雄激素缺乏与勃起功能障碍

雄激素可通过增强性欲、性唤起等间接促进阴茎勃起,在维持阴茎正常的勃起组织结构方面起重要作用。睾酮缺乏可导致小梁平滑肌减少、细胞外基质增多、白膜下脂肪细胞沉积等。勃起时,阴茎组织的上述改变可引起静脉闭塞不全而发生静脉漏,从而出现勃起功能障碍;睾酮还可影响一氧化氮合酶(NOS)、RhoA/Rho激酶的表达及活性从而直接影响阴茎勃起。对单用磷酸二酯酶5(PDE5)抑制剂无反应的性腺功能减退的ED患者补充睾酮可收到良好的治疗效果。     

Intracavernosal vascular endothelial growth factor (VEGF) injection and adeno-associated virus-mediated VEGF gene therapy prevent and reverse venogenic erectile dysfunction in rats

Penile veno-occlusive dysfunction (venogenic erectile dysfunction) is a common cause of erectile dysfunction (ED). We investigated whether vascular endothelial growth factor (VEGF) can be used to prevent and reverse venogenic ED in a rat model. Pharmacological cavernosometry was developed and validated using adult male rats with either arteriogenic or venogenic ED. Castrated animals were treated with intracavernous VEGF as either a recombinant protein (C+VEGF) or adeno-associated virus (AAV)-mediated VEGF gene therapy (C+VEGF gene) in an attempt to prevent the development of venogenic ED. Other animal groups received testosterone replacement (C+testosterone) or intracavernous AAV-LacZ gene (C+LacZ). Animals with documented venogenic ED were treated with intracavernous VEGF in an attempt to reverse their ED. Functional analysis (pharmacological infusion cavernosometry) was performed following treatment. Penile specimens were harvested for immunohistochemistry and electron microscopic evaluation. Castrated rats showed a decrease in papaverine-induced intracavernous pressure and an increase in maintenance and drop rates during pharmacological cavernosometry. These changes were prevented by systemic testosterone and intracavernous VEGF or AAV-VEGF therapy. Moreover, intracavernous VEGF was able to reverse the venogenic ED produced by castration. The quantity of penile smooth muscle detected by alpha actin staining decreased after castration but not in the C+T, C+VEGF, or C+VEGF gene groups. Transmission electron microscopy revealed atrophy of penile smooth muscle cells and nerves in the castrated rats. In VEGF-treated rats, regeneration of smooth muscle and nerves as well as endothelial cell hypertrophy and hyperplasia were the prominent features. In our animal model, systemic testosterone replacement or intracavernous VEGF (protein and VEGF gene) prevented the veno-occlusive dysfunction in castrated animals. In rats with established venous leakage, VEGF treatment reversed the cavernosometric findings of leakage. Intracavernous injection of either VEGF protein or VEGF gene may be a preferred therapy to preserve erectile function in patients in whom testosterone therapy is contraindicated.     

The effects of chronic phosphodiesterase-5 inhibitor use on different organ systems

Phosphodiesterase-5 (PDE-5) inhibitors selectively inhibit PDE-5 enzymes that are present in various tissues like penile tissue, platelets, vascular, and smooth muscle tissue. The drug's actions on these tissues have lead to the successful therapeutic use in patients suffering from conditions such as erectile dysfunction (ED) and pulmonary hypertension. PDE-5 inhibitors (PDE-5i) act on the erectile tissue causing penile smooth muscle relaxation and vasodilatation leading to penile erection. In addition, in particular when used in conjunction with prostaglandin inhibitors, PDE-5i cause vasodilatation in pulmonary vasculature hence decreasing both the pulmonary arterial pressure and resistance. PDE-5i have also shown to mildly decrease blood pressure, increase cardiac index, and increase coronary blood flow in experimental animals as well as in human studies. The Food and Drug Administration (FDA) has approved three PDE-5i for the treatment of ED: sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) and one for pulmonary hypertension: sildenafil (Revatio). These agents are highly selective for PDE-5 enzymes as compared to other subclasses of PDE enzymes and have the almost identical pharmacological action but slightly different pharmacokinetics. Only little data exist about long-term use of PDE-5i and their effects on different organ system. This paper reviews the current information available on chronic PDE-5 inhibitor use.     

