The effects of sympathetic activation on physiological and subjective sexual arousal in women

Serial neurochemical measurement of cerebrospinal fluid during the human sexual response cycle

Recent studies examining the neuroendocrine response pattern underlying the human sexual response cycle revealed transient activation of the sympathoadrenal system and a substantial, long-lasting increase in plasma prolactin concentrations following orgasm in men and women. Prolactin has been discussed as being part of a feedback mechanism that signals centers in the central nervous system, such as the dopaminergic system controlling sexual arousal. To further elucidate the central role of neuropeptides, biogenic monoamines and neurotransmitters in human sexual behavior, a serial cerebrospinal fluid (CSF)-sampling technique was implemented using a previously established experimental paradigm for sexual activity in a laboratory setting. In parallel with peripheral endocrine measures, lumbar CSF was drawn via an indwelling spinal catheter during the sexual response cycle in 10 healthy males and 10 age-matched controls, and analysed for prolactin, oxytocin, biogenic monoamines and/or their metabolites as well as inhibitory and excitatory neurotransmitter concentrations. Parallel to raised peripheral sympathetic activity, norepinephrine also increased in CSF during audiovisual, masturbation-induced sexual arousal and orgasm, and remained elevated for the remainder of the session (F(4,72) = 8.79, P = 0.000). In contrast, none of the other measures, in particular prolactin and dopamine or its metabolites, reflected significant alteration. In conclusion, the human sexual response cycle is characterized by an increase in sympathetic activity in plasma and CSF, and by pronounced secretion of plasma prolactin after orgasm. However, alterations in dopaminergic or peptidergic activity are not found in lumbar CSF, possibly due to local and restricted release in diencephalic and mesencephalic brain regions.

An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141), a melanocortin receptor agonist

INTRODUCTION

Melanocortins affect multiple physiological responses, including sexual behaviors. Bremelanotide is a synthetic peptide melanocortin analog of alpha-melanocyte-stimulating hormone that is an agonist at melanocortin receptors MC3R and MC4R.

AIM

To evaluate a single intranasal dose of bremelanotide for potential effects on physiological and subjective measurements of sexual arousal and desire in premenopausal women with sexual arousal disorder.

MAIN OUTCOME MEASURES

Change in vaginal pulse amplitude during neutral and erotic videos after treatment with bremelanotide or placebo and subjects' perceptions of physiological and sexual response within 24 hours of treatment with bremelanotide or placebo.

METHODS

Eighteen premenopausal women with a primary diagnosis of female sexual arousal disorder were randomly assigned to receive a single intranasal dose of 20 mg bremelanotide or matching placebo in a double-blind manner during the first in-clinic treatment session, and the alternate medication during the second in-clinic treatment session. During each session, subjects viewed a 20-minute neutral video followed by a 20-minute sexually explicit video. Vaginal photoplethysmography was used to monitor vaginal vasocongestion and questionnaires were used to evaluate perceptions of sexual response within the following 24-hour period.

RESULTS

More women reported moderate or high sexual desire following bremelanotide treatment vs. placebo (P = 0.0114), and a trend toward more positive responses regarding feelings of genital arousal occurred after bremelanotide compared with placebo (P = 0.0833). Among women who attempted sexual intercourse within 24 hours after treatment, significantly more were satisfied with their level of sexual arousal following bremelanotide, compared with placebo (P = 0.0256). Vaginal vasocongestion did not change significantly while viewing erotic videos following bremelanotide administration compared with placebo.

CONCLUSION

This preliminary evaluation suggests the potential for bremelanotide to positively affect desire and arousal in women with female sexual arousal disorder and indicates that bremelanotide is a promising candidate for further evaluation in an at-home study.

Psychophysiological sexual arousal in women with a history of child sexual abuse

On the basis of literature that suggests that child sexual abuse (CSA) survivors with post traumatic stress disorder (PTSD) have higher baseline sympathetic nervous system (SNS) activity than healthy controls and research that suggests that the SNS plays a critical role in female physiological sexual arousal, we examined the impact of SNS activation through intense exercise on sexual arousal in women with CSA and PTSD. We measured physiological and subjective sexual arousal in women with CSA (n = 8), women with CSA and PTSD (n = 10), and healthy controls (n = 10) during exposure to nonerotic and erotic videos. After exercise, women with CSA and women with CSA and PTSD showed no significant differences in the physiological sexual response compared with no exercise, which was different from the increased physiological sexual response after exercise observed in control women.

