Sildenafil inhibits phosphodiesterase type 5 in human clitoral corpus cavernosum smooth muscle

Testosterone positively regulates vagina NO-induced relaxation: an experimental study in rats

PURPOSE

Female sexual response involves a complex interplay between neurophysiological mechanisms and the nitric oxide (NO)-mediated relaxation of clitoris and vagina. The aim of this study was to evaluate sex steroids regulation of the relaxant pathway in vagina, using a validated animal model.

METHODS

Subgroups of OVX Sprague-Dawley rats were treated with 17β-estradiol, testosterone, or testosterone and letrozole, and compared with a group of intact animals. Masson's trichrome staining was performed for morphological evaluation of the distal vaginal wall, in vitro contractility studies investigated the effect of OVX and in vivo treatments on vaginal smooth muscle activity. RNA from vaginal tissue was analyzed by semi-quantitative RT-PCR.

RESULTS

Immunohistochemical analysis showed that OVX induced epithelial and smooth muscle structural atrophy, testosterone and testo + letrozole increased the muscle bundles content and organization without affecting the epithelium while 17β-estradiol mediated the opposite effects. In vitro contractility studies were performed on noradrenaline pre-contracted vaginal strips from each experimental group. Acetylcholine (0.001-10 µM) stimulation induced a concentration-dependent relaxation, significantly reduced by NO-synthase inhibitor L-NAME and by guanylate cyclase inhibitor ODQ. OVX resulted in a decreased responsiveness to acetylcholine, restored by testosterone, with or without letrozole, but not by 17β-estradiol. OVX sensitivity to the NO-donor SNP was higher than in the control. Vardenafil, a PDE5 inhibitor, enhanced SNP effect in OVX + testosterone as well as in control, as supported by RNA expression analysis.

CONCLUSIONS

Our study demonstrates that testosterone improves the NO-mediated smooth muscle vaginal cells relaxation confirming its role in maintaining the integrity of muscular relaxant machinery.

Repurposing of the PDE5 Inhibitor Sildenafil for the Treatment of Persistent Pulmonary Hypertension in Neonates

Nitric oxide (NO), an important endogenous signaling molecule released from vascular endothelial cells and nerves, activates the enzyme soluble guanylate cyclase to catalyze the production of cyclic guanosine monophosphate (cGMP) from guanosine triphosphate. cGMP, in turn, activates protein kinase G to phosphorylate a range of effector proteins in smooth muscle cells that reduce intracellular Ca²⁺ levels to inhibit both contractility and proliferation. The enzyme phosphodiesterase type 5 (PDE5) curtails the actions of cGMP by hydrolyzing it into inactive 5'-GMP. Small molecule PDE5 inhibitors (PDE5is), such as sildenafil, prolong the availability of cGMP and therefore, enhance NO-mediated signaling. PDE5is are the first-line treatment for erectile dysfunction but are also now approved for the treatment of pulmonary arterial hypertension (PAH) in adults. Persistent pulmonary hypertension in neonates (PPHN) is currently treated with inhaled NO, but this is an expensive option and around 1/3 of newborns are unresponsive, resulting in the need for alternative approaches. Here the development, chemistry and pharmacology of PDE5is, the use of sildenafil for erectile dysfunction and PAH, are summarized and then current evidence for the utility of further repurposing of sildenafil, as a treatment for PPHN, is critically reviewed.

Type 5 phosphodiesterase (PDE5) and the vascular tree: From embryogenesis to aging and disease

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Vascular development depends on the timely differentiation of endothelial and smooth muscle cells.

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Vascular aging and vascular disease are influenced by endothelial and vascular smooth muscle cell compartments.

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A survey of the literature on the role of PDE5 in vascular development, aging and disease is reported.

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The role of PDE5 on vascular development, aging and disease needs to be further investigated by its genetic ablation.

Vascular tree development depends on the timely differentiation of endothelial and vascular smooth muscle cells. These latter are key players in the formation of the vascular scaffold that offers resistance to the blood flow. This review aims at providing an overview on the role of PDE5, the cGMP-specific phosphodiesterase that historically attracted much attention for its involvement in male impotence, in the regulation of vascular smooth muscle cell function. The overall goal is to underscore the importance of PDE5 expression and activity in this cell type in the context of the organs where its function has been extensively studied.

Differential Effects of Testosterone and Estradiol on Clitoral Function: An Experimental Study in Rats

INTRODUCTION

Female sexual response is a complex phenomenon in which psychological, neurologic, and vascular mechanisms and hormonal factors interact. During the arousal phase, they cooperate to increase genital blood flow, thus inducing engorgement of the clitoris and lubrication of the vagina. Regulation of vascular and non-vascular smooth muscle tone is the crucial event in the erectile process. Preclinical studies have suggested that nitric oxide (NO) is the main vasodilator neurotransmitter modulating, through the second messenger cyclic guanosine monophosphate (cGMP), clitoral flow vessels.

AIM

To investigate the effects of sexual steroid hormones on pro-erectile and relaxant (mediated by NO and cGMP) and anti-erectile and contractile (mediated by ras homolog gene family member A [RhoA] and Rho-associated protein kinase [ROCK]) mechanisms in the clitoris using a validated animal model of female ovariectomized Sprague-Dawley rats.

METHODS

Subgroups of ovariectomized rats were treated with 17β-estradiol, progesterone, testosterone, or testosterone and letrozole for 6 weeks. The experimental groups were compared with a control group of intact rats.

MAIN OUTCOME MEASURES

Sex steroids plasma levels were assessed and in vitro contractility studies were carried out in order to investigate the effect of ovariectomy and in vivo treatments on clitoris smooth muscle activity. Smooth muscle cells (SMCs) from rat clitoral biopsies were isolated and characterized. RhoA activity was determined in SMCs cell cultures. RNA from tissues and cells was analyzed by quantitative real-time RT-PCR.

RESULTS

Using real-time polymerase chain reaction, testosterone treatment upregulated the expression of NO-mediated pathway genes (endothelial and neuronal NO synthase, guanylate cyclase soluble subunit-α₃, guanylate cyclase soluble subunit-β₃, cGMP-dependent protein kinase 1, and phosphodiesterase type 5). Conversely, estrogen replacement upregulated the expression of calcium-sensitizing RhoA-ROCK pathway genes. In vitro contractility studies were performed on phenylephrine pre-contracted clitoris strips. Ovariectomy resulted in a decreased responsiveness to Y-27632, a ROCK inhibitor, which was fully restored by 17β-estradiol supplementation. To further examine the effect of 17β-estradiol on the RhoA-ROCK pathway, smooth muscle cells were isolated from rat clitoris and their migration capacity was evaluated.