Hormonal supplementation and erectile dysfunction

The role of testosterone on sexual desire is well established. However, the effects of low testosterone levels in the pathophysiology of erectile mechanism in humans remains unclear. Recent evidence indicate that approximately 10-20% of men with erectile dysfunction (ED) have hormonal abnormalities, raising up to 35% over the age of sixty. It is now clear that sexual desire and erectile function in humans are both responsive to androgens, probably at different threshold values. In fact, different degrees of testosterone deficiency may determine a sequence of molecular penile events leading to reduced capacity of penile smooth muscle and endothelial cells of relaxation, without greatly affecting sexual desire. Also, androgens may directly control the expression and activity of phosphodiesterase type-5 in human corpus cavernosum. In some selected men with total testosterone below 10-13nmol/l and/or free testosterone below 200-250pmol/l, androgen supplementation may improve therapeutic efficacy of phosphodiesterase type-5 inhibitors. For ageing men with partial androgen deficiency (PADAM) who fail first-line oral treatments in whom androgens are not contraindicated, a combination of testosterone and phosphodiesterase type-5 inhibitors may be considered to improve erectile function and improve the quality of life.     

Sexual functions of men with obstructive sleep apnoea syndrome and hypogonadism may improve upon testosterone administration: a pilot study

This study examined 72 patients with obstructive sleep apnoea syndrome (OSAS), confirmed by polysomnography. Thirty-two patients were suffering from erectile dysfunction (ED) assessed by IIEF-5 questionnaires and confirmed by nocturnal penile tumescence examination. Their testosterone levels were measured. Eight patients had normal testosterone levels and were treated with a PDE-5 inhibitor (vardenafil) only; after 6 months of treatment, 6 of these patients (75%) showed significant improvement in erectile function. The remaining 24 patients with OSAS, ED and hypogonadism (total testosterone <12 nmol l⁻¹), were divided into two groups based on the indication for continuous positive airway pressure (CPAP) therapy: five patients received CPAP therapy (group 1) and 19 patients did not (group 2). The patients of group 2 received only a PDE-5 inhibitor (vardenafil 20 mg) for ED; and eight patients (42%) showed an improvement after 3 months of treatment. The five patients receiving CPAP therapy were treated with a combination of parenteral testosterone undecanoate and a PDE-5 inhibitor (vardenafil) and all had normal erectile function after 3 months of therapy. The results suggest positive effects of addition of testosterone to treatment with PDE-5 inhibitors in hypogonadal men with OSAS, which should be confirmed in larger controlled studies.     

Phosphodiesterase-5 inhibition: the molecular biology of erectile function and dysfunction

This article discusses the role of phosphodiesterase-5 (PDE-5) inhibition in the molecular biology of erectile function and dysfunction. Commercially marketed PDE-5 inhibitors are highly specific for PDE-5, and in the face of continuing cyclic GMP (cGMP) synthesis,elevate cellular cGMP. This elevation results from direct competitive inhibition of PDE-5 and from blocking the negative feedback regulation of the enzyme. Elevation of cGMP activates cGMP-dependent protein kinase, which mediates the effects of the cGMP-signaling pathway to decrease smooth muscle tone and dilate penile vascular smooth muscle. By exploiting features of PDE-5 regulatory mechanisms that modulate PDE-5 function, the inhibitors enhance their own potencies.     

