Biochemical and physiological mechanisms of female genital sexual arousal

Sexual function changes attributed to hormonal contraception use - a qualitative study of women experiencing negative effects

Objective: To increase the understanding of women who experience negative effects on sexual function when using hormonal contraception.Methods: We performed 24 in-depth interviews with women who had previously experienced negative sexual function effects while using hormonal contraceptives. The thematic analysis method was used.Results: 'After experience comes insight', 'Lubrication and desire go hand in hand', 'Mental wellbeing comes before desire' and 'The contraceptive counsellor potentially facilitates insight and decision-making' were the main themes found in the study.Conclusions: This selected group of women described lubrication difficulties and decreased sexual desire associated with both contraceptive use and the menstrual cycle. Contraceptive use became easier with age and with better understanding. The contraceptive counsellor could facilitate the process. Further choice between hormonal or non-hormonal contraceptive methods depended primarily on experienced adverse effects on mood, and secondarily on sexual function, weighed against the advantages or disadvantages experienced during the person's own menstrual cycle.

Animal Models for the Study of Female Sexual Dysfunction

INTRODUCTION

Significant progress has been made in elucidating the physiological and pharmacological mechanisms of female sexual function through preclinical animal research. The continued development of animal models is vital for the understanding and treatment of the many diverse disorders that occur in women.

AIM

To provide an updated review of the experimental models evaluating female sexual function that may be useful for clinical translation.

METHODS

Review of English written, peer-reviewed literature, primarily from 2000 to 2012, that described studies on female sexual behavior related to motivation, arousal, physiological monitoring of genital function and urogenital pain.

MAIN OUTCOMES MEASURES

Analysis of supporting evidence for the suitability of the animal model to provide measurable indices related to desire, arousal, reward, orgasm, and pelvic pain.

RESULTS

The development of female animal models has provided important insights in the peripheral and central processes regulating sexual function. Behavioral models of sexual desire, motivation, and reward are well developed. Central arousal and orgasmic responses are less well understood, compared with the physiological changes associated with genital arousal. Models of nociception are useful for replicating symptoms and identifying the neurobiological pathways involved. While in some cases translation to women correlates with the findings in animals, the requirement of circulating hormones for sexual receptivity in rodents and the multifactorial nature of women's sexual function requires better designed studies and careful analysis. The current models have studied sexual dysfunction or pelvic pain in isolation; combining these aspects would help to elucidate interactions of the pathophysiology of pain and sexual dysfunction.

CONCLUSIONS

Basic research in animals has been vital for understanding the anatomy, neurobiology, and physiological mechanisms underlying sexual function and urogenital pain. These models are important for understanding the etiology of female sexual function and for future development of pharmacological treatments for sexual dysfunctions with or without pain. Marson L, Giamberardino MA, Costantini R, Czakanski P, and Wesselmann U. Animal models for the study of female sexual dysfunction. Sex Med Rev 2013;1:108-122.

Assessment of Introital Lubrication

Vaginal vasocongestion and lubrication serve to prepare the vaginal lumen for sexual activity. Lubrication is important for sexual functioning and difficulties with lubrication are one of the most commonly reported symptoms of sexual dysfunction. Few studies have empirically examined how vasocongestion and lubrication relate to one another and there are currently no well-established measures of lubrication. In this study, we designed and tested a simple method to assess lubrication at the vaginal introitus in 19 healthy women, using litmus test strips. We examined the relationship between lubrication and vaginal vasocongestion (measured with a photoplethysmograph) when elicited by audiovisual sexual stimuli (male-female sexual interactions). Lubrication was elicited by the sexual stimuli and was strongly correlated with reports of sexual arousal. Unexpectedly, lubrication was not correlated with vasocongestion, even though the latter was also elicited by the sexual stimuli. We discuss the implications of these findings for informing our understanding of the female sexual response and the potential clinical and scientific utility of this new measure.

