Effects of immobilization stress on estrogen-induced surges of luteinizing hormone and prolactin in ovariectomized rats

Effect of arousing stimuli on circulating corticosterone and the circadian rhythms of luteinizing hormone (LH) surges and locomotor activity in estradiol-treated ovariectomized (ovx+EB) Syrian hamsters

In most proestrous hamsters, novel wheel exposure phase advances activity rhythms and blocks the preovulatory LH surge, which occurs 2h earlier the next day. Because wheel immobilization does not prevent these effects we hypothesized that arousal alone blocks and phase advances the LH surge. Ovariectomized (ovx) hamsters received a jugular vein cannula and estradiol benzoate (EB) or vehicle was injected sc. The next day (Day 1), at zeitgeber time (ZT) 4-5 (ZT 12 = lights off), after obtaining a blood sample, each hamster was exposed to constant darkness (DD), and either remained in her home cage or was transferred to a new cage and exposed to a running wheel or a 2-hour arousal paradigm. Blood samples were obtained in dim red light and activity was recorded hourly until ~ZT 10-11 on Days 1 and 2. For the next 1-2 weeks, activity was monitored in DD. Plasma LH and corticosterone were assessed by RIA. Novel wheel exposure or arousal at ZT 4 greatly attenuated the Day 1 LH surge in ovx+EB hamsters, and phase advanced the Day 2 LH surge by about 2h. In proestrous hamsters, novel wheel exposure led to a prolonged (>2h) increase in corticosterone levels only when LH surges were blocked. Phase advances in activity rhythms were enhanced by estradiol and arousal. The results suggest that estradiol modulates the effectiveness of non-photic stimuli. The role of the increased activity of the hypothalamic-pituitary-adrenal axis associated with novel wheel-induced attenuation of LH surges in ovx+EB hamsters remains to be determined.

Depressive symptoms and risk of uterine leiomyomata

OBJECTIVE

Uterine leiomyomata (UL) are a major source of gynecologic morbidity and the primary indication for hysterectomy. Depression can cause dysregulation of the hypothalamic-pituitary-adrenal axis, which may affect the synthesis of reproductive hormones involved in UL pathogenesis. We assessed the association between depressive symptoms and UL among 15,963 premenopausal women.

STUDY DESIGN

Data were derived from the Black Women's Health Study, a prospective cohort study. In 1999 and 2005, the Center for Epidemiologic Studies Depression Scale (CES-D) was used to ascertain depressive symptoms. On biennial follow-up questionnaires from 1999 through 2011, women reported physician-diagnosed depression, antidepressant use, and UL diagnoses. Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox regression.

RESULTS

There were 4722 incident UL cases diagnosed by ultrasound (n=3793) or surgery (n=929) during 131,262 person-years of follow-up. Relative to baseline CES-D scores<16, IRRs were 1.05 (95% CI, 0.98-1.13) for CES-D scores 16-24 and 1.16 (95% CI, 1.06-1.27) for CES-D scores≥25 (P-trend=.001). IRRs for current and past physician-diagnosed depression relative to no depression were 1.15 (95% CI, 0.98-1.34) and 1.25 (95% CI, 1.13-1.39), respectively. Results persisted after further control for antidepressant use. IRRs for current and past use of antidepressants (any indication) relative to never use were 1.11 (95% CI, 0.97-1.28) and 1.32 (95% CI, 1.14-1.52), respectively.

CONCLUSION

In this cohort of black women, greater depressive symptoms were associated with UL, independent of antidepressant use, supporting the hypothesis that dysregulation of the hypothalamic-pituitary-adrenal axis increases UL risk.

