Restoration of normal adult penile erectile response in aged rats by long-term treatment with androgens

TNF-α antagonism with etanercept enhances penile NOS expression, cavernosal reactivity, and testosterone levels in aged rats

Erectile dysfunction (ED) has been reported to be associated with inflammation. This study investigated the effects of tumor necrosis factor alpha (TNF-α) inhibitor etanercept on penile neuronal nitric oxide synthase (nNOS) and endothelial nitric oxide synthase (eNOS) expressions, testosterone concentrations, neurogenic and endothelium-dependent relaxations of corpus cavernosum (CC), and circulating and cavernosal levels of inflammatory markers in aged rats. Animals were separated into control, aged, and etanercept-treated aged groups. Aged rats displayed significantly increased serum and cavernosal TNF-α, C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP-1) and intercellular adhesion molecule (ICAM-1) levels, and decreased penile nNOS and eNOS expressions and serum testosterone levels compared with controls. In etanercept-treated aged group, NOS expressions were similar to that of the control group. The circulating and cavernosal concentrations of TNF-α, CRP, MCP-1, ICAM-1, and testosterone were also normalized by etanercept. Neurogenic and endothelium-dependent relaxant responses significantly decreased in aged rats and etanercept treatment markedly improved these relaxation responses. Our findings indicate that aging decreases penile NOS expression, neurogenic and endothelium-dependent relaxations of CC, and also suppresses serum testosterone levels by inducing inflammatory response that may contribute to the development of ED. TNF-α antagonism may be a novel strategy to treat aging-associated ED.

Translational Perspective on the Role of Testosterone in Sexual Function and Dysfunction

INTRODUCTION

The biological importance of testosterone is generally accepted by the medical community; however, controversy focuses on its relevance to sexual function and the sexual response, and our understanding of the extent of its role in this area is evolving.

AIM

To provide scientific evidence examining the role of testosterone at the cellular and molecular levels as it pertains to normal erectile physiology and the development of erectile dysfunction and to assist in guiding successful therapeutic interventions for androgen-dependent sexual dysfunction.

METHODS

In this White Paper, the Basic Science Committee of the Sexual Medicine Society of North America assessed the current basic science literature examining the role of testosterone in sexual function and dysfunction.

RESULTS

Testosterone plays an important role in sexual function through multiple processes: physiologic (stimulates activity of nitric oxide synthase), developmental (establishes and maintains the structural and functional integrity of the penis), neural (development, maintenance, function, and plasticity of the cavernous nerve and pelvic ganglia), therapeutically for dysfunctional regulation (beneficial effect on aging, diabetes, and prostatectomy), and phosphodiesterase type 5 inhibition (testosterone supplement to counteract phosphodiesterase type 5 inhibitor resistance).

CONCLUSION

Despite controversies concerning testosterone with regard to sexual function, basic science studies provide incontrovertible evidence for a significant role of testosterone in sexual function and suggest that properly administered testosterone therapy is potentially advantageous for treating male sexual dysfunction.

A prospective longitudinal survey of erectile function status in symptomatic benign prostatic hyperplasia patients treated with dutasteride

We prospectively evaluated erectile function (EF) using the Sexual Health Inventory for Men (SHIM) and the erectile hardness score (EHS) as well as urinary statuses using the International Prostate Symptom Score (IPSS) and Overactive Bladder Symptom Score (OABSS) before and 3, 6, and 12 months after a daily treatment with 0.5 mg dutasteride (DUT). Significant improvements were observed in IPSS and OABSS in 98 patients with the DUT treatment, and the effects were similar between 28 patients with potency with baseline SHIM of 8 or greater and 70 severe erectile dysfunction (ED) patients at baseline. In the 28 patients with potency, significant decreases were observed in SHIM and EHS after 3, 6, and 12 months of the DUT treatment, with the severity of ED according to SHIM deteriorating in half of these patients after 12 months of the DUT treatment. Eighteen out of 28 patients (64.3%) with potency at baseline had awareness of the occurrence of ED before the DUT treatment, were younger, and had higher SHIM and EHS just before the DUT treatment than their counterparts. Regular assessments of EF may be needed, especially in younger patients and those with higher levels of EF before the administration of DUT.

Deficits in coordinated motor behavior and in nigrostriatal dopaminergic system ameliorated and VMAT2 expression up-regulated in aged male rats by administration of testosterone propionate

The effects of testosterone propionate (TP) supplements on the coordinated motor behavior and nigrostriatal dopaminergic (NSDA) system were analyzed in aged male rats. The present study showed the coordinated motor behavioral deficits, the reduced activity of NSDA system and the decreased expression of vesicular monoamine transporter 2 (VMAT2) in 24 month-old male rats. Long term TP treatment improved the motor coordination dysfunction with aging. Increased tyrosine hydroxylase and dopamine transporter, as well as dopamine and its metabolites were found in the NSDA system of TP-treated 24 month-old male rats, indicative of the amelioratory effects of TP supplements on NSDA system of aged male rats. The enhancement of dopaminergic (DAergic) activity of NSDA system by TP supplements might underlie the amelioration of the coordinated motor dysfunction in aged male rats. TP supplements up-regulated VMAT2 expression in NSDA system of aged male rats. Up-regulation of VMAT2 expression in aged male rats following chronic TP treatment might be involved in the maintenance of DAergic function of NSDA system in aged male rats.

Side Effects of 5-Alpha Reductase Inhibitors: A Comprehensive Review

INTRODUCTION

5α-reductase inhibitors (5ARI) include finasteride and dutasteride, and are commonly prescribed in the treatment of benign prostatic hyperplasia and androgenic alopecia. 5ARIs are associated with several known adverse effects (AEs), with varying reported prevalence rates.

AIM

The aim was to review and summarize findings from published literature detailing AEs associated with 5ARI use. A secondary aim was to review potential mechanisms of action, which may account for these observed and reported AEs.

METHODS

A PubMed search was conducted on articles published from 1992 to 2012, which reported AEs with 5ARIs. Priority was given to randomized, placebo-controlled trials. Studies investigating potential mechanisms of action for 5ARIs were included for review.

MAIN OUTCOME MEASURES

AE data reported from available trials were summarized and reviewed.