CONCLUSION

Collectively, these data demonstrate that testosterone improves the relaxation of vascular smooth muscle cells through the NO-cGMP pathway, and that testosterone and 17β-estradiol are necessary to maintain a functional contractile and relaxant machinery in the clitoris. This new concept might provide support for the concomitant use of estrogen and testosterone during the treatment of sexual arousal disorders related to hormonal imbalance or insufficiency.

Sildenafil citrate in the treatment of pain in primary dysmenorrhea: a randomized controlled trial

STUDY QUESTION

Is a vaginal preparation of sildenafil citrate capable of alleviating acute menstrual pain in patients with primary dysmenorrhea (PD)?

SUMMARY ANSWER

A vaginal preparation of sildenafil citrate is capable of alleviating acute menstrual pain in patients with PD with no observed adverse effects.

WHAT IS KNOWN ALREADY

Oral preparations of nitric oxide (NO) donor drugs augment relaxant effects of NO on myometrial cells, reverse the vasoconstriction caused by prostaglandins and successfully alleviate pain, but the incidence of side effects is too high for routine clinical use. Sildenafil citrate inhibits type 5-specific phosphodiesterase (PDE5), thus preventing the degradation of cyclic guanosine monophosphate (cGMP) in the muscle and augmenting the vasodilatory effects of NO. Therefore, by inhibiting PDE5, the tissue remains relaxed and more blood can circulate through. It has been used previously in a vaginal form with no observed side effects, and it enhances endometrial blood flow.

STUDY DESIGN, SIZE, DURATION

A double-blind, randomized, controlled trial comparing vaginal preparation of sildenafil citrate (100 mg single dose) to a placebo in 62 PD patients at the time of painful menstruation was conducted. The primary outcome was total pain relief over 4 consecutive hours (TOPAR4) comparing sildenafil citrate to placebo, where higher TOPAR4 scores represent better pain relief. Secondary outcomes were pain relief as measured by the visual analog scale (VAS) and uterine artery pulsatility index (PI). Subjects were recruited from December 2007 to January 2011. The trial was stopped due to closeout of the funding for the study.

PARTICIPANTS, SETTINGS, METHODS

Participants were women in good health, were aged 18-35 years and suffered from moderate to severe PD. They were randomized to either vaginal placebo or 100 mg vaginal sildenafil citrate in a 1:1 ratio using random permuted blocks having a block size of 4. At baseline and 1, 2, 3, and 4 h post-treatment, patients were asked to provide assessment of their degree of pain using two scales: (i) pain on the 5-level ordinal scale used for TOPAR4 calculation and (ii) pain level on the VAS. The study ended 4 h after treatment initiation.

MAIN RESULTS AND THE ROLE OF CHANCE

Twenty-five subjects completed the study. Using the TOPAR4 score, the sildenafil citrate group had significantly better pain relief compared with the placebo group [mean (SD): 11.9 (3.2) versus 6.4 (2.1), respectively; difference in means = 5.3; 95% CI: (2.9,7.6); P < 0.001)]. On the VAS, sildenafil citrate provided better pain relief than placebo at each time point. At the 2-h time point, the PI was significantly lower in the sildenafil citrate group compared with the placebo group [mean (SD): 1.6 (0.6) versus 2.3 (0.5), respectively; difference in means = -0.7; 95% CI: (-1.2, -0.1); P = 0.01)].

LIMITATIONS, REASONS FOR CAUTION

Since we did not meet our sample size due to the loss of funding and could not confirm our primary hypothesis, larger studies of longer duration, likely multi-center, are needed to confirm the findings from this study.

WIDER IMPLICATIONS OF THE FINDINGS

A number of medications have been investigated to improve the treatment options for PD, but most have proven unsuccessful or to have an unfavorable risk/benefit ratio. Since PD is a condition that most women suffer from and seek treatment for at some point in their lives, our study offers hope that vaginal sildenafil citrate is a safe and effective option for patients who do not desire or are unresponsive to treatments now available on the market.

STUDY FUNDING/COMPETING INTERESTS

Funding for this study was provided by National Institutes of Health (NIH) grants RO3 TW007438 and K24 HD01476. The authors report no relevant conflicts of interest.

TRIAL REGISTRATION NUMBER

NCT00123162 (Clinical trials.gov).

Expression and distribution of key enzymes of the cyclic GMP signaling in the human clitoris: relation to phosphodiesterase type 5 (PDE5)

The clitoris contributes to the normal female sexual response cycle. A significance of cyclic guanosine monophosphate (GMP) has been assumed in the control of clitoral vascular smooth muscle. As only a few investigations on the physiology of the vascular and non-vascular clitoral tissue have been carried out, knowledge on the mechanisms controlling this particular female genital organ is still vague. It has been suggested that human clitoral corpus cavernosum smooth muscle is regulated by nitric oxide (NO)/cyclic GMP and related key enzymes, such as NO synthases (NOSs) and the phosphodiesterase type 5 (PDE5). The present study evaluated in the human clitoris, by means of immunohistochemistry, the expression and distribution of key enzymes of the cyclic GMP pathway, such as the endothelial NOS, PDE2, PDE11 and cyclic GMP-dependent protein kinase type I (cGKI) in relation to the PDE5. Immunohistochemistry revealed the presence of PDE2, PDE5 and cGKI in the smooth muscle wall of blood vessels transversing the supepithelial and stromal space. Immunosignals specific for PDE2 were also identified in interstitial-like cells located in the basal epithelial layer. Staining for PDE11A was observed in single nerve trunks located in the clitoral stroma. The results are in favor of a role of the cyclic GMP signaling in the control of clitoral blood flow. It seems likely that PDE2 and PDE11 are also involved in the mechanism of local (neuro)transmission in the clitoris.

Assessing the clinical efficacy of sildenafil for the treatment of female sexual dysfunction

OBJECTIVE

To review the clinical data regarding the efficacy and safety of sildenafil for the treatment of female sexual dysfunction (FSD).

DATA SOURCES

A MEDLINE search from 1950 to February 2009 was conducted using the key words sildenafil and female sexual dysfunction. Human studies and publication in English were used as primary limits. A combination of several publication-type limits was used to locate the clinical trials (eg, clinical trial, controlled clinical trial, randomized clinical trial). A bibliographic search was also performed of all located articles.

STUDY SELECTION AND DATA EXTRACTION

Clinical trials involving sildenafil treatment of premenopausal and postmenopausal women with FSD and women with FSD due to concomitant medications and/or disease states were reviewed.

DATA SYNTHESIS

An increasing number of clinical trials have been published regarding the treatment of FSD with sildenafil. Eight studies demonstrated a possible benefit from treatment for FSD in patients receiving sildenafil, regardless of dose, while 4 trials did not show any significant differences with treatment. It appears that sildenafil might be beneficial for women with FSD caused by diseases such as multiple sclerosis, type 1 diabetes, spinal cord injury, and use of antidepressant medications.

