Cavernous Smooth Muscle Relaxation Research Articles

Erectile Dysfunction: Key Role of Cavernous Smooth Muscle Cells.

Erectile dysfunction is increasingly affecting men, from the elderly to young adults, being a sexual disorder related to the inability to generate or maintain a penile erection. This disorder is related to psychosocial factors such as anxiety, depression, and low self-esteem, to organic factors such as the presence of preexisting conditions like hypertension, diabetes and dyslipidemia. The pathophysiology of the disease is related to changes in the neurotransmission of the autonomic or the non-cholinergic non-adrenergic nervous system, as well as the release of local mediators, such as thromboxane A2 and endothelin, and hormonal action. These changes lead to impaired relaxation of cavernous smooth muscle, which reduces local blood flow and impairs penile erection. Currently, therapy is based on oral vasodilation, such as sildenafil, tadalafil, vardenafil and iodenafil, or by direct administration of these agents into the corpus cavernosum or by intraurethral route, such as alprostadil and papaverine. Despite this, studies that consolidate the understanding of its pathophysiological process contribute to the discovery of new more efficient drugs for the treatment of erectile dysfunction. In this sense, in the present work an extensive survey was carried out of the mechanisms already consolidated and the most recent ones related to the development of erectile dysfunction.

In vitro inhibition of phosphodiesterase type 4 enhances rat corpus cavernosum nerve-mediated relaxation induced by gasotransmitters

AimsNitric oxide (NO) and hydrogen sulfide (H2S) are involved in nerve-mediated corpus cavernosum (CC) relaxation. Expression of phosphodiesterase type 5 (PDE5) and type 4 (PDE4), cyclic guanosine monophosphate (cGMP)- and cyclic adenosine monophosphate (cAMP)-specific, respectively, has been described and PDE5- and PDE4-inhibitors induce cavernous smooth muscle relaxation. Whereas the NO/cGMP signaling pathway is well established in penile erection, the cAMP-mediated mechanism is not fully elucidated. The aim of this study is to investigate the localization and the functional significance of PDE4 in rat CC tone regulation. Main methodsWe performed immunohistochemistry for the detection of the PDE4A isoenzyme. Isometric tension recordings for roflumilast and tadalafil, PDE4 and PDE5 inhibitors, respectively, electrical field stimulation (EFS) and β-adrenoceptor agonist isoproterenol and endogenous H2S production measurement. Key findingsA marked PDE4A expression was detected mainly localized in the nerve cells of the cavernous smooth muscle. Furthermore, roflumilast and tadalafil exhibited strong corpus cavernous relaxations. Endogenous H2S production was decreased by NO and H2S synthase inhibitors and increased by roflumilast. Isoproterenol- and EFS-induced relaxations were increased by roflumilast. SignificanceThese results indicate that PDE4A is mainly expressed within the nerves cells of the rat CC, where roflumilast induces a potent corpus cavernous relaxation per se and potentiates the response induced by β-adrenoceptor activation. The fact that roflumilast enhances H2S production, as well as EFS-elicited responses suggests that PDE4 inhibitors modulate, in a positive feedback fashion, nerve-mediated relaxation induced by gasotransmitters, thus indicating a key role for neuronal PDE4 in penile erection.

Identification of mechanisms involved in the relaxation of rabbit cavernous smooth muscle by a new nitric oxide donor ruthenium compound