RESULTS

Reported AEs with 5ARIs include sexual dysfunction, infertility, mood disorders, gynecomastia, high-grade prostate cancer, breast cancer, and cardiovascular morbidity/risk factors, although their true association, prevalence, causality, and clinical significance remain unclear. A pooled summary of all randomized, placebo-controlled trials evaluating 5ARIs (N = 62,827) revealed slightly increased rates over placebo for decreased libido (1.5%), erectile dysfunction (ED) (1.6%), ejaculatory dysfunction (EjD) (3.4%), and gynecomastia (1.3%). The limited data available on the impact of 5ARIs on mood disorders demonstrate statistically significant (although clinically minimal) differences in rates of depression and/or anxiety. Similarly, there are limited reports of reversible, diminished fertility among susceptible individuals. Post-marketing surveillance reports have questioned the actual prevalence of AEs associated with 5ARI use and suggest the possibility of persistent symptoms after drug discontinuation. Well-designed studies evaluating these reports are needed.

CONCLUSIONS

5ARIs are associated with slightly increased rates of decreased libido, ED, EjD, gynecomastia, depression, and/or anxiety. Further studies directed at identifying prevalence rates and persistence of symptoms beyond drug discontinuation are required to assess causality. Trost L, Saitz TR, and Hellstrom WJG. Side effects of 5-alpha reductase inhibitors: A comprehensive review. Sex Med Rev 2013;1:24-41.

Safety concerns regarding 5α reductase inhibitors for the treatment of androgenetic alopecia

PURPOSE OF REVIEW

To examine the clinical and basic studies regarding persistent adverse effects associated with 5α reductase inhibitor treatment for androgenetic alopecia.

RECENT FINDINGS

Recent postmarketing reports and a US Food and Drug Administration analysis have documented uncommon persistent sexual and nonsexual side-effects in a subset of younger men who have taken finasteride 1 mg for androgenic alopecia. While the mechanisms of the sexual side-effects in humans is incompletely understood, one study found lower cerebrospinal fluid concentrations of dihydrotestosterone, progesterone, dihydroprogesterone and allopregnanolone, and higher levels of testosterone, 5α-androstane-3α,17β-diol and pregnenolone. Another study found up-regulation of the androgen receptor in the human foreskin with a mean of 5 years after finasteride discontinuation. Studies of erectile dysfunction in finasteride-treated rats showed fewer autophagosomes in smooth muscle on transmission electron microscopy, increased apoptosis, decreased smooth muscle, increased collagen deposition and decreased endothelial nitric oxide synthase. Finally, 5α reductase inhibitors have also been found to alter semen parameters in healthy men.

SUMMARY

Multiple animal studies provide a biological basis for many of the persistent effects seen in humans such as erectile dysfunction, depression and decreased alcohol consumption. Prescribers of 5α reductase inhibitors should discuss the potential risks with their patients seeking treatment for androgenetic alopecia.

Testosterone replacement alters the cell size in visceral fat but not in subcutaneous fat in hypogonadal aged male rats as a late-onset hypogonadism animal model

Background

Patients with late-onset hypogonadism (LOH) benefit from testosterone replacement by improvement in the parameters of the metabolic syndrome, but fat cell morphology in these patients is still unclear. This study aims to determine the effect of testosterone replacement on the morphology of fat cells in subcutaneous and visceral adipose tissue and on erectile function in hypogonadal aged male rats as a model of LOH.

Methods

Ten male Sprague-Dawley rats aged 20–22 months were randomly allocated to two groups, ie, aged male controls (control group, n=5) and aged males treated with testosterone replacement therapy (TRT group, n=5). Testosterone enanthate 25 mg was injected subcutaneously every 2 weeks for 6 weeks. At 6 weeks, the intracavernous pressure (ICP) and mean arterial blood pressure (MAP) ratio was assessed. Visceral and subcutaneous adipose tissue specimens were collected and analyzed using Image-J software.

Results

Body weight at 2, 4, and 6 weeks after TRT was 800.0±35.4 g, 767.5±46.3 g, and 780±40.4 g, respectively (not statistically significant). The ICP/MAP ratio was 0.341±0.015 in the TRT group and 0.274±0.049 in the control group (not statistically significant). The median subcutaneous fat cell size was 4.85×10³ (range 0.85–12.53×10³) μm² in the control group and 4.93×10³ (range 6.42–19.7×10³) μm² in the TRT group (not statistically significant). In contrast, median visceral fat cell size was significantly smaller in the TRT group (4.93×10³ μm² [range 0.51–14.88×10³]) than in the control group (6.08×10³ μm² [0.77–19.97×10³]; P<0.001, Mann-Whitney U test).

Conclusion

This is the first study clearly indicating that TRT can decrease visceral fat cell size, which is a key modulator in the metabolic syndrome. However, a short course of TRT could not improve the ICP response in hypogonadal aged male rats. Further investigation is necessary to clarify the exact rationale of TRT on the visceral fat cell.

The effects of combined free radical scavenger and sildenafil therapy on age-associated erectile dysfunction: An animal model

Introduction:

Aging results in erectile dysfunction that is partially attributed to decreased nitric oxide (NO) and increased free radical generation. Vitamin E enhances endothelial cell function and acts as a free radical scavenger; however, its benefits on erectile function in the elderly are unknown.

Aims:

The aim of the following study is to determine if Vitamin E alone, or in combination with the phosphodiesterase 5 inhibitor sildenafil, may improve erectile function and the NO signaling in a cohort of aged (13-15 month old) rats.

Materials and Methods:

Male Sprague-Dawley rats (n = 28) were divided based upon age into young (4-5 months old, n = 7) and aged (13-15 months old, n = 21) cohorts. Aged rats were treated with Vitamin E, sildenafil or a combination of both. Penile cavernosal and dorsal nerve tissues were evaluated for neuronal nitric oxide synthase (nNOS) and caveolin-1 expression. Erectile function was assessed through intra-cavernous pressure (ICP) recordings.

Results:

nNOS and cavoelin-1 were significantly decreased in aged rats compared with young controls. In aged rats, both Vitamin E and sildenafil partially recovered nNOS expression but when combined, a synergistic elevation in nNOS was observed. The significant decreases in ICP recorded in aged rats were improved with sildenafil; however, Vitamin E did not yield any additional improvements in ICP.

Conclusions:

Diminished levels of nNOS and caveolin-1 are found in aged rats. When combined with sildenafil, Vitamin E synergistically increased nNOS expression. Since biochemical gains were not realized physiologically, other contributing factors likely exist.