2014 Female Athlete Triad Coalition consensus statement on treatment and return to play of the female athlete triad: 1st International Conference held in San Francisco, CA, May 2012, and 2nd International Conference held in Indianapolis, IN, May 2013

The Female Athlete Triad is a medical condition often observed in physically active girls and women, and involves 3 components: (1) low energy availability with or without disordered eating, (2) menstrual dysfunction, and (3) low bone mineral density. Female athletes often present with 1 or more of the 3 Triad components, and an early intervention is essential to prevent its progression to serious endpoints that include clinical eating disorders, amenorrhea, and osteoporosis. This consensus statement represents a set of recommendations developed following the first (San Francisco, California) and second (Indianapolis, Indianna) International Symposia on the Female Athlete Triad. It is intended to provide clinical guidelines for physicians, athletic trainers, and other health care providers for the screening, diagnosis, and treatment of the Female Athlete Triad and to provide clear recommendations for return to play. The 2014 Female Athlete Triad Coalition Consensus Statement on Treatment and Return to Play of the Female Athlete Triad Expert Panel has proposed a risk stratification point system that takes into account magnitude of risk to assist the physician in decision-making regarding sport participation, clearance, and return to play. Guidelines are offered for clearance categories, management by a multidisciplinary team, and implementation of treatment contracts. This consensus paper has been endorsed by The Female Athlete Triad Coalition, an International Consortium of leading Triad researchers, physicians, and other health care professionals, the American College of Sports Medicine, and the American Medical Society for Sports Medicine.

Atrazine-induced elevation or attenuation of the LH surge in the ovariectomized, estrogen-primed female rat: role of adrenal progesterone

Multiple exposures to the herbicide atrazine (ATRZ) were shown to suppress the LH surge in both cycling female rats and those ovariectomized (OVX) and primed with estradiol (E2). A single ATRZ administration was found to induce a prompt and marked increase in progesterone (P4). As exogenous P4 is known to have a differential effect on the LH surge depending on its temporal relationship with the surge, it was hypothesized that a single treatment in an OVX, E2-primed rat would augment the surge, whereas several exposures would cause a decrease. Following four daily treatments with 100 mg/kg, LH surge was suppressed. In contrast, a single ATRZ exposure elevated the surge. Two treatments were without effect. The single administration caused a large increase in P4 at 30 and 60 min that was likely attributable to adrenal secretion. Four exposures also elevated P4 after the final treatment, although the duration of the increase was shortened. A single treatment with 0, 10, 30, and 100 mg/kg ATRZ showed similar elevations at the highest concentration in P4, the LH peak, and area under the curve (AUC), whereas four exposures reduced the AUC. An increase at 1 h in the expression of Kiss1 in the anteroventral periventricular nucleus suggests that this regional kisspeptin neuronal population has a role in the ATRZ augmentation of the surge. These data support the hypothesis that ATRZ-induced changes in adrenal P4 can either augment or attenuate the surge depending on the temporal proximity of exposure to the rise in LH.

Lifetime abuse victimization and risk of uterine leiomyomata in black women

OBJECTIVE

Uterine leiomyomata (UL) are a major contributor to gynecologic morbidity and medical costs, and black women are disproportionately affected by the condition. Previous studies have linked UL to psychosocial stress, including child abuse. We assessed the association between lifetime abuse victimization and UL among 9910 premenopausal women.

STUDY DESIGN

Data were derived from the Black Women's Health Study, a prospective cohort study. In 2005, participants reported their experiences of physical and sexual abuse within each life stage (childhood, adolescence, adulthood). Biennial follow-up questionnaires from 2005 through 2011 ascertained new UL diagnoses. Rate ratios (RRs) and 95% confidence intervals (CIs) were estimated using Cox regression.

RESULTS

There were 1506 incident UL cases diagnosed by ultrasound or surgery. UL incidence was higher among women who reported child abuse, particularly sexual abuse. Relative to no abuse across the life span, RRs were 1.16 (95% CI, 1.02-1.33) for physical abuse only, 1.34 (95% CI, 1.09-1.66) for sexual abuse only, and 1.17 (95% CI, 0.99-1.39) for both physical and sexual abuse in childhood. RRs for 1-3 and 4 or more incidents of child sexual abuse were 1.29 (95% CI, 1.04-1.61) and 1.41 (95% CI, 1.07-1.85), respectively, whereas the RRs for low, intermediate, and high frequencies of child physical abuse were 1.19, 1.04, and 1.23, respectively. The association was strongest for the highest category of child abuse severity (RR, 1.57; 95% CI, 1.19-2.07). No associations were found for teen or adult abuse.

