The role of prostaglandins in the aetiology and treatment of erectile dysfunction

Erectile Dysfunction in Men on the Rise: Is There a Link with Endocrine Disrupting Chemicals?

Erectile dysfunction (ED) is one of the most prevalent chronic conditions affecting men. ED can arise from disruptions during development, affecting the patterning of erectile tissues in the penis and/or disruptions in adulthood that impact sexual stimuli, neural pathways, molecular changes, and endocrine signalling that are required to drive erection. Sexual stimulation activates the parasympathetic system which causes nerve terminals in the penis to release nitric oxide (NO). As a result, the penile blood vessels dilate, allowing the penis to engorge with blood. This expansion subsequently compresses the veins surrounding the erectile tissue, restricting venous outflow. As a result, the blood pressure localised in the penis increases dramatically to produce a rigid erection, a process known as tumescence. The sympathetic pathway releases noradrenaline (NA) which causes detumescence: the reversion of the penis to the flaccid state. Androgen signalling is critical for erectile function through its role in penis development and in regulating the physiological processes driving erection in the adult. Interestingly, estrogen signalling is also implicated in penis development and potentially in processes which regulate erectile function during adulthood. Given that endocrine signalling has a prominent role in erectile function, it is likely that exposure to endocrine disrupting chemicals (EDCs) is a risk factor for ED, although this is an under-researched field. Thus, our review provides a detailed description of the underlying biology of erectile function with a focus on the role of endocrine signalling, exploring the potential link between EDCs and ED based on animal and human studies.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Regular use of ibuprofen reduces rat penile prostaglandins and induces cavernosal fibrosis

Ibuprofen is a commonly used non-steroidal anti-inflammatory drug that is noted for its favorable safety profile. It exerts its therapeutic effect through inhibition of prostaglandin (PG) production at inflammatory sites. However, the inhibition of PG synthesis at other sites is responsible for the occurrence of adverse events. Evidence regarding the effect of regular ibuprofen intake on penile PG homeostasis or penile histopathologic changes is lacking. The aim of this study was to examine the effect of regular administration of analgesic therapeutic doses of ibuprofen on penile PG E1 and F2α and penile microscopic changes of the treated rats. This study included four groups of adult male Wistar rats; a control group (I) injected intraperitoneally with saline (2 ml/kg/day) for 30 days and 3 ibuprofen-treated groups (IIa, IIb, and IIc) injected intraperitoneally with 6 mg/kg/day, 12 mg/kg/day, and 18 mg/kg/day ibuprofen, respectively, for 30 days, respectively. Mean levels of penile PGE1 and PGF2α in the control group were significantly higher than ibuprofen-treated groups IIa, IIb, and IIc. The percentage area of collagen around cavernous tissue was significantly higher in ibuprofen-treated groups IIa, IIb, and IIc than control rats. Our findings suggest that despite ibuprofen's safety profile, regular use of ibuprofen is associated with reduced penile PG and increased cavernosal fibrosis.

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.

Evaluation of some prostaglandins modulators on rat corpus cavernosum in-vitro: Is relaxation negatively affected by COX-inhibitors?

INTRODUCTION

Prostaglandins (PGs) play an important role in corpus cavernosum relaxation, as evidenced by alprostadil being used as a drug for erectile dysfunction. Reports about the effect of cyclooxygenase (COX) inhibitors on erectile function are highly contradictory.

AIM

To compare the potential effects of some COX inhibitors with varying COX-1/COX-2 selectivities (indomethacin, ketoprofen and diclofenac) with that of the selective COX-2 inhibitor (DFU) on corpus cavernosal tone in-vitro. The role played by PGE₁, PGI₂-analogue and PGE₄ receptor (EP₄)-agonist in controlling corpus cavernosum function and the modulation of their action by sildenafil is also studied.

METHODS

Organ bath experiments were performed using isolated rat corpus cavernosum. Direct relaxations and changes to electric field stimulation (EFS, 2-16 Hz, 60 V, 0.8 ms, 10 s train)-induced relaxation by the effect of the selected drugs were studied. Strips were precontracted using phenylephrine (PE, 10^-5 M). Results are expressed as mean ± SEM of 5-9 rats.

