Evidence for the involvement of endothelial nitric oxide synthase from smooth muscle cells in the erectile function of the human corpus cavernosum

An Advanced Method for the Immunohistochemical Detection of Nitric Oxide Synthase (NOS) in the Female Genital Tract

The expression of nitric oxide synthase (NOS) in male and female urogenital tissues has been investigated by using conventional light microscopical immunoperoxidase staining. We present an improved immunohistochemical method for the specific and simultaneous detection of endothelial and neuronal NOS (eNOS/nNOS) in vaginal tissue. Specific antibodies have been used in combination with the tyramide signal amplification method. We found a subepithelial meshwork of varicose nerve fibers. A subpopulation of fibers presented immunoreactivity specific for nNOS. Epithelial cells also showed cytoplasmatic labeling for nNOS. Arteries presenting signals for eNOS in their endothelial layer were found in close proximity to nNOS-positive nerve fibers.

Pharmacology and perspectives in erectile dysfunction in man

Penile erection is a perfect example of microcirculation modulated by psychological factors and hormonal status. It is the result of a complex neurovascular process that involves the integrative synchronized action of vascular endothelium; smooth muscle; and psychological, neuronal, and hormonal systems. Therefore, the fine coordination of these events is essential to maintain penile flaccidity or allow erection; an alteration of these events leads to erectile dysfunction (ED). ED is defined as the consistent or recurrent inability of a man to attain and/or maintain a penile erection sufficient for sexual activity. A great boost to this research field was given by commercialization of phosphodiesterase-5 (PDE5) inhibitors. Indeed, following the discovery of sildenafil, research on the mechanisms underlying penile erection has had an enormous boost, and many preclinical and clinical papers have been published in the last 10 years. This review is structured to provide an overview of the mediators and peripheral mechanism(s) involved in penile function in men, the drugs used in therapy, and the future prospective in the management of ED. Indeed, 30% of patients affected by ED are classified as "nonresponders," and there is still an unmet need for therapeutic alternatives. A flowchart suggesting the guidelines for ED evaluation and the ED pharmacological treatment is also provided.

Glu298Asp Endothelial Nitric Oxide Synthase Polymorphism Is a Risk Factor for Erectile Dysfunction in the Mexican Mestizo Population

Penile erection depends on the balanced action between antagonist vasoactive molecules such as nitric oxide (NO) and angiotensin. Endothelial nitric oxide synthase (eNOS) and angiotensin-converting enzyme (ACE) polymorphisms have been associated with endothelial dysfunction, which is described as a cause of erectile dysfunction (ED). Endothelial NOS and ACE are both regulators of vascular and corporal smooth muscle tone, which are connected by interaction between the NO-cyclic guanosine monophosphate pathway and the renin-angiotensin system. We analyzed the frequencies of 894 G/T (Glu298Asp) eNOS and ACE I/D polymorphisms in Mexican patients with ED (n=53) and in an age-matched control group (n=62). The populations analyzed were in Hardy Weinberg equilibrium. We found significant differences in allelic (chi2=4.42; P=.03) and genotypic frequencies (chi2=3.96; P=.04) between patients and controls for the 894 G/T eNOS polymorphism. Presence of the 894T allele in carriers increased the risk of ED (odds ratio [TT + GT versus GG] = 2.37; 95% confidence interval, 1.08 to 5.21; P=.02). Multiple logistic regression analysis showed that the Glu298Asp polymorphism was an independent factor for ED, as was diabetes mellitus, hypertension, cardiac disease, and cigarette smoking. No association was found between ACE I/D polymorphism and ED in the population studied. Therefore, our results suggest that Glu298Asp eNOS polymorphism plays a role as a genetic susceptibility factor for ED.

Sexual satisfaction among men living with HIV in Europe

This study determined risk factors for decreased sexual satisfaction among men living with HIV (MLHIV). Self-administered questionnaires were distributed consecutively to all MLHIV attending 17 European HIV treatment centres. The sample included 1,017 MLHIV, among whom 79.2% self-identified as homosexual or bisexual. Sexual satisfaction was measured for five domains of sexual functioning and 33.2% reported low satisfaction in at least one domain. Decreased sexual satisfaction was associated with psychosocial factors, i.e. depression (OR 2.77, P < 0.001), anxiety (OR 1.77, P < 0.001), stress (OR 2.27, P < 0.001) and social factors, such as low partner support (OR 2.28, P < 0.001) and experiences of HIV related discrimination (OR 1.69, P < 0.001). Discussing satisfaction with sexuality should be integrated in regular HIV care, considering patients' personal and relationship-related resources next to medical treatment if indicated.

Male sexual dysfunction: diagnosis and treatment from a sexological and interdisciplinary perspective

BACKGROUND

Among all types of sexual disturbance in men, disturbances of sexual function are the most important in clinical practice. These are classified by the segment of the sexual reaction cycle in which they arise (appetence, arousal, orgasm, and resolution). Partial functional impairment must be distinguished from dysfunction causing significant suffering and requiring treatment.

METHODS

The authors' clinical experience is supplemented with a selective review of the literature on sexual dysfunction, its association with underlying diseases, and its impact on sexual and relational satisfaction.

RESULTS

The sexual history (including the partner's sexual history, as far as this can be obtained) is of prime importance in the diagnostic evaluation of sexual disturbances. This evaluation must take the multidimensionality and multiple functions of human sexuality into account. Chronic frustration of the fundamental psychosocial needs for acceptance, closeness, and security is a very important factor that has been neglected until now by the prevailing conceptions of the etiology and pathogenesis of sexual disturbances. Their treatment involves a combination of elements from sexual medicine and psychotherapy, along with somatic medical and pharmacotherapeutic intervention, if needed. The goal of syndyastic sex therapy, a further development of the previous therapies, is to fulfill these fundamental needs and thereby to improve the patient's sexual function and deepen his satisfaction with the relationship in its entirety.

