STUDIES ON THE MECHANISMS INVOLVED IN THE ATP-INDUCED RELAXATION IN HUMAN AND RABBIT CORPUS CAVERNOSUM

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.

The inflammasome NLRP3 plays a dual role on mouse corpora cavernosa relaxation

NLRP3 plays a role in vascular diseases. Corpora cavernosa (CC) is an extension of the vasculature. We hypothesize that NLRP3 plays a deleterious role in CC relaxation. Male C57BL/6 (WT) and NLRP3 deficient (NLRP3^−/−) mice were used. Intracavernosal pressure (ICP/MAP) measurement was performed. Functional responses were obtained from CC strips of WT and NLRP3^−/− mice before and after MCC950 (NLRP3 inhibitor) or LPS + ATP (NLRP3 stimulation). NLRP3, caspase-1, IL-1β, eNOS, nNOS, guanylyl cyclase-β1 (GCβ1) and PKG1 protein expressions were determined. ICP/MAP and sodium nitroprusside (SNP)-induced relaxation in CC were decreased in NLRP3^−/− mice. Caspase-1, IL-1β and eNOS activity were increased, but PKG1 was reduced in CC of NLRP3^−/−. MCC950 decreased non-adrenergic non-cholinergic (NANC), acetylcholine (ACh), and SNP-induced relaxation in WT mice. MCC950 did not alter NLRP3, caspase-1 and IL-1β, but reduced GCβ1 expression. Although LPS + ATP decreased ACh- and SNP-, it increased NANC-induced relaxation in CC from WT, but not from NLRP3^−/− mice. LPS + ATP increased NLRP3, caspase-1 and interleukin-1β (IL-1β). Conversely, it reduced eNOS activity and GCβ1 expression. NLRP3 plays a dual role in CC relaxation, with its inhibition leading to impairment of nitric oxide-mediated relaxation, while its activation by LPS + ATP causes decreased CC sensitivity to NO and endothelium-dependent relaxation.

Tetracarpidium conophorum Müll. Arg modulates sexual behaviour and biochemical parameters relevant to sexual function in male Wistar rats

Walnut (Tetracarpidium conophorum Müll. Arg) has been reported to be an essential ingredient in folklore medicine for sexual enhancement with little scientific validation. Hence, this study investigated the effects of walnut supplemented diet on sexual behaviour and biochemical parameters relevant to erection in male Wistar rats. Forty animals used in this study were divided into five groups (n = 8); Group 1 - normal control rats fed with basal diet, Group II - rats fed diet supplemented with 10% processed walnut, Group III - rats fed diet supplemented with 10% raw walnut, Group IV - rats fed diet supplemented with 20% processed walnut and Group V - rats fed diet supplemented with 20% raw walnut. Behavioural studies (copulation tendency and anxiety) associated with sexual function, measurement of nitric oxide (NO) levels, adenosine deaminase (ADA), arginase and acetylcholinesterase (AChE) activities in the Corpus cavernosum as well as characterization of bioactive components of the nut were evaluated. Marked reductions in ADA and arginase activities and a concomitant increase (% inclusion dependent) in the level of NO as well as enhanced sexual behaviours were observed in rat fed supplemented walnut when compared to the control. Furthermore, analysis of the walnut using high performance liquid chromatography indicated the presence of some polyphenols. From our findings, it showed that walnut improves sexual behaviour and modulates activities of key enzymes relevant to erection in male rats which may justify its used in traditional medicine.

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.

ATP evokes inward currents in corpus cavernosum myocytes

INTRODUCTION

Although adenosine triphosphate (ATP) has often been reported to relax the corpus cavernosum, this may be mediated by indirect effects, such as release of nitric oxide from the endothelium. Recent data suggest that P2X(1) receptors may be up-regulated in diabetes, and these exert an anti-erectile effect by causing the corpus cavernosum smooth muscle cells (CCSMCs) to contract. However, to date, there is no functional evidence that ATP can directly stimulate CCSMC.

AIMS

This study aims to (i) to directly examine the effect of ATP on membrane currents in freshly isolated CCSMC, where influences of endothelium and other cells are absent; and (ii) to determine the receptor subtypes, ionic currents, and Ca(2+) signals stimulated by ATP.

METHODS

CCSMCs were enzymatically dispersed from male New Zealand White rabbits for patch clamp recording and measurement of intracellular Ca(2+) in fluo-4-loaded cells using spinning disk confocal microscopy.

