The endocrinology of sexual arousal

Testosterone relaxes rabbit seminal vesicle by calcium channel inhibition

Recent studies have documented that testosterone relaxes several smooth muscles by modulating K(+) channel activities. Smooth muscles of seminal vesicles play a fundamental role in ejaculation, which might involve testosterone. This study was aimed to assess the role of testosterone in seminal vesicular motility by studying its effects on contractile agents and on the ion channels of single vesicular myocytes in a rabbit model. The contractile responses of circular smooth muscle strips of rabbit seminal vesicles to norepinephrine (10 microM), a high concentration of KCl (70 mM), and testosterone (10 microM) were observed. Single vesicular myocytes of rabbit were isolated using proteolytic enzymes including collagenase and papain. Inside-out, attached, and whole-cell configurations were examined using the patch clamp technique. The applications of 10 microM norepinephrine or 70 mM KCl induced tonic contractions, and 10 microM testosterone (pharmacological concentration) evoked dose-dependent relaxations of these precontracted strips. Various K(+) channel blockers, such as tetraethylammonium (TEA; 10 mM), iberiotoxin (0.1 microM), 4-aminopyridine (4-AP, 10 microM), or glibenclamide (10 microM) rarely affected these relaxations. Single channel data (of inside-out and attached configurations) of BK channel activity were also hardly affected by testosterone (10 microM). On the other hand, however, testosterone reduced L-type Ca(2+) currents significantly, and found to induce acute relaxation of seminal vesicular smooth muscle and this was mediated, at least in part, by Ca(2+) current inhibition in rabbit.

Neuroendocrine regulation of feminine sexual behavior: lessons from rodent models and thoughts about humans

Much has been learned concerning the neuroendocrine processes and cellular mechanisms by which steroid hormones influence reproductive behaviors in rodents and other animals. In this review, a short discussion of hormones and feminine sexual behavior in some rodent species is followed by an outline of the main principles that have been learned from these studies. Examples are given of the importance of considering the timing of hormone treatments, dosage of hormone, use of a specific hormone, particular class of hormones, or form of hormone, interactions between hormones, route of administration, peripheral factors that influence hormonal response, and the possible mechanisms of action by which hormones and other factors influence sexual behaviors. Although cellular studies in humans are presently impossible to perform, mechanistic studies in rodents may provide clues about the neuroendocrine mechanisms by which hormones act and interact in the brain to influence behavior in all species, including humans.

Care of Women in Menopause: Sexual Function, Dysfunction and Therapeutic Modalities

Introduction: The physiological changes that occur in menopause alter sexual function and affect well-being. Hormonal changes contribute significantly to reduced sexual function in older women and sexual dysfunction may well be amenable to treatment with exogenous hormones or other agents. Materials and Methods: Relevant clinical studies were identified by a computerised literature search. The collated data were presented to fellow gynaecologists for review, analysis of results and discussion in a series of meetings dedicated to finding the best evidence in menopause management. The evidence was assessed and used to prepare guidelines around the management of women who are affected by sexual dysfunction in menopause. Results: Hormone therapy benefits many women who have dyspareunia related to vaginal atrophy, reduced libido and decreased satisfaction, particularly if these symptoms adversely affect their quality of life. Alternative agents such as tibolone and sildenafil citrate can be useful adjuncts. Conclusions: It is increasingly important to recognise postmenopausal sexual dysfunction. Treatment of this syndrome must be individualised to the specific complaints of each woman. Hormones and other agents are relevant treatment options for properly-selected women. Key words: Androgen, Dyspareunia, Oestrogen, Postmenopause, Sex disorders

Ginkgo biloba extract enhances male copulatory behavior and reduces serum prolactin levels in rats

The aim of this study was to investigate the effects of Ginkgo biloba extract (EGb 761) on male copulatory behavior in rats. EGb 761 (1 mg/ml) induced significant production of testosterone (T) in rat Leydig cells in vitro. Its effects on sexual behavior were then tested in Long-Evans male rats after 7, 14, 21, or 28 days of oral gavage of vehicle (distilled water) or EGb 761 at doses of 10, 50, or 100 mg/kg. Administration of 50 mg/kg of EGb 761 for 28 days and of 100 mg/kg for 14 or 21 days significantly increased intromission frequency compared to controls on the same day. An increase in ejaculation frequency was seen after treatment with 50 mg/kg of EGb 761 for 14, 21, or 28 days when compared to either the control group on the same day or the same group on day 0. A reduction in ejaculation latency was only seen after administration of 50 mg/kg of EGb 761 for 14 days compared to the vehicle-treated group. After treatment for 28 days, no significant difference was seen in mount latency, intromission latency, serum T levels, reproductive organ weight, sperm number, or levels of the metabolite of dopamine, 3,4-dihydroxyphenylacetic acid in the brain with any dose of EGb 761, but significantly reduced serum prolactin levels and increased dopamine levels in the medial preoptic area and arcuate nucleus were seen at the dose of 50 mg/kg. These findings show that EGb 761 (especially at the dose of 50 mg/kg) enhances the copulatory behavior of male rats and suggest that the dopaminergic system, which regulates prolactin secretion, may be involved in the facilitatory effect of EGb 761.

