence-accelerated mouse model as a reliable tool to analyse the basic ageing mechanisms of the CC.

Purinergic signalling in the reproductive system in health and disease

There are multiple roles for purinergic signalling in both male and female reproductive organs. ATP, released as a cotransmitter with noradrenaline from sympathetic nerves, contracts smooth muscle via P2X1 receptors in vas deferens, seminal vesicles, prostate and uterus, as well as in blood vessels. Male infertility occurs in P2X1 receptor knockout mice. Both short- and long-term trophic purinergic signalling occurs in reproductive organs. Purinergic signalling is involved in hormone secretion, penile erection, sperm motility and capacitation, and mucous production. Changes in purinoceptor expression occur in pathophysiological conditions, including pre-eclampsia, cancer and pain.

Role of adenosine signaling in penile erection and erectile disorders

INTRODUCTION

Penile erection is a hemodynamic process, which results from increased flow and retention of blood in the penile organ due to the relaxation of smooth muscle cells. Adenosine, a physiological vasorelaxant, has been shown to be a modulator of penile erection.

AIM

To summarize the research on the role of adenosine signaling in normal penile erection and erectile disorders.

MAIN OUTCOME MEASURES

Evidence in the literature on the association between adenosine signaling and normal and abnormal penile erection, i.e., erectile dysfunction (ED) and priapism.

METHODS

The article reviews the literature on the role of endogenous and exogenous adenosine in normal penile erection, as well as in erectile disorders namely, ED and priapism.

RESULTS

Adenosine has been shown to relax corpus cavernosum from various species including human in both in vivo and in vitro studies. Neuromodulatory role of adenosine in corpus cavernosum has also been demonstrated. Impaired adenosine signaling through A(2B) receptor causes partial resistance of corpus cavernosum, from men with organic ED, to adenosine-mediated relaxation. Increased level of adenosine has been shown to be a causative factor for priapism.

CONCLUSION

Overall, the research reviewed here suggests a general role of exogenous and endogenous adenosine signaling in normal penile erection. From this perspective, it is not surprising that impaired adenosine signaling is associated with ED, and excessive adenosine signaling is associated with priapism. Adenosine signaling represents a potentially important diagnostic and therapeutic target for the treatment of ED and priapism.

The birth and postnatal development of purinergic signalling

The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.

A functional study of purinergic signalling in the normal and pathological rabbit corpus cavernosum

OBJECTIVE

To examine rabbit cavernosal smooth muscle (CSM) relaxation to ATP, ADP and UTP in normal rabbits and in models of conditions that predispose to erectile dysfunction (ED), diabetes mellitus (DM; induced for 6 months) and bladder outlet obstruction (BOO, 6 weeks after surgery).

MATERIALS AND METHODS

Concentration-response curves (CRCs) were constructed to ATP, ADP and UTP on CSM from control rabbits in the absence and presence of antagonists. In addition, CRCs were constructed to ATP in CSM from rabbits with DM and BOO.

RESULTS

ATP and UTP caused equipotent, dose-dependent relaxations of pre-contracted normal rabbit CSM; ADP was more potent. Relaxation was inhibited by Reactive Blue 2, but not by suramin, 8-p-sulfophenyltheophylline or L-N(G)-nitroarginine methyl ester. In rabbits with DM and those with partial BOO, ATP-mediated CSM relaxation was less than in control rabbits. Pharmacological profiling suggests that purine-induced CSM relaxation might be mediated by P2Y(1) and P2Y(4) receptors in the rabbit.

CONCLUSIONS

In healthy rabbits, ATP released from nerves appears to produce relaxation of CSM via P2Y(4) receptors on smooth muscle, while ADP, acting on P2Y(1) receptors on endothelial cells, produces relaxation via nitric oxide. Alterations in CSM purinergic signalling might be implicated in the pathophysiology of ED associated with DM and BOO. Characterization of purinergic signalling in CSM might highlight new therapeutic targets for treating ED.