The impact of anxiety on sexual arousal in women

This study examined the impact of state anxiety, trait anxiety, and anxiety sensitivity on physiological and self-report measures of sexual arousal and sexual function in a non-clinical sample of women. Physiological sexual responses to an erotic stimulus were assessed using vaginal photoplethysmography, and subjective reactions were measured using questionnaires. Results suggested a curvilinear relationship between state anxiety and physiological sexual arousal (vaginal pulse amplitude; VPA). Trait anxiety and anxiety sensitivity were correlated with self-reported sexual arousal outside the laboratory. The findings may be interpreted in light of sympathetic nervous system (SNS) influences on sexual arousal and potential cognitive interference mechanisms associated with anxiety.

The relationship between women's subjective and physiological sexual arousal

Previous literature presents discordant results on the relationship between physiological and subjective sexual arousal in women. In this study, the use of hierarchical linear modeling (HLM) revealed a significant concordance between continuous measures of physiological and subjective sexual arousal as assessed during exposure to erotic stimuli in a laboratory setting. We propose that past studies that have found little or no association between the two measures may have been in part limited by the methodology and statistical analyses employed.

Tactile sensitivity in women with sexual arousal disorder

Evidence suggests that tactile sensitivity may differ between women with sexual arousal difficulties and women with normal sexual functioning. Tactile sensitivity was examined on the distal portion of the dominant hand index finger and on the lower lip in women with female sexual arousal disorder (FSAD) (n = 17) and in normally functioning women (n = 17). The two groups did not differ significantly in age, length of current relationship or on measures of sexual experience and sexual desire. Hierarchical binary logistic regression indicated that finger threshold was significantly associated with FSAD women versus control women, and hierarchical linear regression indicated that finger threshold was associated with severity of arousal dysfunction. Logistic regression showed that 76.5% of participants were correctly classified and 23.5% were incorrectly classified using tactile sensation as a predictor variable. Possible underlying mechanisms and clinical implications are discussed.

The physiological basis of human sexual arousal: neuroendocrine sexual asymmetry

Normal sexual arousal and response suppose an integrated process involving both physiological and psychological processes. However, the current understanding of sexual arousal does not provide a coherent model that accounts for the integration of multiple physiological systems that subsequently generate a coordinated sexual response at both the spinal peripheral and cerebral central levels. Herein we suggest a model that involves both sympathetic and parasympathetic activation during sexual arousal via the two classes of gonadal hormones, androgens and oestrogens. We discuss the manner in which gonadal hormones may activate such a system, transforming pre-pubertal (non-erotic) genital stimulation to post-pubertal erogenization of stimulation and subsequent sexual arousal. Finally, we indicate that the different balance of androgens and oestrogens in men and women may generate asymmetric effects on each of the components of the autonomic nervous system, thereby explaining some of the differences in patterns of sexual arousal and the responses cycle across the sexes.

Evaluation of autonomic innervation of the clitoris and bulb

PURPOSE

Female sexual dysfunction is a common disorder but there are few objective measures of female genital function. We present a novel technique to record electrical activity of the female genital erectile tissue.

MATERIALS AND METHOD

We placed concentric needle electrodes in the right clitoral crus and the bulb of 22 healthy women. Following spontaneous activity recording we stimulated the median nerve to activate the sympathetic nervous system. We simultaneously measured evoked activity in the clitoris and bulb, and hand sympathetic skin responses (SSRs).

RESULTS

Spontaneous electrical activity of the clitoris and bulb was present in 13 subjects. A total of 21 subjects had evoked activity in the bulb, while 18 had evoked activity in the clitoris. All subjects had hand SSRs. Evoked genital response latencies were similar to hand SSR latency (p > 0.05). Evoked electrical activity was recordable in the clitoris and bulb but it was more easily performed in the bulb.