Pedophilia is linked to reduced activation in hypothalamus and lateral prefrontal cortex during visual erotic stimulation

BACKGROUND

Although pedophilia is of high public concern, little is known about underlying neural mechanisms. Although pedophilic patients are sexually attracted to prepubescent children, they show no sexual interest toward adults. This study aimed to investigate the neural correlates of deficits of sexual and emotional arousal in pedophiles.

METHODS

Thirteen pedophilic patients and 14 healthy control subjects were tested for differential neural activity during visual stimulation with emotional and erotic pictures with functional magnetic resonance imaging.

RESULTS

Regions showing differential activations during the erotic condition comprised the hypothalamus, the periaqueductal gray, and dorsolateral prefrontal cortex, the latter correlating with a clinical measure. Alterations of emotional processing concerned the amygdala-hippocampus and dorsomedial prefrontal cortex.

CONCLUSIONS

Hypothesized regions relevant for processing of erotic stimuli in healthy individuals showed reduced activations during visual erotic stimulation in pedophilic patients. This suggests an impaired recruitment of key structures that might contribute to an altered sexual interest of these patients toward adults.

Designing drugs for the treatment of female sexual dysfunction

Dysfunction of female sexual desire, arousal, or orgasm affects approximately 30% of women. Early attempts to treat female sexual dysfunction arose out of programs developed for male erectile dysfunction and have proven largely unsuccessful. A new wave of targets is now being pursued; many of these targets are postulated to modulate central pathways. Classical neurotransmitter systems, such as dopamine and serotonin, as well as the neuropeptide melanocortin, are receiving the most attention. Early clinical data look promising; however, clinical trial methodology in female sexual dysfunction is not well developed and only further testing will determine whether these treatments meet regulatory hurdles and satisfy patient need.

Testosterone decreases reactive astroglia and reactive microglia after brain injury in male rats: role of its metabolites, oestradiol and dihydrotestosterone

Previous studies have shown that the neuroprotective hormone, testosterone, administered immediately after neural injury, reduces reactive astrogliosis. In this study we have assessed the effect of early and late therapy with testosterone or its metabolites, oestradiol and dihydrotestosterone, on reactive astroglia and reactive microglia after a stab wound brain injury in orchidectomized Wistar rats. Animals received daily s.c. injections of testosterone, oestradiol or dihydrotestosterone on days 0-2 or on days 5-7 after injury. The number of vimentin immunoreactive astrocytes and the volume fraction of major histocompatibility complex-II (MHC-II) immunoreactive microglia were estimated in the hippocampus in the lateral border of the wound. Both early and delayed administration of testosterone or oestradiol, but not dihydrotestosterone, resulted in a significant decrease in the number of vimentin-immunoreactive astrocytes. The volume fraction of MHC-II immunoreactive microglia was significantly decreased in the animals that received testosterone or oestradiol in both early and delayed treatments and in animals that received early dihydrotestosterone administration. Thus, both early and delayed administration of testosterone reduces reactive astroglia and reactive microglia and these effects may be at least in part mediated by oestradiol, while dihydrotestosterone may mediate part of the early effects of testosterone on reactive microglia. In conclusion, testosterone controls reactive gliosis and its metabolites, oestradiol and dihydrotestosterone, may be involved in this hormonal effect. The regulation of gliosis may be part of the neuroprotective mechanism of testosterone.

The effects of oral contraceptives on androgen levels and their relevance to premenstrual mood and sexual interest: a comparison of two triphasic formulations containing norgestimate and either 35 or 25 μg of ethinyl estradiol

PURPOSE

This study compared two oral contraceptives (OCs) with the same triphasic regimen of progestin (norgestimate 0.18, 0.215 and 0.25 mg) but differing doses of ethinyl estradiol (EE) - 25 and 35 microg EE - in their effects on androgens, mood and sexual interest in women starting on OCs.