MAIN OUTCOME MEASURES

Patch clamp recordings were made of ATP-evoked membrane currents and spontaneous membrane currents. Spinning disk confocal imaging of intracellular Ca(2+) was performed, and the response to ATP was recorded.

RESULTS

ATP evoked repeatable inward currents in CCSMC (1st application: -675 ± 101 pA; 2nd application: -694 ± 120 pA, N = 9, P = 0.77). ATP-induced currents were reduced by suramin from -380 ± 121 to -124 ± 37 pA (N = 8, P < 0.05), by α,β-methylene ATP from -755 ± 235 to 139 ± 49 pA (N = 5, P < 0.05), and by NF449 from -419 ± to -51 ± 13 pA (N = 6, P < 0.05). In contrast, MRS2500, a P2Y1(1,12,13) antagonist, had no effect on ATP responses (control: -838 ± 139 pA; in MRS2500: -822 ± 184 pA, N = 13, P = 0.84) but blocked inward currents evoked by 2-MeSATP, a P2Y1,12,13 agonist (control: -623 ± 166 pA; in MRS2500: -56 ± 25 pA, N = 6, P < 0.05). The ATP-evoked inward current was unaffected by changing the transmembrane Cl(-) gradient but reversed in direction when extracellular Na(+) was reduced, indicating that it was a cation current.

CONCLUSIONS

ATP directly stimulates CCSMC by evoking a P2X-mediated cation current.

Adenosine signaling: good or bad in erectile function?

The erectile status of penile tissue is governed largely by the tone of cavernosal smooth muscle cells, which is determined by the balance of vascular relaxants and constrictors. Vascular relaxants play a key role in regulating the tone of cavernosal smooth muscle and thus the initiation and maintenance of penile erection. Early studies drew attention to the potential role of adenosine signaling in this process. However, the serendipitous discovery of the effect of sildenafil on erectile physiology drew more attention toward nitric oxide (NO) as a vasodilator in the process of penile erection, and a recently discovered, unexpected erectile phenotype of adenosine deaminase-deficient mice reemphasizes the importance of adenosine as a key regulatory of erectile status. Adenosine, like NO, is a potent and short-lived vasorelaxant that functions via cyclic nucleotide second messenger signaling to promote smooth muscle relaxation. Recent studies reviewed here show that adenosine functions to relax the corpus cavernosum and promote penile erection. Excess adenosine in penile tissue contributes to the disorder called priapism, and impaired adenosine signaling is associated with erectile dysfunction. More recent research summarized in this review reveals that adenosine functions as a key endogenous vasodilator in the initiation and maintenance of normal penile erection. This new insight highlights adenosine signaling pathways operating in penile tissue as significant therapeutic targets for the treatment of erectile disorders.

Animal models of erectile dysfunction (ED): potential utility of non-human primates as a model of atherosclerosis-induced vascular ED

Erectile dysfunction (ED) is a prevalent medical condition affecting 18 million men and their sexual partners in the United States alone. In the majority of patients, ED is related to alterations in the flow of blood to or from the penis. Undeniably, significant progress has been made in understanding the multifactorial mechanisms that modulate erectile capacity and predispose one to ED, and this, in turn, has led to the availability of more effective treatment options. Nonetheless, all current therapies have untoward side effects, and moreover, there are still no satisfactory treatments for many patients with ED. Further enhancements in the treatment of ED would logically result from both early intervention and more detailed mechanistic insight into the characteristics of the disease process per se. This fact underscores the importance of improved understanding of the initiation, development and progression of ED. However, to do so requires longitudinal studies on animal models that more closely approximate the corresponding clinical features and time course of human disease. The goal of this report is twofold. First, to provide a brief general overview of the applicability of commonly used animal models for the study of ED. The second and primary goal is to highlight the scientific rationale for using non-human primates to evaluate the impact of atherosclerosis-induced vascular disease on the penile and systemic circulatory systems. This latter goal seems especially relevant in light of the recent literature documenting a link between ED and systemic vascular disease, a finding that has major implications in an aging US male population consuming a high fat diet.

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α₁-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E₁. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.