CONCLUSIONS

Evoked electrical activity is more consistently obtained than spontaneous activity. These tests represent possible objective measures of female genital autonomic innervation, which may have relevance to female sexual function.

A randomized, placebo-controlled, crossover study of ephedrine for SSRI-induced female sexual dysfunction

The objective of this study was to determine whether ephedrine, an alpha- and beta-adrenergic agonist previously shown to enhance genital blood flow in women, has beneficial effects in reversing antidepressant-induced sexual dysfunction. Nineteen sexually dysfunctional women receiving either fluoxetine, sertraline, or paroxetine participated in an eight-week, double-blind, placebo-controlled, cross-over study of the effects of ephedrine (50 mg) on self-report measures of sexual desire, arousal, orgasm, and sexual satisfaction. Although there were significant improvements relative to baseline in sexual desire and orgasm intensity/pleasure on 50 mg ephedrine 1-hr prior to sexual activity, significant improvements in these measures, as well as in sexual arousal and orgasmic ability also were noted with placebo. These findings highlight the importance of conducting placebo-controlled trials for this condition.

Biochemical and functional characterization of alpha-adrenergic receptors in the rabbit vagina

Vascular and non-vascular smooth muscle within the vagina mediate important physiological changes during sexual arousal in women. In this study, we have characterized alpha-adrenergic receptors (AR) in rabbit vagina by assessment of radioligand binding, contractility of isolated tissue strips and genital hemodynamics. [3H]Prazosin and [3H]RX821002 (alpha-1 and alpha-2 AR selective antagonists) bound to rabbit vaginal membrane preparations with high affinity and limited capacity. Competition binding assays using both non-selective and subtype selective ligands for AR (phentolamine, prazosin, delequamine, rauwolscine and UK14304) further confirmed the presence of alpha-1 and alpha-2 AR in vaginal tissue. In organ bath preparations of vaginal tissue strips, norepinephrine-induced contraction was attenuated by alpha-1 and alpha-2 AR antagonists (prazosin, tamsulosin, delequamine and phentolamine). In anesthetized rabbits, intravaginal injection of the alpha-1 AR selective antagonist REC 15/2615 (50 and 100 microg/kg) caused a 2 to 3-fold increase in genital tissue oxyhemoglobin (OHb) concentration. Similar increases in tissue OHb were observed with intravaginal injection of phentolamine (500 microg/kg) or a tri-mixture of vasodilators (PGE1, papaverine, phentolamine). REC 15/2615, phentolamine or the tri-mixture also enhanced the amplitude and/or duration of change in genital tissue OHb after pelvic nerve stimulation. Thus, vaginal tissue expresses functional alpha-1 and alpha-2 AR, which modulate vaginal smooth muscle contractility and genital engorgement.

Are our definitions of women's desire, arousal and sexual pain disorders too broad and our definition of orgasmic disorder too narrow?

Since each individual female sexual dysfunction is complex, it is necessary to subtype them in addition to dividing them into life-long or acquired disorder. The complexity of women's sexual arousal necessitates appreciation of a number of different types of arousal disorders that vary not only in etiology but also in management. The coexistence of sexual arousal and sexual desire, which develops during a sexual experience, explains the frequent comorbidity of arousal and desire disorders. Subtyping of hypoactive sexual desire disorder allows analysis of lack of receptivity and of any marked loss of the traditional markers of sexual desire over and beyond a normative lessening with relationship duration. Dyspareunia and vaginismus require further analysis prior to any definitive therapy. The definition of orgasmic disorder needs to include loss of orgasmic intensity and the possibility of coincident arousal disorder.

Reexploring the concept of sexual desire

This article explores how sexual desire operates in ordinary life in both sexes. Fifteen considerations divided into six categories are provided: basic aspects; easily overlooked aspects; energy concepts; politically sensitive aspects; maintaining desire; and toward a definition. Sexual desire is the sum of the forces that incline us toward and away from sexual behavior. Clinicians need to conceptualize desire richly to understand its disorders. Scientists need to simplify the concept in order to conduct pharmacological research. Ideally, the limitations of both approaches must be accepted; in anyone's hands, sexual desire can be a slippery concept.