CONCLUSIONS

It is essential to understand the different types of sexual disturbance in their biopsychosocial context as well as the significance of sexuality for the individual, and for the couple, with respect to reproduction, sexual pleasure, and bonding. Sexual disturbances are common, and patients therefore expect their physicians to be proficient in sexual medicine. The coverage of this subject in both undergraduate and postgraduate medical education in Germany needs to be improved.

Prostanoids and phosphodiesterase inhibitors in experimental pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease with a poor prognosis, characterized by intimal lesions, medial hypertrophy, and adventitial thickening of precapillary pulmonary arteries. Several approved therapies are currently available for the treatment of PAH, of which intravenous epoprostenol is the best explored over the past decade. Newly available oral endothelin receptor antagonists, although clinically efficacious, bear the risk of liver toxicity in a significant portion of patients. Substances that stimulate the formation of the second messengers cyclic adenosine monophosphate (cAMP) or guanosine monophosphate (cGMP) have proved useful in the treatment of various forms of pre-capillary pulmonary hypertension. These second messengers of the endogenous vasodilator mediators that include prostacyclin and nitric oxide (NO) are hydrolyzed by cyclic nucleotide phosphodiesterases (PDEs), a class of enzymes from which 11 isoforms have been characterized. This chapter highlights developments in the treatment of experimental pulmonary hypertension with special attention to prostanoids and PDE inhibitors. We summarize findings for the acute vasodilatory as well as chronic effects of prostanoids, PDE inhibitors, or combinations of both, in animal models of pulmonary hypertension.

Nitric oxide synthesis leads to vascular endothelial growth factor synthesis via the NO/cyclic guanosine 3',5'-monophosphate (cGMP) pathway in human corpus cavernosal smooth muscle cells

INTRODUCTION

Vascular smooth muscle cells express endothelial nitric oxide synthase (eNOS) and produce nitric oxide (NO). Recently, increased NO production has been reported to induce the synthesis and secretion of vascular endothelial growth factor (VEGF) via the NO/cyclic guanosine 3',5'-monophosphate (cGMP) pathway. L-arginine (L-arg), the precursor of NO, and selective phosphodiesterase type 5 (PDE-5) inhibitors that increase levels of intracellular cGMP may complementarily enhance VEGF synthesis in corpus cavernosal smooth muscle cells (CCSMCs), and may consequently restore impaired endothelial function. Expression of eNOS in corpus cavernosal smooth muscle has also been reported. However, it is unclear whether CCSMCs can generate NO.

AIM

To elucidate whether CCSMCs can synthesize NO and whether NO synthesis enhances VEGF synthesis via the NO/cGMP pathway.

METHODS

Corpus cavernosal cells were cultured and characterized by immunocytochemistry and immunoblotting. CCSMCs were treated with L-arg. CCSMCs were also incubated with L-arg and with vardenafil, an inhibitor of PDE-5.

MAIN OUTCOME MEASURES

Release of NO from cells was confirmed by assay of NO metabolites (NOx). Intracellular cGMP concentration and VEGF concentration in the medium were measured.

RESULTS

Isolated cells were determined to be CCSMCs. The expression of eNOS by CCSMCs was also identified. NOx and cGMP levels in the L-arg-treated group were significantly greater than those in the control group. VEGF and cGMP levels in the L-arg-treated group were also significantly greater than those in the control group. VEGF and cGMP levels in the L-arg + vardenafil-treated group were significantly greater than those in the L-arg-treated group and the control group.

CONCLUSIONS

CCSMCs express eNOS and synthesize NO. NO synthesis leads to enhancement of VEGF synthesis via the NO/cGMP pathway. Combined L-arg and vardenafil treatment, which can enhance VEGF production, may provide a novel therapeutic strategy for the treatment of erectile dysfunction as well as endothelial dysfunction in general.

Oral phosphodiesterase-5 inhibitors: effect of heme oxygenase inhibition on cGMP signalling in rat cavernous tissue

This work postulated that heme oxygenase (HO) is partly responsible for controlling phosphodiesterase-5 inhibitor actions by modulating cyclic guanosine monophosphate (cGMP) cavernous tissue levels. Five hundred and four male Sprague-Dawley rats, divided into five groups, were investigated. Group 1 (n=72) included controls, group 2 (n=72) received sildenafil citrate (Viagra) orally, group 3 (n=72) received vardenafil hydrochloride (Levitra), group 4 (n=72) received tadalafil (Cialis). Group 5 (n=216), subdivided into three subgroups (A, B and C, 72 each), received the same dose of each drug with the HO inhibitor, Zn protoporphyrin. Eight rats from each group/subgroup were killed at 0.5, 1, 2, 3, 4, 6, 18, 24 and 36 h when cGMP levels in the cavernous tissues were estimated. Cavernous tissue cGMP levels increased significantly in sildenafil, vardenafil and tadalafil-treated rats compared to the controls with significant decreases after HO inhibition. It is concluded that the effects of these PDE-5 inhibitors in rat cavernous tissue are partly mediated through HO activity via the cGMP signalling pathway.