Benefits and risks of testosterone treatment for hypoactive sexual desire disorder in women: a critical review of studies published in the decades preceding and succeeding the advent of phosphodiesterase type 5 inhibitors

With advancing age, there is an increase in the complaints of a lack of a libido in women and erectile dysfunction in men. The efficacy of phosphodiesterase type 5 inhibitors, together with their minimal side effects and ease of administration, revolutionized the treatment of erectile dysfunction. For women, testosterone administration is the principal treatment for hypoactive sexual desire disorder. We sought to evaluate the use of androgens in the treatment of a lack of libido in women, comparing two periods, i.e., before and after the advent of the phosphodiesterase type 5 inhibitors. We also analyzed the risks and benefits of androgen administration. We searched the Latin-American and Caribbean Health Sciences Literature, Cochrane Library, Excerpta Medica, Scientific Electronic Library Online, and Medline (PubMed) databases using the search terms disfunção sexual feminina/female sexual dysfunction, desejo sexual hipoativo/female hypoactive sexual desire disorder, testosterona/testosterone, terapia androgênica em mulheres/androgen therapy in women, and sexualidade/sexuality as well as combinations thereof. We selected articles written in English, Portuguese, or Spanish. After the advent of phosphodiesterase type 5 inhibitors, there was a significant increase in the number of studies aimed at evaluating the use of testosterone in women with hypoactive sexual desire disorder. However, the risks and benefits of testosterone administration have yet to be clarified.

The opioid neuropeptides in uterine fibroid pseudocapsules: a putative association with cervical integrity in human reproduction

The myoma pseudocapsule (MP) is a fibro-vascular network rich of neurotransmitters, as a neurovascular bundle, surrounding fibroid and separating myoma from myometrium. We investigated the distribution of the opioid neuropeptides, as enkephalin (ENK) and oxytocin (OXT), in the nerve fibers within MP and their possible influence in human reproduction in 57 women. An histological and immunofluorescent staining of OXT and ENK was performed on nerve fibers of MP samples from the fundus, corpus and isthmian-cervical regions, with a successive morphometric quantification of OXT and ENK. None of the nerve fibers in the uterine fundus and corpus MPs contained ENK and the nerve fibers in the isthmian-cervical region demonstrated an ENK value of up to 94 ± 0.7 CU. A comparatively lower number of OXT-positive nerve fibers were found in the fundal MP (6.3 ± 0.8 CU). OXT-positive nerve fibers with OXT were marginally increased in corporal MP (15.0 ± 1.4 CU) and were substantially higher in the isthmian-cervical region MP (72.1 ± 5.1 CU) (p < 0.01). The distribution of OXY neurofibers showed a slight into the uterine corpus, while are highly present into the cervico-isthmic area, with influence on reproductive system and sexual disorders manifesting after surgical procedures on the cervix.

Characterization of nitric oxide-releasing microparticles for the mucosal delivery

For the treatment of female sexual arousal disorder (FSAD), we developed microparticles made of PLGA containing nitric oxide (NO) donor (DETA NONOate) to efficiently deliver NO to vaginal mucosa. The NO-releasing microparticles were prepared by various emulsion methods. SEM and DSC studies were performed to examine the microparticles. The release studies were conducted under various conditions to optimize the loading dose in the microparticles. NO diffusivity through vaginal epithelial cells was evaluated and pharmacological activity of NO-releasing microparticles was examined by assessment of intracellular cGMP level in vaginal cells. Through the modified double emulsion solvent evaporation method (w/o/w(a)), the acid labile DETA NONOate was stabilized during the fabrication process and homogenous morphology and high entrapment efficiency were achieved. DETA NONOate was protected under the acidic conditions of the vagina and NO was released from the microparticles in a controlled manner. A significant amount of NO produced from DETA NONOate penetrated through the vaginal epithelial cells. The intracellular cGMP level increased with the treatment of NO-releasing microparticles in vaginal cells. These findings suggest that NO-releasing microparticles could improve the vaginal blood perfusion and open up the possibilities of novel treatment of FSAD.

Phosphodiesterase type 5 inhibitors and female sexual response: faulty protocols or paradigms?

INTRODUCTION

Phosphodiesterase type 5 inhibitors (PDE5), such as sildenafil, tadalafil, and vardenafil, have revolutionized the treatment of erectile dysfunction. Few successes, in contrast, have been reported for the use of these agents in treatment of sexual arousal problems in women.

AIM

To review research examining efficacy of PDE5 in women, critique the methods and models employed, and integrate the findings within a broader, gender-specific understanding of female sexual response.

METHODS

A conceptual and methodological review of all published studies examining PDE5 efficacy in female samples.