The dark side of 5α-reductase inhibitors' therapy: sexual dysfunction, high Gleason grade prostate cancer and depression

With aging, abnormal benign growth of the prostate results in benign prostate hyperplasia (BPH) with concomitant lower urinary tract symptoms (LUTS). Because the prostate is an androgen target tissue, and transforms testosterone into 5α-dihydrotestosterone (5α-DHT), a potent androgen, via 5α-reductase (5α-R) activity, inhibiting this key metabolic reaction was identified as a target for drug development to treat symptoms of BPH. Two drugs, namely finasteride and dutasteride were developed as specific 5α-reductase inhibitors (5α-RIs) and were approved by the U.S. Food and Drug Administration for the treatment of BPH symptoms. These agents have proven useful in the reducing urinary retention and minimizing surgical intervention in patients with BPH symptoms and considerable literature exists describing the benefits of these agents. In this review we highlight the adverse side effects of 5α-RIs on sexual function, high grade prostate cancer incidence, central nervous system function and on depression. 5α-Rs isoforms (types 1-3) are widely distributed in many tissues including the central nervous system and inhibition of these enzymes results in blockade of synthesis of several key hormones and neuro-active steroids leading to a host of adverse effects, including loss of or reduced libido, erectile dysfunction, orgasmic dysfunction, increased high Gleason grade prostate cancer, observed heart failure and cardiovascular events in clinical trials, and depression. Considerable evidence exists from preclinical and clinical studies, which point to significant and serious adverse effects of 5α-RIs, finasteride and dutasteride, on sexual health, vascular health, psychological health and the overall quality of life. Physicians need to be aware of such potential adverse effects and communicate such information to their patients prior to commencing 5α-RIs therapy.

Adrenomedullin and angiopoietin-1 additively restore erectile function in diabetic rats: comparison with the combination therapy of vascular endothelial growth factor and angiopoietin-1

INTRODUCTION

Erectile dysfunction (ED) is a major health problem. We have shown that adrenomedullin (AM) restores erectile function in diabetic rats.

AIM

The aim of this study is to explore a better treatment for ED, we examined whether combination of AM and angiopoietin-1 (Ang-1) was more effective to treat ED than treatment with AM alone or Ang-1 alone. We also compared the effect of the combination therapy with that of treatment with vascular endothelial growth factor-A (VEGF-A).

METHODS

Male Wistar rats were injected with streptozotocin (STZ) to induce diabetes. Adenoviruses expressing AM (AdAM), Ang-1 (AdAng-1), and VEGF-A (AdVEGF-A) were injected into the penis 6 weeks after STZ administration. Erectile function, penile histology, and protein expression were analyzed 4 weeks after the injection of the adenoviruses.

MAIN OUTCOME MEASURES

Intracavernous pressure and mean arterial pressure were measured to evaluate erectile function. The morphology of the penis was analyzed by Elastica van Gieson stain and immunohistochemistry. The expression of α-smooth muscle actin (SMA), VE-cadherin and type I collagen was assessed by Western blot analysis.

RESULTS

Infection with AdAM plus AdAng-1 more effectively restored erectile function than infection with AdAM alone or AdAng-1 alone. This combination therapy restored erectile function to a level similar to that observed in the age-matched Wistar rats. Expression of SMA and VE-cadherin increased more significantly in the AdAM plus AdAng-1-treated group than in the AdAM- or AdAng-1-treated group. Although AdVEGF-A infection restored erectile function significantly, it also caused enlargement of the trabeculae of the cavernous body, aberrant angiogenesis, and overproduction of type I collagen.

CONCLUSIONS

These results suggested that combination therapy with AM and Ang-1 potently restored erectile function and normal morphology of the cavernous body compared with VEGF-A administration. This combination therapy will be useful to treat ED patients with a severely damaged cavernous body.

Androgen depletion in humans leads to cavernous tissue reorganization and upregulation of Sirt1-eNOS axis

Aging and physiological androgen decay leads to structural changes in corpus cavernosum (CC) that associate with erectile function impairment. There is evidence that such changes relate to nitric oxide (NO) bioavailability, an endothelial compound produced by the action of endothelial NO synthase (eNOS), and is regulated by sirtuin-1 (Sirt1), a NAD(+)-dependent protein deacetylase. Taking into account the reduced NO synthesis observed in aging and erectile dysfunction, we aimed to characterize human CC of androgen-deprived, young, and aged individuals postulating that androgen deprivation induces modifications similar to those observed in aging. Human penile fragments were collected from young individuals submitted to male-to-female sex reassignment procedure, who undergone an androgen deprivation chemical regimen, from young organ donors and from aged patients submitted to penile deviation surgery. They were processed for histomorphometric analysis of smooth muscle (SM) and connective tissues (CT), and dual-immunofluorescence of alpha-actin/vWf or Sirt1, and endothelin-1/eNOS. Estrogen receptors were analyzed by immunohistochemistry and semiquantification of Sirt1, eNOS, and phospho-Akt was assayed by Western blotting. Androgen withdrawal, similarly to aging, leads to a noteworthy reduction of SM-to-CT ratio in CC. However, in contrast to young and aged, a significant increase in penile Sirt1 expression accompanied by an increase in total eNOS expression was observed in androgen-depleted individuals. No changes were evidenced in phospho-Akt system and estrogen receptors were undetectable. These findings indicate that Sirt1 regulates the expression of eNOS in human CC employing mechanisms influenced by androgen depletion.

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.

