Effects of androgen and ageing on gene expression of vasoactive intestinal polypeptide in rat corpus cavernosum

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.

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.

Effects of testosterone supplementation on prevention of age-related penile remodeling

Erectile dysfunction develops among 46.2% of men between 40 and 70 years. Studies demonstrated substitution on detrusor muscle by collagen due testosterone deprivation. It is clear the correlation among aging and oxidative stress, accelerating apoptosis process in many tissues. This study aims to demonstrate the collagen substitution over the muscle fibers on muscle structure of rat's penis and the effects of testosterone supplementation. Sixteen senescent Wistar rats were divided into two groups: treatment (receiving standard supplementation testosterone dose) and control (receiving equivalent saline solution). Testosterone was dosed on D0 and D56 of study. All penises were prepared with picrosirius colored histology; stereology was applied to determine the volumetric density of collagen fibers (Vv). Analysis of variance demonstrated testosterone group's replacement therapy to be effective, while the androgenic decline continued by the time of experiment in control group (p < 0.05). Testosterone group had Vv of 20.6%, lower than control group (47.8%); t-test (p < 0.001). Pearson's correlation demonstrated an inverse correlation between the Vv and testosterone's levels (p < 0.001). This is a pioneer study on demonstration of structural alterations over the cavernous corpora muscle caused by deprivation of testosterone on elderly rat. These finding implicate that the testosterone levels can influence, not only the libido, but also the erectile function.

Testosterone supplementation's effects on age-related bladder remodeling - experimental study in rats

OBJECTIVE

This study was designed to evaluate the effect of testosterone replacement on the fibrotic process of the detrusor bladder muscle during the normal aging process.

METHODS

15 Wistar senile rats, aged between 18 and 20 months were divided into two groups: testosterone group - 11 animals submitted to the administration of testosterone undecanoate (50 mg/kg intramuscular), once per month; and, Control group - four animals underwent a sham procedure. At the end of eight weeks, animals from both groups were sacrificed; bladders were removed and subsequently stereologically evaluated to determine the volumetric density of collagen fibers. The success of testosterone administration was confirmed by the measurement of serum testosterone at the beginning and end of the experiment.

RESULTS

In the replacement group, testosterone average was 3.2 ng/ml, whereas in the control group, the mean testosterone at the end of the experiment was 0.64 ng/ml (p < 0.05). Analysis of stereological collagenous fiber showed higher density in the control group compared to the testosterone group I (56% versus 37.02%, respectively). The difference of volume concentration of collagen between both groups was statistically significant (p < 0.000).

CONCLUSION

Bladder wall fibrosis was reduced in senile rats subjected to testosterone replacement.

Differential effects of estrogen/androgen on the prevention of nonalcoholic fatty liver disease in the male rat

It is important to clarify the distinct contributions of estrogen/estrogen receptor (ER) and androgen/androgen receptor (AR) signaling and their reciprocal effects on the regulation of hepatic lipid homeostasis. We studied the molecular mechanisms underlying the preventive effects of estradiol (E2), dihydrotestosterone (DHT), or E2+DHT on high-fat diet-induced nonalcoholic fatty liver disease (NAFLD) in an orchidectomized Sprague-Dawley (SD) rat model. E2 is shown to be associated with decreased fatty acid synthesis in hepatic zone 3-specific manner by increasing the phosphorylation of acetyl coenzyme-A carboxylase via an ERα-mediated pathway. DHT is shown to be associated with decreased lipid accumulation and cholesterol synthesis in a hepatic zone 1-specific manner by increasing expression of carnitine palmitotyltransferase1 and phosphorylation of 3-hydroxy-3-methyl-glutaryl-CoA reductase via an AR-mediated pathway. E2+DHT showed an additive positive effect and normalized all three impaired zones of the liver. Gene expression changes in human severe liver steatosis were similar to those of experimental rat NAFLD. Steroids reversed the histopathological NAFLD changes, likely by decreasing fatty acid and cholesterol synthesis and increasing β-oxidation. The diverse steroid effects (ER/AR) on NAFLD prevention in male rats indicate the potential applicability of ER/AR modulators for NAFLD treatment.

Effects of oral finasteride on erectile function in a rat model

INTRODUCTION

Many clinical studies reported finasteride-related erectile dysfunction, but to date, few animal experiments have focused on it.

AIM

To investigate the effects of oral finasteride on erectile function in a rat model.

MAIN OUTCOME MEASURES

Erectile responses and morphological changes.

METHODS

Adult, male Sprague-Dawley rats were divided into four groups (25/group): (i) control; (ii) castration; (iii) castration with testosterone (T) replacement; and (iv) oral finasteride treatment. Four weeks later, erectile function was measured by the ratio of intracavernosal pressure and mean arterial blood pressure upon electrical stimulation of the cavernous nerve. Serum T and dihydrotestosterone (DHT) and intraprostatic DHT were measured. The weights and histopathological features of the penile corpus cavernosum and prostate were examined.