The aim of this study was to evaluate the relaxation in vitro of cavernous smooth muscle induced by a new NO donor of the complex nitrosil-ruthenium, named trans-[Ru(NH3)4(caffeine)(NO)]C13 (Rut-Caf) and sodium nitroprusside (SNP). The tissues, immersed in isolated bath systems, were pre-contracted with phenilephrine (PE) (1 µM) and then concentration-response curves (10 (-12) - 10(-4) M) were obtained. To clarify the mechanism of action involved, it was added to the baths ODQ (10 µM, 30 µM), oxyhemoglobin (10 µM), L-cysteine (100 µM), hydroxicobalamine (100 µM), glibenclamide, iberotoxin and apamine. Tissue samples were frozen in liquid nitrogen to measure the amount of cGMP and cAMP produced. The substances provoked significant relaxation of the cavernous smooth muscle. Both Rut-Caf and SNP determined dose-dependent relaxation with similar potency (pEC50) and maximum effect (E(max)). The substances showed activity through activation of the soluble guanylyl cyclase (sGC), because the relaxations were inhibited by ODQ. Oxyhemoglobin significantly diminished the relaxation effect of the substances. L-cysteine failed to modify the relaxations caused by the agents. Hydroxicobalamine significantly diminished the relaxation effect of Rut-Caf. Glibenclamide significantly increased the efficacy of Rut-Caf (pEC50 4.09 x 7.09). There were no alterations of potency or maximum effect of the substances with the addition of the other ion channel blockers. Rut-Caf induced production of significant amounts of cGMP and cAMP during the relaxation process. In conclusion, Rut-Caf causes relaxation of smooth muscle of corpus cavernosum by means of activation of sGC with intracellular production of cGMP and cAMP; and also by release of NO in the intracellular environment. Rut-Caf releases the NO free radical and it does not act directly on the potassium ion channels.

Effect of Angiotensin II and its Receptor Antagonists on Human Corpus Cavernous Contractility and Oxidative Stress: Modulation of Nitric Oxide Mediated Relaxation

To our knowledge the interaction between angiotensin II and nitric oxide in the control of human corpus cavernous function has not been assessed previously. We determined the presence and role of angiotensin II and its receptors in human penile function. Corpus cavernous tissue was obtained from 35 patients undergoing gender reassignment surgery. Immunohistochemical analysis was done to determine angiotensin II peptide tissue distribution. Organ bath studies were done to determine the angiotensin II/nitric oxide interaction on corpus cavernous smooth muscle function. The role of oxidative stress in the angiotensin II response was also examined using the nicotinamide adenine dinucleotide phosphate oxidase inhibitor apocynin. Angiotensin II was distributed in arteriolar endothelium, endothelium lining sinusoids and smooth muscle cells, and caused dose dependent contraction of human corpus cavernous smooth muscle strips that was inhibited by the angiotensin type 1 receptor antagonist losartan. Relaxation of corpus cavernous smooth muscle induced by the nitric oxide donor sodium nitroprusside or electrical field stimulation was potentiated by losartan. Apocynin decreased angiotensin II induced corpus cavernous contraction. Angiotensin II and nitric oxide interact to modulate human cavernous function since losartan potentiated sodium nitroprusside and electrical field stimulation mediated corpus cavernous smooth muscle relaxation. The angiotensin II response involves the production of superoxide and the development of oxidative stress. These findings support the role of angiotensin II in the regulation of human penile smooth muscle tone and suggest that angiotensin type 1 receptor inhibition may be a therapeutic approach to erectile dysfunction.

Changes of contractility and relaxation of corpus cavernosum in hyperlipidemic rabbit in vitro