CONCLUSION

In the present study, child sexual abuse was an independent risk factor for UL, supporting the hypothesis that childhood adversity increases UL risk.

Divergent roles of the CRH receptors in the control of gonadotropin secretion induced by acute restraint stress at proestrus

CRH has been implicated as a mediator of stress-induced effects on the hypothalamus-pituitary-gonad axis, acting via CRH receptors in various brain regions. We investigated whether the effects of restraint stress on the secretion of gonadotropins on the morning of proestrus are mediated by the CRH-R1 or CRH-R2 receptors in the oval subdivision of the anterolateral BST, the central amygdala, the locus coeruleus (LC), or the A1 and A2 neuron groups in the medulla. At proestrus morning, rats were injected with antalarmin (a CRH-R1 antagonist), asstressin2-B (a CRH-R2 antagonist) or vehicles. Thirty minutes after the injection, the animals were placed into restraints for 30 min, and blood was sampled for 2 h. At the end of the experiment, the brains were removed for immunofluorescence analyses. Restraint stress increased the levels of FSH and LH. Antalarmin blocked the stress-induced increases in FSH and LH secretion, but astressin2-B only blocked the increase in FSH secretion. LC showed intense stress-induced neuronal activity. FOS/tyrosine-hydroxylase coexpression in LC was reduced by antalarmin, but not astressin2-B. The CRH-R1 receptor, more than CRH-R2 receptor, appears to be essential for the stimulation of the hypothalamus-pituitary-gonad axis by acute stress; this response is likely mediated in part by noradrenergic neurons in the LC. We postulate that the stress-induced facilitation of reproductive function is mediated, at least in part, by CRH action through CRH-R1 on noradrenaline neurons residing in the LC that trigger GnRH discharge and gonadotropin secretion.

The CRH-R₁ receptor mediates luteinizing hormone, prolactin, corticosterone and progesterone secretion induced by restraint stress in estrogen-primed rats

Acute stress has been shown to modify hypothalamus-pituitary-gonadal (HPG) axis activity. Corticotropin-releasing hormone (CRH), the principal regulator of the hypothalamus-pituitary-adrenal (HPA) axis, has been implicated as a mediator of stress-induced effects on the reproductive axis. The role of the specific CRH receptor subtypes in this response is not completely understood. In the current study, we investigated the role of the CRH-R(1) receptor on luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), progesterone (P) and corticosterone (CT) secretion in stress-induced responses under the influence of estrogen (E(2)). Estrogen-primed ovariectomized rats (estradiol cypionate, 10 μg sc) received an i.v. administration of antalarmin (0.1 or 1mg/kg), a selective CRH-R(1) antagonist, or vehicle before restraint stress for 40 min. Seven blood samples were collected from two experimental groups (one from 10:00 h to 14:00 h and the other from 10:00 h to 18:00 h). An increase of plasma LH induced by restraint acute-stress was followed by alteration of the secretion pattern in the estrogen-induced afternoon surge. In a similar manner, we observed a suppression of the afternoon surge in plasma FSH, a delay of E(2)-induced PRL secretion, and an increase in plasma P and CT. Antalarmin attenuated stress-induce LH increase, decreased CT and P secretion and blocked the stress effects on PRL secretion. These findings suggest that CRH-R(1) mediates, at least in part, the restraint stress effects on the HPA, PRL, and reproductive axes.