Nebivolol induces eNOS activation and NO-liberation in murine corpus cavernosum

Erectile function is critically dependent upon the activation of the endothelial nitric oxide synthase (eNOS) in the smooth muscle cells of penile corpus cavernosum tissue. Nebivolol is a beta(1)-selective beta-adrenoceptor blocker (beta-ARB) with additional vasodilating properties, which have been attributed to eNOS-activation. Our study investigated whether nebivolol is able to increase eNOS activity in erectile tissue. Murine penile tissue was incubated in an organ bath under control conditions and in the presence of nebivolol or metoprolol. Immunofluorescence staining was performed using specific antibodies against eNOS-activation or eNOS-serine 1177 phosphorylation. Corpus cavernosum smooth muscle tissue was identified using a smooth muscle actin antibody. In addition, slices of murine erectile tissue were incubated with diaminofluorescein (DAF), a specific fluorescence marker for NO-liberation. Under control conditions and after application of metoprolol, we observed a small eNOS-activation and serine 1177-phosphorylation in murine corpus cavernosum tissue. A significant increase in eNOS-activation and serine 1177-phosphorylation of eNOS was observed only in the presence of nebivolol (10 muM). These alterations of the eNOS protein induced after application of nebivolol were associated with a time-dependent increase in DAF fluorescence in murine erectile tissue. We conclude that beta-adrenoceptor blockers differentially influence erectile tissue. Since cardiovascular diseases are often associated with the development of erectile dysfunction, the nebivolol-induced eNOS-activation in corpus cavernosum may be beneficial when treating patients suffering from cardiovascular disease.

NITRIC OXIDE, ERECTILE DYSFUNCTION AND BETA-BLOCKER TREATMENT (MR NOED STUDY): BENEFIT OF NEBIVOLOL VERSUS METOPROLOL IN HYPERTENSIVE MEN

1. Hypertensive men treated with beta-blockers frequently complain of erectile dysfunction. The present study investigated the effects of two beta(1)-adrenoceptor-selective antagonists, namely nebivolol and metoprolol, on erectile function in hypertensive men. 2. Male out-patients (age range 40-55 years) with newly diagnosed or existing stage 1 essential hypertension (mean seated systolic blood pressure 140-159 mmHg; diastolic blood pressure 90-99 mmHg) were enrolled in the study. All patients lived in a stable, heterosexual partnership and had no history of sexual dysfunction. After a 2-week placebo run-in period, patients were randomized double-blind to either Treatment group A (comprising nebivolol 5 mg once daily for 12 weeks, followed by placebo for 2 weeks and then metoprolol succinate 95 mg once daily for 12 weeks) or Treatment group B (comprising metoprolol succinate 95 mg for 12 weeks, placebo for 2 weeks and then nebivolol 5 mg for 12 weeks). An international index of erectile function (IIEF) questionnaire and a diary documented patients' sexual function and activity. 3. Nebivolol and metoprolol lowered blood pressure to a similar extent. Metoprolol, but not nebivolol, significantly decreased the IIEF erectile function subscore by 0.92 in the first 8 weeks after onset of beta-blocker treatment. In contrast with metoprolol, nebivolol improved secondary sexual activity scores and other IIEF subscores. 4. Despite similar antihypertensive efficacy of the cardioselective beta(1)-adrenoceptor antagonists nebivolol and metoprolol, nebivolol may offer additional benefits by avoiding erectile dysfunction in male hypertensive patients on long-term beta-adrenoceptor antagonist therapy.

Endothelium Dependent Relaxation in Rabbit Genital Resistance Arteries is Predominantly Mediated by Endothelial-Derived Hyperpolarizing Factor in Females and Nitric Oxide in Males

PURPOSE

In nongenital arteries a sex difference has been postulated in the dominant endothelium-derived relaxant factor(s), eg nitric oxide, prostacyclin or endothelial-derived hyperpolarizing factor. Knowledge of endothelium-derived relaxant factor mechanisms in genital tissues could influence the development of novel treatments for sexual dysfunction. We compared nitric oxide and endothelial-derived hyperpolarizing factor contributions to acetylcholine induced relaxation in the genital arteries of the 2 sexes.

MATERIALS AND METHODS

Male dorsal and cavernous penile arteries, and female extravaginal and intravaginal arteries from New Zealand White rabbits were studied. Acetylcholine concentration-vasodilator response curves were constructed in the presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester, K(+) channel blockers (apamin and charybdotoxin) or a combination. Indomethacin was present throughout to exclude prostacyclins.

RESULTS

Extravaginal artery relaxation was predominantly endothelial-derived hyperpolarizing factor induced. Apamin plus charybdotoxin decreased maximal relaxations from a mean +/- SEM of 77% +/- 4% to 23% +/- 3% in 6 preparations (p <0.01). However, nitric oxide and endothelial-derived hyperpolarizing factor contributed to overall function. Dorsal artery relaxation was largely nitric oxide induced. Nomega-nitro-L-arginine methyl ester decreased maximal relaxations from 90% +/- 3% to 41% +/- 9% (p <0.001) with no endothelial-derived hyperpolarizing factor involvement (p >0.05). In cavernous and intravaginal arteries nitric oxide and endothelial-derived hyperpolarizing factor contributed to acetylcholine induced relaxation, while nitric oxide predominated. Blocking nitric oxide synthase or K(+) channels indicated that myogenic tone and constitutive activity of endothelium-derived relaxant factors were present. Vasodilator nerve mediated responses were influenced by each with the former more effective.

CONCLUSIONS

Vaginal inflow arteries showed a dominance of endothelial-derived hyperpolarizing factor, contrasting with nitric oxide in penile arteries. Penile arteries followed the trend that endothelial-derived hyperpolarizing factor involvement increased with decreasing vessel caliber, while the reverse was demonstrated in female arteries.

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Pharmacology of erectile dysfunction in man

Erectile dysfunction (ED) is defined as the consistent or recurrent inability of a man to attain and/or maintain a penile erection sufficient for sexual activity (2nd International Consultation on Sexual Dysfunction-Paris, June 28th-July 1st, 2003). Following the discovery and introduction of sildenafil, research on the mechanisms underlying penile erection has had an enormous boost and many preclinical and clinical papers have been published in the last 5 years. This review is structured in order to give the reader an overview of the clinical and preclinical data available on the peripheral regulation of and the mediators involved in human penile erection. The most widely accepted risk factors for ED are discussed. The article is focused on human data, and the safety and effectiveness of the 3 commercially available Phosphodiesterase-5 (PDE5) inhibitors used to treat ED are also discussed.