RESULTS

Alprostadil, iloprost and L902688 (selective EP₄ agonist) induced direct relaxation where L902688 showed greater relaxant effect. Sildenafil potentiated the E_max of alprostadil and iloprost but not L902688. EFS and acetylcholine (ACh)-induced relaxations were significantly potentiated in presence of indomethacin, ketoprofen and diclofenac (20, 100 μM) but not in presence of selective COX-2 inhibitor (DFU, 1 μM). GR32191B (Thromboxane A₂ receptor antagonist, 10^-6 M) significantly reduced the potentiatory effect of indomethacin. Only diclofenac succeeded to potentiate sodium nitroprusside (SNP)-induced relaxation.

CONCLUSIONS

EP₄ receptors may play an important nitric oxide (NO)/cGMP-independent role in corpus cavernosal relaxation. Nonselective COX inhibitors seem of no harm concerning cavernosal tissue relaxation, possibly because they inhibit the synthesis of the highly contracting mediator thromboxane A₂.

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.

Age-related changes in kallikreins-kinins system in rat corpus cavernosum

Many factors, such as nitric oxide synthase, androgen and growth factors, can regulate the tone of corpus cavernosum (CC) smooth muscle with an age-related tendency. It has been shown that the active metabolites of kallikreins-kinins system (KKS), including bradykinin, Lys-BK and Met-Lys-BK, can also relax the CC smooth muscle significantly in vitro. Our aim was to evaluate the specific association between KKS and age in rat CC. CC and thoracic aorta were isolated from rats at postnatal weeks (PW) of 2, 8, 12, 20, 30, 40 and 60, respectively. Tissue kallikrein-I (KLKI) and kinin B2 receptor (B2R) mRNA in CC and thoracic aorta were detected by real-time polymerase chain reaction (PCR). Protein expression of KLKI and B2R were determined with immunofluorescence in situ and Western blot. Real-time PCR, immunofluorescence in situ and Western blot all demonstrated that the age-related changes in expression of KLKI were similar between the CC and thoracic aorta. It significantly increased with age from PW2 to PW30, reached the peak at PW30 and then declined gradually. However, there was no statistically significant difference among PW30, PW40 and PW60. Similarly, the expression of B2R increased gradually with age reached and remained at the peak during adult stages and no significant differences were found among PW20, PW30 and PW40; then, it decreased significantly at PW60. The changes in the expression of B2R in CC and age-matched aorta were similar except that it was significantly less than that in the aorta at PW60. The expression of KLKI and B2R changed in an age-dependent pattern in rat CC and have a tendency to decline during ageing, which is of the same tendency as reported for erection capacity in ageing males and suggests why ageing is an independent predictor of ED, to some extent.

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.

Functional inhibition of erectile process in rats by indomethacin

OBJECTIVES

Despite the important role played by prostaglandins in the control of erection, the potential contribution of non-steroidal anti-inflammatory drugs in erectile dysfunction in experimental animals has not been investigated. We examined the effect of the selective COX-2 inhibitor, celexocib, and the non-selective COX-inhibitors, indomethacin and diclofenac on erectile process in vivo.

METHODS

Erectile responses to electrical stimulation of the cavernous nerve in anesthetized male rats were recorded after single and repeated administration and intracavernosal pressure/mean arterial pressure (ICP/MAP) was calculated. The effect on blood pressure during erection and total plasma nitrite/nitrate level was also investigated.

RESULTS

Single-dose administration of indomethacin significantly reduced erectile responses to electrical stimulation at all frequencies tested; 15 mg/kg further reduced ICP/MAP to 0.016 ± 0.005 compared to 0.064 ± 0.012 and 0.104 ± 0.035 for indomethacin (5 mg/kg) and control, respectively at 0.5 Hz. Longer-term treatment with indomethacin completely abolished erectile responses at low frequencies and significantly reduced ICP/MAP at higher frequencies, accompanied by significant reduction in total plasma nitrite/nitrate level. Diclofenac reduced erectile responses only at low frequencies in contrast to celexocib that failed to negatively affect erectile responses.

CONCLUSION

Indomethacin, and to a lower extent diclofenac, may adversely affect erectile responses in rats.

Treatment of Erectile Dysfunction: Update

Erectile dysfunction (ED) is the inability to achieve and maintain an erection. Erectile function is dependent upon complex interactions of neural and vascular pathways. A major neurotransmitter that facilitates erectile function is nitric oxide. Treatment of ED has expanded to include effective oral agents. Previous ED treatments have consisted of intracavernosal injection, transurethral dilators, and vascular constriction devices. Clinical management of ED will be presented with some discussion on the prostatectomy client.