Attention, arousal and expectancies in anxiety and sexual disorders

This paper reviews experimental studies of sexual disorders and anxiety disorders. Studies were mainly carried out in the laboratories and clinics with which each of the two authors is associated. Sex and anxiety are rather antipodal emotions but contrary to traditional views, there is no reason to believe that anxiety disorders are driven by underlying sexual problems or that sexual problems are maintained by anxiety. Both sex research and anxiety research focused on selective processing of disorder relevant information in patients. More in particular, studies are clustered in three groups. First, the authors examined selective attention for threat-related material in anxious patients and for non-sex-related material in sexually dysfunctional patients. Second, the (mis)interpretation of response information in both disorders is compared. Finally the authors discuss biased expectancies in anxiety and sexual disorders. Symmetries and asymmetries are highlighted and lines for further research are sketched.

Evidence that serotonin affects female sexual functioning via peripheral mechanisms

A review of the literature indicates that serotonin is active in several peripheral mechanisms that are likely to affect female sexual functioning. Serotonin has been found in several regions of the female genital tract in both animals and humans. In the central nervous system (CNS), serotonin acts primarily as a neurotransmitter, but in the periphery, serotonin acts primarily as a vasoconstrictor and vasodilator. Since, in the periphery, the principal component of sexual arousal is vasocongestion of the genital tissue, it is likely that serotonin participates in producing normal sexual arousal. In addition, serotonin administration produces contraction of the smooth muscles of the genito-urinary system and is found in nerves innervating the sexual organs. Taken together, this evidence suggests that peripheral serotonergic activity may be involved in the normal sexual response cycle. In addition, exogenous substances that alter serotonin activity, such as selective serotonin uptake inhibitors (SSRIs) and the atypical antipsychotics, can produce sexual dysfunction. It is possible that sexual side effects seen with these drugs may result, at least in part, from their action on peripheral mechanisms.

Sympathetic nervous system activity and female sexual arousal

The results of a series of human and animal studies that were conducted in an effort to better understand autonomic nervous system influences on female sexual arousal are presented. The effects of sympathetic nervous system (SNS) activation on self-report and vaginal photoplethysmographic measures of sexual arousal were examined in 4 studies using intense acute exercise, and in 1 study using ephedrine, to activate the SNS. The effects of SNS inhibition on sexual responses in the female rat were examined in 3 studies using clonidine, an alpha(2)-adrenergic agonist; guanethidine, a postganglionic noradrenergic blocker; and naphazoline, an alpha(2)-adrenoreceptor agonist, to inhibit sympathetic outflow. In humans, the effects of SNS inhibition on subjective and physiologic sexual arousal were also examined using clonidine to suppress SNS activity. Together, the findings from these studies suggest that SNS activation may facilitate, and SNS inhibition inhibit, the early stages of sexual arousal in sexually functional women and in women with low sexual desire.

Cardiovascular and endocrine alterations after masturbation-induced orgasm in women

OBJECTIVE

The present study investigated the cardiovascular, genital, and endocrine changes in women after masturbation-induced orgasm because the neuroendocrine response to sexual arousal in humans is equivocal.

METHODS

Healthy women (N = 10) completed an experimental session, in which a documentary film was observed for 20 minutes, followed by a pornographic film for 20 minutes, and another documentary for an additional 20 minutes. Subjects also participated in a control session, in which participants watched a documentary film for 60 minutes. After subjects had watched the pornographic film for 10 minutes in the experimental session, they were asked to masturbate until orgasm. Cardiovascular (heart rate and blood pressure) and genital (vaginal pulse amplitude) parameters were monitored continuously throughout testing. Furthermore, blood was drawn continuously for analysis of plasma concentrations of adrenaline, noradrenaline, cortisol, prolactin, luteinizing hormone (LH), beta-endorphin, follicle-stimulating hormone (FSH), testosterone, progesterone, and estradiol.