RESULTS

Serum T and DHT and intraprostatic DHT concentrations, erectile function, and mean weights of the corpus cavernosum and prostate were lowest in group 2. There was no significant difference in the serum T concentration and erectile function between groups 4 and 1. However, the serum and intraprostatic DHT concentrations were significantly lower in group 4 than in group 1 (both P < 0.001). The tissue weights of the corpus cavernosum and prostate were reduced by 25.9% and 92.3% in group 4 compared with group 1 (both P < 0.001). Histopathology revealed a significant atrophy of the prostate in groups 2 and 4. There was a significant decrease in the smooth muscle content in group 2, but not in groups 3 and 4.

CONCLUSIONS

In a rat model, finasteride treatment for 4 weeks reduces the weight of the corpus cavernosum but appears not to affect the erectile responses to electrical stimulation of the cavernous nerve. As erection is a complex process involving important signaling in the brain, further studies are necessary to demonstrate the long-term effects of finasteride on both central and peripheral neural pathways of erection.

Changes in androgen receptor, estrogen receptor alpha, and sexual behavior with aging and testosterone in male rats

Reproductive aging in males is characterized by a diminution in sexual behavior beginning in middle age. We investigated the relationships among testosterone, androgen receptor (AR) and estrogen receptor alpha (ERalpha) cell numbers in the hypothalamus, and their relationship to sexual performance in male rats. Young (3months) and middle-aged (12months) rats were given sexual behavior tests, then castrated and implanted with vehicle or testosterone capsules. Rats were tested again for sexual behavior. Numbers of AR and ERalpha immunoreactive cells were counted in the anteroventral periventricular nucleus and the medial preoptic nucleus, and serum hormones were measured. Middle-aged intact rats had significant impairments of all sexual behavior measures compared to young males. After castration and testosterone implantation, sexual behaviors in middle-aged males were largely comparable to those in the young males. In the hypothalamus, AR cell density was significantly (5-fold) higher, and ERalpha cell density significantly (6-fold) lower, in testosterone- than vehicle-treated males, with no age differences. Thus, restoration of serum testosterone to comparable levels in young and middle-aged rats resulted in similar preoptic AR and ERalpha cell density concomitant with a reinstatement of most behaviors. These data suggest that age-related differences in sexual behavior cannot be due to absolute levels of testosterone, and further, the middle-aged brain retains the capacity to respond to exogenous testosterone with changes in hypothalamic AR and ERalpha expression. Our finding that testosterone replacement in aging males has profound effects on hypothalamic receptors and behavior has potential medical implications for the treatment of age-related hypogonadism in men.

Cyclic nucleotide signaling in cavernous smooth muscle

INTRODUCTION

Penile erection depends on cavernous smooth muscle relaxation that is principally regulated by cyclic nucleotide signaling. It is hoped that a comprehensive review of publications relevant to this subject will be helpful to both scientists and clinicians who are interested in the sciences of erectile function/dysfunction. AIMS. To review the roles of extracellular signaling molecules, their receptors, intracellular effectors, and phosphodiesterases in cyclic nucleotide signaling that leads to cavernous smooth muscle relaxation. The involvement of these molecules in the development of erectile dysfunction and the possibility of using them as therapeutic agents or targets are also discussed.

METHODS

Entrez, the search engine for life sciences, was used to search for publications relevant to the topics of this review. Keywords used in the searches included vascular, cavernous, penis, smooth muscle, signaling molecules (adenosine, nitric oxide, etc.), and key elements in the cyclic nucleotide signaling pathways (cAMP, cGMP, cyclases, PKG, PKA, etc.). Articles that are dedicated to the study of erectile function/dysfunction were prioritized for citation.

RESULTS

More than 1,000 articles were identified, many of which are studies of the vascular system and are therefore reviewed but not cited. Studies on erectile function have identified both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling pathways in cavernous smooth muscle. Many signaling molecules of these two pathways have been shown capable of inducing erection when administered intracavernously. However, for sexually induced erection, nitric oxide (NO) is the responsible signaling molecule and it passes on the signal through soluble guanyl cyclase (sGC), cGMP, and protein kinase G (PKG).

CONCLUSIONS

The NO/sGC/cGMP/PKG pathway is principally responsible for sexually stimulated erection. Detumescence is mainly carried out by the degradation of cGMP by phosphodiesterase 5. Both cAMP and cGMP signaling pathways are susceptible to genetic and biochemical alterations in association with erectile dysfunction. Several key elements along these pathways are potential therapeutic targets.