Evaluation of tetrahydrobiopterin (BH4) as a potential therapeutic agent to treat erectile dysfunction

AIM

Nitric oxide (NO)-mediated smooth muscle relaxation causes penile erections. The endothelial NO synthase (eNOS) coenzyme tetrahydrobiopterin (BH4) converts eNOS-mediated catalytic activity from oxygen radical to NO production, improving endothelial function and vascular smooth muscle relaxation.

METHODS

Using quantitative immunohistochemistry, 8-isoprostane and nitrotyrosine concentrations were compared in cavernosal tissue from 17 potent and 7 impotent men, and the effect of single oral doses of BH4 on penile rigidity and tumescence was investigated. The pharmacodynamic effect of single oral doses of BH4 on penile rigidity and tumescence was investigated in a randomized, placebo-controlled, double-blind cross-over fashion in 18 patients with erectile dysfunction (ED) while receiving visual sexual stimulation.

RESULTS

8-Isoprostane content in endothelium and smooth muscle was significantly higher in impotent patient samples; the level of nitrotyrosine was unchanged in ED patients. Relative to placebo, a single dose of 200 mg BH4 led to a mean increase in duration of > 60% penile rigidity (33.5 min [95% confidence interval (CI): 13.1-49.3] at base and 29.4 min [95% CI: 8.9-42.2] at tip). A 500-mg dose increased the relative duration of > 60% penile rigidity by 36.1 min (95% CI: 16.3-51.8) at the base and 33.7 min (95% CI: 11.4-43.9) at the tip. Treatments were well tolerated.

CONCLUSION

BH4 treatment is suggested to switch eNOS catalytic activity from super-oxide to NO formation, leading to a reduced formation of free radical reaction product 8-isoprostane without alteration of nitrotyrosine. The observed results make BH4 a suitable candidate as an ED treatment through reconstitution of altered catalytic activity of the eNOS.

[Erectile dysfunction: the role of laboratory in the diagnostic and pronostic evaluation]

OBJECTIVE

To review and to update the different laboratory tests recommended for etiologic diagnostic of erectile dysfunction and to evaluate the effect these tests could have on the pronostic and therapeutic strategy of this pathology.

MATERIAL AND METHODS

We review the last articles related with etiopathogenics and pathophysiologics mechanisms of erectile dysfunction, including our studies on endothelial dysfunction and erectile dysfunction.

RESULTS

The depth and extension of the laboratory protocol in erectile dysfunction is not necessaryly the same in all situations. The age, coincidence of comorbilities, set a different limit between patients demanding complementaries investigations that go beyond the basic request.

CONCLUSIONS

The etiopathogenic laboratory work up in erectile dysfunction is currently changing incorporating news tests. The traditional search of commorbilities like diabetes, hepatic dysfunction, hypogonadism, hyperglucemia is getting broad with recents analitics evaluations related with potential markers of endothelial disease.

Cholesterol Feeding Reduces Vascular Endothelial Growth Factor Signaling in Rabbit Corporal Tissues

PURPOSE

Hypercholesterolemia is a major risk factor for erectile dysfunction (ED), but the mechanisms are not completely understood. Vascular endothelial growth factor (VEGF) is reduced in rabbit corporal tissue with cholesterol feeding. VEGF signaling leads to the phosphorylation of Akt and endothelial nitric oxide synthase (p-Akt and p-eNOS).

MATERIAL AND METHODS

New Zealand White rabbits (n = 50) were fed a 1% cholesterol (n = 8, 8, 8, 4) or normal (n = 6, 6, 6, 4) diet for 2, 4.5, 7.5, and 12 weeks. Akt, p-Akt, and p-Akt/Akt were measured by enzyme-linked immunosorbent assay. Levels of eNOS, p-eNOS, and neuronal and inducible nitric oxide synthase (nNOS and iNOS) mRNA and protein were assessed by polymerase chain reaction and Western analysis.

RESULTS

Cholesterol feeding was associated with a significant decrease in p-Akt/Akt 2.16-fold (P < 0.05), 3.28-fold (P < 0.02), and 3.42-fold (P < 0.02) at 4.5, 7.5, and 12 weeks, respectively. The reduction in p-Akt/Akt with the cholesterol diet at 2 weeks was not significantly different, but the correlation between the duration of cholesterol feeding and the reduction in p-Akt/Akt was high (r( 2) = 0.858). eNOS protein or mRNA did not change with cholesterol feeding, but p-eNOS was significantly decreased at 4.5 weeks and all subsequent time points. nNOS mRNA and protein levels were decreased at 4.5 weeks and all subsequent time points, while iNOS was not different between groups.

CONCLUSIONS

Hypercholesterolemia results in decreased VEGF signaling and decreased levels of the active form of eNOS in corporal tissue. Levels of nNOS were reduced by a different mechanism. VEGF signaling may provide a target to modulate ED.

Role of adenosine triphosphate-dependent potassium channels in canine penile erection

OBJECTIVES

To define the physiologic role and hemodynamic features of nitric oxide (NO) and the adenosine triphosphate (ATP)-dependent K(+) (K(ATP)) channel in canine penile erection.

METHODS

Mongrel dogs were anesthetized, and penile erection was induced by electrical stimulation of the pelvic nerve. Changes in the intracavernous pressure (ICP) were measured with a transducer.