To investigate the mechanisms of erectile dysfunction induced by hyperlipidemia through studying the changes of contractility and relaxation of corpus cavernosum in hypercholesterolemic rabbit in vitro. New Zealand white rabbits were randomly divided into control and experiment groups. The control group (n = 20) received a regular diet for 8 weeks while the experimental group (n = 20) were fed a 1% cholesterol diet for 8 weeks. The authors conducted isometric tension studies with phenylephrine, endothelium-dependent vasodilators (acetylcholine), endothelium-independent vasodilators (sodium nitroprusside) and rho kinase inhibitor (Fasudil) on isolated strips of corpus cavernosum. The weight and total serum cholesterol significantly improved (P < 0.01) in experimental group as compared with the non-fed experimental group. The total serum cholesterol significantly improved (P < 0.01) in experimental group as compared with the control group. The contractility responses to phenylephrine in experiment group in doses (0.5, 1, 5, 10, 50, 100 micromol) were 4.79% +/- 2.00%, 8.84% +/-2.95%, 12.81% +/- 3.77%, 14.63% +/- 5.38%, 25.01% +/- 6.14% and 34.69% +/- 8.53% respectively. The contractility responses to phenylephrine in control group were 1.00% +/- 0.3%, 2.60% +/- 0.72%, 4.28% +/- 1.27%, 5.91% +/- 2.09%, 6.49% +/- 4.02% and 5.64% +/- 11.87% respectively. The contractility responses to phenylephrine significantly improved (P < 0.01) in experimental group in these doses as compared with the control group. The relaxation responses to acetylcholine in experimental group in doses (1, 10 and 100 micromol) were 36.28% +/- 4.71%, 48.81% +/- 4.36% and 56.27% +/- 11.93% respectively. The relaxation responses in control group were 48.04% +/- 4.78%, 69.12% +/- 5.27% and 78.23% +/- 5.30% respectively. There was significant reduction (P < 0.01) in experimental group in these doses as compared with the control group. No difference were found among the two groups in the relaxation response to sodium nitroprusside. The relaxation responses to fasudil in experimental group in doses (0.25, 1.25, 2.5 and 12.5 micromol) were 1.56% +/- 0.43%, 5.03% +/- 1.02%, 8.28% +/- 1.35% and 16.77% +/- 3.57% respectively. The relaxation responses in control group were 4.69% +/- 1.23%, 10.39% +/- 2.05%, 15.08% +/- 3.04% and 25.22% +/- 3.72% respectively. There was significant reduction (P < 0.01) in experimental group in these doses as compared with the control group. The improvement of cavernous smooth muscle contractility and the impairment of cavernous smooth muscle relaxation in response to endothelium-mediated stimuli are the mechanisms of erectile dysfunction induced by hyperlipidemia.

Effects of arginase inhibitors on the contractile and relaxant responses of isolated human penile erectile tissue

An impairment in the local availability of nitric oxide (NO) may impair male erectile function. The activity of l-arginine-degrading arginase enzymes may attenuate the relaxation of cavernous smooth muscle by reducing local NO production. Arginase enzymes compete with the nitric oxide synthases for the common substrate, the amino acid l-arginine. Very little data are available regarding the significance of arginase enzymes in the control of human penile erectile tissue. The aim of the present study was to elucidate the effects of drugs known to inhibit arginase activity on the relaxation of isolated human corpus cavernosum (HCC) and the production of cyclic GMP. Using the organ bath technique, the effects of the arginase inhibitors DFMO, H-Orn-OH·HCl, H-lle-OH and nor-NOHA (10 nM–10 μM) on the tension induced by NE (1 μM) and the relaxation induced by electrical field stimulation (EFS) of HCC were investigated. HCC strips were also exposed to increasing concentrations of the compounds, and the production of cGMP was determined by means of a radioimmunoassay. Only marginal effects of the arginase inhibitors were registered on the tension induced by NE and the relaxation exerted by EFS. Mean reversion of tension ranged from 18 to 8%. Only DFMO and nor-NOHA amplified the EFS-induced relaxation by 11 and 29%, respectively. These effects were not paralleled by an increase in tissue levels of cGMP. Arginase inhibitors appeared to be ineffective in reversing the adrenergic tension and increasing the electrically induced relaxation of isolated HCC.

Penile erection induced in vivo by a purified toxin from the Brazilian spider Phoneutria nigriventer

To verify the effect on erectile tissue of mice of two neuropeptides extracted from the poison of a spider, Phoneutria nigriventer, (Tx2-5 and -6, termed 'eretina') after direct injection into the corpus cavernosum, to assess the minimum dosage necessary for effect, the time for initiation of action, the local duration of the erection, histological effects and the presence of local and systemic side-effects. When applied intraperitoneally, eretina promotes the relaxation of cavernous smooth muscle, thus causing penile erection. Thirty-five mice were divided in two groups; 10 control mice were injected 20 microL of saline solution, and in the treated group, 25 mice were divided into groups of five and each subgroup received eretina in decreasing doses (0.024, 0.012, 0.006, 0.003 and 0.0015 microg/kg) until the minimum dose that produced an erection was determined. After treatment all mice were monitored to determine the response and any collateral effects. The minimum dose producing an erection was 0.006 microg/kg, the five mice in this group having evidence of an erection at 35-45 min after injection. The histology of the cavernosum of mice treated with eretina showed dilatation and congestion of the vascular spaces with more blood than in controls. With the minimum dose there were no local or systemic collateral effects and the erection was lost after 120-140 min. The minimum dose of eretina producing an erection in mice was determined, and the agent was safe for this use as it did not produce any collateral toxic effects. These studies indicate a possible means of determining the mechanism of action of eretina.