Effects of testosterone on erectile function: implications for the therapy of erectile dysfunction

Sexual potency declines with age, as does the efficiency of erection. Many studies show that different patterns of erectile dysfunction (ED), varying from occasional inability to obtain a full erection, impairment throughout intercourse and total absence of erectile response, might not be triggered by psychological factors only. Recent research indicates that ED relies on organic causes, and has challenged the development of new therapies. One therapeutic approach in patients who have testosterone deficiency is based on androgen therapy. Thus, we reviewed data on testosterone-induced effects relative to erectile function, summarizing the results from studies reported in 1991-2006 on testosterone therapy in patients with ED and hypogonadism, with a special focus on men not responding to phosphodiesterase-5 (PDE-5) inhibitors. We searched several computerized databases parallel with printed bibliographic references. Many studies have established animal models, which confirm that testosterone is important in modulating the central and peripheral regulation of ED. Testosterone deprivation has a strong negative impact on the structure of penile tissues and erectile nerves, which can be prevented by androgen administration. Combined therapy regimens with PDE-5 inhibitors and testosterone might improve ED in patients with hypogonadism of different causes. Thus, androgen treatment in hypogonadic patients, including those unresponsive to PDE-5 inhibitors, often results in an improvement of ED. Testosterone therapy is safe and convenient, while rapidly correcting low testosterone levels.     

Erectile dysfunction and treatment of carcinoma of the prostate

Prostate cancer is the leading malignancy in men in the United States and causes more than 60,000 deaths annually. Treatment of prostate cancer, whether it be with surgery, radiation therapy, cryotherapy, or medical treatment, is associated with significant life-altering morbidity. Incontinence and erectile dysfunction (ED) too often are sequelae of these treatment alternatives. ED can be a significant complication and can alter the life of the patient with prostate cancer and his partner. Newer modifications of the radical prostatectomy with nerve-sparing techniques are the cornerstone of erection preservation. Time following radical prostatectomy has been shown to increase erectile function such that more patients have functional erections at 3 years than 1 year after surgery. With the advent of phosphodiesterase-5 (PDE-5) inhibitors, many men can have improved functional erections and return to active coitus. Prevention of ED also is an important management technique. Evidence is gathering that prophylaxis with regular vasoactive injection or daily PDE-5 agents may be an integral part of preservation of corpus cavernosum smooth muscle function. Combination medical therapy and surgical penile prosthesis implantation also are options for patients who do not respond to oral PDE-5 inhibitors.     

Testosteron und erektile Dysfunktion

Primary hypogonadism represents a classic but rare cause of erectile dysfunction (ED) in men. Therapy with testosterone as monotherapy is therefore unlikely to cure ED in the typical ED patient. However, recent developments indicate a much greater role of testosterone in erectile function than has been supposed in the past. Serum testosterone levels decline in men with increasing age. Aging men might develop late-onset hypogonadism (LOH) associated with characteristic symptoms. Typical symptoms of LOH are represented by decreased libido and sexual function, osteoporosis, altered distribution of body fat, overall reduction in physical strength, and alterations in the general mood. Experimental and clinical studies over the last few years have also pointed out that hypogonadism results in characteristic alterations of the erectile tissue of the penis. These alterations might be reversible in response to hormone therapy with testosterone. Particularly testosterone might be a helpful supportive therapy in cases where PDE-5 antagonists have tended to lose their effectiveness on the erectile tissue in the treatment of ED.     

Synergetic effect of testosterone and phophodiesterase-5 inhibitors in hypogonadal men with erectile dysfunction: A systematic review

Testosterone deficiency seems to impair the clinical response to phophodiesterase-5 (PDE-5) inhibitors in patients with erectile dysfunction (ED). In hypogonadal men, testosterone repletion was associated with enhanced sexual function in patients who failed initial treatment with sildenafil or tadalafil. We conducted a systematic review of studies that evaluated combination therapy of testosterone and PDE-5 inhibitors in patients with ED and low, low-normal testosterone levels who failed monotherapy. The studies we examine are heterogeneous with several methodological drawbacks and that, overall, the addition of testosterone to PDE-5 inhibitors might benefit patients with ED associated with testosterone <300 ng/dL (10.4 nmol/L) who failed monotherapy. Further studies, with a randomized placebo-controlled and double blind design, are needed to describe the appropriate target patient group, testosterone cut-off and to define the optimal dose and duration of combination therapy.     