Adenosine deaminase enzyme therapy prevents and reverses the heightened cavernosal relaxation in priapism

INTRODUCTION

Priapism featured with painful prolonged penile erection is dangerous and commonly seen in sickle cell disease (SCD). The preventive approaches or effective treatment options for the disorder are limited because of poor understanding of its pathogenesis. Recent studies have revealed a novel role of excess adenosine in priapism caused by heightened cavernosal relaxation, and therefore present an intriguing mechanism-based therapeutic possibility.

AIM

The aim of this study was to determine the therapeutic effects of adenosine deaminase (ADA) enzyme therapy to lower adenosine in priapism.

METHODS

Both ADA-deficient mice and SCD transgenic (Tg) mice display priapism caused by excessive adenosine. Thus, we used these two distinct lines of mouse models of priapism as our investigative tools. Specifically, we treated both of these mice with different dosages of polyethylene glycol-modified ADA (PEG-ADA) to reduce adenosine levels in vivo. At the end points of the experiments, we evaluated the therapeutic effects of PEG-ADA treatment by measuring adenosine levels and monitoring the cavernosal relaxation.

MAIN OUTCOME MEASURES

Adenosine levels in penile tissues were measured by high-performance liquid chromatography, and cavernosal relaxation was quantified by electrical field stimulation (EFS)-induced corporal cavernosal strip (CCS) assays.

RESULTS

We found that lowering adenosine levels in penile tissues by PEG-ADA treatment from birth in ADA-deficient mice prevented the increased EFS-induced CCS relaxation associated with priapism. Intriguingly, in both ADA-deficient mice and SCD Tg mice with established priapism, we found that normalization of adenosine levels in penile tissues by PEG-ADA treatment relieved the heightened EFS-induced cavernosal relaxation in priapism.

CONCLUSIONS

Our studies have identified that PEG-ADA is a novel, safe, and mechanism-based drug to prevent and correct excess adenosine-mediated increased cavernosal relaxation seen in two independent priapic animal models, and suggested its therapeutic possibility in men suffering from priapism.

Future sexual medicine physiological treatment targets

INTRODUCTION

Sexual function in men and women incorporates physiologic processes and regulation of the central and peripheral nervous systems, the vascular system, and the endocrine system. There is need for state-of-the-art information as there is an evolving research understanding of the underlying molecular biological factors and mechanisms governing sexual physiologic functions.

AIM

To develop an evidence-based, state-of-the-art consensus report on the current knowledge of the major cellular and molecular targets of biologic systems responsible for sexual physiologic function.

METHODS

State-of-the-art knowledge representing the opinions of seven experts from four countries was developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURES

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Scientific investigation in this field is needed to increase knowledge and foster development of the future line of treatments for all forms of biological-based sexual dysfunction. This article addresses the current knowledge of the major cellular and molecular targets of biological systems responsible for sexual physiologic function. Future treatment targets include growth factor therapy, gene therapy, stem and cell-based therapies, and regenerative medicine.

CONCLUSIONS

Scientific discovery is critically important for developing new and increasingly effective treatments in sexual medicine. Broad physiologic directions should be vigorously explored and considered for future management of sexual disorders.

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.

Characterization of the effects of various drugs likely to affect smooth muscle tension on isolated human seminal vesicle tissue

OBJECTIVES

To investigate the effects of different classes of drugs on the isometric tension of isolated human seminal vesicle (SV) tissue. The contractility of human SV contributes to the process of seminal emission during ejaculation. Different endogenous compounds, such as serotonin (5-HT), adenosine triphosphate (ATP), and nitric oxide, have been suggested to be involved in the control of contraction and relaxation of human SV smooth muscle. However, only limited data are available regarding the effects of compounds known to affect smooth musculature on SV contractile activity.

METHODS

Using the organ bath technique, the effects of increasing concentrations (10 nm-1 microm/10 microm) of norepinephrine (NE), phenylephrine, endothelin 1, ATP, and 5-HT on human SV tissue at basal tension were studied. In another set-up, SV strip preparations were preincubated with prazosin (alpha-adrenergic blocker), nifedipine and verapamil (Ca(2+)-channel blockers), 2-aminoethoxydiphenyl borate [inositol 1,4,5-trisphosphate (IP(3)) antagonist], cromakalim (K(+)-channel opener), or Y-27632 (ROK inhibitor) (1 microm each, for 10 minutes), followed by the application of NE (0.1 microM, 1 microM, and 10 microm).