Gene transfer of vasoactive intestinal polypeptide into the penis improves erectile response in the diabetic rat

OBJECTIVES

To determine the feasibility of transfecting penile corpora cavernosa with pcDNA3/vasoactive intestinal polypeptide (VIP) cDNA, which encodes for VIP in streptozotocin (STZ)-diabetic rats, to clarify whether transfection of VIP cDNA into the cavernosum affects the physiological response to cavernosal nerve stimulation, and whether this process would affect other organs in the diabetic rat model in vivo.

MATERIALS AND METHODS

pcDNA3/VIP cDNA was injected into the corpus cavernosum of STZ-induced diabetic Sprague-Dawley rats. The intracavernosal pressure (ICP) and response to electrical stimulation of the cavernosal nerve (15 Hz, 1.5 ms, 20 V, 1 min) were measured in subsamples of rats at 1, 3, 7 and 14 days after injection; after measuring the ICP the animals were killed, and penile, hepatic, renal artery and abdominal aorta tissue samples were frozen in liquid nitrogen and stored at -80 degrees C. The gene expression of VIP in all samples, assessed as the expression of VIP mRNA, was estimated using a semiquantitative reverse-transcription polymerase chain reaction.

RESULTS

The mean amplitude of ICP and expression of VIP mRNA in the cavernosa of the VIP-treated rats was greater at 1, 3, 7 and 14 days after injection (P < 0.05) than in the control animals. There were no changes in the expression of VIP mRNA in hepatic, renal and abdominal aorta samples after injection (P > 0.05).

CONCLUSIONS

VIP cDNA is easily incorporated into corpus cavernosum, and the expression is sustained for > or = 2 weeks in the penis in vivo. The transfer of VIP is capable of altering the physiologically relevant erectile response, as measured by an increase in the ICP after stimulating the cavernosal nerve. The intracorporal micro-injection of pcDNA3/VIP cDNA had little effect on the expression of VIP mRNA in other important organs.

Vasoactive intestinal polypeptide (VIP) is not an androgen-dependent neuromediator of penile erection

The effects of castration on vasoactive intestinal polypeptide (VIP) immunostaining in human corpus cavernosum (CC) and the relationship between VIP immunostaining and erectile function were studied in patients with localised prostate cancer who had (Group 1 = castrated) or had not (Group 2 = control) undergone 3-month neoadjuvant chemical castration before radical prostatectomy. Evaluation of erectile function included medical and sexual history, physical examination, and measurement of total serum testosterone. CC biopsies were taken at the end of radical prostatectomy and samples immunostained with anti-human VIP antibody. Specific staining was quantified by image analysis and expressed in arbitrary units (AU). Chemical castration induced erectile function deterioration in 70% of patients due to loss of sexual interest and confidence in the ability of having an erection rather than reduced ability of obtaining sexually induced erections. Average VIP content was 34.5 AU in Group 1 and 39 AU in Group 2 and this difference was not statistically significant. Chemical castration does not influence VIP immunostaining of human CC, suggesting that VIP is not an androgen-dependent neuromediator of penile erection and that it can be responsible for sexually induced erections in castrated patients.

Characterization of VIP and PACAP receptors in cultured rat penis corpus cavernosum smooth muscle cells and their interaction with guanylate cyclase-B receptors

Penile corpus cavernosum smooth muscle relaxation can be induced by both cyclic AMP and cyclic GMP-elevating agents, but possible interactions between these two signalling pathways are still poorly understood. Using in vitro cultured rat penile corpus cavernosum smooth muscle (CCSM) cells, we have characterized the local expression and functional activities of receptors for the cAMP-elevating peptides, PACAP and VIP, and for the cGMP-elevating peptides, CNP and ANP. Stimulation of the cells with various concentrations of PACAP(-27/-38) or VIP resulted in rapid and dose-dependent increases in cyclic AMP levels. RT-PCR analyses revealed gene expression of PAC(1) and VPAC(2) but not of VPAC(1) receptors in the cells. The natriuretic peptide, CNP, and the nitric oxide donor, sodium nitroprusside, were capable of enhancing cyclic GMP formation, indicating the presence of membrane-associated in addition to soluble guanylate cyclase (sGC) activities in these cells. Findings that cyclic GMP formation was preferentially activated by CNP but not by the related peptide, ANP, were consistent with RT-PCR analyses, demonstrating gene expression of the CNP receptor, GC-B, but not of the ANP receptor, GC-A, in these cells. Prior exposure of the cells to 10(-8) M PACAP resulted in a marked down-regulation of GC-B activity, whereas sGC was not affected. These findings provide functional and molecular evidence for the presence of three receptors, PAC(1), VPAC(2) and GC-B, involved in cyclic nucleotide signalling in penile CCSM cells. The observed cross-talk of the PACAP/VIP receptors with GC-B but not with sGC may have implications for the therapy of erectile dysfunction.