METHODS

Total testosterone (T), free testosterone (FT), sex-hormone-binding globulin (SHBG) and dehydroepiandrosterone sulphate (DHEA-S), together with measures of mood [Beck Depression Inventory (BDI)], sexual interest [Dyadic and Solitary subscales of the Sexual Desire Inventory (SDI)] and self-reported side effects were assessed before starting on the OC and again after 3 months of use.

RESULTS

Sixty women, all university students, were randomized to receive either the 25 microg EE (N/EE25) or the 35 microg EE (N/EE35) pill; 12 women discontinued, leaving 48 who completed the 3-month study. Their mean age was 19.7 years (18-30) and they were predominantly white and single. Both OCs produced reductions in mean T [N/EE35: from 1.33 to 0.60 nmol/L, p<.001; N/EE25: from 1.12 to 1.02 nmol/L; nonsignificant (NS)] and FT (N/EE35: from 41.3 to 4.4 pmol/L, p<.001; N/EE25: from 25.4 to 7.9 pmol/L, p<.01), but the reduction in both T and FT was significantly greater with the higher EE dose (N/EE35) (p=.05 and p=.03, respectively). DHEA-S was also reduced with both formulations (N/EE35: from 7.26 to 5.22 micromol/L); N/EE25: from 7.50 to 5.39 micromol/L), although the reduction was only significant in the N/EE35 group (p<.02). Considerable variability in changes in mood was evident with both OCs, with some women showing predominantly negative effects (10 in N/EE35, 5 in N/EE25); others, positive effects (9 in N/EE35, 17 in N/EE25) and some, no change (four in each group). Women using N/EE25 were significantly more likely to show improvement in premenstrual mood than those in the N/EE35 group (p<.02), although there was no correlation between changes in BDI and FT or DHEA-S. Sexual interest scores did not change significantly from baseline to posttreatment with either OC (N/EE35: dyadic, from 40.5 to 39.6, NS; solitary, from 5.9 to 6.4, NS; N/EE25: dyadic, from 36.7 to 37.0, NS; solitary, from 5.0 to 4.2, NS).

CONCLUSION

The lower EE pill reduced FT less and was associated with greater improvement in premenstrual mood. A causal relation between these two effects is uncertain.

ORIGINAL RESEARCH—WOMEN’S SEXUAL HEALTH: Physiological Changes in Female Genital Sensation During Sexual Stimulation

INTRODUCTION

A normal sexual response in the female depends on the integrity of afferent sensory input from the genital region. So far genital sensation has been investigated only during a non-excitatory state, and the sensory physiological changes, which occur during the sexual cycle in this region, are still obscured.

AIM

To investigate the sensory status of the female genital region during sexual arousal and orgasm.

MAIN OUTCOME MEASURES

Genital sensory thresholds measured by Quantitative Sensory Testing (vibratory and thermal) were compared in a non-excitatory vs. excitatory state in normal sexually functioning females.

METHODS

Eleven healthy female volunteers were recruited and attended three separate visits. During each session only one anatomical site, either clitoris or vagina was tested for either vibratory or thermal stimuli. A psychophysical method of limits was employed for threshold determination of warm or vibratory stimuli. In each session, all women were tested at baseline, immediately after arousal, after orgasm and three more measurements - 5, 10, and 20 minutes during the recovery state.

RESULTS

A significant decrease in clitoral vibratory sensation threshold was observed between the baseline and the arousal phases (P = 0.003). Comparison of vibratory sensation between baseline and following orgasm at the clitoral and vaginal region showed a significant difference (P < 0.001) for both regions. These changes were not significant for thermal threshold sensation at the clitoral region (P = 0.6).

CONCLUSIONS

This is the first time that genital sensation has been measured during the excitatory phase of the female sexual cycle. This normative data may serve as a baseline for further investigations of the sensory input of the genital organs during intercourse in pathological states.

ORIGINAL RESEARCH—ENDOCRINOLOGY: Improvement of Sexual Function in Men with Late-Onset Hypogonadism Treated with Testosterone Only

AIM

Late-onset hypogonadism is associated with relatively mild testosterone deficiencies. This study investigated the effects of restoring testosterone levels to normal in men with complaints of low sexual desire and erectile dysfunction.

MAIN OUTCOME MEASURES

Sexual function was assessed with the International Index of Erectile Function (IIEF) at baseline and after 24 weeks of testosterone administration.