RESULTS

SV smooth muscle was most effectively contracted by NE (mean = 75% of calibrated scale), phenylephrine (mean = 82% of calibrated scale), and endothelin 1 (mean = 70% calibrated scale), whereas only minor responses to ATP (mean = 10.65% calibrated scale) and 5-HT (mean = 6.3% calibrated scale) were observed. The contraction induced by NE was significantly inhibited after pre-exposure of the tissue to prazosin (-92.4%), cromakalim (-83.7%), 2-aminoethoxydiphenyl borate (-43.1%), Y-27632 (-42.8%), and nifedipine (-32.7%).

CONCLUSIONS

alpha-adrenoceptor antagonism, activation of potassium channels, and inhibition of Rho-kinase decrease the sympathetic contraction of SV smooth muscle. This might be of significance with regard to the identification of new pharmacologic avenues to affect the male ejaculatory system.

Effects of ageing and streptozotocin-induced diabetes on connexin43 and P2 purinoceptor expression in the rat corpora cavernosa and urinary bladder

OBJECTIVE

To investigate whether ageing and diabetes alter the expression of the gap junction protein connexin43 (Cx43) and of particular purinoceptor (P2R) subtypes in the corpus cavernosum and urinary bladder, and determine whether changes in expression of these proteins correlate with development of erectile and bladder dysfunction in diabetic and ageing rats.

MATERIALS AND METHODS

Erectile and bladder function of streptozotocin (STZ)-induced diabetic, insulin-treated and age-matched control Fischer-344 rats were evaluated 2, 4 and 8 months after diabetes induction by in vivo cystometry and cavernosometry. Corporal and bladder tissue were then isolated at each of these sample times and protein expression levels of Cx43 and of various P2R subtypes were determined by Western blotting.

RESULTS

In the corpora of control rats ageing was accompanied by a significant decrease in Cx43 and P2X(1)R, and increase in P2X(7)R expression. There was decreased Cx43 and increased P2Y(4)R expression in the ageing control rat bladder. There was a significant negative correlation between erectile capacity and P2X(1)R expression levels, and a positive correlation between bladder spontaneous activity and P2Y(4)R expression levels. There was already development of erectile dysfunction and bladder overactivity at 2 months after inducing diabetes, the earliest sample measured in the study. The development of these urogenital complications was accompanied by significant decreases in Cx43, P2Y(2)R, P2X(4)R and increase in P2X(1)R expression in the corpora, and by a doubling in Cx43 and P2Y(2)R, and significant increase in P2Y(4)R expression in the bladder. Changes in Cx43 and P2R expression were largely prevented by insulin therapy.

CONCLUSION

Ageing and diabetes mellitus markedly altered the expression of the gap junction protein Cx43 and of particular P2R subtypes in the rat penile corpora and urinary bladder. These changes in Cx43 and P2R expression provide the molecular substrate for altered gap junction and purinergic signalling in these tissues, and thus probably contribute to the early development of erectile dysfunction and higher detrusor activity in ageing and in diabetic rats.

Penile doppler ultrasound in patients with erectile dysfunction (ED): role of peak systolic velocity measured in the flaccid state in predicting arteriogenic ED and silent coronary artery disease

INTRODUCTION

The use of the penile peak systolic velocity (PSV) measured in the flaccid state during penile color Doppler ultrasound (PCDU) examination has been questioned without substantial evidence.

AIM

To assess the validity of PSV measured in the flaccid state during PCDU, in patients consulting for erectile dysfunction (ED).

METHODS

A consecutive series of 1,346 (mean age 55.0 +/- 12.0 years) male patients was studied.

MAIN OUTCOMES MEASURES

All patients underwent PCDU performed both in the flaccid state and dynamic (after prostaglandin E1 stimulation) conditions. A subset of 20 subjects with uncomplicated type 2 diabetes underwent diagnostic testing for silent coronary heart disease by means of adenosine stress myocardial perfusion scintigraphy (SPECT). In these subjects penile arterial flow was simultaneously assessed by PCDU before and after systemic adenosine administration.