Etiología neurógena en pacientes con disfunción erectil

Erectile dysfunction (ED) is a disorder with a high prevalence that increases with age. It is estimated that 18.9% of men's between 25 and 70 years suffer it in Spain. Most cases have a multifactorial origin and it is admitted the influence on its pathogenesis of systemic diseases, different kind of drugs, psychogenic factors, cardiovascular, endocrinological and neurological diseases. Neurologic cause erectile dysfunction may have its origin in the central or peripheral nervous system. Among possible process of neurogenic erectile dysfunction of central origin would be tumors, cerebral vascular accidents, encephalitis, Parkinson disease, multiple sclerosis and other demyelinization diseases, dementias, olivopontocerebellar degeneration and epilepsy. Myelopathies of any etiology may be, depending on their localization and extension, cause of erectile dysfunction. At the peripheral level, disorders of the sensitive tracts constituting the afferent limb of the erection spinal reflex, and the efferent vegetative or somatic tracts mediating arterial vasodilatation, cavernous smooth muscle relaxation or pelvic floor striated muscle contraction. The aim of this work is to review in detail the most relevant causes of neurogenic erectile dysfunction, their etiopathogenic mechanisms and therapeutic approaches currently considered more adequate for each particular case. The correct diagnostic approach to patients with erectile dysfunction passes through identification, if possible, of the etiopathogenic factors implied. Regarding this, detection and identification of a possible neurogenic risk factor will contribute to a better understanding of the physiopathologic mechanisms, and more adequate diagnostic, prognostic and therapeutic approaches, mainly in those patients refractory to first line therapy.

Alterations of NOS, arginase, and DDAH protein expression in rabbit cavernous tissue after administration of cigarette smoke extract

Cigarette smoking is an independent risk factor for vasculogenic erectile dysfunction (ED). Nitric oxide (NO) has been demonstrated to be the principal mediator of cavernous smooth muscle relaxation and penile erection. Therefore, we examined whether or not enzyme activities and factors involved in the NO generation pathway are affected in rabbit corpus cavernosum after administration of nicotine- and tar-free cigarette smoke extract (CSE). CSE was prepared by bubbling a stream of cigarette smoke into phosphate-buffered saline. CSE was injected subcutaneously into adult male rabbits once a day for 5 wk. In the CSE group, significantly decreased cyclic GMP production as a marker of NO generation was associated with attenuated overall nitric oxide synthase (NOS) activity, enhanced arginase activity, accumulation of endogenous NOS inhibitors such as monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA), and decreased dimethylarginine dimethylaminohydrolase (DDAH) activity as an metabolizing enzyme of endogenous NOS inhibitors. Neuronal NOS (nNOS) and DDAH I protein expression were decreased without altering endothelial NOS expression, while arginase I expression was upregulated. These results suggest that impaired NO production would result from blunted NOS activity, which is possibly brought about by the downregulation of nNOS protein, accumulation of endogenous NOS inhibitors, and enhanced arginase activity together with upregulation of arginase I protein in cavernous tissue. The impaired DDAH activity due to decreased expression of DDAH I protein would result in an accumulation of endogenous NOS inhibitors with CSE. These alterations may be relevant to induction of the erectile dysfunction following CSE.

Effects of l-norgestrel on the endothelium-dependent relaxation response of rabbit clitoral cavernous smooth muscles