Recent trends in the treatment of testosterone deficiency syndrome

Testosterone deficiency syndrome (TDS) is defined as a clinical and biochemical syndrome associated with advancing age and is characterized by typical symptoms and deficiency in serum testosterone levels. TDS is a result of the interaction of hypothalamo-pituitary and testicular factors. Now, treatment of TDS with testosterone is still controversial due to a lack of large, controlled clinical trials on efficacy. The risks of treatment with testosterone appear to be minimal, although long-term studies on the safety of testosterone therapy are lacking. The aim of the therapy is to establish a physiological concentration of serum testosterone in order to correct the androgen deficiency, relieve its symptoms and prevent long-term sequelae. All of the available products, despite their varying pharmacodynamic and pharmacokinetic profiles, are able to reach this goal. Newer testosterone patches seem not to cause severe skin irritation. Testosterone gels minimize the skin irritation while providing flexibility in dosing and a low discontinuation rate. Oral testosterone undecanoate (TU) is free of liver toxicity. Recent formulation of oral TU markedly increased shelf-live, a major drawback in the older preparation. Producing swings in testosterone levels rising rapidly to the supraphysiological range is not the case with the new injectable long-acting preparation of TU. To be able to rapidly react and stop treatment in cases where side-effects and contraindications are detected, the short-acting transdermal and oral delivery modes have certain advantages. However, there is no evidence that the use of an injectable long-acting TU in men with TDS has limitations in clinical application for this reason. The use of dehydroepiandrosterone is still controversial because of a lack of well designed long-term trials, although some recent studies suggest positive effects on various body systems. Only a few studies have been carried out to investigate the effect of hCG (human chorionic gonadotropin) in TDS with some positive results on various body systems.

Recovery of erectile function in aging hypertensive and normotensive rats using exercise and caloric restriction

INTRODUCTION

Using aging spontaneously hypertensive rats (SHR), we established that antihypertensive drugs can improve erections and penile vascular structure, and lower arterial pressure. Using kidney cross-transplantations, our findings revealed that the benefit of this treatment resulted from drug-induced changes specific to the penile circulation, and not to the kidney-mediated lowering of pressure.

AIM

The objective of the present study was to determine whether increased exercise and/or caloric restriction (CR) can reverse the decline in sexual responses in aging hypertensive and normotensive rats.

METHODS

From 30 to 40 weeks, food intake was restricted (10-40%), and SHR, Wistar, and Sprague-Dawley rats ran on treadmills (30 minutes/day, 5 days/week). Exercise was withdrawn at 40 weeks, and CR was stopped at 50 weeks. Using a separate group of older Wistars (56 weeks) and Sprague-Dawley rats (67 weeks), the effects of 10% CR or exercise plus 10-40% CR on erectile function were determined.

MAIN OUTCOME MEASURE

Apomorphine-induced erectile responses and body weight were monitored weekly.

RESULTS

An age-related decline in erections was seen from 15 to 29 weeks of age in all strains. This decline paralleled increases in body weight, particularly in the normotensive strains. Exercise and CR induced a 10% weight loss in normotensive rats and improved erections in all animals. In SHR, increased erections occurred without decreasing body weight. Body weight and erectile responses were maintained by CR alone after exercise was withdrawn, but erectile function rapidly declined soon after CR was stopped and paralleled increases in body weight. In aged Wistar and Sprague-Dawley rats treated with exercise and CR, erectile function was also significantly improved.

CONCLUSIONS

Similar to previous studies, erectile function progressively decreased with age in both hypertensive and normotensive rats. Erectile responses were found to be substantially improved by an intervention involving exercise and CR, but not necessarily involving weight loss.

Exogenous testosterone reverses age-related atrophy in a spinal neuromuscular system

Aging is associated with a variety of pathologies, including motor dysfunctions and reductions in sexual behavior. In male rats, declines in sexual behavior during the aging process may be caused in part by the loss of the lumbar spinal cord motoneurons that innervate the penile musculature. Alternatively, declining sexual behavior may be caused by the precipitous reductions in circulating testosterone that occur during aging. In this paper, we report two experiments examining these issues. In Experiment 1, we counted motoneurons in the lumbar motor nuclei and measured several androgen-sensitive morphological properties of the penile muscles and their innervating motoneurons at several time points during the aging process. Motoneuron number in the lumbar nuclei did not change over time, even with very advanced age. In contrast, the penile muscles and their innervating motoneurons underwent profound atrophy, with muscle weight and motoneuron dendritic length declining to less than 50% of young adult levels. In Experiment 2, we treated aged animals with exogenous testosterone, and then examined their penile neuromuscular systems for morphological changes. Testosterone treatment, both acute and chronic, completely reversed age-related declines in the weight of the penile muscles and in the soma size and dendritic length of their innervating motoneurons. Together, these data suggest that reductions in male sexual behavior during the aging process are caused primarily by declines in testosterone levels rather than motoneuron loss. Furthermore, they raise the possibility that testosterone treatment could play an important role in maintaining neuronal connectivity in the aging body.

REVIEWS: Are Androgens Critical for Penile Erections in Humans? Examining the Clinical and Preclinical Evidence

Androgens are deemed critical for penile-tissue development, growth, and maintenance of erectile function, however, their role in erection, especially in humans, remains controversial. In this review, we summarize information from clinical and animal model studies to provide a comprehensive and rational argument for the role of androgens, or lack thereof, on penile erection ability in humans. The goal of this review is to present the clinical and preclinical evidence available in the literature with regard to testosterone and erectile physiology and engage the reader in this discussion. Ultimately, each reader will have to form his or her own conclusions based on the existing evidence. In humans, androgen-deficiency manifestations are noted in clinical situations such as: (i) inadequate development of the penis; and (ii) loss of erectile function in prostate cancer and benign prostatic hyperplasia patients managed with medical or surgical castration or antiandrogen therapy. Androgen treatment causes: (i) improvement in sexual function in hypogonadal patients treated with androgen supplementation; (ii) improvement in nocturnal penile tumescence in hypogonadal patients treated with androgens; (iii) improvement in erectile function with androgen supplementation in patients who did not respond to phosphodiesterase type 5 inhibitor therapy initially; and (iv) improvement in the well-being, mood, energy, and sexual function in aging men who have testosterone deficiency treated with androgen therapy. In contrast to animals, especially rodents in which the adrenal cortex does not synthesize androgens, the human adrenal is a source of peripherally circulating androgen precursors, thus, complete androgen insufficiency may not be observed in men at a younger age. Furthermore, in light of the concept that a threshold of androgen levels exists in animals and humans below which sexual function is diminished, further contributes to the complexity of understanding androgens role in erections, especially in humans. Nevertheless, based on the preclinical and clinical data available in the literature, to date, we infer that androgens play a critical role in maintaining erectile physiology in humans.