METHODS

Twenty-two hypogonadal men (mean age 58 years) with erectile dysfunction were studied. Fifteen patients had serum testosterone below 6.9 nmol/L, and seven between 7.2 and 11.7 nmol/L (reference values in our laboratory >/=12.0 nmol/L); there were considerable comorbidities. The duration of sexual complaints was on average 3.8 years. Patients received intramuscular long-acting testosterone undecanoate.

RESULTS

In all patients, serum testosterone levels were restored to normal within 6-8 weeks. Twelve patients reported a significant improvement in the sexual desire domain (from 4.5 to 8.4) and experienced an improvement in the erectile function domain (from 12 to 25 [Questions 1-5 plus 15)], following treatment with this long-acting testosterone; in 9 of 12 patients, this occurred only after at least 12-24 weeks. The remaining 10 patients reported an improvement of sexual desire (from 4.5 to 7.5), but no significant improvement in the erectile function domain (from 12 to 14). No changes in serum prostate-specific antigen or prostate volume were noticed while receiving this long-acting testosterone preparation.

CONCLUSION

Restoring testosterone levels to normal in men with proven subnormal testosterone levels improves libido in most subjects, and erectile function in more than 50% of these men. It may take 12-24 weeks before the effects of testosterone become manifest.

Sexual dysfunction in men and women with endocrine disorders

Endocrine disease frequently interrupts sexual function, and sexual dysfunction may signal serious endocrine disease. Diabetic autonomic neuropathy and endothelial dysfunction impair erectile function, and phosphodiesterase inhibition produces only moderate benefit. The effect of diabetes on women's sexual function is complex: the most consistent finding is a correlation between sexual dysfunction and depression. Reductions in testosterone level in men are associated with low sexual desire and reduced nocturnal erections and ejaculate volume, all of which improve with testosterone supplementation. The age-dependent decline in testosterone production in men is not associated with precise sexual symptoms, and supplementation has not been shown to produce sexual benefit. In women, sexual dysfunction has not been associated with serum testosterone, but this may be confounded by limitations of assays at low concentrations and by the greater importance of intracellular production of testosterone in women than in men. Testosterone supplementation after menopause does improve some aspects of sexual function in women, but long-term outcome data are needed. More research on the sexual effects of abnormal adrenal and thyroid function, hyperprolactinaemia, and metabolic syndrome should also be prioritised. We have good data on local management of the genital consequences of oestrogen lack, but need to better understand the potential role of systemic oestrogen supplementation from menopause onwards in sexually symptomatic women.

Sexual function in men and women with neurological disorders

The advent of non-invasive functional brain imaging has clarified which regions of the brain are recruited during sexual arousal. Injuries to those regions, and to the spinal cord and peripheral nerves that link genitalia to limbic and cognitive centres, can profoundly influence sexual wellbeing. In epilepsy, expressions of hypersexuality and hyposexuality interact with the location of epileptogenic foci in the temporolimbic circuitry, and are tempered by the sexual effects of drug treatments. We outline the sexual consequences of epilepsy, stroke, multiple sclerosis, Parkinson's disease, and other common neurological disorders. Management of sexual dysfunction from both disease and treatment is discussed. Nerve-sparing techniques could mitigate the substantial sexual dysfunction in both men and women through surgical disruption of the autonomic nerves during radical pelvic surgery.

Sexual sequelae of general medical disorders

That sexual symptoms can signal serious underlying disease confirms the importance of sexual enquiry as an integral component of medical assessment. Data on sexual function are sparse in some medical specialties. However, increased scientific understanding of the central and peripheral physiology of sexual response could help to identify the pathophysiology of sexual dysfunction from disease and medical interventions, and also to ameliorate or prevent some dysfunctions. Many common general medical disorders have negative effects on desire, arousal, orgasm, ejaculation, and freedom from pain during sex. Chronic disease also interferes indirectly with sexual function, by altering relationships and self-image and causing fatigue, pain, disfigurement, and dependency. Current approaches to assessment of sexual dysfunction are based on models that combine psychological and biological aspects.

Increased Male–Male Courtship in Ecdysone Receptor Deficient Adult Flies

Male-male courtship is infrequent among mature adult Drosophila melanogaster. After pairs of mature adult males expressing a temperature-sensitive allele of the ecdysone receptor (EcR) gene were treated at a restrictive temperature, however, they engaged in elevated levels of male-male courtship. EcR-deficient males courted wildtype males and females, but were not courted by wildtype males. These results suggest that the ecdysone steroid hormone system may have a role in courtship initiation by adult male fruit flies.