To determine the effect of a popular oral contraceptive, L-norgestrel (a synthetic progestogen), on relaxing response of clitoral cavernous smooth muscles. Prospective, randomized study. Academic facility. Thirty adult female New Zealand White rabbits. We conducted isometric tension studies with norepinephrine, endothelium-dependent (acetylcholine) and endothelium-independent (sodium nitroprusside) vasodilators, and L-norgestrel. The effects of nonspecific nitric oxide synthase inhibitor (N(w)-nitro-L-arginine methyl ester) and the potassium channel blockers (1 and 10 mM tetraethylammonium as well as 10 microM glibenclamide) on the reactivities of clitoral cavernous strips were investigated. Causation and power of developed tension after treatment. Acetylcholine, sodium nitroprusside, and L-norgestrel produced concentration-dependent relaxation of the norepinephrine-precontracted strips. Both endothelium removal and treatment with 10 microM N(w)-nitro-L-arginine methyl ester completely inhibited the relaxation response to acetylcholine and L-norgestrel, and supplementation with 10 mM L-arginine partially reversed the inhibition. Incubation with either tetraethylammonium (TEA) or glibenclamide reduced the L-norgestrel-induced relaxation in a dose-independent manner. The L-norgestrel-induced relaxation of the clitoral cavernous smooth muscle is endothelium and nitric oxide dependent and may be related to more than two types of potassium channels activation.

Butea superba Roxb. enhances Penile erection in rats

This study aimed to investigate the effects of ethanol extracts of Butea superba in increasing intracavernous pressure (ICP) in vivo. The extracts were prepared from fresh and dried root cores and fresh and dried root barks. Penile erection was induced in aged rats by electrical stimulation of the cavernous nerve. Cavernous smooth muscle relaxation was also observed in vitro in the presence of the extract, cGMP or isobutyl-methylxanthine (IBMX) alone or the extract together with cGMP or IBMX. The dried root core extract from Phrae was the most effective in increasing the ICP. The dose-response relationship study revealed a bell-shape curve with the maximum effective dose at 1 mg/kg. The ICP of the control and 1 mg/kg extract-treated animals were 45.3 +/- 2.5 and 100.9 +/- 14.0 mmHg, respectively. The extract, cGMP and IBMX alone induced dose dependent muscle relaxation. B. superba significantly enhanced the effects of cGMP and IBMX. The results suggest that ethanol extracts of B. superba are effective in enhancing penile erection. The dried root core extract from Phrae is the most effective part with a maximal dose of 1 mg/kg. The results also suggest that B. superba may act through cAMP/cGMP pathways.

Treatment with Hypotensive Agents Affects the Impaired Relaxation of the Penile Corpus Cavernosum in Hypertensive Rats

Treatment of erectile dysfunction (ED) in hypertensive subjects remains to be formally established. There is currently no standardized treatment for ED in hypertensive subjects. In this study, we tested our hypothesis that hypotensive drugs would improve impaired relaxation in the corpus cavernosum of spontaneously hypertensive rats (SHR). Ten-week-old SHR was treated with amlodipine, imidapril or hydralazine for 4 weeks. Although all three drugs achieved an equivalent decrease in systolic blood pressure (SBP), only amlodipine and imidapril induced an increase in relaxation in response to electrical field stimulation (EFS) of the corpus cavernosum. In the case of amlodipine, this effect was dose- and SBP-dependent. Nitric oxide (NO)-dependent relaxation was increased by amlodipine over a wide range of EFS frequencies, was increased by imidapril at low EFS frequencies, and was decreased by hydralazine. Carbon monoxide (CO)-dependent relaxation was only increased by hydralazine, and this increase occurred over a wide range of frequencies. The NOx and cGMP levels in the EFS-stimulated corpus cavernosum were increased by amlodipine. Amlodipine did not affect the thiobarbituric acid-reacting substance levels in the serum and the corpus cavernosum, but did decrease superoxide dismutase activity in the tissue. Imidapril and hydralazine inhibited the acetylcholine-induced relaxation in the corpus cavernosum. Sodium nitroprusside-induced relaxation in the tissue was increased by amlodipine. All three agents similarly inhibited the phenylephrine-induced contraction. These results suggest that impaired neurogenic relaxation in the corpus cavernosum of SHR is improved by amlodipine and imidapril through an increase in the synthesis and/or release of neuronal NO, but not CO, and presumably the inhibited detumescence of erection, which is induced by norepinephrine being released from sympathetic neuron. These findings indicate that amlodipine and imidapril may ameliorate the decreased relaxation of cavernous smooth muscle in the setting of hypertension.