RESULTS

Flaccid PSV showed a significant (r = 0.513, P < 0.0001) correlation with dynamic PSV. Receiver operating characteristic (ROC) curve analysis demonstrated that when a threshold of 13 cm/seconds was chosen, flaccid PSV was predictive for dynamic PSV < 25 and <35 cm/seconds with an accuracy of 89% and 82%, respectively. Among the subset of patients who underwent SPECT, an impaired coronary flow reserve (ICFR) occurred in nine cases (45%). When the same threshold of <13 cm/seconds was chosen, PSV before SPECT was predictive of ICFR with an accuracy of 80% (area under the ROC curve = 0.798 +/- 0.10; P < 0.05). After adjustment for confounders, anxiety symptoms were related to dynamic PSV (Adj. r = -0.154, P < 0.05) but not to flaccid PSV.

CONCLUSIONS

Our results show that flow in the cavernosal arteries can be routinely evaluated by PCDU in the flaccid state. Performing PCDU only in the flaccid state allows identifying subjects with pathological dynamic PSV with accuracy higher than 80%. Furthermore, our preliminary data suggest that the same examination could identify diabetic subjects with ICFR with an accuracy of 80%.

Excess adenosine in murine penile erectile tissues contributes to priapism via A2B adenosine receptor signaling

Priapism, abnormally prolonged penile erection in the absence of sexual excitation, is associated with ischemia-mediated erectile tissue damage and subsequent erectile dysfunction. It is common among males with sickle cell disease (SCD), and SCD transgenic mice are an accepted model of the disorder. Current strategies to manage priapism suffer from a poor fundamental understanding of the molecular mechanisms underlying the disorder. Here we report that mice lacking adenosine deaminase (ADA), an enzyme necessary for the breakdown of adenosine, displayed unexpected priapic activity. ADA enzyme therapy successfully corrected the priapic activity both in vivo and in vitro, suggesting that it was dependent on elevated adenosine levels. Further genetic and pharmacologic evidence demonstrated that A2B adenosine receptor-mediated (A2BR-mediated) cAMP and cGMP induction was required for elevated adenosine-induced prolonged penile erection. Finally, priapic activity in SCD transgenic mice was also caused by elevated adenosine levels and A2BR activation. Thus, we have shown that excessive adenosine accumulation in the penis contributes to priapism through increased A2BR signaling in both Ada -/- and SCD transgenic mice. These findings provide insight regarding the molecular basis of priapism and suggest that strategies to either reduce adenosine or block A2BR activation may prove beneficial in the treatment of this disorder.

Effect of hypothyroidism on the purinergic responses of corpus cavernosal smooth muscle in rabbits

AIMS

Several studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. In the present study, we examined purinergic relaxation responses in hypothyroidism in an experimental rabbit model and compared them with controls to evaluate the possible involvement of the purinergic pathway.

MATERIALS AND METHODS

The study comprised 20 male New Zealand white rabbits. The rabbits were divided into two equal groups. We tested the effects of ATP, alpha beta ATP, and adenosine precontracted with phenylephrine on the isolated corpus cavernosum preparations from control and hypothyroid rabbits. We also evaluated the effects of ATP, alpha beta ATP, and adenosine on the cGMP levels in the isolated corpus cavernosum preparations from control and hypothyroid rabbits.

RESULTS

T3, T4, and testosterone levels were significantly lower in hypothyroid rabbits. ATP, alpha beta ATP, carbachol, and electrical field stimulation (EFS)-induced frequency-dependent relaxation responses in the isolated rabbit corpus cavernosum strips precontracted with phenylephrine reduced significantly (P<0.05). Adenosine-induced relaxation responses did not change significantly in hypothyroid rabbits.

CONCLUSION

Reduction of relaxation response in hypothyroid rabbits corpus cavernosum can depend on a decreased release of nitric oxide (NO) from nitrergic nerves and endothelium.

The participation of adenosine receptors in the adenosine 5'-triphosphate-induced relaxation in the isolated rabbit corpus cavernosum penis

AIM

To investigate the participation of adenosine receptors in the adenosine 5'-triphosphate (ATP)-induced relaxation in the corpus cavernosum penis (CCP) of rabbits.

METHODS

The ATP-induced relaxation was assessed on the noradrenaline precontracted CCP of rabbits in the presence and absence of 8-(3-chlorostyryl)caffeine (CSC); an adenosine A(2A) receptor antagonist; alloxazine and MRS1754; adenosine A(2B) receptor antagonists; and ARL67156, an inhibitor of ecto-nucleoside triphosphate diphosphohydrolases.