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.

Plasma levels of endothelin-1, angiotensin II, nitric oxide and prostaglandin E2 in the venous and cavernosal blood of patients with erectile dysfunction

OBJECTIVES

To determine the alterations in the plasma levels of endothelin-1, angiotensin II, nitric oxide (NO) and prostaglandin E(2) (PGE(2)) in the venous and cavernosal blood of patients with organic and psychogenic erectile dysfunction (ED).

PATIENTS, SUBJECTS AND METHODS

The study included 32 patients complaining of ED; they were subdivided into two equal groups with either organic or psychogenic ED. Fifteen healthy potent age-matched male volunteers were enrolled as a control group. For each patient, venous and cavernosal blood samples were obtained, while venous blood was obtained from the controls.

RESULTS

There were significantly greater mean plasma levels of endothelin-1 and angiotensin II, and significantly lower mean plasma levels of NO and PGE(2), in the venous blood of patients with ED than in the controls. Patients with organic ED had significantly higher levels of endothelin-1 and significantly lower levels of NO in both venous and cavernosal blood than had those with psychogenic ED. There were significant positive correlations in both venous and cavernosal blood between endothelin-1 and angiotensin II, and between NO and PGE(2) in all patients with ED and the two subgroups. There were significant negative correlations between venous and cavernosal endothelin-1 and NO, endothelin-1 and PGE(2), angiotensin II and NO, and between angiotensin II and PGE(2).

CONCLUSION

The present results suggest that endothelin-1 could be a clinical marker of diffuse endothelial disease manifested by ED. As angiotensin-converting enzyme (ACE) activity controls angiotensin II there might be a rationale for the use of ACE inhibitors to prevent or treat ED. NO and PGE(2) may provide new strategies for the pharmacological treatment of ED.

Effects of the Rho-kinase inhibitors, Y-27632 and fasudil, on the corpus cavernosum from diabetic mice

Relaxant responses to two Rho-kinase inhibitors, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632) and fasudil, were compared in the corpus cavernosum obtained from diabetic and non-diabetic mice. Streptozotocin (100 mg kg(-1) day(-1), for 2 days) induced diabetes with a blood glucose level of 318+/-55.4 mg dl(-1); whereas it was 85.4+/-4.1 mg dl(-1) in control mice (P<0.05). Electrical field stimulation (40 V, 0.5 ms, 1, 2, 4, 8, 16 Hz for 15 s) and acetylcholine-induced relaxations were markedly attenuated in the corpus cavernosum from streptozotocin-diabetic mice whereas responses to Y-27632 (10(-9)-3 x 10(-5) M) and fasudil (10(-9)-3 x 10(-5) M) were not altered. EC(50) values for Y-27632 were 2.98+/-0.89 and 4.19+/-2.71 microM in the corpus cavernosum from control and diabetic mice, respectively (P>0.05). The values for fasudil were 7.42+/-4.91 and 3.53+/-1.41 microM in the corpus cavernosum from control and diabetic mice, respectively (P>0.05). These results may suggest that, in diabetes, the relaxant effects of the Rho-kinase inhibitors may not be changed and thus, they may have a beneficial therapeutic effect in diabetic erectile dysfunction.

New achievements and pharmacotherapeutic approaches to impotence in the elderly

Erectile dysfunction (ED) has a negative impact on the quality of life of elderly men, but impotence is not an absolute concomitant of aging. Aging changes influencing sexual function in men consist of a decreased capacity to reach arousal by imagination or view, fragility of erection, and an increase in the refractory period. These events may be part of the andropause syndrome, which includes a decrease in intellectual activity, fatigue, depression, decreases in body hair, lean body mass and bone mineral density, accompanied by an increase in weight. As a consequence, the overlap of aging processes, concurrent diseases and social situations to which elderly men are subject, results in the great variability reported in epidemiological studies. In the same way, the complex physiology of erection depends on the social, environmental, or physical context in which it occurs. New achievements in research on intracellular mechanisms of erection and on the neuroendocrinology of aging contribute to better understanding the pathophysiology of ED in the elderly. For example, testosterone declines with age with great interindividual variability, since other hormonal changes are also involved. What currently can be easily identified is the alteration of LH-testosterone feedback alterations, although hormone levels fall in the normal range. Nevertheless, the extent to which age-dependent decline in hormones leads to health problems that may affect the quality of life remains to be clarified. Several concepts on aging-related processes have been challenged, and conditions that were once accepted as physiologically age-related are now thought to lead to medical problems, but until now erectile dysfunction remains underreported, underdiagnosed, and undertreated, especially in the elderly. Nowadays, we are witnessing a rapid growth in available pharmacotherapies, from intracavernous injections of vasoactive drugs, to powerful new oral agents, with differing pharmacological dynamic and kinetic properties. New options for treatment are therefore possible, taking into account both the possibility of changing ineffective drugs and augmenting efficacy by means of synergistic associations. This rich generation of progress is certainly contributing to a better medical approach to sexuality in aging people.