CONCLUSIONS

Although data suggest a possible role of sildenafil for the treatment of FSD, the information should be interpreted cautiously, as many of the studies included small sample sizes, used inappropriate statistical tests, and used nonvalidated assessment tools. A better FSD classification system and consistent use of validated assessment tools might help alleviate differences among clinical trials and provide a more cohesive foundation for assessing the safety and efficacy of sildenafil for the treatment of FSD.

A literature review and case reports series on the use of phosphodiesterase inhibitors in the treatment of female sexual dysfunction

Summary

The term ‘female sexual dysfunction’ (FSD) encompasses a number of different disorders, and while their aetiologies are not fully understood, the sub-classifications of this broad umbrella term are increasingly becoming more established and accepted. However, there is less consensus regarding the optimal treatment of these conditions. While it is known that phosphodiesterase (PDE5) is involved in the female sexual response, the clinical and research evidence supporting the unlicensed use of PDE5 inhibitors (PDE5i) in women is inconclusive and at times contradictory. In this article we explore this further by means of a comprehensive literature review on the use of PDE5i in the treatment of FSD and we also present our clinical experience of using these drugs in this context.

Erectile dysfunction and lower urinary tract

During the last decades it turned out that the NO/cGMP signaling cascade is one of the most prominent regulators of a variety of physiological and pathophysiological processes in a broad range of mammalian tissues. Thus cGMP is a key second messenger and targeting this pathway by increasing intracellular cGMP levels is a very successful approach in pharmacology as shown for nitrates, PDE5 inhibitors and more recently for stimulators of the guanylate cyclase. Besides the beneficial effects of cGMP elevation in cardiac, vascular, pulmonary, renal or liver disorders the launch of PDE5 inhibitors for the treatment of erectile dysfunction 10 years ago, has directed a lot of attention to the NO/cGMP signaling in the lower urinary tract. Triggered by the use of PDE5 inhibitors in ED it turned out that cGMP is a common regulatory mechanism for lower urinary tract function also beyond ED. In recent years intense research and development efforts were undertaken to elucidate the role of the NO/cGMP and to fully exploit the therapeutic implications of cGMP elevation in urological disorders in ED and beyond. Therefore we have summarized the effects of cGMP elevation for treatment of erectile dysfunction in males and in females. We have also reviewed the recent pre-clinical and clinical lines of evidence for treatment options of benign prostatic hyperplasia and lower urinary tract symptoms in male patients and overactive bladder and urinary incontinence in female patients. In addition we also touch more speculative concepts using cGMP elevating drugs for the treatment of premature ejaculation, peyornies disease and stone disease.

Zaprinast, a phosphodiesterase type-5 inhibitor, alters paced mating behavior in female rats

Nitric oxide (NO) is the primary mediator of blood flow in female genital tissues and drugs that enhance the activity of nitric oxide, such as phosphodiesterase type-5 (PDE-5) inhibitors, increase vaginal blood flow in anesthetized rats. The goal of the present study was to test the effects of one PDE-5 inhibitor, zaprinast, on the display of sexual behaviors in gonadectomized, estrogen- and progesterone-treated female rats. Experiment 1 demonstrates that zaprinast alters paced mating behavior by lengthening the contact-return latency to ejaculation; there is a significant relationship between dose of zaprinast (range 1.5-6 mg/kg) and contact-return latency to ejaculation. Experiment 2 illustrates that zaprinast has no effect on preference for an intact male as measured in a No Contact partner preference test. Rats receiving zaprinast tend to exhibit reduced locomotor activity in both experiments. Collectively, these findings demonstrate that modulation of the NO-cGMP pathway using a PDE-5 inhibitor alters the display of paced mating behaviors in rats.

Short- and long-term effects of Ginkgo biloba extract on sexual dysfunction in women

Ginkgo biloba extract (GBE) facilitates blood flow, influences nitric oxide systems, and has a relaxant effect on smooth muscle tissue. These processes are important to the sexual response in women and, hence, it is feasible that GBE may have a therapeutic effect. The present study was the first to provide an empirical examination of the effects of both short- and long-term GBE administration on subjective and physiological (vaginal photoplethysmography) measures of sexual function in women with Sexual Arousal Disorder. A single dose of 300 mg GBE had a small but significant facilitatory effect on physiological, but not subjective, sexual arousal compared to placebo in 99 sexually dysfunctional women. The long-term effects of GBE on sexual function were assessed in 68 sexually dysfunctional women who were randomly assigned to 8 weeks treatment of either (1) GBE (300 mg/daily), (2) placebo, (3) sex therapy which focused on training women to attend to genital sensations, or (4) sex therapy plus GBE. When combined with sex therapy, but not alone, long-term GBE treatment significantly increased sexual desire and contentment beyond placebo. Sex therapy alone significantly enhanced orgasm function compared with placebo. Long-term GBE administration did not significantly enhance arousal responses beyond placebo. It was concluded that (1) neither short- or long-term administration of GBE alone substantially impacts sexual function in women, (2) a substantial placebo effect on sexual function exists in women with sexual concerns, and (3) teaching women to focus on genital sensations during sex enhances certain aspects of women's sexual functioning.

Expression of messenger ribonucleic acid encoding for phosphodiesterase isoenzymes in human female genital tissues

OBJECTIVES

The use of inhibitors of phosphodiesterase 5 (PDE5) has been suggested to treat symptoms of female sexual dysfunction (FSD). Nonetheless, there has been a relatively low success rate of PDE5 inhibitors in FSD in comparison with male erectile dysfunction. The elevated expression of PDE5 in the human penile erectile tissue is considered the reason for the high clinical efficacy of PDE5 inhibitors in the pharmacotherapy of male erectile dysfunction.

AIM

To evaluate by means of molecular biology the expression of messenger ribonucleic acid expression (mRNA) encoding for cyclic AMP and cyclic GMP PDE isoenzymes in female genital tissues.

MAIN OUTCOME MEASURES

The amount of mRNA transcripts specifically encoding for cyclic AMP- and/or cyclic GMP-degrading PDE isoenzymes was determined.

METHODS

Human clitoral, labial, and vaginal tissue was obtained from four female cadavers (age at death: 18-42 years). The expression of mRNA specifically encoding for PDE1A, 1B, 1C, 2A, 4A, 5A, 10A, and 11A was elucidated by means of real-time polymerase chain reaction (PCR) analysis (TaqMan). Human penile erectile tissue (corpus cavernosum [HCC]) was used as a reference tissue.