Molecular mechanisms and pharmacokinetics of phosphodiesterase-5 antagonists

The prominence of phosphodiesterase-5 (PDE-5) inhibitors in the treatment of male erectile dysfunction and other diseases related to vascular dysfunction mandates a comprehensive understanding of the properties and effects of these compounds. Three potent and selective PDE-5 inhibitors (sildenafil, tadalafil, and vardenafil) have been approved for clinical use. The clinical efficacy and safety profiles of these medications are related to their molecular mode of action, the selectivity for PDE-5, and the pharmacokinetic properties (absorption, bioavailability, time to onset of action, distribution, metabolism, and elimination). These PDE-5 inhibitors share some common properties with regard to mechanisms of action and selectivities for PDE-5. They also have distinctive characteristics that may impact their clinical use. This article focuses on the basic biochemistry of cyclic guanosine monophosphate signaling and the pharmacokinetic parameters that describe characteristics of drug action of these PDE-5 inhibitors in facilitating smooth muscle relaxation, leading to improved penile erectile response or causing side effects.     

Erectile dysfunction secondary to nerve-sparing radical retropubic prostatectomy: Comparative phosphodiesterase-5 inhibitor efficacy for therapy and novel prevention strategies

Postprostatectomy erectile dysfunction appears to be initiated by neuropraxia and perpetuated by cavernosal smooth muscle apoptosis. Phosphodiesterase-5 (PDE-5) inhibitor therapy is the current cornerstone of erectile dysfunction (ED) therapy in this population. Although no head-to-head trials have been performed with sildenafil, vardenafil, and tadalafil in this population, there are numerous studies in the general ED population. The results of these studies demonstrate that neither of the new PDE-5 inhibitors met statistical noninferiority to sildenafil. Sildenafil has been studied in a novel primary prevention modality using nightly administration after a bilateral nerve-sparing prostatectomy. In this novel approach, it effected a sevenfold improvement in return of spontaneous, normal erectile function 2 months after drug discontinuation. This effect appears to be mediated by properties unique to sildenafil that include improved endothelial function and neuronal regeneration and neuroprotection. In primary prevention, unlike ED therapy, one has only “one shot” by definition. Therefore, it is even more critical to apply evidence-based medicine.     

Pathophysiology of Erectile Dysfunction

Physiology of erection and pathophysiology erectile dysfunction is reviewed. Analysis is obtained from basic and clinical research including animals studies, anatomical studies, and molecular and cellular research on corporal tissue obtained during penile prosthesis implantation. Supraspinal influences and spinal influence on penile erection has been learned from spinal cord injury patient. Corporal smooth muscle relaxation of penile arteries and corpus cavernosum leads to penile erection, results from parasympathetic/nonadrenergic noncholinergic neural pathway activation and simultaneous inhibition of sympathetic outflow. Anatomical studies taught understanding of the mechanism for restriction of blood outflow from the corpora cavernosa. The change of smooth muscle tone has emerged as a key factor in erection and detumescence. Many independent factors converge on the modulation of corporal smooth muscle tone. Neuronal and local neurotransmitter effects via gap junction, potassium channels, and calcium channel. A nitric oxide/cyclic guanosine monophosphate mechanism as well as cyclic aminomonophosphate has an important role in mediating the corporal smooth muscle relaxation necessary for erectile function. Erectile dysfunction can be due to vasculogenic, neurogenic, hormonal, veno-occlusive, psychogenic and/or pharmacogenic factors as well as alterations in the nitric oxide/cyclic guanosine monophosphate (cGMP) or cyclic aminophosphate (cAMP) pathway or other regulatory mechanisms including gap junction or ionic channel resulting in an imbalance in corporal smooth muscle contraction and relaxation. Our present knowledge of the hemodynamics, functional anatomy, neurophysiology, and neuropharmacology of penile erection and dysfunction at the cellular and molecular level has led to better understanding of physiology and pathophysiology of erectile dysfunction.     