RESULTS

The basal ICP was 12.8 +/- 5.0 mm Hg. Pelvic nerve stimulation (5 to 20 V, 5 to 15 Hz, for 1-minute intervals) significantly increased the ICP to 86.2 +/- 11.4 mm Hg (n = 5, P <0.05). Treatment with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (10 mg/kg intravenously) abolished this increase (15.4 +/- 5.0 mm Hg, n = 5). Intracavernous injection of the K(ATP) channel opener cromakalim (3 and 10 microg) increased the ICP (103 +/- 14.4 mm Hg and 106 +/- 12.1 mm Hg, respectively; n = 4). This response was abolished by the prior intracavernous injection of the selective K(ATP) channel-specific blocker glibenclamide (10 mg). Glibenclamide did not affect the increase in ICP induced by electric stimulation of the pelvic nerve (88 +/- 24.2 mm Hg).

CONCLUSIONS

Our results indicate that relaxation of canine cavernous smooth muscle and penile tumescence are mediated by NO. The failure of glibenclamide to affect the increase in ICP induced by pelvic nerve stimulation suggests that ATP-dependent K(+) channels probably do not play a physiologic role in canine penile erection.

Therapeutic interventions targeting the nitric oxide system: current and potential uses in obstetrics, bone disease and erectile dysfunction

Nitric oxide is involved in a countless number of physiological processes and is known to have cytoprotective as well as cytotoxic effects. Increased knowledge about the multifaceted role of nitric oxide in a variety of disease states has led to the design of multiple treatment strategies involving the nitric oxide system. The current review focuses on recent research advances in the fields of obstetrics, bone disease and erectile dysfunction that have led to current or potential future therapies involving nitric oxide.

Role of nitric oxide and K+ channels in relaxation induced by polygodial in rabbit corpus cavernosum in vitro

This study examines the relaxation produced by the sesquiterpene polygodial and compares its action with those caused by acetylcholine (ACh) and sodium nitroprusside (SNP) in the rabbit corpus cavernosum (RbCC) in vitro. RbCC was set up in a 5-ml bath containing Krebs solution at 37 degrees C, at pH 7.2, and under 2 g of tension. Polygodial, ACh, and SNP elicited graded relaxation in RbCC with mean EC50 values of 46.70 microM, 0.38 microM, and 0.30 microM, respectively. The nitric oxide (NO) synthase inhibitor L-NOARG and the guanylate cyclase inhibitors LY 83583 and ODQ markedly inhibited the relaxation induced by polygodial (% of inhibition of 79, 48, and 51, respectively) and those caused by ACh (% of inhibition of 100, 49, and 32, respectively). Tetraethylammonium (TEA) and glibenclamide inhibited the relaxation induced by polygodial (52% and 43%, respectively), but only TEA caused shift to the right on ACh-mediated relaxation. In contrast, apamin, charybdotoxin, and 4-aminopyridine or the protein kinase A inhibitor KT 5720 all failed to affect either polygodial or ACh-mediated relaxation in these preparations. The authors concluded that polygodial produced graded relaxation in the RbCC in vitro via a mechanism that was partially dependent on the release of NO or a NO-derived substance through an activation of guanylate cyclase but was independent of adenylate cyclase mechanism. In addition, the opening of K+ channels sensitive to TEA and glibenclamide, but not those sensitive to apamin, 4-aminopyridine, or charybdotoxin, also contributed to the relaxant action produced by polygodial in the RbCC.

Physiological mechanisms regulating the expression of endothelial-type NO synthase

Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-beta, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-alpha and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.

MAP kinase 1/2 (Erk 1/2) and serine/threonine specific protein kinase Akt/PKB expression and activity in the human corpus cavernosum

Nitric oxide (NO) is an important mediator in the cavernosal smooth muscle relaxation that causes erections. The purpose of this study was to examine the existence, distribution and phosphorylation stage of two recently discovered key enzymes for NO regulation in human cavernosal tissue, the MAP Kinase 1/2 (Erk 1/2) and the serine/threonine specific protein kinase Akt/PKB. The expression of the enzymes was examined in corpus cavernosum specimens taken from both potent men and from patients with long-term impotence. There was a distinct difference in the activation stage of the MAP Kinase 1/2 (Erk 1/2) between endothelium and smooth muscle cells in potent patients. This finding gives evidence for a cell-type-specific regulation of the eNOS-dependent NO release. Furthermore, we found a higher basal level of active MAP Kinase 1/2 (Erk 1/2) in impotent patients. This finding gives the first evidence for an inhibitory influence of MAP Kinase 1/2 (Erk 1/2) on cavernosal eNOS activity.

Intracavernosal injection of vascular endothelial growth factor induces nitric oxide synthase isoforms

OBJECTIVE

To identify genes that are affected by vascular endothelial growth factor (VEGF), as an intracavernosal injection with VEGF improved the recovery of erectile function in a rat model of arteriogenic impotence, specifically examining the three nitric oxide synthase (NOS) genes, nNOS, eNOS, and iNOS.

MATERIALS AND METHODS

Male rats had their pudendal arteries ligated or underwent a sham operation. They were then treated by an intracavernosal injection with 4 microg of VEGF in phosphate-buffered saline (PBS) or PBS alone. At 6 and 24 h after treatment electrostimulation was applied to the cavernosal nerve and the intracorporal pressure measured. The erectile tissue was then harvested for RNA isolation and cryo-sectioning. The isolated RNA was used for microarray and reverse transcription-polymerase chain reaction (RT-PCR) analyses, and the tissue sections for immunohistochemical analysis.

RESULTS

Microarray analysis detected nNOS, eNOS and iNOS at very low expression levels in PBS-treated rats; expression levels were higher for eNOS and iNOS in all VEGF-treated rats. These results were further confirmed by RT-PCR analysis. Immunohistochemical analysis identified the cavernosal endothelium and smooth muscle as the tissue types where eNOS and iNOS were up-regulated, respectively.