RhoA/Rho-kinase in erectile tissue: mechanisms of disease and therapeutic insights

Penile erection is a complicated event involving the regulation of corpus cavernosal smooth muscle tone. Recently, the small monomeric G-protein RhoA and its downstream effector Rho-kinase have been proposed to be important players for mediating vasoconstriction in the penis. RhoA/Rho-kinase increases MLC (myosin light chain) phosphorylation through inhibition of MLCP (MLC phosphatase) thereby increasing Ca2+ sensitivity. This review will outline the RhoA/Rho-kinase signalling pathway, including the upstream regulators, guanine nucleotide exchange factors, GDP dissociation inhibitors and GTPase-activating proteins. We also summarize the current knowledge about the physiological roles of RhoA/Rho-kinase in both male and female erectile tissues and its aberrations contributing to erectile dysfunction in several disease states. Understanding the RhoA/Rho-kinase signalling pathway in the regulation of erection is important for the development of therapeutic interventions for erectile dysfunction.

Androgen Deficiency in the Etiology and Treatment of Erectile Dysfunction

The evaluation and management of erectile dysfunction (ED) has evolved dramatically following the introduction of oral phosphodiesterase-5 inhibitors. Despite the limited role of directed diagnostic testing in the evaluation of the impotent patient, routine de-termination of a serum testosterone likely is indicated based on evidence that testosterone modulates erectile function, that hypogonadism is prevalent among elderly men and men with ED, and that symptomatology alone rarely detects hypogonadism. Forms of testosterone commonly used include oral, parenteral, transdermal, and implantable preparations, each with significant advantages and disadvantages. The risks and benefits of testosterone supplementation have been characterized incompletely and will require further validation before widespread use of testosterone as hormone replacement therapy in aging men.

ORIGINAL RESEARCH—ENDOCRINOLOGY: The Physiological Role of Androgens in Penile Erection: Regulation of Corpus Cavernosum Structure and Function

It is generally accepted that androgens are critical for development, growth, and maintenance of penile erectile tissue. However, their role in erectile function, especially in humans, remains controversial. Clinical and preclinical studies have suggested that venoocclusion is modulated by the tone of the vascular smooth muscle of the resistance arteries and the cavernosal tissue and a balance between trabecular smooth muscle content and connective tissue matrix. In men with erectile dysfunction, venous leakage is thought to be a common condition among nonresponders to medical management and is attributed to penile smooth muscle atrophy. In the animal model, androgen deprivation produces penile tissue atrophy concomitant with alterations in dorsal nerve structure, endothelial morphology, reduction in trabecular smooth muscle content, and increased deposition of extracellular matrix. Further, androgen deprivation results in accumulation of fat-containing cells (adipocytes) in the subtunical region of the corpus cavernosum. Androgen deficiency diminishes protein expression and enzymatic activity of nitric oxide synthases (eNOS and nNOS) and phosphodiesterase type 5 (PDE5). The androgen-dependent loss of erectile response is restored by androgen administration but not by administration of PDE5 inhibitors alone. These data suggest that androgens regulate trabecular smooth muscle growth and connective tissue protein synthesis in the corpus cavernosum. Further, androgens may stimulate differentiation of progenitor cells into smooth muscle cells and inhibit their differentiation into adipocytes. Thus, we conclude that androgens exert a direct effect on penile tissue to maintain erectile function and that androgen-deficiency produces a metabolic and structural imbalance in the corpus cavernosum, resulting in venous leakage and erectile dysfunction. .

Adipocyte accumulation in penile corpus cavernosum of the orchiectomized rabbit: a potential mechanism for veno-occlusive dysfunction in androgen deficiency

Androgens are deemed to be critical for the development, growth, and maintenance of penile tissue as well as for erectile function. Androgens are also reported to inhibit differentiation of stroma progenitor cells into adipocytes and promote differentiation into smooth muscle. The objective of this study was to investigate whether androgen deprivation results in accumulation of adipocytes in the corpus cavernosum. Mature, New Zealand white male rabbits were subjected to sham surgery (control) or orchiectomy. Two weeks after surgery, erectile function was assessed by monitoring changes in intracavernosal blood pressure (ICP) in response to pelvic nerve stimulation. All ICP measurements were normalized to the mean systemic arterial blood pressure. In parallel studies, penile cross sections from control and orchiectomized rabbits were fixed and stained with either Masson's trichrome or hematoxylin and eosin to assess smooth muscle and connective tissue content. Alternatively, tissue sections were stained with Toluidine blue to assess accumulation of fat-containing cells. Orchiectomy resulted in loss of erectile function and penile atrophy, associated with reduced trabecular smooth muscle and increased connective tissue content. Most strikingly, tissue from orchiectomized animals exhibited accumulation of fat-containing cells (adipocytes) in the subtunical region of the corpus cavernosum. We hypothesize that androgen deprivation promotes differentiation of progenitor stroma cells into an adipogenic lineage producing fat-containing cells, thus altering erectile function.

Rho-kinase inhibition improves erectile function in aging male Brown-Norway rats

Physiological aging is a significant risk factor in the on-set of male erectile dysfunction (ED) and an imbalance in factors that modulate cavernosal smooth-muscle tone may play a role in these altered penile hemodynamic mechanisms. To evaluate the association between aging and male erectile function, we monitored neurogenic erectile response and its correlation to systemic arterial pressure changes in old (21-23 months of age) vs young (6-9 months of age) Brown-Norway (BN) rats. We tested the hypothesis that age-associated ED is due to unregulated vasoconstrictive tone, contributed in part by an increased Rho-kinase activity, and that antagonism of Rho-kinase activity attenuates the age-related decline in male erectile function. We also examined the hypothesis that a combination of Rho-kinase antagonism and phosphodiesterase-5 (PDE-5) inhibition has a synergistic effect in improving the erectile response in these aging animals. Erectile function in old BN rats was evaluated before and after intracavernosal injection of a specific inhibitor of Rho-kinase (Y-27632) alone or in combination with zaprinast, a PDE-5 inhibitor. Erectile capabilities of the young and old BN rat groups were significantly different in corpus cavernosum pressure response after electrical-field stimulation of the major pelvic ganglion. Y-27632 administration attenuated the aging-related changes in male erectile function seen in BN rats. Rho-kinase antagonism and PDE-5 inhibition had a synergistic effect in improving erectile function in old rats. Our data indicate that aging leads to impairment in the neurogenic erectile response in BN rats involving a possible derangement in penile hemodynamic mechanisms of the erectile tissue. Rho-kinase inhibition may be of value in treating age-related ED.

Corporal veno-occlusive dysfunction in aging rats: Evaluation by cavernosometry and cavernosography

OBJECTIVES

To determine whether the rat develops corporal veno-occlusive dysfunction (CVOD) during the aging process.