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.

Expression of PGT in MDCK cell monolayers: polarized apical localization and induction of active PG transport

The PG transporter (PGT) is expressed in subapical vesicles in the kidney collecting duct. To gain insight into the possible function of the PGT in this tubule segment, we tagged rat PGT with green fluorescent protein at the COOH terminus and generated stable PGT-expressing Madin-Darby canine kidney cell lines. When grown on permeable filters, green fluorescent protein-PGT was expressed predominantly at the apical membrane. Although the basal-to-apical transepithelial flux of [(3)H]PGE(2) was little changed by PGT expression, the apical-to-basolateral flux was increased 100-fold compared with wild-type cells. Analysis of driving forces revealed that this flux represents PGT-mediated active transepithelial PGE(2) transport. We propose that endogenous PGT is exocytically inserted into the collecting duct apical membrane, where it could control the concentration of luminal PGs.

Impulse magnetic-field therapy for erectile dysfunction: a double-blind, placebo-controlled study

This double-blind, placebo-controlled study assessed the efficacy of 3 weeks of impulse magnetic-field therapy for erectile dysfunction (ED). Twenty volunteers who suffered from ED or orgasmic disturbances were randomly assigned to either active treatment or placebo (n = 10 each). Efficacy was assessed in terms of intensity and duration of erection, general well-being, sexual activity, and warm sensation in the genital area. In the active-treatment group, all efficacy endpoints were significantly improved at study end (P < or = .01), with 80% reporting increases in intensity and duration of erection, frequency of genital warmth, and general well-being. The remaining 20%, who experienced minor improvements, were found to have an influenza-like infection after the study that may have influenced their results. Only 30% of the placebo group noted some improvement in their sexual activity; 70% had no change. No side effects were reported.

MUSE: clinical experience

INTRODUCTION

In the UK, an estimated 17-19% of men suffer from erectile dysfunction (ED). Until the introduction of sildenafil, the medical treatment of ED mainly depended on intracavernosal injections. The introduction of MUSE has generated interest, since it obviates the use of 'needles'. MUSE is an intra-urethral method of alprostadil (prostaglandin E1 analogue) administration. We investigated the safety and efficacy of MUSE in 100 patients.

PATIENTS AND METHODS

After confirming the diagnosis of ED, treatment was started with MUSE. Once we were satisfied that the patients could self-administer MUSE, they were discharged from our clinic. They were contacted six months later and asked to complete a questionnaire.

RESULTS

Only 35% of the 100 patients (aged 46-73 years) with ED of mixed aetiology were initially successfully treated with MUSE. All but two of them needed 1,000 microg. After six months, only 43% of these initially successfully treated patients continued to use MUSE; of these, 33% only found it effective on every third occasion, or worse. The remaining 57% of the initially successfully treated patients stopped taking MUSE because it was no longer effective or it caused side-effects (such as urethral bleeding and/or irritation).

DISCUSSION

MUSE, in our experience, is moderately effective in treating ED. However, MUSE is an alternative in some patients with ED who do not respond to other treatments or where these options are contraindicated. Owing to the high dropout rate, patients treated with MUSE should be followed-up closely.

The choice of antihypertensive drugs in patients with erectile dysfunction

It is well established that hypertension and the more traditional anti-hypertensive drugs are associated with erectile dysfunction (ED). There is evidence showing that two antihypertensive drugs--doxazosin and losartan--have a positive effect on erectile function. Therefore these drugs may decrease the incidence of ED in patients who need treatment for hypertension. Doxazosin and/or losartan can also be beneficial in patients who develop ED after starting treatment with other antihypertensive drugs. These options could, in turn, ensure better compliance and blood pressure control. A fall in the overall cost of treatment will also be anticipated if there is a reduced need for drugs prescribed for ED in patients with hypertension.