RESULTS

mRNA encoding for all PDE isoforms mentioned above is expressed in the female genital tissues. Different magnitudes of mRNA expression were observed: a predominant expression of mRNA encoding for PDE1A but only insignificant amounts of PDE1B, 1C, 4A, 10, and 11A mRNA were registered. With PDE1A being the only exception, the mRNA expression was always higher in the HCC than in the female genital tissues. Especially, the expression of mRNA encoding for PDE5 was several-fold higher in the HCC.

CONCLUSION

On the mRNA level, various PDE isoforms are expressed in the clitoris, labia, and vagina. It remains to be established as to whether the low expression of PDE5 in female genital tissue might be a negative predictor for the success of PDE5 inhibitors in the treatment of FSD.

PDE5 inhibitors beyond erectile dysfunction

The phosphodiesterase type-5 (PDE5) inhibitors sildenafil, vardenafil and tadalafil are widely used first-line therapy for erectile dysfunction (ED). Since the advent of sildenafil in 1998, more than 40 million men worldwide have been successfully treated with these compounds. The safety and high tolerability of PDE5 inhibitors make them an attractive tool to investigate further physiological functions of PDE5, for example the modulation of intracellular cyclic GMP (cGMP) pools. As cGMP is a key component of intracellular signaling this may provide novel therapeutic opportunities beyond ED even for indications in which chronic administration is necessary. The approval of sildenafil for the treatment of pulmonary hypertension in 2005 was a notable success in this area of research. A number of other potential new indications are currently in various phases of preclinical research and development. In recent years, extensive but very heterogeneous information has been published in this field. The aim of this review is to summarize existing preclinical and clinical knowledge and critically discuss the evidence to support potential future indications for PDE5 inhibitors.

Immunohistochemical distribution of cyclic nucleotide phosphodiesterase (PDE) isoenzymes in the human vagina: A potential forensic value?

OBJECTIVES

Phosphodiesterase (PDE) isoenzymes are key proteins involved in the maintenance of the normal function of various tissues of the human body including those of the male and female urogenital tract. More recently, PDEs and their main substrates, cyclic GMP and cyclic AMP, have also been assumed to play a crucial role in the control of the human vagina. In order to elucidate the potential significance of phosphodiesterases as marker proteins in female genital organs, it was the aim of the present study to evaluate by means of immunohistochemistry the distribution of cGMP- and cAMP-PDE isoenzymes in specimens of the human vagina.

METHODS

Conventional immunohistochemical techniques (double antibody technique, laser fluorescence microscopy) were applied to sections of the human vaginal wall in order to evaluate the presence of the PDE isoenzymes 1, 2, 3, 4, 5 and 10.

RESULTS

Immunoreactivities (IR) specific for PDE1 (cAMP/cGMP-PDE, Ca(2+)/Calmodulin-dependent), PDE2 (cAMP-PDE, cGMP-dependent) and PDE5 (cGMP-PDE) were exclusively registered in the smooth musculature of vaginal arterial vessels, whereas no signals were detected in non-vascular tissue. IR indicating the expression of the cAMP-degrading PDE4 was mainly observed in the vaginal epithelium. Vaginal epithelial cells also presented immunosignals specific for PDE3 (cAMP-PDE, inhibited by cGMP) and PDE10 (dual substrate PDE), nevertheless, these stainings were less abundant than those related to the PDE4. IR for PDE10 was also registered in inflammatory cells located in the subepithelial region of the vaginal wall.

CONCLUSION

Our study revealed the presence of IR specific for PDE1, PDE2, PDE4, PDE5 and PDE10 in sections of the human vagina and demonstrated that these enzymes are not evenly distributed in the tissue. Especially, the prominent expression of the cyclic AMP-PDE4A in the vaginal epithelium may give hint to a potential significance of this isoenzyme as a forensic marker protein. The findings give a rationale to investigate further as to whether the immunohistochemical detection of PDE4 may represent a new forensic tool in order to identify human vaginal epithelial cells.

Immunohistochemical description of cyclic nucleotide phosphodiesterase (PDE) isoenzymes in the human labia minora

INTRODUCTION

Up until now, only minimal research has been carried out on those female genital organs known to contribute to the normal cycle of sexual arousal and orgasm. Some findings indicated that there might be a significance of cyclic nucleotide-mediated pathways in the control of the normal function of female genital tissues.

AIM

To elucidate, by means of immunohistochemistry, the distribution of the phosphodiesterase (PDE) isoenzymes 1, 3, 4, 5, 10, and 11 in the human labia minora.

MAIN OUTCOME MEASURES

The amount of immunohistochemical staining specific for cyclic adenosine monophosphate (cAMP)- and/or cyclic guanosine monophosphate (cGMP)-degrading PDE isoenzymes was detected.

METHODS

Human labial tissue was obtained from four female cadavers (age at death: 18-42 years). Vibratome sections prepared from formaldehyde-fixated tissue specimens were incubated with primary antibodies directed against the respective PDE isoenzymes. Sections were then incubated with fluorochrome (fluorescein isothiocyanate, Texas Red)-labeled secondary antibodies. Visualization was commenced by means of a laser fluorescence microscope.

RESULTS

Immunostaining indicating the expression of PDE4 and PDE5 was abundantly observed in the smooth musculature of vessels interspersing the tissue. Immunoreactions specific for PDE3 were recognized in epithelial and subepithelial layers, sebaceous glands, and interstitial or neuroendocrine-like single cells located in the epithelium. Signals related to PDE10 and PDE11 were limited to the epithelium or glandular-like structures, respectively.

CONCLUSIONS

Our results, for the first time, demonstrate the presence of cAMP- and cGMP-PDE isoenzymes in the human labia minora and give a hint to a significance of PDE4 and PDE5 in the control of labial vascular tissue function.

[Sexuality and pharmacotherapy. Medication-induced disorders of sexual response and pharmacotherapeutic options for the treatment of sexual dysfunctions]

This contribution addresses two different areas of the complex relationship between pharmacotherapy and sexual function and dysfunction in men and women. As many impairments of sexual function are caused by side effects of medications, particularly psychotropic drugs, the first part of the paper describes substances and mechanisms often related to sexual dysfunction with a special focus on antidepressants and neuroleptics. While serotonin reuptake inhibitors entail a high risk of sexual dysfunction, it is often difficult to differentiate the negative impact of the drug from the impairment caused by the mental disorder itself. Ways to deal with these dysfunctions and remedial measures are discussed. In the second section, current pharmacological treatments for female and male sexual dysfunctions are reviewed. While there is no approved pharmacotherapy with established efficacy for female sexual dysfunction with the possible exception of the transdermal testosterone patch for surgically menopausal women, effective pharmacological therapies are available for male erectile disorders. In addition, testosterone substitution is the treatment of choice for hypoactive sexual desire disorders caused by hypogonadism. As sexual dysfunctions are often caused by a mixture of psychological and organic factors, treatment strategies combining pharmacological options and sex therapy are advocated.