Endothelial rehabilitation: the impact of chronic PDE5 inhibitors on erectile function and protein alterations in cavernous tissue of diabetic rats

BACKGROUND: Diabetic men generally have reduced efficacy with PDE-5 inhibitors (PDE5i) for the treatment of erectile dysfunction (ED). OBJECTIVE: To determine whether chronic vardenafil exposure alters cavernous protein expression predicting improved erectile function in diabetes. DESIGN: Forty-two adult male Sprague Dawley rats with streptozotocin-induced (50mg/kg IP) diabetes for 4 wk, were exposed to either vehicle or vardenafil for 6 wk. Assessments compared the impact of vardenafil given at 1h and 20 h to erectile function and cellular alterations and downstream translation of cavernous protein profiles were aimed. INTERVENTION: Vehicle or vardenafil 0.5mg/kg/day by oral gavage for 6 wk. MEASUREMENTS: Erectile function, penile tissue morphology, protein expression and surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI) protein profiling were determined. RESULTS AND LIMITATIONS: A significant increase of intracavernous pressure was seen in both treatment arms compared to diabetic rats not receiving vardenafil. Immunohistochemical staining showed improved endothelial and smooth muscle cell staining with chronic vardenafil use. Western blot analysis demonstrated increased endothelial cell eNOS and smooth muscle alpha-actin protein content. SELDI protein profiling showed enhanced proteins expression at molecular weights of 14.7, 20, 41.9, 66.2, and 83.9 kDa in the chronically treated vardenafil group. CONCLUSIONS: Vardenafil was effective in treating diabetic-induced ED with the greatest effect achieved through chronic dosing, with no additive effect measured with the final acute dose. Changes noted in the histology and protein expression indicate that vardenafil may have a protective effect in this disease state. This finding may serve as a basis for further work evaluating the utility of chronic vardenafil dosing in diabetic men.     

阴茎负压吸引治疗PDE5i无效型勃起功能障碍疗效分析(附70例报告)

目的:探讨使用Osbon助勃器阴茎负压治疗磷酸二酯酶抑制剂-5(PDE-5i)无效型勃起功能障碍(ED)患者的有效性和安全性。方法:收集口服PDE-5i无效ED患者70例,年龄25～66(38.9±9.1)岁,指导患者使用Osbon助勃器(美国Timm Medical公司)负压锻炼1个月;负压锻炼结束后,使用紧缩张力环进行性生活治疗,比较负压治疗前和治疗后3个月IIEF-5评分变化,以及患者和性伴侣的满意度,评价负压应用的安全性和有效性。结果:PDE-5i治疗无效的ED患者负压治疗后3个月IIEF-5评分较负压治疗前有显著提高(P<0.05),IIEF-5评分由治疗前(10.2±4.0)分上升到(13.3±4.7)分。负压治疗口服PDE-5i无效ED患者的有效率77.1%(54/70)。负压治疗后PDE-5i无效ED患者及性伴侣性生活满意率分别为64.3%(45/70)和65.7%(46/70)。结论:PDE-5i治疗无效型ED患者行阴茎负压治疗,可显著改善患者勃起功能及夫妻双方性生活满意率,值得临床应用。     