METHODS

We divided male Fisher 344 rats into four groups with 5 to 8 rats in each group. Group 1 rats were 5 months old and not orchiectomized (young intact); group 2 were 5 months old and had undergone castration (control CVOD); group 3 were 24 months old and not orchiectomized (aged intact); and group 4 rats were 24 months old, nonorchiectomized rats who had undergone deep dorsal vein (DDV) ligation (aged ligated). Serum testosterone was measured, and dynamic infusion cavernosometry and cavernosography (by dual-energy x-ray absorptiometry scan) were performed.

RESULTS

Compared with the young intact animals, the aged intact rats had a 73% reduction in testosterone, a 30% reduction in intracavernosal pressure after papaverine injection, and an 84% and a 44% increase in the maintenance and drop rate, respectively, during dynamic infusion cavernosometry. The extent of CVOD as measured by cavernosometry in the aged rats was similar to that in the young castrated rats, but was more pronounced when measured by dynamic infusion cavernosometry. Cavernosography confirmed that the aged rats had venous leakage primarily by way of the DDV. By applying DDV ligation, distal penile engorgement occurred, showing that a small venous leakage occurred primarily by way of the cavernosal veins.

CONCLUSIONS

These data have demonstrated that CVOD occurs in the aged rat, mainly through the DDV. This supports the concept that the aged rat is an appropriate animal model to study erectile dysfunction associated with CVOD.

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

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

Effect of testosterone supplementation on sexual function in hypogonadal men with erectile dysfunction

OBJECTIVES

To evaluate the impact of normalization of testosterone levels in men with documented hypogonadism and erectile dysfunction on erectile function and sexual satisfaction. Although the data support the role of testosterone in the preservation of libido and nocturnal erectile function, the evidence supporting the use of testosterone supplementation in hypogonadal men with erectile dysfunction is weak.

METHODS

This analysis used two validated questionnaires, the International Index of Erectile Function and the Erectile Dysfunction Inventory of Treatment Satisfaction, in a serial fashion at baseline (before treatment) and 1, 3, and 6 months after the achievement of a therapeutic testosterone level.

RESULTS

A total of 32 men met all inclusion criteria; 69% of men achieved therapeutic testosterone levels using transdermal testosterone gel, 19% required a transdermal patch, and 12% required intramuscular delivery. Statistical significance was reached for the difference between the baseline and 1-month International Index of Erectile Function erectile function domain score and all post-treatment International Index of Erectile Function libido scores. A steady decrease occurred in the Erectile Dysfunction Inventory of Treatment Satisfaction scores from the 1 to 6-month values that reached statistical significance.

CONCLUSIONS

In men with documented hypogonadism and erectile dysfunction, normalization of serum testosterone levels was associated with only short-term improvement in erectile function and sexual satisfaction. The use of testosterone supplementation in this population for the treatment of erectile dysfunction is questionable.

Effects of medical or surgical castration on erectile function in an animal model

The goal of this study was to investigate the effects of medical castration (luteinizing hormone-receptor hormone [LH-RH] agonist treatment) or surgical castration on erectile function in an animal model. New Zealand White male rabbits were either kept intact (control); surgically orchiectomized; or treated for 2, 4, or 8 weeks with the LH-RH agonist leuprolide acetate (107 microg/kg/mo). At 2 weeks, plasma testosterone levels of orchiectomized and leuprolide acetate-treated animals were 12.8% and 57.4% of intact control animals, respectively. Erectile function was assessed by continuously recording systemic arterial pressure (SAP) and intracavernosal blood pressure (ICP) and determining the ICP:SAP ratios in response to electrical stimulation of the pelvic nerve at varying frequencies (2.5-32 Hz). Androgen deprivation by surgical (orchiectomy) or medical (leuprolide acetate) castration reduced ICP at all frequencies tested but did not alter SAP. Administration of the phosphodiesterase type 5 inhibitor vardenafil (10 microg/kg) did not enhance ICP in surgically orchiectomized or leuprolide acetate-treated animals. Nitric oxide synthase and arginase activities in the corpus cavernosum were not significantly altered by surgical or medical castration. Further, Masson trichrome staining of erectile tissue from androgen-ablated animals showed a reduction in smooth muscle content. These data demonstrate that androgen deprivation achieved by surgical or medical castration adversely affects penile hemodynamics and erectile function without producing significant changes in the activities of nitric oxide synthase or arginase. We conclude that androgen deprivation produces structural alterations in the corpus cavernosum leading to corporal veno-occlusive dysfunction.

Patient satisfaction with testosterone supplementation for the treatment of erectile dysfunction

The long-term efficacy of testosterone supplementation for erectile dysfunction was evaluated using standardized questionnaires and differences between testosterone delivery systems analyzed. Forty-four patients receiving parenteral depo-testosterone, Testoderm scrotal patches, or Testoderm-TTS nonscrotal patches were evaluated with the Erectile Dysfunction Inventory of Treatment Satisfaction and International Index of Erectile Function questionnaires. Global questions regarding libido, energy, and improved erections demonstrated a significantly better response with depo-testosterone and Testoderm-TTS nonscrotal patches as compared to Testoderm scrotal patches. Testoderm-TTS nonscrotal patches and depo-testosterone resulted in significantly higher overall treatment satisfaction (p <.001), confidence in ability to engage in sexual activity (p <.001), and total Erectile Dysfunction Inventory of Treatment Satisfaction and International Index of Erectile Function scores (p <.001). Testoderm-TTS nonscrotal patches were significantly better than depo-testosterone with regard to satisfaction with sexual intercourse (International Index of Erectile Function question 5, p <.05). Testosterone replacement improved the quality of erections and level of libido in patients with erectile dysfunction. Treatment delivery systems appear to impact the success of therapy.