MAIN OUTCOME MEASURES

Study methods, populations, outcome measures, study results.

RESULTS

A total of 16 studies were reviewed. Studies using self-reported measures of sexual functioning showed mixed results whereas studies examining physiological effects of PDE5 on genital vasocongestion consistently report significant effects on genital sexual response.

CONCLUSIONS

The lack of efficacy of PDE5 treatment in women is likely attributable to gender differences in the concordance between physiological and psychological components of sexual response. Discordance between genital and subjective measures of sexual response in women may be augmented by PDE5 effects on genital vasocongestion in some populations, rendering successful treatment unlikely via pharmacological treatment alone.

Are gonadal steroids linked with orgasm perceptions and sexual assertiveness in women and men?

Past findings suggest links between orgasms and testosterone (T), as well as sexuality and estradiol (E), and we examined hormone-orgasm links in this study via two hypotheses (below). Participants were 86 women and 91 men who provided a saliva sample and completed a demographics questionnaire, the Orgasm Checklist (Mah and Binik, 2002), the Hurlbert (1991) Index of Sexual Assertiveness, and the Sexual Desire Inventory (Spector and Fremeth, 1996). Results supported the first hypothesis of correlations between T and positive orgasm experience in women, specifically with the relaxation, soothing, and peaceful items in both partnered and solitary orgasm contexts. Results also indicated correlations between E and flooding and spreading items in a solitary orgasm context. There were no associations between hormones and men's perceptions of their orgasm experiences. There was no support for the second hypothesis of associations between higher T and more sexual assertiveness. Post hoc analyses showed associations between E and women's sexual desire, and T and men's sexual desire. We discuss implications of these findings including that solitary vs. partnered orgasm experiences may differ, and suggest that T might be associated with perceptions of psychological experiences of orgasms, and E might be associated with perceptions of physical experiences of orgasms.

Estradiol restores diabetes-induced reductions in sex steroid receptor expression and distribution in the vagina of db/db mouse model

Sex steroid hormones and receptors play an important role in maintaining vaginal physiology. Disruptions in steroid receptor signaling adversely impact vaginal function. Limited studies are available investigating the effects of diabetic complications on steroid receptor expression and distribution in the vagina. The goals of this study were to investigate type 2 diabetes-induced changes in expression, localization and distribution of estrogen (ER), progesterone (PR) and androgen receptors (AR) in the vagina and to determine if estradiol treatment ameliorates these changes. Eight-week-old female diabetic (db/db) mice (strain BKS.Cg-m+/+ Lepr(db)/J) were divided into two subgroups: untreated diabetic and diabetic animals treated with pellets containing estradiol. Control normoglycemic littermates were subcutaneously implanted with pellets devoid of estradiol. At 16 weeks of age, animals were sacrificed, vaginal tissues excised and analyzed by Western blot and immunohistochemical methods. Diabetes produced marked reductions in protein expression of ER, PR, and AR. Diabetes also resulted in marked differences in the distribution, staining intensity and proportion of immunoreactive cells containing these steroid receptors in the epithelium, lamina propria and muscularis. Treatment of diabetic animals with estradiol restored receptor protein expression and distribution similar to those levels observed in control animals. This study demonstrates that type 2 diabetes markedly reduces steroid receptor protein expression and distribution in the vagina. Estradiol treatment of diabetic animals ameliorates these diabetes-induced changes.

Increased vaginal oxidative stress, apoptosis, and inducible nitric oxide synthase in a diabetic rat model: implications for vaginal fibrosis

OBJECTIVE

To determine whether vaginal fibrosis occurs in diabetic animals and is associated with oxidative stress and cell death and with the expression of inducible nitric oxide synthase (iNOS), as a putative antifibrotic mechanism.

DESIGN

Research experimental project.

SETTING

University research laboratory.

ANIMAL(S)

Female Wistar rats.

INTERVENTION(S)

Female rats were injected with streptozotocin or saline and killed at 3 months. The vaginas were excised and processed for paraffin-embedded sections (n = 6 per group) or were frozen for biochemical and molecular biology procedures.