CONCLUSIONS

This is the first report of the induction of both eNOS and iNOS in the penis after intracavernosal VEGF. These events may help support a significant recovery of erectile function after interrupting the blood supply to the penis.

Prevention of a hypoxic Ca(2+)(i) response by SERCA inhibitors in cerebral arterioles

1. The aim of the study was to investigate the mechanism of a novel effect of hypoxia on intracellular Ca(2+) signalling in rabbit cerebral arteriolar smooth muscle cells, an effect that was resistant to the L-type Ca(2+) channel antagonist methoxyverapamil (D600). 2.[Ca(2+)](i) of smooth muscle cells in intact arteriolar fragments was measured using the Ca(2+)-indicator dye fura-PE3. Hypoxia (PO(2) 10 - 20 mmHg) lowered basal [Ca(2+)](i) but did not inhibit Ca(2+) entry pathways measured by Mn(2+)-quenching of fura-PE3. 3. The effect of hypoxia was completely prevented by thapsigargin or cyclopiazonic acid, selective inhibitors of sarcoplasmic reticulum Ca(2+) ATPase (SERCA). Since these inhibitors do not block Ca(2+) extrusion or uptake via the plasma membrane, the data indicate that the effect of hypoxia depends on a functional sarcoplasmic reticulum. 4. Because actions of nitric oxide (NO) on vascular smooth muscle are also prevented by SERCA inhibitors it was explored whether the effect of hypoxia occurred via modulation of endogenous NO release. Residual NOS-I and NOS-III were detected by immunostaining, and there were NO-dependent effects of NOS inhibitors on Ca(2+)(i)-signalling. Nevertheless, inhibition of endogenous NO production did not prevent the effect of hypoxia on [Ca(2+)](i). 5. The experiments reveal a novel nitric oxide-independent effect of hypoxia that is prevented by SERCA inhibitors.

Nitric oxide synthase expression and function in embryonic and adult cardiomyocytes

Nitric oxide (NO) is an important signalling molecule that plays a relevant role in different cell systems, among them the adult heart. The effects of NO are primarily mediated through modulation of Ca(2+) homeostasis, myofibrillar contractility, and metabolic regulation in cardiomyocytes. Recent evidence also suggests an important role of NO for cardiomyogenesis by modulating proliferation and differentiation and regulating cardiac function. In the embryonic, but also the healthy and diseased, adult mammalian heart, the inducible (iNOS) and the endothelial (eNOS) nitric oxide synthases (NOS) are detected. However, the expression pattern of NO and its function differ during development. Furthermore, under pathophysiological conditions NOS expression can also change and cause impairment of cardiac performance and cytotoxic effects. The present review focuses on the role and function of NO during cardiomyogenesis, the mechanisms responsible for eNOS availability, and the paracrine effects of NO generated by cardiomyocytes.

Erection and NO override the vasoconstrictive effect of alpha-adrenergic stimulation in the rat penile vasculature

Studies in this laboratory are designed to determine the effects of vasoconstrictor agents on the erectile response in rats. We have previously demonstrated that the vasoconstrictor effect of endothelin-1 (ET-1) is sharply reduced by erection and by nitric oxide (NO) administration. The present study was performed to determine if vasoconstriction, resulting from alpha-adrenergic stimulation, is altered by erection and NO. During continuous monitoring of corpus cavernosum pressure (CCP) and mean arterial pressure (MAP), erection was induced by electrical stimulation of the autonomic ganglion for the innervation of the penis. When the alpha-adrenergic agonist methoxamine (METH, 10 microg/kg) was injected before erection (ie, into the non-erect penis), the subsequent erectile response (CCP/MAP) was significantly reduced from 0.68+/-0.03 before METH to 0.34+/-0.08 after METH. Injection of METH into the erect penis (ie, during erection) reduced the vasoconstrictor action of METH; CCP/MAP was 0.74+/-0.02 before METH and 0.55+/-0.05 after METH (P<0.05). The vasoconstrictor action of METH was slightly reduced when given in conjunction with NOR-1, a NO donor drug; CCP/MAP was 0.70+/-0.05 before METH, 0.55+/-0.09 after METH but this change was not significant. These results demonstrate that the response to alpha-adrenergic stimulation is attenuated during erection in response to ganglionic stimulation. Furthermore, it appears that NO, produced during erection, may serve to override agonist-induced vasoconstriction. These results support our hypothesis that NO acts to directly stimulate relaxation of cavernous smooth muscle and to inhibit the vasoconstrictor actions of agents like ET-1 and alpha-adrenergic agonists including norepinephrine.

Effects of estrogen on nitric oxide synthase and histological composition in the rabbit clitoris and vagina

We investigated the functional and histological changes after oophorectomy in the rabbit clitoris and vagina to determine the mechanism responsible for the development of arousal disorder in postmenopausal women. Twenty mature female New Zealand white rabbits were randomly divided into three groups: control; oophorectomy; and estrogen replacement after oophorectomy. We compared the nitric oxide synthase (NOS) activity and the degree of expression of neuronal (nNOS) and endothelial NOS (eNOS) using biochemical and Western blot analysis in clitoral and vaginal tissues. Histological change of smooth muscle and collagen contents in those tissues were also compared using Masson's trichrome staining. NOS activity and the expression of nNOS and eNOS were significantly increased in the oophorectomized group while there was a decrease to the level of the control group in the estrogen replacement group. Histological examination showed that oophorectomy induced a significant increase in collagen and decrease in muscle content in both clitoris and vagina, while the ratio of smooth muscle content was increased significantly after the estrogen replacement. Our results clearly demonstrate that estrogen deficiency induces compensatory NOS production which may be related to decreases in muscle to collagen ratio in female rabbit genital organs.