Gene therapy and erectile dysfunction： the current status

Current available treatment options for erectile dysfunction （ED） are effective but not without failure and/or side effects. Although the development of phosphodiesterase type 5 （PDE5） inhibitors （i.e. sildenafil, tadalafil and vardenafil） has revolutionized the treatment of ED, these oral medications require on-demand access and are not as effective in treating ED related to diabetic, post-prostatectomy and severe veno-occlusive disease states. Improvement in the treatment of ED is dependent on understanding the regulation of human corporal smooth muscle tone and on the identification of relevant molecular targets. Future ED therapies might consider the application of molecular technologies such as gene therapy. As a potential therapeutic tool, gene therapy might provide an effective and specific means for altering intracavernous pressure ＂on demand＂ without affecting resting penile function. However, the safety of gene therapy remains a major hurdle to overcome before being accepted as a mainstream treatment for ED. Gene therapy aims to cure the underlying conditions in ED, including fibrosis. Furthermore, gene therapy might help prolong the efficacy of the PDE5 inhibitors by improving penile nitric oxide bioactivity. It is feasible to apply gene therapy to the penis because of its location and accessibility, low penile circulatory flow in the flaccid state and the presence of endothelial lined （lacunar） spaces. This review provides a brief insight of the current role of gene therapy in the management of ED.     

Hypogonadism and erectile dysfunction： an overview

In humans androgen decline is presented as a clinical picture which includes decreased sexual interest, diminished erectile capasity, delayed or absent orgasms and reduced sexual pleasure. Additionally, changes in mood, diminished well being, fatigue, depression and irritability are also associated with androgen insufficiency. The critical role of androgens on the development, growth, and maintanence of the penis has been widely accepted. Although, the exact effect of androgens on erectile physiology still remains undetermined, recent experimental studies have broaden our understanding about the relationship between androgens and erectile function. Preclinical studies showed that androgen deprivation leads to penile tissue atrophy and alterations in the nerve structures of the penis. Furthermore, androgen deprivation caused to accumulation of fat containing cells and decreased protein expression of endothelial and neuronal nitric oxide synthases （eNOS and nNOS）, and phosphodiesterase type-5 （PDE-5）, which play crucial role in normal erectile physiology. On the light of the recent literature, we aimed to present the direct effect of androgens on the structures, development and maintanence of penile tissue and erectile physiology as well. Furhermore, according to the clinical studies we conclude the aetiology, pathophysiology, prevalance, diagnosis and treatment options of hypogonadism in aging men.     

A castrated mouse model of erectile dysfunction

To establish a mouse model for the study of venoocclusive erectile dysfunction, we investigated erectile function in wild-type (WT), castrated (CAST), and castrated mice receiving immediate testosterone replacement (TEST). Adult C57BL6 mice ( approximately 30 g) underwent electrical stimulation of the cavernous nerve in vivo (parameters: 16 Hz frequency, 5 ms duration, 4V stimulatory voltage) with intracavernosal pressure (ICP) monitoring. A total of 55 mice (5 WT, 25 CAST, and 25 TEST) were evaluated. CAST and TEST (5.0 mg/pellet, 60-day release) mice were divided into groups of 5 and evaluated at 24 hours, 72 hours, 1 week, 2 weeks, and 4 weeks. Penile tissue was immunohistochemically stained for alpha-actin (marker for smooth muscle cells) and CD-31 (marker for endothelial cells). Stained slides were analyzed using Image Pro-plus software. In secondary studies, a Doppler flow meter was employed to evaluate penile blood flow. ICP measurements (mm Hg) were significantly decreased in CAST mice at 24 hour-, 72 hour-, 1 week-, 2 week-, and 4-week time points compared with WT mice (41.9 +/- 14.9, 19.1 +/- 4.2, 17.5 +/- 8.2, 14.2 +/- 4.4, and 10.0 +/- 3.8, respectively, vs 50.2 +/- 2.8), but TEST animals maintained or had an increase in ICP in comparison with WT mice (48.0 +/- 1.4, 52.3 +/- 1.3, 60.8 +/- 7.6, 80.5 +/- 2.1, and 81.5 +/- 1.2, respectively). Mean systemic arterial pressure remained approximately 80 mm Hg irrespective of treatment. CAST mouse penis specimens revealed decreased alpha-actin and CD-31 immunoreactivity only at the 4-week interval, compared with WT and TEST specimens. Doppler ultrasound flow rates (centimeter per second), taken before, during, and immediately after cavernous nerve stimulation, were WT 45.4 +/- 7.3, 30.6 +/- 5.2, 55.3 +/- 8.2 vs CAST (2 weeks) 22.2 +/- 2.5, 25.0 +/- 1.5, 23.1 +/- 2.0 vs TEST (2 weeks) 30.5 +/- 6.5, 25.7 +/- 2.0, 45.2 +/- 4.5. This prominently showed that intrapenile flow was not reduced normally during erectile stimulation in CAST mice. This is the first described mouse model of castration-induced veno-occlusive erectile dysfunction. Erectile response abnormalities as measured by ICP and Doppler ultrasound studies in CAST mice may be attributed to hypogonadal effects on erectile tissue function. Morphologic changes in the cavernosal tissue of CAST mice coincide with these abnormalities to some extent. This study defines an androgen-dependent mechanism of veno-occlusive erectile function in the mouse. The castrated mouse model can be applied in future studies of veno-occlusive erectile dysfunction.     