Gene therapy of erectile dysfunction in the rat with penile neuronal nitric oxide synthase

Gene transfer to the penile corpora cavernosa of constructs of the inducible and endothelial nitric oxide synthase (NOS) cDNAs ameliorates erectile dysfunction in aged rats. In this study, we investigated whether the neuronal NOS (nNOS) variant responsible for erection, penile nNOS (PnNOS), can exert a similar effect, and whether the combination of electroporation with a helper-dependent adenovirus (AdV) improves gene transfer. PnNOS and beta-galactosidase cDNAs were cloned in plasmid (pCMV-PnNOS; pCMV-beta-gal) and "gutless" AdV (AdV-CMV-PnNOS; AdV-CMV-beta-gal) vectors, and injected into the penis of adult (beta-gal) or aged (PnNOS) rats, with or without electroporation. Penile erection was measured at different times after PnNOS cDNA injection, by electrical field stimulation of the cavernosal nerve. The expression of beta-galactosidase or PnNOS was estimated in penile tissue by either histochemistry and luminometry or Western blot, and the effects of AdV-CMV-PnNOS on mRNA expression were examined by a DNA microarray. We found that electroporation increased pCMV-beta-gal uptake, and its expression was detectable at 56 days. In the aged rats treated with pCMV-PnNOS and electroporation, the maximal intracavernosal:mean arterial pressure ratios were elevated for 11 and 18 days when compared with those in controls. Electroporation intensified penile uptake of as few as 10(6) viral particles (vp) of AdV-CMV-beta-gal, and with 10(7) vp beta-galactosidase was still detectable at 60 days. Electroporated AdV-CMV-PnNOS (10(7) vp) was effective at 18 days in stimulating the erection of aged rats, without inducing the expression of cytotoxic genes. In conclusion, intracavernosal gene therapy with PnNOS cDNA corrected the aging-related erectile dysfunction for at least 18 days when given by electroporation in a helper-dependent AdV at low viral loads.

The clinical relevance of sex hormone levels and sexual activity in the ageing male

OBJECTIVES

To assess the changes in sex hormone levels with age and the relationship of sexual functioning to testosterone levels, evaluating serum testosterone levels and erectile function in men with lower urinary tract symptoms (LUTS).

PATIENTS AND METHODS

The study included 213 men with LUTS (age range 31-78 years) who had no confirmed erectile dysfunction. Their serum total and free testosterone, and sex-hormone binding globulin (SHBG) levels were measured, and they completed the International Index of Erectile Function (IIEF) questionnaire.

RESULTS

The total and free testosterone levels decreased and SHBG increased with age, but only the change in free testosterone and SHBG were statistically significant. The correlation with age was closer for free testosterone (r = - 0.356, P < 0.001) than for SHBG (r = 0.177, P = 0.010). Regression analysis of the five domain scores of the IIEF and three hormonal levels, after correcting for age, showed that free testosterone level was significantly correlated with erectile function (r = 0.2136, P = 0.005) and orgasmic function (r = 0.179, P = 0.020), but SHBG levels were significantly correlated only with orgasmic function (r = - 0.154, P = 0.046). Total testosterone levels showed no significant correlation with any of the five domains of the IIEF.

CONCLUSIONS

Of the sex hormone levels, the change in free testosterone correlated most closely with ageing and had the closest correlation with sexual activity. Contrary to previous reports, free testosterone and SHBG levels were significantly correlated with orgasmic function and/or erectile function rather than sexual desire. A complete study of sex hormone levels is needed to evaluate patients with erectile dysfunction.

Effects of testosterone on pelvic autonomic pathways: progress and pitfalls

Testosterone has potent effects on reproductive behavior, many of which are due to actions on brain nuclei and spinal motoneurons controlling perineal muscles. The autonomic circuits involved in penile erection, ejaculation and emission, have been less commonly considered as targets for circulating androgens. This review demonstrates that many components of pelvic autonomic reflex pathways, including preganglionic neurons, autonomic ganglion cells and primary afferent neurons, are likely to be influenced by testosterone. The steroid appears to play an important role in maintaining neuronal morphology, transmitter synthesis and receptor expression throughout adulthood. Surprisingly, the effects of testosterone are not limited to neurons involved in reproductive reflexes. The challenge is now to determine the range of neuronal features influenced by androgens, and the mechanisms by which these occur. Studies of androgen receptor location indicate that in many autonomic neurons gene expression may be directly influenced by androgens, but a mismatch between receptor distribution and androgen action shows that in some cells other mechanisms must exist. It is also possible that androgens are metabolised to estrogens by some peripheral neurons. Irrespective of the mechanism, it is time to acknowledge that testosterone is an important "maintenance factor" for autonomic neurons.

The autonomic nerve supply of male sex organs--an important target of circulating androgens

The autonomic nervous system plays a critical role in the regulation of smooth muscle contraction, exocrine secretion and blood flow in the male reproductive organs. Many of the autonomic neurons that supply these targets lie in the pelvic ganglia, which contain both sympathetic and parasympathetic ganglion cells. In rats, removal of circulating androgens by castration before or after puberty has profound effects on the structure, chemistry and function of particular classes of pelvic autonomic neurons. While most of these effects occur in reproductive pathways, some bladder- or bowel-projecting neurons also exhibit androgen-sensitivity. Our studies on these ganglion cells and their spinal preganglionic inputs show that testosterone (or a metabolite) has potent actions both before and after puberty and can be considered essential for the normal maturation and maintenance of some pelvic autonomic reflex pathways. Androgen receptors are distributed widely throughout various components of these circuits, suggesting that testosterone may have direct effects on neuronal gene expression. Together, the studies show that in addition to powerful effects on some central neurons controlling reproductive behaviour, testosterone has similarly important effects on peripheral neurons that trigger and complete copulatory reflexes.

Unusual autonomic ganglia: connections, chemistry, and plasticity of pelvic ganglia

The pelvic ganglia provide the majority of the autonomic nerve supply to reproductive organs, urinary bladder, and lower bowel. Of all autonomic ganglia, they are probably the least understood because in many species their anatomy is particularly complex. Furthermore, they are unusual autonomic ganglia in many ways, including their connections, structure, chemistry, and hormone sensitivity. This review will compare and contrast the normal structure and function of pelvic ganglia with other types of autonomic ganglia (sympathetic, parasympathetic, and enteric). Two aspects of plasticity in the pelvic pathways will also be discussed. First, the influence of gonadal steroids on the maturation and maintenance of pelvic reflex circuits will be considered. Second, the consequences of nerve injury will be discussed, particularly in the context of the pelvic ganglia receiving distributed spinal inputs. The review demonstrates that in many ways the pelvic ganglia differ substantially from other autonomic ganglia. Pelvic ganglia may also provide a useful system in which to study many fundamental neurobiological questions of broader relevance.