Male sexual function and its disorders: physiology, pathophysiology, clinical investigation, and treatment

This review is designed to help the reproductive endocrinologist integrate his or her professional activity with those of other disciplines including urology, radiology, neurology, and psychology in order to successfully manage all of the inseparable aspects of male sexual and reproductive functioning. Significant advances in the field of male sexual physiology and pathophysiology and new methods of investigation and treatment of male sexual disorders are outlined. The review synthesizes available data on the following: norms of sexual organs, aging and sexuality, role of central and peripheral neurochemicals in each stage of the sexual cycle, role of corporeal smooth muscles in the hemodynamic control of erection and detumescence, influence of psychological factors, drugs, and disease on all aspects of sexual functioning, and use of nocturnal penile tumescence monitoring, imaging investigations, and neurophysiologic studies in the diagnostic workup of males with sexual dysfunction. Clinical algorithms are presented where appropriate. Extensive discussions on newly developed strategies in psychological and behavioral counseling, drug therapy, tissue engineering, nonsurgical devices, and surgical treatments for all forms of sexual disorders are also provided. Lastly, the effect of sexual dysfunction and its treatment on quality of life in affected men is addressed, along with recommendations for future research endeavors.

Pharmacology of erectile function and dysfunction

Central regulation of the erectile process involves several transmitters, including dopamine, serotonin, noradrenaline, and nitric oxide, and peptides, such as oxytocin and ACTH/alpha-MSH. These systems may be targets for future drugs designed to treat erectile dysfunction. Peripherally, the different steps involved in neurotransmission, impulse propagation, and intracellular transduction of neural signals in penile smooth muscles need further investigation. Continued studies of the interactions between different transmitters/modulators may reveal new combination therapies. Increased knowledge of the changes in penile tissues associated with erectile dysfunction may explain the pathogenetic mechanisms and help to prevent the disorder.

The role of nitric oxide in penile erection

The functional state of the penis, flaccid or erect is governed by smooth muscle tone. Sympathetic contractile factors maintain flaccidity whilst parasympathetic factors induce smooth muscle relaxation and erection. It is generally accepted that nitric oxide (NO) is the principal agent responsible for relaxation of penile smooth muscle. NO is derived from two principal sources: directly from non-adrenergic non-cholinergic parasympathetic nerves and indirectly from the endothelium lining cavernosal sinusoids and blood vessels in response to cholinergic stimulation. The generation of NO from L-arginine is catalysed by nitric oxide synthase (NOS). There has been controversy over the relative prevalence of endothelial or neuronal NOS within the penis of different animal species. This review examines the role of NO in the penis in detail. Established and new treatments for erectile dysfunction whose effects are mediated via manipulation of the NO pathway are also described.

A standardized procedure for using human corpus cavernosum strips to evaluate drug activity

The main problem of using human corpus cavernosum (HCC) tissue to perform bioassay is linked to its limited availability further complicated by the heterogeneous source of the tissues used. Here, we show that gender reassignment is a reliable source of human tissue without major ethical problems. Indeed, the entire corpus cavernosum is obtained from the surgery procedure, which allows creating a standardized procedure to prepare HCC strip. In addition, human tissue, if kept in the fridge in the condition described, does not loose its ability to contract to phenylephrine (PE; alpha agonist), angiotensin II (AG II) and KCl up to 4 days. Furthermore, once contracted with PE, HCC relaxes to acetylcholine (endothelium-dependent mechanism); sodium nitroprusside (endothelium-independent mechanism); cromakalim (CRK), a K(ATP) channel opener; or alprostadil, a synthetic PGE2 (ALPR). In conclusion, we have standardized a procedure that allows the use of HCC strips to evaluate drug activity and/or to study pathophysiological mechanisms with an intact functional human tissue up to 4 days from the surgery procedure.

Temporal regulation of endothelial ET-1 and eNOS expression in intact human conduit vessels exposed to different intraluminal pressure levels at physiological shear stress

OBJECTIVE

By using a computerized vascular perfusion model, we investigated temporal effects of sub-acute pressure elevation on vasomotor behavior and expression of endothelin-1 (ET-1) and endothelial nitric oxide synthase (eNOS) in intact human conduit vessels.

METHODS

Paired umbilical veins were perfused during 1.5, 3 and 6 h under high/low intraluminal pressure (40/20 mmHg) and at identical shear stress level of 10 dyn/cm(2). ET-1 and eNOS gene and protein expression was quantified with real-time reverse-transcribed polymerase chain reaction and quantitative immunohistochemistry, respectively.

RESULTS

Pressure induced differential temporal regulation patterns of ET-1 and eNOS gene expression. During the high pressure condition, eNOS mRNA was upregulated after 3 h and leveled off after 6 h of perfusion, while ET-1 mRNA was elevated after 6 h perfusion. Immunohistochemistry verified synchronal changes at the protein level. Significant vasodilation was observed after 3 h in the high-pressure system.

CONCLUSION

Thus, subacute pressure elevation exerts differential effects on the endothelial eNOS/ET-1 expression, which dynamically regulate the vasomotor tone.

Nitric oxide based influence of nitrates on micturition in patients with benign prostatic hyperplasia

BACKGROUND

Nitric oxide (NO) is involved in the physiologic regulation of smooth muscle relaxation in the prostate. Organic nitrates act as NO donors. In this prospective open study we prove the influence of orally given nitrates on micturition.

METHODS

Thirty-two patients underwent a urological medical check-up prior to starting nitrate medication for cardiovascular disease. We examined peak flow rates, residual urine, IPS-score, PSA level and prostate volume. Exact inclusion and exclusion criteria were defined. Fifteen patients suffered from obstructive symptoms, 17 patients reported no subjective micturition problems. Urological re-evaluation was performed two weeks and three months after nitrate medication.