RESULTS

Adenosine and ATP relaxed the noradrenaline precontracted CCP of rabbits in a concentration-dependent manner. The adenosine- and ATP-induced relaxations were suppressed by alloxazine and MRS1754, but not by 8-(3-chlorostyryl)caffeine. ARL67156 potentiated the ATP-induced relaxation but not the adenosine-induced one. MRS1754 suppressed the ATP-induced relaxation potentiated by ARL67156.

CONCLUSIONS

The above results suggest that, in the CCP of rabbits, the adenosine receptor mediating adenosine-induced relaxation is of the A(2B) receptor and the ATP directly causes relaxation through the A(2B) receptor on the CCP.

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.

Determination of adenosine effects and adenosine receptors in murine corpus cavernosum

This study tested the hypothesis that adenosine, in murine corpora cavernosa, produces direct relaxation of smooth muscle cells and inhibition of contractile responses mediated by sympathetic nerve stimulation. Penes were excised from anesthetized male C57BL/6 mice, dissected, and cavernosal strips were mounted to record isometric force. Adenosine, 2-chloroadenosine (stable analog of adenosine), and 2-phenylaminoadenosine (CV1808) (A2(A)/A2(B) agonist) produced concentration-dependent relaxations of phenylephrine-contracted tissues. Relaxation to 2-chloroadenosine was inhibited, in a concentration-dependent manner, by 2-(2-furanyl)-7-(2-phenylethyl)-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5-amine (SCH58261; A2(A) antagonist; 10(-9)-10(-6) M) and N-(4-acetylphenyl)-2-[4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)phenoxy]acetamida (MRS1706; A2(B) antagonist; 10(-8)-10(-6) M). The combination of both antagonists abrogated 2-chloroadenosine-induced relaxation. Electrical field stimulation (EFS; 1-32 Hz) of adrenergic nerves produced frequency-dependent contractions that were inhibited by compounds that increase adenosine levels, such as 5'-iodotubercidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)adenine (adenosine deaminase inhibitor), and dipyridamole (inhibitor of adenosine transport). The adenosine A1 receptor agonist N(6)-cyclopentyladenosine (C8031) right-shifted contractile responses to EFS, with a significant inhibitory effect at 10(-6) M. Blockade of adenosine A1 receptors with 8-cyclopentyl-1,3-dipropylxanthine (C101) (10(-7) M) enhanced contractile responses to EFS and eliminated the inhibitory effects of 5'-iodotubercidin. Dipyridamole and 5'-iodotubercidin had no effect on adenosine-mediated relaxation. In summary, adenosine directly relaxes cavernosal smooth muscle cells, by the activation of A2(A)/A2(B) receptor subtypes. In addition, adenosine negatively modulates sympathetic neurotransmission, by A1 receptor subtype activation, in murine corpora cavernosa. Adenosine may subserve dual roles in modulating the physiological mechanisms of erection in mice.

Testosterone Restores Diabetes‐Induced Erectile Dysfunction and Sildenafil Responsiveness in Two Distinct Animal Models of Chemical Diabetes

INTRODUCTION

Hypogonadism is often associated with diabetes and both conditions represent major risk factors for erectile dysfunction (ED).

AIM

To investigate the role of hypogonadism on phosphodiesterase type 5 (PDE5) expression and sildenafil responsiveness in diabetes.

METHODS

Two different models of experimental diabetes were used: (i) alloxan-induced diabetic rabbit; and (ii) streptozotocin (STZ)-induced diabetic rat. In both experimental models, animals were separated into three groups: control, diabetic, diabetic supplemented with testosterone (T) enanthate. Rabbits were used for "in vitro" experiments. Conversely, each rats group was further subdivided: no further treatment or acute sildenafil dosing (25 mg/kg, 1 hour before "in vivo" electrical stimulation [ES]).

MAIN OUTCOME MEASURE

Erectile capacity was evaluated either by "in vitro" contractility study (alloxan-induced diabetic rabbit) and "in vivo" evaluation of erectile response elicited by ES of cavernous nerve (STZ-induced diabetic rats). Also endothelial nitric oxide synthase, neural nitric oxide synthase (nNOS), and PDE5 protein (Western blot) and mRNA (quantitative real-time reverse transcriptase polymerase chain reaction [RT-PCR]) expression were measured in rat penile samples of each group.