ORIGINAL RESEARCH—BASIC SCIENCE: Cyclic Nucleotide Signaling in Cavernous Smooth Muscle

ABSTRACT Introduction Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. Aims To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed. Methods Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation. Results More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG). Conclusions The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

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 ω-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 μg) 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.

Nitric oxide-cyclic GMP pathway with some emphasis on cavernosal contractility.

Nitric oxide (NO) is formed from the conversion of L-arginine by nitric oxide synthase (NOS), which exists in three isoforms: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). nNOS is expressed in penile neurons innervating the corpus cavernosum, and eNOS protein expression has been identified primarily in both cavernosal smooth muscle and endothelium. NO is released from nerve endings and endothelial cells and stimulates the activity of soluble guanylate cyclase (sGC), leading to an increase in cyclic guanosine-3',5'-monophosphate (cGMP) and, finally, to calcium depletion from the cytosolic space and cavernous smooth muscle relaxation. The effects of cGMP are mediated by cGMP dependent protein kinases, cGMP-gated ion channels, and cGMP-regulated phosphodiesterases (PDE). Thus, cGMP effect depends on the expression of a cell-specific cGMP-receptor protein in a given cell type. Numerous systemic vasculature diseases that cause erectile dysfunction (ED) are highly associated with endothelial dysfunction, which has been shown to contribute to decreased erectile function in men and a number of animal models of penile erection. Based on the increasing knowledge of intracellular signal propagation in cavernous smooth muscle tone regulation, selective PDE inhibitors have recently been introduced in the treatment of ED. Phosphodiesterase 5 (PDE5) inactivates cGMP, which terminates NO-cGMP-mediated smooth muscle relaxation. Inhibition of PDE5 is expected to enhance penile erection by preventing cGMP degradation. Development of pharmacologic agents with this effect has closely paralleled the emerging science.

Priapism

There are three different types of priapism: low-flow, ischemic, anoxic or veno-occlusive priapism; high-flow, arterial or nonischemic priapism; and recurrent or stuttering priapism. To provide recommendations/guidelines concerning state-of-the-art knowledge for the diagnosis and treatment of priapism. An International Consultation in collaboration with the major urology and sexual medicine associations assembled over 200 multidisciplinary experts from 60 countries into 17 committees. Committee members established specific objectives and scopes for various male and female sexual medicine topics. The recommendations concerning state-of-the-art knowledge in the respective sexual medicine topic represent the opinion of experts from five continents developed in a process over a 2-year period. Concerning the Priapism Committee, there were 10 experts from six countries. Expert opinion was based on grading of evidence-based medical literature, widespread internal committee discussion, public presentation and debate. Concerning ischemic priapism, persistent cavernous smooth muscle relaxation and failure of contraction is a compartment syndrome with increasing intracavernosal anoxia, rising pCO2 and acidosis. Urgent medical attention should be sought for an erection lasting >4 hours; 90% with priapism >24 hours develop complete erectile dysfunction. After diagnosis and counselling, intracavernosal aspiration and alpha-blockers should precede surgical shunting. Concerning high-flow priapism (congenital, traumatic or iatrogenic), intervention is not urgent and often unnecessary. Definitive management is by selective embolization with autologous blood clot. Concerning recurrent/stuttering priapism, the pathophysiology may be central or local (sickle cell disease). Management needs to be individualized; androgen deprivation has proved useful but has adverse effects. There is need for prospective, clinical trials to define safe and effective management strategies for patients with low-flow, high-flow or recurrent priapism.

Effects of estrogen on the relaxation response of rabbit clitoral cavernous smooth muscles.

We investigated whether estrogen has a peripheral effect on the smooth muscle relaxation response of the clitoris, similar to that of androgens in cavernous tissues of the penis. Forty-two New Zealand White female rabbits (2.3-2.7 kg) were randomly divided into control (sham operation) and bilateral oophorectomy groups (acute and chronic groups with or without estradiol replacement). The acute and chronic groups were killed at 5 days and 12 weeks post-oophorectomy, respectively. Relaxation responses of the clitoral cavernous strips to endothelium-dependent and independent vasodilators and electrical field stimulation (EFS) were observed. Serum total cholesterol and low-density lipoprotein increased significantly and acetylcholine-induced relaxation of the clitoral strips wa significantly attenuated in the oophorectomy group with chronic estrogen deficiency but not in the chronic oophorectomy group with estradiol replacement or in the acute estrogen deficiency group. No significant differences in the relaxation responses of the cavernous strips to sodium nitroprusside or to the non-adrenergic, non-cholinergic-selective relaxation response to the EFS were found among the control, acute and chronic estrogen deficiency groups. These findings suggest that estrogen may not have a direct peripheral effect on clitoral cavernous smooth muscle relaxation. Hypercholesterolemia might be a possible explanation for the impaired endothelium-dependent relaxation of clitoral smooth muscle in chronic estrogen deficiency.