Antidepressant‐Induced Inhibition of Genital Vascular Responses Is Reversed by Vardenafil in Female Rabbits

INTRODUCTION

Administration of serotonin reuptake inhibitors (SRI) or serotonin and norepinephrine reuptake inhibitors (SNRI) relieves depressive symptoms but may cause sexual dysfunction in women and men.

AIM

The aim of the present study was to evaluate the effects of the phosphodiesterase type 5 (PDE5) inhibitor, vardenafil, on inhibition of genital vascular responses (GVR) induced by SRI or SNRI administration in female rabbits.

METHODS

Vaginal and clitoral vasodilatory responses to pelvic nerve electrical stimulation were measured by laser Doppler flow needle probes.

RESULTS

GVR were significantly potentiated by vardenafil even at the low dose of 0.1 mg/kg, in clitoris and vagina (181 +/- 22% and 180 +/- 31% of control, in vagina and clitoris, respectively, at 8 Hz). The selective SRI, paroxetine (5 mg/kg), significantly inhibited GVR in female rabbits (54 +/- 5% and 48 +/- 6% of control). GVR were also significantly inhibited by the SNRIs, venlafaxine (5 mg/kg) (57 +/- 3% and 32 +/- 11%) and duloxetine (1 mg/kg) (40 +/- 7% and 28 +/- 5%). Treatment with vardenafil (0.1 and 0.3 mg/kg) completely reversed the inhibition of GVR induced by paroxetine, venlafaxine, or duloxetine.

CONCLUSIONS

Potentiation of the nitric oxide (NO) pathway by vardenafil improves vascular sexual responses in female rabbits and overcomes the inhibitory effects of acutely administered antidepressants on GVR, irrespective of the underlying pathophysiologic mechanism, i.e., disruption of the NO pathway or enhancement of alpha-adrenergic mechanisms. PDE5 inhibition may represent a reasonable approach to treat SRI- or SRNI-induced female sexual dysfunction, in particular, arousal disorders.

Use of Sildenafil for Female Sexual Dysfunction

Objective:

To review the pathophysiology of female sexual dysfunction (FSD) and the literature regarding the use of sildenafil in its treatment.

Data Sources:

Literature was accessed through MEDLINE (1966—April 2006), Iowa Drug Information Service (1966—April 2006), EMBASE (1966—April 2006), and bibliographies of pertinent articles. Search terms included female sexual dysfunction; sexual dysfunction, psychological; phosphodiesterase inhibitors; and sildenafil.

Data Synthesis:

The lack of a clear understanding of FSD contributes to the limited treatment options available. Studies regarding the safety and efficacy of the phosphodiesterase 5 inhibitor sildenafil in the management of FSD were evaluated. Many trials have been of poor quality, making clinical application of their results difficult. The current literature does not show sildenafil to be an effective treatment option for FSD.

Conclusions:

Treatment of FSD should include both physical and psychological components. Based on the limited data available, it appears that sildenafil, while well tolerated, offers little or no benefit to most patients with FSD.

Expression of cAMP and cGMP-phosphodiesterase isoenzymes 3, 4, and 5 in the human clitoris: immunohistochemical and molecular biology study

OBJECTIVES

Only a little research has focused on the evaluation of female sexual function. With sexual stimulation, the clitoris becomes engorged with blood and tumescent. Nevertheless, only little is known about the significance of the cyclic nucleotide-mediated signal transduction in the control of this process. We sought to elucidate the presence of the phosphodiesterase (PDE) isoenzymes 3, 4, and 5 in the human clitoris using immunohistochemical and molecular biology methods.

METHODS

Thin sections of clitoral specimens were incubated with primary antibodies directed against PDE isoenzymes 3, 4, and 5. Next, the sections were incubated with either Texas red or fluorescein isothiocyanate-labeled secondary antibodies, and visualization was done using laser microscopy. The expression of mRNA encoding for various PDE isoenzymes was evaluated using reverse transcriptase polymerase chain reaction.

RESULTS

Immunofluorescence indicating the presence of PDE4 (cyclic adenosine monophosphate-PDE) was observed in the nonvascular smooth musculature of the corpus cavernosum clitoris, sinusoidal endothelial and subendothelial layers, and nerve fibers innervating the tissue. Immunoreactivity specific for PDE5 (cyclic guanosine monophosphate-PDE) was limited to the smooth muscle of the clitoral erectile tissue. The fluorescein isothiocyanate reaction indicating the expression of PDE3 (cyclic adenosine monophosphate-PDE) was registered to a certain degree only in the clitoral epidermis. In the reverse transcriptase polymerase chain reaction studies, a predominant expression of mRNA encoding for PDE1A was registered, but only small amounts of mRNA encoding for PDE4 and PDE5 were detected.

CONCLUSIONS

Our results have demonstrated the presence of cyclic adenosine monophosphate-PDE and cyclic guanosine monophosphate-PDE in the human clitoris and may indicate a regulatory function of these enzymes in the cyclic nucleotide-mediated control of smooth muscle tone.

Immunohistochemical Distribution of cAMP- and cGMP-Phosphodiesterase (PDE) Isoenzymes in the Human Prostate

OBJECTIVES

With the introduction of sildenafil citrate (Viagra), the concept of phosphodiesterase (PDE) inhibition has gained tremendous interest in the field of urology. Cyclic nucleotide second messengers cGMP and cAMP have been assumed to be involved in the control of the normal function of the prostate. The aim of the present study was to evaluate by means of immunohistochemistry the expression and distribution of some cAMP- and cGMP-PDE isoenzymes in the prostate.

MATERIAL & METHODS

Cryostat sections (10 microM) of formaldehyde-fixated tissue segments excised from the transition zone of human prostates were incubated with primary antibodies directed against the PDE isoenzymes 3, 4, 5, and 11. Then, sections were exposed to either fluorescein isothiocyanate- (FITC) or Texas Red- (TR) labeled secondary antibodies and visualization was commenced by means of laser fluorescence microscopy.

RESULTS

TR-immunofluorescence indicating the presence of PDE4 (cAMP-PDE) was abundantly observed in the fibromuscular stroma as well as in glandular structures of the transition zone. In contrast to the distribution of PDE4, immunoactivity indicating PDE5 (cGMP-PDE) and 11 (dual substrate PDE) was mainly observed in glandular and subglandular areas. No immunostaining for PDE3 (cGMP-inhibited PDE) was detected.

CONCLUSION

Our results confirm the presence of PDE isoenzymes 4, 5 and 11 in the transition zone of the human prostate and present evidence that these isoenzymes are not evenly distributed. These findings are in support of the hypothesis that there might be a rationale for the use of PDE inhibitors in the pharmacotherapy of BPH and LUTS.