Pathophysiology of erectile dysfunction: the contributions of trabecular structure to function and the role of functional antagonism

Erectile dysfunction (ED) is estimated to impact more than 150 million men this year worldwide. An understanding of the pathophysiology of ED both furthers the basic scientific knowledge of disease processes and provides a rational design of pharmacotherapy. At present, there are two major views regarding the pathophysiology of ED. In the first hypothesis, the oxygen tension-dependent changes in the penis during erection are proposed to impact corpus cavernosum structure by inducing various cytokines, vasoactive factors and growth factors at the two different oxygen tensions (flaccidity and erection) which, in turn, alter smooth muscle metabolism and connective tissue synthesis. Decreases in the corpus cavernosum smooth muscle/connective tissue ratio have been correlated with an increased likelihood of diffuse venous leak and a failure of the veno-occlusive mechanism in prospective patient studies. Evidence for such a hypothesis incorporates nocturnal penile tumescence and circadian changes in oxygenation as important in maintaining erectile health. The alternate hypothesis proposes that ED is the result of a metabolic imbalance between relaxatory and contractile processes within the trabecular smooth muscle such that contractile processes predominate. Based on this hypothesis, therapy can be accomplished via drugs which shift this balance towards vasodilatation, or by gene therapy approaches to supplement the deficient components favoring smooth muscle relaxation. Both of these hypotheses predict a management strategy for ED that impacts pharmacotherapeutics. In this review of the pathophysiology of ED, each hypothesis will be examined and a synthesis devised incorporating both views. The future of research in this area as well as pharmacotherapy in ED in terms of pathophysiology is discussed including the merits and drawbacks of prophylaxis and prevention of ED. International Journal of Impotence Research (2000) 12, Suppl 4, S39-S46.     

The Role of Andorgens in the Erectile Response: A 1999 Perspective

Evidence from several laboratories strongly supports a critical role for androgens in the maintenance of the mammalian erectile response. In animal studies, androgens appear to act at the end-organ level (i.e., corporal tissue and vasculature), as well as in the portions of the nervous system which mediate erection. Particularly in the rat model, androgens act centrally to support copulatory behavior and peripherally to maintain the production of nitric oxide and support the veno-occlusive mechanisms. Other studies suggest that alternative, non-NO-dependent, pathways may also be androgen sensitive. However, despite this expanding knowledge base about how androgens act in the erectile response in laboratory animals, the recent studies have not greatly clarified the role of androgens in human penile erection. There does not seem to be a strong cause and effect relation between blood androgen concentrations and erectile function; even in severely hypogonadal men, the erectile response is not always lost, and testosterone treatment of hypogonadal men with erectile dysfunction does not necessarily restore lost erectile function. In addition, different types of erection (nocturnal, in response to visual sexual stimulation, in response to sexual partner) may require different degrees of androgenic support.