MAIN OUTCOME MEASURE(S)

Immunohistochemistry and quantitative image analysis were applied to tissue sections to measure alpha-smooth muscle actin, transforming growth factor beta1, plasminogen activator inhibitor, NOS isoforms, Cu/Zn superoxide dismutase, apoptotic index, and nitrotyrosine. Xanthine dehydrogenase, reactive oxygen species (ROS), and hydroxyproline were measured in fresh vaginal tissue (n = 5 per group). Reactive oxygen species also were determined in blood.

RESULT(S)

Diabetes was associated with vaginal fibrosis, as evidenced by increased collagen, transforming growth factor beta1, plasminogen activator inhibitor, and apoptosis, and by decreased alpha-smooth muscle actin. The increment of ROS and the reduction of superoxide dismutase indicated oxidative stress in diabetic tissue, accompanied by iNOS induction and increased nitric oxide-ROS reaction.

CONCLUSION(S)

Diabetes in the rat causes oxidative stress and fibrosis in the vagina, which may be compensated partially by iNOS induction to reduce ROS.

Modeling and Simulation of Sexual Activity Daily Diary Data of Patients with Female Sexual Arousal Disorder Treated with Sildenafil Citrate (Viagra®)

PURPOSE

To develop a model to explore the dose-response of sildenafil citrate in patients with female sexual arousal disorder (FSAD) based on telephone sexual activity daily diary (TSADD) data obtained in double-blind, placebo controlled clinical studies.

MATERIALS

Data were available on 614 patients with FSAD. A parametric model (Weibull distribution) was developed to describe the probability density function of the time between sexual events. Orgasm satisfaction scores and overall sexual satisfaction scores were simultaneously modeled as ordered categorical variables. Simulations were performed to evaluate the expected clinical response in patients with FSAD.

RESULTS

The expected time between sexual events was approximately 3.5 days. Satisfaction scores increased with time to achieve a plateau after 3 to 4 weeks on treatment. The expected probability of satisfying orgasm (score of 3 and higher) ranged from 34.7% for placebo to 41.6% for 100 mg sildenafil citrate. Treatment effect (difference from placebo) was 6.9% for 100 mg sildenafil citrate, ranging from 0.6 to 24.7% for testosterone levels of 0.1 to 4.0 pg/ml. The treatment effect in postmenopausal women was larger than in premenopausal women.

CONCLUSION

A modeling and simulation framework to support drug development in FSAD was developed. Sildenafil citrate demonstrated a dose-dependent effect in patients with FSAD.

Genital sympathetic skin responses in fibromyalgia syndrome

The study was designed to investigate the autonomic dysfunction in fibromyalgia syndrome (FMS) by recording sympathetic skin response (SSR) from palmar, plantar and genital regions. The second aim was to evaluate the relation between sexual problems and autonomic dysfunction in FMS. SSR potential was recorded from palmar, plantar and genital regions in 28 married, female FMS patients and 18 married, healthy females. Fibromyalgia Impact Questionnaire (FIQ) was used to show the clinical severity and functional disability in FMS patients. Glombok Rust Inventory of Sexual Satisfaction (GRISS), a 28-item questionnaire, was used to assess the existence and severity of sexual problems. Beck test was used to evaluate anxiety and depression. The amplitude of SSR recorded from palmar, plantar and genital regions was lower than in the control subjects (P < 0.05). GRISS (total and subscale), Beck test and FIQ scores of FMS patients were higher than in the control subjects (P < 0.05). No correlation was found between the SSR potential and GRISS scores. The results of our study reveal that abnormality in SSR recorded from palmar, plantar and genital regions reflects the abnormality in the autonomic nervous system (ANS) of FMS patients. These patients have more sexual problems than healthy subjects, and we think this finding is related to increased anxiety and depression in these patients.

Evidence for the presence of the spinal pattern generator involved in the control of the genital ejaculatory pattern in the female rat

Substantial progress has been made during recent years in elucidating the control of male ejaculatory function by the central nervous system. These efforts have revealed the participation of a central pattern generator in the control of ejaculation. There is a strong similarity in the neural organization of male and female sexual functions. In the present study, the hypothesis that the spinal generator for ejaculation was present and functional in the female rat was evaluated. To this purpose, the expression of the ejaculatory motor pattern and its pharmacological activation in spinally transected female rats were investigated. Results revealed the presence in females of the already described rhythmic ejaculatory motor pattern of male rats. This ejaculatory motor pattern could be registered in the urethralis muscle of the female rat after mechanical stimulation of the urethra, vagina and clitoris and consisted, as in the male rat, of a first ejaculatory motor train followed by an after-discharge component. Besides, the female genital ejaculatory motor pattern could be pharmacologically induced by the systemic injection of sodium nitroprusside with similar motor characteristics. No significant differences between the sensorial and pharmacologically induced female genital motor patterns were found. Present findings provide evidence for the presence of the genital motor pattern of ejaculation in female rats and suggest that the spinal generator for ejaculation is also present and functional in this gender.