Physiology of female sexual function: animal models

INTRODUCTION

Data concerning the physiology of desire, arousal, and orgasm in women are limited because of ethical constraints. Aim. To gain knowledge of physiology of female sexual function through animal models.

METHODS

To provide state-of-the-art knowledge concerning female sexual function in animal models, representing the opinions of seven experts from five countries developed in a consensus process over a 2-year period.

MAIN OUTCOME MEASURE

Expert opinion was based on the grading of evidence-based medical literature, widespread internal committee discussion, public presentation, and debate.

RESULTS

Sexual desire may be considered as the presence of desire for, and fantasy about, sexual activity. Desire in animals can be inferred from certain appetitive behaviors that occur during copulation and from certain unconditioned copulatory measures. Proceptive behaviors are dependent in part on estrogen, progesterone, and drugs that bind to D1 dopamine receptors, adrenergic receptors, oxytocin receptors, opioid receptors, or gamma-amino butyric acid receptors. Peripheral arousal states are dependent on regulation of genital smooth muscle tone. Multiple neurotransmitters/mediators are involved including adrenergic, and nonadrenergic, noncholinergic agents such as vasoactive intestinal polypeptide, nitric oxide, neuropeptide Y, calcitonin gene-related peptide, and substance P. Sex steroid hormones, estrogens and androgens, are critical for structure and function of genital tissues including modulation of genital blood flow, lubrication, neurotransmitter function, smooth muscle contractility, mucification, and sex steroid receptor expression in genital tissues. Orgasm may be investigated by urethrogenital (UG) reflex, in which genital stimulation results in rhythmic contractions of striated perineal muscles and contractions of vagina, anus, and uterine smooth muscle. The UG reflex is generated by a multisegmental spinal pattern generator involving the coordination of sympathetic, parasympathetic, and somatic efferents innervating the genital organs. Serotonin and dopamine may modulate UG reflex activity.

CONCLUSIONS

More research is needed in animal models in the physiology of female sexual function.

Effects of Sildenafil Citrate on Defibrillation Efficacy

INTRODUCTION

Although fatal arrhythmia and sudden death have been reported in patients taking sildenafil citrate, its effect on defibrillation efficacy has not been investigated. The aim of this study was to test the hypothesis that sildenafil citrate increases the shock strength required to successfully defibrillate during ventricular fibrillation (VF).

METHODS AND RESULTS

A total of 26 pigs (20-25 kg) were randomly assigned into three groups. In each group, the defibrillation threshold (DFT) was determined at the beginning of the study using a three-reversal up/down protocol. Each shock (RV-SVC, biphasic) was delivered after 10 seconds of VF. Group 1 (n = 10) received 50 mg and group 2 (n = 10) received 100 mg of sildenafil citrate intravenously at a rate of 2 mL/minute for 50 minutes. Group 3 (n = 6) received 100 mL of saline intravenously at the same rate as in group 1. The DFT was determined again after the drug (drug-DFT) and saline (saline-DFT) administration. For 100-mg sildenafil citrate infusion, the DFT (483 +/- 39 V, 18 +/- 3 J) was significantly (P < 0.003 and P < 0.01, respectively) higher than the control-DFT (407 +/- 123 V, 13 +/- 7 J). This sildenafil citrate infusion increased the DFT approximately 19% by voltage, and approximately 38% by total energy. After 50-mg sildenafil citrate infusion, the DFT (454 +/- 28 V, 15 +/- 2 J) was not different than the control DFT (449 +/- 28 V, 15 +/- 2 J). Saline infusion (391 +/- 18 V, 12 +/- 1 J) did not alter the control DFT (399 +/- 22 V, 12 +/- 1 J).

CONCLUSION

The 100-mg sildenafil citrate infusion, representing a supra-therapeutic plasma level, significantly increased the DFT. This finding indicates that VF occurring during supra-therapeutic sildenafil citrate treatment would require a stronger shock to successfully defibrillate.

Physiology of female sexual function and dysfunction

Female sexual dysfunction is age-related, progressive, and highly prevalent, affecting 30-50% of American women. While there are emotional and relational elements to female sexual function and response, female sexual dysfunction can occur secondary to medical problems and have an organic basis. This paper addresses anatomy and physiology of normal female sexual function as well as the pathophysiology of female sexual dysfunction. Although the female sexual response is inherently difficult to evaluate in the clinical setting, a variety of instruments have been developed for assessing subjective measures of sexual arousal and function. Objective measurements used in conjunction with the subjective assessment help diagnose potential physiologic/organic abnormalities. Therapeutic options for the treatment of female sexual dysfunction, including hormonal, and pharmacological, are also addressed.

Late-stage clinical development in lower urogenital targets: sexual dysfunction

In recent years, late-stage clinical drug development that primarily focuses on urogenital targets has centered around four areas of medical need (both unmet need and aiming to improve on existing therapies). These include male sexual dysfunction (MSD), female sexual dysfunction (FSD), prostatic pathology (neoplastic, pre-neoplastic, and non-neoplastic), and improvement in lower urinary tract symptoms. Despite the regulatory approval of compounds to treat erectile dysfunction (ED), benign prostatic hyperplasia, a number of treatments for overactive bladder, and stress urinary incontinence, there remains a deficiency in addressing a number of conditions that arise out of pathophysiological dysfunction resulting in lower urogenital tract sexual conditions. In terms of late-stage clinical development, significant progress has most recently been made in MSD development, especially in understanding further a common and complex sexual dysfunction--that of premature ejaculation. The search also continues for compounds that improve ED in terms of better efficacy and superior safety profile compared to the currently marketed phosphodiesterase-5-inhibitors. Whilst there are no approved medications to treat the subtypes of FSD, there has been significant progress in attempting to better understand how to appropriately assess treatment benefit in clinical trial settings for this difficult to diagnose and treat condition. This review will focus on late-stage human clinical development pertaining to MSD and FSD.

Aetiology and management of male erectile dysfunction and female sexual dysfunction in patients with cardiovascular disease

The historical basis for understanding erectile function as a neurovascular phenomenon and the advance from fanciful to effective treatment of erectile dysfunction (ED) are reviewed, with emphasis on patients with cardiovascular disease (CVD). ED occurs in 60% of CVD patients by 40 years of age. Male ED and female sexual dysfunction (FSD) diminish quality of life and often warn of occult CVD. ED is often unrecognised but is readily diagnosed during a 5-minute interview using a truncated International Index of Erectile Function questionnaire. Erection of the penis and clitoral engorgement result from local, arousal-induced release of neuronal and endothelial-derived nitric oxide (NO). Arterial vasodilatation and relaxation of cavernosal smooth muscle cells cause arterial blood to flood trabecular spaces, compressing venous drainage, resulting in tumescence. Cyclic guanosine monophosphate (cGMP)-induced activation of protein kinase G mediates the effects of NO by enhancing calcium sequestration and activating large-conductance, calcium-sensitive K+ channels. Future treatment strategies will likely enhance these pathways. Phosphodiesterase-5 inhibitors (sildenafil, tadalafil and vardenafil) increase cGMP levels in erectile tissue. These agents are effective in 80% of CVD patients with ED and can be used safely, even in the presence of stable coronary disease or congestive heart failure, provided nitrates are avoided and patients do not have hypotension, severe aortic stenosis or evocable myocardial ischaemia. Second-line therapies (vacuum constrictor device and transurethral or intracavernosal prostaglandin E1) can also be used in CVD patients. Treatment of FSD and its relationship to CVD are less well established, but similarities to ED exist. ED can be prevented by reduction of CVD risk factors, exercise, weight loss and abstinence from smoking.