Efficacy of sildenafil as the first-step therapeutic tool for Japanese patients with erectile dysfunction

The aim of this study was to assess the efficacy of sildenafil as the first-step tool for erectile dysfunction (ED) in Japanese males. Between March 1999 and March 2003, 281 patients were prescribed five tablets of sildenafil (50 mg) as the first step in the therapeutic management of ED. Of the 281 patients, 206 were evaluable patients. The overall success rate in achieving sexual intercourse in subjects after taking sildenafil was 77.2% (159/206), while 22.8% (47/206) were unsuccessful. The success rates in men with functional ED and organic ED were 91.4% (85/93) and 65.5% (74/113), respectively (P<0.0001). Overall, transient adverse effects of sildenafil occurred in 16 (8%) males. Intolerable adverse effects (edema and dizziness) occurred in only 1% of patients (2/206). Sildenafil citrate may be recommended as the first choice drug for ED because of its high success rate and low invasiveness.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Aging impairs nitric oxide-mediated relaxant responses of rabbit corporal smooth muscle

Aging has been reported to cause impotence, the mechanism of which is unknown. Therefore, we investigated the effect of aging on electrical stimulation-induced neurogenic, carbachol-induced, endothelium-dependent, and sodium nitroprusside-induced cGMP-dependent relaxant responses of rabbit corporal smooth muscle. Male New Zealand white rabbits were divided into young (4 months), intermediate (8 months), and old (24 months) groups. Electrical stimulation-, carbachol-, sodium nitroprusside-, and papaverine-induced relaxant response in isolated corporal smooth muscle strips were determined using in vitro muscle technique. Although there was no significant difference in the relaxant response of corporal strips to papaverine among the groups, relaxant responses to carbachol and sodium nitroprusside were significantly lower in corporal strips of old group than both young and intermediate groups. However, in the old and intermediate groups, electrical field stimulation-induced neurogenic relaxation was significantly reduced compared with the young group. KCl-induced (124 mM) contractile responses were the same in all groups. Our data indicate that the presence of age-dependent differences in the NO/cGMP-mediated relaxant responses of corporal tissue in the male rabbits. This may contribute to the development of impotence.

Role of adenosine and P2 receptors in the penile tumescence in anesthetized dogs

We studied the role of adenosine and P2 receptors in the pelvic nerve stimulation-induced penile tumescence in anesthetized dogs. A local intracavernous injection of adenosine induced the tumescence, which was abolished by intracavernous 8-(p-sulfophenyl)theophylline (8-SPT), an unspecific adenosine receptor antagonist, and by 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-yl amino]ethyl)phenol (ZM241385), an adenosine A(2A) receptor antagonist. ATP also induced the tumescence, which was diminished by 8-SPT, but not by reactive blue-2, a P2 receptor antagonist. Neither intracavernous beta, gamma-meATP nor ADP(beta)S, P2X and P2Y receptor agonists, induced tumescence. N(G)-nitro-L-arginine (L-NAME), a nitric oxide synthase inhibitor, and T-1032, a phosphodiesterase type V inhibitor, had no effects on the tumescence induced by adenosine. 8-SPT and reactive blue-2 had no effects on the tumescence induced by pelvic nerve stimulation. These results show that although exogenous adenosine and ATP induce tumescence, neither the adenosine nor the P2 receptor is involved in the tumescence induced by pelvic nerve stimulation in anesthetized dogs.

Erectile dysfunction in the ageing man

Most studies have shown an increase in the prevalence of erectile dysfunction with ageing. Penile erection is a vascular phenomenon resulting from smooth muscle relaxation, arterial dilatation and venous restriction. The atherosclerosis of the penis that occurs with ageing causes a decrease in penile oxygen tension. This change in oxygen tension impacts directly upon both the physiologic function and the trabecular structure of the corpora cavernosa. Chronic ischaemia of the penis is associated with fibrosis of smooth muscle fibres and with endothelial and neuronal NO/cGMP pathways. The effects of androgens on libido and sexual behaviour are well established but their role in the erectile mechanism remains unclear. The histologic and haemodynamic causes responsible for the erectile decline in the ageing man are reviewed.