Plasma levels of cyclic guanosine-3',5'-monophosphate in the cavernous and systemic blood of healthy males during different functional conditions of the penis.

The relaxation of cavernous arterial and trabecular smooth muscle is dependent upon the stimulation of guanylyl cyclase activity by nitric oxide (NO), which is released from nerve terminals and endothelial cells within the cavernous tissue, and the subsequent accumulation of cyclic guanosine-3',5'-monophosphate (cGMP) in the intracellular space. The present study was undertaken to determine whether or not plasma levels of cGMP in the systemic and cavernous blood of healthy male subjects change from penile flaccidity to tumescence, rigidity and detumescence. Fifteen adult healthy males were exposed to visual and tactile erotic stimuli to elicit penile tumescence and rigidity. Whole blood was simultaneously aspirated from the corpus cavernosum and the cubital vein in the respective penile stages, and cGMP was determined in plasma aliquots by means of a radioimmunoassay. Mean systemic and cavernous plasma levels of cGMP in the blood samples obtained from the healthy volunteers ranged from 1.2-1.7 pmol/ ml. cGMP levels in the systemic circulation and in the cavernous blood did not change during developing erection, rigidity and detumescence. No significant differences were found between cGMP plasma levels in the systemic and cavernous blood in the different penile stages. Our results may reflect the fact that the stimulation of NO production in healthy males during sexual arousal and developing penile erection either does not yield substantial quantities of cGMP or that the rate of cGMP-extrusion from cavernous smooth muscle cells into the extracellular space accounts only for a minor fraction of plasma cGMP. Moreover, basal levels of cGMP in the blood flushing the lacunar spaces of the cavernous body in the state of developing erection may conceal any local release of cGMP that may occur within the penile erectile tissue. Thus, we conclude that the quantification of cGMP is of no use in the evaluation of the physiologic mechanisms of penile erection in vivo.

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.

Effectiveness of Oral L-Arginine in First-Line Treatment of Erectile Dysfunction in a Controlled Crossover Study

Background and Aims: Relaxation of cavernous smooth muscle is a parasympathetic and non-adrenergic, non-cholinergic mediated process which requires nitric oxide (NO). NO is synthesized from L-arginine by NO synthase (NOS). Some studies report good clinical results under oral L-arginine medication in the treatment of erectile dysfunction. We examined the effectiveness and safety of L-arginine in the treatment of mixed-type impotence. Methods: 32 patients (mean age 51.6 years) with mixed-type impotence diagnosed according to the results of sexual history and urological examination were enrolled in a randomized, placebo-controlled, crossover comparison of an oral placebo with 3 × 500 mg L-arginine/day. A validated questionnaire (KEED) was used to define the grade of impotence with a score. The treatment consisted of two 17-day courses (50 tablets). After a 7-day washout period the patients who initially received the placebo for 17 days were switched to L-arginine and vice versa. We assessed the efficacy with the validated questionnaire at the end of each drug period. Results: 30 patients (94%) completed the whole treatment schedule. Five (17%) patients reported a significant improvement in erectile function at the end of the L-arginine phase and 6 (20%) patients after the placebo period. 17 (56%) patients showed little improvement with L-arginine and 13 (43%) with placebo. In 8 patients (27%) of the verum group there was either no change in the ED score or even a slight worsening. No statistical difference in the impotence scores were found. No drug-related adverse effects occurred with L-arginine treatment. Conclusion: Oral L-arginine 3 × 500 mg/day is not better than placebo as a first-line treatment for mixed-type impotence.