Preliminary clinical experience with androgen administration for pre- and postmenopausal women with hypoactive sexual desire

The present study examined effects of testosterone on hypoactive sexual desire in pre- and postmenopausal women (treated) compared with an age-matched reference group (reference). Treated participants received 100 mg of testosterone cypionate in oil injected intramuscularly (i.m.) monthly for 3 months. We measured salivary testosterone and scores on the Sexual Desire Inventory pretreatment and posttreatment. Treated and reference participants' baseline testosterone was equivalent, however, treated participants exhibited higher testosterone levels than did reference participants posttreatment. As expected, treated participants exhibited lower baseline sexual desire than did reference participants and showed a significant increase in sexual desire posttreatment. This research suggests that testosterone may effectively alleviate hypoactive sexual desire, even in women with normal testosterone levels.

Pharmacotherapy for sexual dysfunction in women

In the setting of multiple studies claiming a high prevalence of sexual problems amongst women, new conceptualisation of the sexual response in women and definitions of sexual dysfunction, which reflect the need for biopsychosocial management, are being developed. The biological underpinnings of the sexual response in women may be influenced by environmental factors, as well as by medications, disease processes and normative changes in endogenous hormones. Psychological factors can alter both the physiological processes and the experience of sexual response. The new models clarify the importance of sexual motivations other than desire, sexual arousability and subtypes of arousal disorder. The role of pharmacotherapy to potentially augment desire, arousability, genital congestion and to lessen the pain of chronic dyspareunia must be envisaged within the holistic biopsychosocial model.

Effects of stress on female rat sexual function

This study was undertaken to investigate whether prolonged stress interferes with sexual behavior and changes biochemical and physiologic mechanisms. Experiments were repeated three times with different rats in each period. In all, 63 female Sprague-Dawley rats were employed, with 21 rats in each period, and the control group was maintained at room temperature with free access to food and water. The stress group was maintained under a scheduled stress condition for 10 days, and seven rats from the group were randomly selected and exposed to the control environment for 10 days as the recovery group. Sexual behavior, hormonal values, and neuronal and endothelial nitric oxide synthase (nNOS and eNOS) expressions of vaginal tissue were analyzed and compared. Serum testosterone levels were significantly elevated in the stress and recovery groups (P<0.05). Female rats in the stress group showed reduced receptivity to their male mates (P<0.05). Western blot analysis demonstrated that nNOS and eNOS expressions were significantly lower in the stress group (P<0.05) than in the other groups. We conclude that chronic physical stress modifies the sexual behavior of female rats through a mechanism believed to involve complex changes in sex hormones, endocrine factors, and neurotransmitters.

Topical administration of a novel nitric oxide donor, linear polyethylenimine-nitric oxide/nucleophile adduct (DS1), selectively increases vaginal blood flow in anesthetized rats

The aim of the present study was to test the effects of a topical administration of a novel nitric oxide donor, linear polyethylenimine-nitric oxide/nucleophile adduct (DS1), on vaginal blood flow and hemodynamics in rats. Laser Doppler flowmetry was used to measure blood flow changes following topical application of DS1 (0.3 or 1.5 mg in 0.15 ml saline) into the vagina of anesthetized Wistar rats. In vivo hemodynamic parameters were measured with Millar-tip-catheter placed in the left ventricle. DS1 (1.5 mg) increased vaginal blood flow by 191+/-24, 226+/-22 and 166+/-23% of the baseline value (at 5, 15 and 30 min, respectively, after application) without affecting systemic blood pressure, heart rate and cardiac function. The increased vaginal blood flow following DS1 application returned to baseline between 45 and 60 min. Thus, topical application of nitric oxide donors such as DS1 may be useful for the treatment of female sexual dysfunction that develops due to an impairment of local blood flow supply to the vaginal tissue.