RESULTS

In both models, hypogonadism was observed, characterized by reduced T and atrophy of androgen-dependent accessory glands. T substitution completely reverted hypogonadism and diabetes-induced penile hyposensitivity to "in vitro" (acetylcholine, rabbit) or "in vivo" (ES, rat) relaxant stimuli, along with nNOS expression, which was reduced (P < 0.05) in STZ rats. In diabetic animals, T substitution reinstated sildenafil-induced enhancement of both "in vitro" nitric oxide donor (NCX 4040) relaxant effect (rabbit) and "in vivo" ES-induced erection (rat). PDE5 was reduced in diabetic STZ rats (P < 0.05) and normalized by T. In STZ rats, sodium nitroprusside (SNP) intracavernous injection induced a more sustained erection than in control rats, which was no further enhanced by sildenafil. T substitution normalized both hyper-responsiveness to SNP and sildenafil efficacy.

CONCLUSION

In two models of diabetes T deficiency underlies biochemical alterations leading to ED. Normalizing T in diabetes restores nNOS and PDE5, and reinstates sensitivity to relaxant stimuli and responsiveness to sildenafil.

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.

Suramin inhibits the in vitro expression of encephalitis B virus proteins NS3 and E

In this study, the mechanism by which Suramin inhibits the replication of epidemic encephalitis B virus was explored to provide a theoretical basis for its further application in clinical practice. After viral infection of HepG2 and IMR-32 cells, different concentrations of Suramin were added to the culture media, and then the cultural supernatants and infected cells were collected 48 h later. For the evaluation of the curative effect, cytopathic effect (CPE), virus titers, the expression of viral protein and viral RNA were determined by Western blot, RT-PCR and in vitro RNA synthesis, respectively. At the concentration of 50 microg/ml of Suramin, HepG2 and IMR-32 infected with epidemic encephalitis B virus decreased by 51.8% and 0.03% respectively, as compared with controls. It was suggested that expression of encephalitis B virus proteins NS3 and E was notably reduced by Suramin. This is especially true of E protein. At RNA level, however, no difference in RNA virus was found between Suramin-treated virus and non-treated cells. Our results suggest that Suramin can inhibit viral replication by blocking the production of viral proteins.

Development of novel EDG3 antagonists using a 3D database search and their structure-activity relationships

Sphingosine-1-phosphate (S1P) is an intracellular second messenger and an extracellular mediator through endothelial differentiation gene (EDG) receptors, which are a novel class of G-protein-coupled receptors. Although EDG has attracted much attention because of its various roles, no selective agonists or antagonists have yet been developed. This could account for the delay in clarifying the physiological roles of members of the EDG family. Because precise structural information on EDG receptors is not yet available, pharmacophore models were generated based on structural information for S1P using the rational drug design software Catalyst. Novel antagonists, 2-alkylthiazolidine-4-carboxylic acids, were retrieved from a three-dimensional database search using the pharmacophore models, and these showed activity for EDG3. On the basis of their nonphosphoric acid structure, more potent antagonists, 2-(m- or p-heptylphenyl)thiazolidine-4-carboxylic acid, were developed.

Effect of chronic renal failure on the purinergic responses of corpus cavernosal smooth muscle in rabbits

OBJECTIVE

To examine purinergic relaxation responses in chronic renal failure (CRF) in an experimental rabbit model, and thus evaluate the possible involvement of the purinergic system in erectile dysfunction with CRF.

MATERIALS AND METHODS

The relaxant effects of ATP were measured in strips of corpus cavernosum smooth muscle taken from control and CRF rabbits. CRF was induced in New Zealand white rabbits as previously described. Penises were excised from CRF rabbits 4 weeks after inducing uraemia. In an organ bath the strips from controls and CRF rabbit corpus cavernosum were pre-contracted with phenylephrine and increasing doses of adenosine and ATP added.

RESULTS

In the pre-contracted rabbit cavernosal tissue the relaxations induced by adenosine and ATP were unchanged in CRF.

CONCLUSION

The lack of any relaxant effect of adenosine or ATP on the relaxation of cavernosal smooth muscle in rabbits with CRF might be because the relaxant effects of these agents are endothelium-independent and the endothelial purinergic receptor density was unchanged in CRF.

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.

The molecular basis of penile erection

Over the past two decades our understanding of the physiology and the various mediators involved in the pathway of penile erection has greatly increased. This has enabled us to develop effective pharmacological treatments for ED.