Androgen-sensitive preganglionic neurons innervate the male rat pelvic ganglion

In adult male rats many pelvic autonomic ganglion cells change in structure and function after androgen deprivation. In this study we have investigated whether preganglionic neurons in the lumbar and sacral spinal cord that innervate these ganglion cells are also androgen-sensitive. Numerous spinal neurons retrogradely labelled from the pelvic ganglion possessed androgen receptor immunoreactivity and this was diminished by castration or enhanced by additional testosterone exposure. These comprised 27-77% of all preganglionic neurons innervating the pelvic ganglion, depending on the spinal level and whether animals were administered testosterone prior to sacrifice or not. When adult animals were castrated, no change occurred in the soma size or number of primary dendrites in these lumbar or sacral preganglionic neurons. Mean dendrite length was also determined in lumbar preganglionic neurons supplying the pelvic ganglion, but was not affected by castration. However, the total volume of lumbar preganglionic terminal varicosities supplying each noradrenergic pelvic ganglion cell decreased in parallel with the volume of the target neuron. These studies show that many preganglionic autonomic neurons involved in pelvic reflexes are androgen-sensitive, but that androgens selectively influence particular neuronal compartments. The prevalence of androgen receptors in these neurons suggests that testosterone may directly influence gene expression of preganglionic neurons. Together these studies suggest that testosterone (or a metabolite) has widespread actions on pelvic reflex circuits during adulthood and that under conditions of diminished circulating androgens a variety of reflex activities may not function optimally.

The effects of long-term oral administration of L-arginine on the erectile response of rabbits with alloxan-induced diabetes

OBJECTIVE

To investigate the effects of the long-term oral administration of L-arginine on the impaired neurogenic and endothelium-dependent relaxation responses of corpus cavernosum smooth muscle from alloxan-induced diabetic rabbits.

MATERIALS AND METHODS

Thirty-two New Zealand white rabbits were used in four groups of eight each. In group 1, the rabbits received no treatment after the induction of diabetes with alloxan hydrochloride given intravenously; in group 2, L-arginine (1 mg/mL) was administered orally after the induction of diabetes; in group 3, 6 U/day of insulin was injected subcutaneously; group 4 was maintained with no treatment (as litter-mate controls) for 8 weeks. Thereafter, the rabbits were killed by exsanguination and the penis removed en bloc. The reactivity of corpus cavernosum strips from the penis was then assessed in organ chambers.

RESULTS

Relaxation and contraction responses of corpus cavernosum strips to sodium nitroprusside and potassium chloride, respectively, were similar in all groups. Relaxation responses of corpus cavernosum strips elicited by electrical field stimulation and carbachol from rabbits in group 1 were less than in controls; the responses to carbachol were not significantly impaired in group 2 and 3, whereas responses to electrical field stimulation were impaired in both groups when compared with the control group.

CONCLUSION

The impairment of endothelium-dependent and nerve-mediated relaxation by diabetes appears to involve an alteration in nitric oxide/cyclic GMP pathway. Administration of oral L-arginine increased endothelium-dependent relaxation, probably through activating nitric oxide synthase. Additionally, decreasing elevated blood glucose concentration and advanced glycosylation products by insulin treatment protected endothelium-dependent relaxation, whereas neither L-arginine nor insulin treatment restored impaired neurogenic relaxation.

Effects of androgens on the expression of nitric oxide synthase mRNAs in rat corpus cavernosum

OBJECTIVE

To examine the effects of androgens on erectile response and the expression of nitric oxide synthase (NOS) isoform mRNAs in the penile corpus cavernosum of castrated rats.

MATERIALS AND METHODS

The study comprised 50 adult male Sprague-Dawley rats in five groups: sham controls; castrated; castrated and receiving testosterone; castrated and receiving dihydrotestosterone (DHT); castrated and receiving testosterone and 5alpha-reductase inhibitor (finasteride). Androgen replacements were administered via implants of silicone tubing. After 7 days, some animals underwent electrical stimulation of the cavernosal nerves and the remainder were used for further analysis. NOS activity was measured in the soluble fraction of the corpus cavernosum, using the Griess reaction. Total RNA was isolated and nNOS and eNOS mRNA expression examined using semiquantitative reverse-transcriptase polymerase chain reaction.

RESULTS

Castration caused a marked decrease in erectile response and the ratio of maximal intracavernosal pressure (ICPmax) to systemic blood pressure (SBP), although both testosterone and DHT effectively restored the response to normal. NOS activity and the amount of nNOS mRNA were reduced in castrated rats but restored by androgen replacement. Although there was no significant difference in NOS activity between the androgens, nNOS mRNA expression was higher in rats treated with DHT. There were no effects of androgen in rats treated with finasteride, as the ICPmax/SBP ratio, NOS activity and amount of nNOS mRNA decreased. eNOS mRNA expression was independent of androgen.

CONCLUSIONS

Androgens enhance nNOS gene expression in the penile corpus cavernosum of rats, suggesting that they play an important role in maintaining NOS activity. Of the two androgens, DHT was more potent.

Androgenic maintenance of inflow and veno-occlusion during erection in the rat

Ongoing studies in this laboratory are designed to determine the role of androgens in the maintenance of the erectile response in the rat. Testosterone-treated castrated rats (TESTO) and untreated castrated rats (CASTRATE) were used for measurement of the rate at which blood flows into the cavernous sinuses by timed collections of blood after partial amputation of the penis. A laser Doppler flow meter was employed to determine whether androgens also regulate the veno-occlusive mechanism that controls the rate of blood flow out of the sinuses. Erection was induced by direct electrical stimulation of the autonomic ganglion that controls cavernosal blood flow in the erectile response. The results of these studies showed that blood flow into the sinuses was approximately twice as great in the TESTO animals as the CASTRATE rats. Furthermore, during ganglionic stimulation, veno-occlusion occurred in the TESTO rats but failed to occur in the CASTRATE rats. The dependence of these responses on nitric oxide (NO) was demonstrated by showing that injection of sodium nitroprusside (SNP) enhances the intracavernosal pressure response in TESTO rats but not CASTRATE animals. However, when SNP injection was combined with ganglionic stimulation, veno-occlusion did occur in the CASTRATE animals. Taken together, these studies show that both the rate of blood flow into the cavernous sinuses and the blood flow out are under androgenic regulation and may involve the actions of NO.