RESULTS

A significant improvement of peak urinary flow rates (+3.1 ml/s; p<0.05), IPS score and significant decrease of residual urine volume (-22 ml; p<0.05) were found in the symptomatic patients. No significant changes of micturition parameters were found in asymptomatic patients. PSA levels and prostate volumes did not change in either groups.

CONCLUSIONS

Organic nitrates influence micturition parameters in patients with obstructive benign prostatic hyperplasia. This might be explained by the known mechanism of NO donation (smooth muscle relaxation) of nitrates. More functional controlled studies are necessary to describe the grade of influence of nitrates on the prostate. Concomitant oral medication with nitrates must be considered as a relevant bias factor on BPH in future clinical studies.

Repeated PGE1 treatment enhances nitric oxide and erection responses to nerve stimulation in the rat penis by upregulating constitutive NOS isoforms

PURPOSE

To assess whether intracavernosal injections of prostaglandin E1 (PGE1) can influence nitric oxide (NO) release in the corpora in a rat model of penile erection.

MATERIALS AND METHODS

The extracellular levels of NO were monitored at 100 seconds intervals in the corpus cavernosum of anesthetized rats by using differential normal pulse voltammetry with porphyrin-Nafion coated carbon fiber microelectrodes. The intracavernosal pressure (ICP) was simultaneously recorded. PGE1 was given either as a single dose (ranging from 0.2 to 15 microg.) or as repeated 2 microg. injections in alternate days for two weeks. The NO and ICP responses to electrostimulation of the cavernosal nerve (SCN) was studied in the animals in the repeated treatment schedule at 1, 7, 15 and 30 days after its termination. The levels of the three NO synthase (NOS) isoforms in the cavernous tissue were measured by immunoblotting.

RESULTS

Acute PGE1 treatment dose-relatedly increased NO levels in the corpora, with a concomitant ICP increase with the highest dose. Repeated 2 microg. PGE1 injections increased the NO and ICP responses to SCN as compared with intact or vehicle-injected animals. This treatment also increased the penile content of the neuronal and endothelial NOS proteins. The inducible NOS isoform remained unchanged after either vehicle or PGE1 injections. The effects of the repeated PGE1 treatment were greater in the group studied 24 hours after the last injection and decreased progressively thereafter.

CONCLUSIONS

Stimulation of NO release can contribute to the erectogenic effect of intracavernous PGE1 injections. The increased levels of constitutive NOS isoforms in the corpora could contribute to the improvement of the erectile function reported by some patients following repeated treatment with vasorelaxant agents.

Ejaculatory abnormalities in mice lacking the gene for endothelial nitric oxide synthase (eNOS-/-)

Nitric oxide (NO) has been established as a neurotransmitter in both the central and peripheral nervous systems. Three isoforms of its synthetic enzyme, NO synthase (NOS), have been identified: 1) in the endothelial lining of blood vessels (eNOS), 2) an inducible form found in macrophages (iNOS), and 3) in neurons (nNOS). Previous studies using pharmacological agents that block all three isoforms of NOS have revealed that NO mediates several aspects of reproductive physiology and behavior, including anomalies in male sexual behavior and erectile function. To determine the specific contribution of the endothelial isoform of NOS in male reproductive behavior, we studied mice missing the gene for only eNOS (eNOS-/-). Wild-type (WT) and eNOS-/- animals were placed with an estrous WT female and observed for 45 min. Both WT and eNOS-/- mice displayed equivalent motivation to mount the stimulus female. However, eNOS-/- mice exhibited striking anomalies in ejaculatory function. A higher percentage of eNOS-/- than WT mice ejaculated during the testing period (p < 0.001). This increased propensity to ejaculate was apparently due to reduced stimulation required to elicit ejaculation; eNOS-/- mice required significantly fewer mounts (p < 0.003) and intromissions (p < 0.001) to ejaculate compared to WT mice. Taken together, these results suggest that NO synthesized by eNOS may be involved in ejaculatory physiology, but not sexual motivation.

Transcutaneous penile oxygen pressure during bicycling

OBJECTIVE

To evaluate the blood supply to the penis during bicycling and thus determine whether the associated perineal compression might be responsible for some cases of impotence.

SUBJECTS AND METHODS

The transcutaneous penile oxygen partial pressure (pO2 ) at the glans of the penis was measured in 25 healthy athletic men; pO2 is readily measured by noninvasive techniques currently widely used in the management of premature infants, and which have been shown to give pO2 levels that correlate with arterial pO2 levels. The measurements in the healthy subjects were taken in various positions, before, during and after bicycling.

RESULTS

The mean (sd) pO2 of the glans when standing before cycling was 61.4 (7.2) mmHg; it decreased after 3 min of cycling to 19.4 (4. 7) mmHg. After 1 min of cycling in a standing position it increased significantly to 68 (7.6) mmHg; when cycling was continued in a seated position, after 3 min the pO2 fell to 18.4 (4.2) mmHg and there was a full return to normal pO2 values after a 10-min recovery period.

CONCLUSION

The pO2 seems to correlate with the blood supply to the penis. The present results support the hypothesis that as the penile arteries are compressed against the pubic bone by the saddle during bicycling, the pO2 values decrease. Additionally, shifting from a seated to a standing position while cycling significantly improved the pO2 value of the penis and penile blood oxygenation was then even greater. Therefore, we suggest that cyclists change their body position frequently during cycling. Correcting the handlebars or the height of the saddle, tipping the nose of the saddle to produce a more horizontal, or even downward pointing position, and attention to the design of the saddle may be the only required precautions.