Management of erectile dysfunction following radical prostatectomy

Radical prostatectomy is the standard treatment for organ/specimen-confined prostate cancer, yet erectile dysfunction in selected series is still reported as high as 90% after this procedure. Thus, most men need adjuvant treatments to be sexually active following radical prostatectomy. These include vacuum constriction devices, intracorporeal injections of vasoactive drugs, and transurethral dilators, all of which have reported response rates of 50% to 70%. Unfortunately, long-term compliance is suboptimal, with a discontinuation rate of nearly 50% at one year. These non-oral options should be offered on an individual basis to patients who have failed oral therapy since efficacy and compliance vary. Also, these options should be considered in the early postoperative period to enhance sexual activity and penile oxygenation, which may prevent corporeal fibrosis. Early penile rehabilitation with intracavernosal injections or vacuum constriction devices should be encouraged to increase chances for recovery of rigid erections. In patients with some preservation of nerve tissue, oral sildenafil may be effective in promoting an earlier return of erectile function. The potential impact of sildenafil and other new oral therapies should encourage urologists to continue to perform and perfect the nerve-sparing approach.

Neuropathy is a major contributing factor to diabetic erectile dysfunction

Erectile dysfunction (ED) in diabetes is multifactorial. So far, the impact of neuropathy has not been well determined. This study was performed to assess the frequency of abnormal neurophysiological tests in patients with ED due to diabetes compared to patients with ED due to nondiabetic neuropathies in order to estimate the contribution of neuropathy in diabetic ED. Forty-nine men with ED were studied. We classified ED as 'diabetic', 'neuropathic' or 'ED of other origin'. 26.6% of the men fulfilled the criteria of diabetic ED, 42.9% had neuropathic ED. In every patient history taking, a questionnaire focusing on autonomic symptoms other than ED, clinical examination, nerve conduction studies (NCS), sphincter ani electromyography (EMG), heart rate variability testing (HRV) and quantitative sensory testing (QST) was performed. Vascular function was assessed by the intracavernosal prostaglandin E1 (PGE1) injection test. The frequency of abnormal results in diabetic and neuropathic patients was compared. Vascular function was abnormal in only one patient with diabetic ED and three patients with neuropathic ED. Both groups had similar frequencies of autonomic symptoms other than ED (64% in diabetic vs. 64% in neuropathic patients), abnormal EMG (33% vs. 40%) and abnormal QST (vibratory perception 83% vs. 84%, cold perception 9% vs. 19%, warm perception 42% vs. 43%). Abnormal clinical findings (50% vs. 33%), NCS (75% vs. 50%) and HRV (39% vs. 25%) were slightly, but not significantly more frequent in men with diabetic ED than neuropathic ED. The tests indicating neuropathy showed abnormalities in men with diabetic ED as frequently as in men with neuropathic ED. Some tests even suggested neuropathy more often in diabetic than in neuropathic ED. The findings support the hypothesis that neuropathy contributes significantly to the pathophysiology of ED in diabetes mellitus.

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.

RhoA/Rho-kinase: a novel player in the regulation of penile erection

Current research has centered around the role of nitric oxide in the stimulation of cavernosal vasodilation and erection. However, recent evidence from our lab details the importance of endogenous vasoconstrictor mechanisms in maintaining a flaccid penile state, and further demonstrates that the inhibition of endogenous vasoconstriction is sufficient to stimulate erection in a rat model. In this article, we suggest inhibition of endogenous vasoconstriction as a potential therapeutic avenue in the treatment of erectile dysfunction. We also speculate on potential physiologic mechanisms by which endogenous vasoconstriction is inhibited in order for arousal-initiated vasorelaxation, and erection, to occur.

The role of prostaglandins in penile erection

The balance of penile smooth muscle tone is finely controlled, with contractile factors acting in opposition to relaxant factors. The principal agents in this process are undoubtedly noradrenaline and nitric oxide. Prostaglandins probably have a crucial role in the 'fine tuning' of corporal smooth muscle tone. Their effects on control mechanisms in the healthy penis are more likely to be modulatory rather than direct.