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Association of specific symptoms and metabolic risks with serum testosterone in older men

CONTEXT

Although attention and concern about health disorders in aging men have been growing, the structure of psychological and somatic complaints of actual patients, not population-based cohorts, has not been elucidated in relation to sex hormone patterns and metabolism.

OBJECTIVE

The objective of the study was investigation of factors influencing complaint structures in aging male patients.

DESIGN

This was a cross-sectional cohort study.

SETTING

The study was conducted in an andrological outpatient department.

PATIENTS

Subjects included 434 consecutive male patients aged 50-86 yr.

MAIN OUTCOME MEASURES

The following hypotheses were measured: 1) psychosomatic complaints and metabolic factors in aging male patients are related to sex hormone levels in a symptom-specific manner, and 2) patients form subcohorts.

RESULTS

A clear-cut threshold for late-onset hypogonadism was not found; rather, prevalence of psychosomatic symptoms and metabolic risk factors accumulated with decreasing androgen levels. For example, androgen-induced prevalence of loss of libido or vigor increased below testosterone concentrations of 15 nmol/liter (P < 0.001), whereas depression and diabetes mellitus type 2 (also in nonobese men) were significantly more present in men with testosterone concentrations below 10 nmol/liter (P < 0.001). Erectile dysfunction was identified as a composite pathology of metabolic risk factors, smoking, and depressivity, whereas only testosterone concentrations below 8 nmol/liter contributed to that symptom (P = 0.003). Cluster analysis revealed aging men to present within three independent groups characterized by psychosomatic complaints, metabolic disorders, and sexual health problems. These subgroups of patients exhibit distinct features in terms of androgen levels, age, and body mass index.

CONCLUSIONS

There is no evidence that a uniform structure of testosterone concentrations and complaints exists within the cohort of elderly male patients. Rather, in aging male patients, psychosomatic complaints and metabolic risk relate to testosterone in a symptom-specific manner.

Nipple/Breast stimulation and sexual arousal in young men and women

INTRODUCTION

The role of nipple/breast stimulation in influencing sexual arousal in men and women during lovemaking has only been the subject of opinion-based comment rather than evidence-based study. No attempt to question people about such sexual behavior has ever been undertaken.

AIM

The study was designed to ascertain the effects of nipple/breast manipulation in young men and women on their sexual arousal.

METHODS

A short questionnaire about nipple/breast stimulation during sexual activity was administered to 301 (148 men; 153 women) sexually experienced undergraduates (age range 17-29 years, 95% between 18 and 22).

MAIN OUTCOME MEASURES

Replies to questions in questionnaire.

RESULTS

The major findings in regard to the women were that 81.5% reported that stimulation of their nipples/breasts caused or enhanced their sexual arousal, 78.2% agreed that when sexually aroused such manipulation increased their arousal, 59.1% had asked to have their nipples stimulated during lovemaking, and only 7.2% found that the manipulation decreased their arousal. In regard to the men, 51.7% reported that nipple stimulation caused or enhanced their sexual arousal, 39% agreed that when sexually aroused such manipulation increased their arousal, only 17.1% had asked to have their nipples stimulated, and only 7.5% found that such stimulation decreased their arousal.

CONCLUSION

Manipulation of the nipples/breasts causes or enhances sexual arousal in approximately 82% of young women and 52% of young men with only 7-8% reporting that it decreased their arousal.

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

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

Androgens in the demography of male life course--a review

While the basics of testosterone production, effects and metabolism have been known for decades, there has been a flow of novel insights in the genomics of testosterone action on a molecular and cellular level, as well as in the clinical effects from modern clinical trials, improving the understanding of the role of testosterone in male life course. Androgens are produced under the control of an endocrine cascade from GnRH via gonadotropins to the testicular Leydig cells. In some organs, testosterone is reduced to 5alpha-dihydrotestosterone prior to the receptor binding by the 5alpha reductase. The androgen receptor gene is located on the X chromosome in the q11-12 region, each mutation in the gene will induce phenotypic manisfestations. In the first stage of the male life course, testosterone moderates the male embryonic development under the control of a complex molecular genetic network. The next important phase of male maturation is the puberty, in which testosterone levels increase and induce the development of somatic and psychological characteristics of male sexuality. In the adult male, testosterone maintains sexual functions and fertility. In aging men, testosterone levels decrease slowly. Testosterone supplementation in the aging male is able to restore the function of androgen target organs only in part.