Progress in Female Sexual Dysfunction

INTRODUCTION

Female sexual dysfunction (FSD) is a significant age-related, progressive and highly prevalent problem that affects a substantial number of women that causes personal distress and has negative effects on quality of life and interpersonal relationships.

DEFINITIONS

The female sexual response cycle consists of three phases: desire, arousal, and orgasm, and is initiated by non-adrenergic/non-cholinergic, e.g. vasoactive intestinal polypeptide and nitric oxide, neurotransmitters that maintain vascular and non-vascular smooth muscle relaxation resulting in increased pelvic blood flow, vaginal lubrication, and clitoral and labial engorgement. Furthermore, hormonal status may influence female sexual function. For the diagnosis of FSD, a detailed history should be taken initially, followed by a physical examination and laboratory studies.

CONCLUSION

Due to the fact that there has been little research and attention on FSD, our knowledge in this field is quite limited and there is still no approved therapy. Future advances in evaluation and treatment of female sexual problems are forthcoming.

Phosphodiesterase inhibitors in female sexual dysfunction

Based on the increasing knowledge on both the physiology of penile erection and the pathophysiology of erectile dysfunction, selective phosphodiesterase (PDE) inhibitors have been successfully introduced in the oral treatment of male erectile dysfunction. Because of their central role in smooth muscle tone regulation, PDEs remain an attractive target for drug development in urology. Since the distribution and functional significance of PDE isoenzymes vary in different tissues, selective inhibitors of the isoenzymes have the potential to exert at least partially specific effects on the target tissue. Currently, PDE inhibitors are under investigation with potential uses in urinary stone disease, overactive bladder and the so-called benign prostatic syndrome. The convincing clinical data on the use of the orally active PDE5 inhibitors sildenafil (VIAGRA), vardenafil (LEVITRA) and tadalafil (CIALIS) in the treatment of erectile dysfunction are accompanied by boosting research activities on intracellular signal transduction and PDE characterisation in female genital tissues with the aid of immunohistochemistry and immunocytochemistry and molecular biology. The expression of various PDE isoforms in the human clitoris, vagina and labia minora was shown by means of immunohistochemistry and RT-PCR analyses and it was concluded from functional studies that an increase in cGMP or cAMP might be involved in the regulation of female genital blood flow and the control of genital non-vascular smooth muscle. As a consequence, the efficacy and safety of the PDE5 inhibitor sildenafil in the treatment of symptoms of female sexual dysfunction (FSD), including female sexual arousal disorders (FSAD), have been evaluated. Although the experiences from these early clinical studies have so far not been conclusive, they suggest that, after appropriate evaluation of patients, inhibition of PDE5 might be of benefit for selected individuals with FSAD. Such research efforts will possibly allow the identification of efficacious and diagnostic tools for erectile dysfunction and of even more selective drugs in its therapy.

ANATOMY OF THE CLITORIS

PURPOSE

We present a comprehensive account of clitoral anatomy, including its component structures, neurovascular supply, relationship to adjacent structures (the urethra, vagina and vestibular glands, and connective tissue supports), histology and immunohistochemistry. We related recent anatomical findings to the historical literature to determine when data on accurate anatomy became available.

MATERIALS AND METHODS

An extensive review of the current and historical literature was done. The studies reviewed included dissection and microdissection, magnetic resonance imaging (MRI), 3-dimensional sectional anatomy reconstruction, histology and immunohistochemical studies.

RESULTS

The clitoris is a multiplanar structure with a broad attachment to the pubic arch and via extensive supporting tissue to the mons pubis and labia. Centrally it is attached to the urethra and vagina. Its components include the erectile bodies (paired bulbs and paired corpora, which are continuous with the crura) and the glans clitoris. The glans is a midline, densely neural, non-erectile structure that is the only external manifestation of the clitoris. All other components are composed of erectile tissue with the composition of the bulbar erectile tissue differing from that of the corpora. The clitoral and perineal neurovascular bundles are large, paired terminations of the pudendal neurovascular bundles. The clitoral neurovascular bundles ascend along the ischiopubic rami to meet each other and pass along the superior surface of the clitoral body supplying the clitoris. The neural trunks pass largely intact into the glans. These nerves are at least 2 mm in diameter even in infancy. The cavernous or autonomic neural anatomy is microscopic and difficult to define consistently. MRI complements dissection studies and clarifies the anatomy. Clitoral pharmacology and histology appears to parallel those of penile tissue, although the clinical impact is vastly different.

CONCLUSIONS

Typical textbook descriptions of the clitoris lack detail and include inaccuracies. It is impossible to convey clitoral anatomy in a single diagram showing only 1 plane, as is typically provided in textbooks, which reveal it as a flat structure. MRI provides a multiplanar representation of clitoral anatomy in the live state, which is a major advantage, and complements dissection materials. The work of Kobelt in the early 19th century provides a most comprehensive and accurate description of clitoral anatomy, and modern study provides objective images and few novel findings. The bulbs appear to be part of the clitoris. They are spongy in character and in continuity with the other parts of the clitoris. The distal urethra and vagina are intimately related structures, although they are not erectile in character. They form a tissue cluster with the clitoris. This cluster appears to be the locus of female sexual function and orgasm.

Non-COX-2 targets and cancer: Expanding the molecular target repertoire of chemoprevention

Chemoprevention represents a highly promising approach for the control of cancer. That nonsteroidal anti-inflammatory drugs (NSAIDs) prevent colon and other cancers has led to novel approaches to cancer prevention. The known inhibitory effect of NSAIDs on the eicosanoid pathway prompted mechanistic and drug development work focusing on cyclooxygenase (COX), culminating in clinical trials of cyclooxygenase 2 (COX-2) inhibitors for cancer prevention or treatment. However, two COX-2 inhibitors have been withdrawn due to side effects. Here we review several pathways of the eicosanoid cascade that are relevant to cancer; summarize the evidence regarding the role of COX-2 as a target for cancer prevention; and discuss several of the molecular targets that may mediate the chemopreventive effect of NSAIDs. The clinically modest results obtained to date with COX-2 specific inhibitors used in cancer prevention; the multiple COX-2-independent targets of both NSAIDs and COX-2 inhibitors; and the limitations of some COX-2 inhibitors indicate that exploiting these (non-COX-2) molecular targets will likely yield effective new approaches for cancer chemoprevention.