RESULTS

Orgasm induced elevations in cardiovascular parameters and levels of plasma adrenaline and noradrenaline. Plasma prolactin substantially increased after orgasm, remained elevated over the remainder of the session, and was still raised 60 minutes after sexual arousal. In addition, sexual arousal also produced small increases in plasma LH and testosterone concentrations. In contrast, plasma concentrations of cortisol, FSH, beta-endorphin, progesterone, and estradiol were unaffected by orgasm.

CONCLUSIONS

Sexual arousal and orgasm produce a distinct pattern of neuroendocrine alterations in women, primarily inducing a long-lasting elevation in plasma prolactin concentrations. These results concur with those observed in men, suggesting that prolactin is an endocrine marker of sexual arousal and orgasm.

Inhibition of subjective and physiological sexual arousal in women by clonidine

OBJECTIVE

The present investigation was designed to provide the first empirical examination of the effects of clonidine, a selective alpha 2-adrenergic agonist, on sexual arousal in women with and without prior sympathetic nervous system [SNS] stimulation by exercise. The purpose was to help elucidate the influence of adrenergic mechanisms on sexual function in women.

METHODS

Thirty sexually functional women participated in two experimental sessions in which subjective (self-report) and physiological (vaginal photoplethysmograph) sexual responses to erotic stimuli were measured after either clonidine (0.2 mg) or placebo administration in a randomized, double-blind, crossover protocol. Before viewing the experimental films, 15 subjects engaged in 20 minutes of intense exercise designed to elicit significant SNS activation.

RESULTS

Clonidine significantly decreased vaginal pulse amplitude, vaginal blood volume, and subjective sexual responses to the erotic films in subjects who were in a state of heightened (via exercise), but not baseline (no exercise) SNS arousal.

CONCLUSIONS

Clonidine can significantly inhibit subjective and physiological sexual arousal in women. These findings have implications for deriving an etiological theory of sexual function in women and for understanding the effects of psychotherapeutic drugs on female sexual function.

Effects of sympathetic inhibition on receptive, proceptive, and rejection behaviors in the female rat

The present investigation was designed to examine the effects of sympathetic nervous system (SNS) inhibition on sexual behavior in ovariectomized, steroid-treated female rats. Clonidine, an alpha2-adrenergic agonist, guanethidine, a postganglionic noradrenergic blocker, and naphazoline, an alpha2-adrenoreceptor agonist were used to inhibit SNS activity. Intraperitoneal injections of either 33 micrograms/ml or 66 micrograms/ml clonidine significantly decreased receptive (lordosis) and proceptive (ear wiggles) behaviors and significantly increased rejection behaviors (vocalization, kicking, boxing). Either 25 mg/ml or 50 mg/ml guanethidine significantly decreased receptive and proceptive behavior and had no significant effect on rejection behaviors. Naphazoline significantly inhibited lordosis behavior at either 5 mg/ml or 10 mg/ml doses, significantly inhibited proceptive behavior at 5 mg/ml, and had no significant effect on rejection behaviors. These findings support the hypothesis that SNS inhibition decreases sexual activity in the female rat.

The effects of immediate, delayed, and residual sympathetic activation on sexual arousal in women

In a recent experiment, Meston and Gorzalka (1995) [Behaviour, Research and Therapy, 33, 651-664] demonstrated a facilitatory effect of sympathetic activation, via acute exercise, on female sexual arousal. The present investigation was designed to examine the time course of this effect. Thirty-six sexually functional women participated in two experimental sessions in which they viewed a neutral film followed by an erotic film. In one of these sessions, Ss were exposed to 20 min of intense exercise (stationary cycling) prior to viewing the films. Subjective (self-report) and physiological (photoplethysmograph) sexual arousal were measured at either 5 min, 15 min, or 30 min post-exercise. Acute exercise marginally decreased vaginal pulse amplitude (VPA) and had no effect on vaginal blood volume (VBV) responses to an erotic film when measured 5 min post-exercise. At 15 min post-exercise, exercise significantly increased VPA and marginally increased VBV responses. At 30 min post-exercise, both VPA and VBV responses to an erotic film were marginally increased. Acute exercise had no significant effect on subjective perceptions of sexual arousal in any of the experimental conditions.