Past, present, and future: a 7-year update of Viagra (sildenafil citrate)

More than 30 million men are estimated to have erectile dysfunction (ED) in the United States. Worldwide, ED is estimated to affect more than 150 million men, and that number is expected to exceed 300 million men by the year 2025. The prevalence of ED ranges from 7% in men aged 18-29 years to 85% in men aged 76-85 years. In addition, a recent report showed that 68% of patients with ED aged 18 years and older have at least one comorbid diagnosis of hypertension, hyperlipidaemia, diabetes or depression, and research suggests that ED may be an early indicator of systemic vascular disease. Viagra (sildenafil citrate), the first-in-class phosphodiesterase type 5 (PDE5) inhibitor, was introduced in 1998 for the treatment of ED. In the 7 years since its market launch, more than 750,000 physicians have prescribed sildenafil to more than 23 million men, helping establish an excellent safety and efficacy record. Clinical studies have demonstrated that sildenafil successfully treats ED of varied organic, psychogenic or mixed aetiology, and is effective in men with ED and comorbidities such as hypertension, hyperlipidaemia, diabetes or depression. Sildenafil was a breakthrough medication that addressed a previously unfulfilled medical need. The impact of sildenafil has stimulated academic, clinical and industrial research to better understand the nature of sexual function and develop better treatment and management for sexual dysfunctions such as ED. With the advent of other erectogenic therapies for the treatment of ED, this 7-year update will focus on the unique history and development of sildenafil, its current use and applications and its future directions and indications. Special emphasis is placed on the impact of sildenafil on our understanding of sexual health and on the extensive safety and efficacy data that have been amassed from numerous clinical trials.

The neurovascular mechanism of clitoral erection: nitric oxide and cGMP-stimulated activation of BKCa channels

Female sexual function is under-studied, and mechanisms of clitoral engorgement-relaxation are incompletely understood. Penile erection results from nitric oxide (NO) -induced cyclic guanosine monophosphate (cGMP) accumulation. cGMP-dependent protein kinase (PKG) activates large-conductance, calcium-activated potassium channels (BK(Ca)), thereby hyperpolarizing and relaxing vascular and trabecular smooth muscle cells, allowing engorgement. We hypothesize rat clitorises relax by a similar mechanism. Rat clitorises express components of the proposed pathway: neuronal and endothelial NO synthases, soluble guanylyl cyclase (sGC), type 5 phosphodiesterase (PDE-5), and BK(Ca) channels. The NO donor diethylamine NONOate (DEANO), the PKG activator 8-pCPT-cGMP, and the PDE-5 inhibitor sildenafil, cause dose-dependent clitoral relaxation that is inhibited by antagonists of PKG (Rp-8-Br-cGMPS) or BK(Ca) channels (iberiotoxin). Electrical field stimulation induces tetrodotoxin-sensitive NO release and relaxation that is inhibited by the Na+ channel blocker tetrodotoxin or sGC inhibitor 1H-(1,2,4)oxadiozolo(4,3-a)quinoxalin-1-one. Human BK(Ca) channels, transferred to Chinese hamster ovary cells via an adenoviral vector, and endogenous rat clitoral smooth muscle K+ current are activated by this PKG-dependent mechanism. Laser confocal microscopy reveals protein expression of BK(Ca) channels on clitoral smooth muscle cells; these cells exhibit BK(Ca) channel activity that is activated by both DEANO and sildenafil. We conclude that neurovascular derived NO causes clitoral relaxation via a PKG-dependent activation of BK(Ca) channels. The BK(Ca) channel is an appealing target for drug therapy of female erectile dysfunction.

Female sexual dysfunction: the important points to remember

Media exposure regarding male sexual dysfunction and the growing number of viable treatment alternatives for erectile dysfunction has resulted in increasing numbers of men seeking clinical appointments and treatment for the condition, which has previously been considered taboo. Because these problems usually arise within the context of relationships, some investigators have alluded to increased rates of sexual dysfunction among the partners of these men. Also, since general practitioners, gynaecologists, geriatrists, and urologists are also seeing female patients for evaluation of various types of dysfunction, certain groups of these women with underlying chronic conditions have been noted to have high rates of concomitant sexual dysfunction. Physicians who have good rapport with these patients are in a privileged position to help with these intimate problems, which are often difficult for patients to discuss. Therefore, it is of extreme importance that these professionals become knowledgeable about and comfortable with the initial evaluation and possible treatment of female sexual dysfunction.

REVIEW: Review of Phosphodiesterases in the Urogenital System: New Directions for Therapeutic Intervention

INTRODUCTION

With the success of Phosphodiesterase (PDE) type 5 inhibitors (i.e., sildenafil, tadalafil, vardenafil) in the treatment of erectile dysfunction (ED), PDEs are considered attractive targets for drug intervention in the urogenital tract.

AIM

To review the role of PDEs, which exist as a superfamily of enzymes comprising 11 distinct families, in the urogenital system, focusing on anatomical locations, functions and dysfunctions, potential disorders that could be treated, and any promising new selective PDE inhibitors under development.

METHODS

Included are (i) abstracts from 2001, 2002, and 2003; (ii) a MEDLINE search from 1996 through December 2003; and (iii) a pipeline search for therapeutics in development. Data from animal experiments are presented when there is a paucity of human data, but with the caveat that the distribution of PDE isozymes in a specific tissue can vary between species.

RESULTS

PDE mRNA and protein have been localized throughout the normal human urogenital tract. Double-blind, placebo-controlled studies suggest possible new clinical roles for sildenafil, including prophylaxis to preserve penile smooth muscle and erectile function after radical prostatectomy, and treatment of ejaculatory delay secondary to serotonergic reuptake inhibitor antidepressant therapy. Open-label studies suggest a potential clinical role for: vinpocetine (a PDE1 inhibitor) in the treatment of incontinence and low-compliance bladder; and sildenafil in the treatment of premature ejaculation, prostate-related lower urinary tract symptoms, and in women who have had unsuccessful in vitro fertilization. Several new orally administered PDE5 inhibitors are in early clinical development for the treatment of ED. Potential indications for PDE inhibitors that are suggested by preclinical data include Peyronie's disease, ureteral colic, male and female birth control, and prevention of preterm labor.

CONCLUSIONS

Drug selectivity and differential PDE tissue distribution allow for potential targeted intervention for numerous disorders related to the urogenital tract.