Acute stress may induce ovulation in women

BACKGROUND

This study aims to gather information either supporting or rejecting the hypothesis that acute stress may induce ovulation in women. The formulation of this hypothesis is based on 2 facts: 1) estrogen-primed postmenopausal or ovariectomized women display an adrenal-progesterone-induced ovulatory-like luteinizing hormone (LH) surge in response to exogenous adrenocorticotropic hormone (ACTH) administration; and 2) women display multiple follicular waves during an interovulatory interval, and likely during pregnancy and lactation. Thus, acute stress may induce ovulation in women displaying appropriate serum levels of estradiol and one or more follicles large enough to respond to a non-midcycle LH surge.

METHODS

A literature search using the PubMed database was performed to identify articles up to January 2010 focusing mainly on women as well as on rats and rhesus monkeys as animal models of interaction between the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes.

RESULTS

Whereas the HPA axis exhibits positive responses in practically all phases of the ovarian cycle, acute-stress-induced release of LH is found under relatively high plasma levels of estradiol. However, there are studies suggesting that several types of acute stress may exert different effects on pituitary LH release and the steroid environment may modulate in a different way (inhibiting or stimulating) the pattern of response of the HPG axis elicited by acute stressors.

CONCLUSION

Women may be induced to ovulate at any point of the menstrual cycle or even during periods of amenorrhea associated with pregnancy and lactation if exposed to an appropriate acute stressor under a right estradiol environment.

Blunted opiate modulation of prolactin response in smoking men and women

Endogenous opioids are integral in modulating drug reward, but it is believed that these may act through several mechanisms including hypothalamic-pituitary-adrenocortical (HPA) and dopamine pathways. This study was developed to examine how nicotine dependence alters endogenous opioid regulation of prolactin response, a peripheral marker of dopaminergic activity. Smokers and nonsmokers completed two sessions during which placebo or 50mg of naltrexone was administered, using a double-blind, counterbalanced design. Blood samples and mood measures were obtained during a resting absorption period, after exposure to two noxious stimuli (cold pressor and thermal pain), and during an extended recovery period. Opioid blockade increased prolactin response, indicating an inhibitory effect of the endogenous opioid system on prolactin, possibly mediated by reduced stimulatory effects of dopamine on this hormone. These responses were attenuated in smokers relative to nonsmokers. There was also a gender disparity in prolactin response, with women showing a stronger response to endogenous opioid modification than men regardless of smoking status. The attenuated effects of opioid blockade may reflect dysregulated opiodergic and dopaminergic effects. Results extend previous reports showing blunted opioid regulation of the HPA response in dependent smokers.

Childhood abuse and early menarche: findings from the black women's health study

OBJECTIVES

We examined the association between childhood abuse and early menarche in a sample of US Black women.

METHODS

We conducted multivariable log-binomial regression on data from 35 330 participants in the Black Women's Health Study to estimate risk ratios and 95% confidence intervals for the relation of childhood physical and sexual abuse with early age at menarche (i.e., < 12 years).

RESULTS

In adjusted analyses, sexual abuse was positively associated with early menarche, and the risk of early menarche increased with increasing frequency of sexual abuse incidents. We observed a weak but statistically significant association between physical abuse and early menarche. Associations between sexual abuse and early menarche were stronger when we used a more stringent cutpoint for early menarche (i.e., < 11 years).

CONCLUSIONS

Our data suggest an increased risk of early menarche among Black women who experienced childhood sexual abuse. Evidence for an association between childhood physical abuse and early menarche was equivocal.

Perceived racial discrimination and risk of uterine leiomyomata

BACKGROUND

The incidence of uterine leiomyomata (fibroids, myomas) is 2-3 times higher in black women than white women. Black women also report higher levels of racial discrimination. We evaluated the hypothesis that greater exposure to racism increases myoma risk in black women.

METHODS

Data were derived from the Black Women's Health Study, a prospective cohort study of US black women age 21-69 years in 1995. In 1997, women reported on "everyday" and "lifetime" experiences of racism. From 1997 through 2003, we followed 22,002 premenopausal women to assess the association between self-reported racism and risk of myomas. Incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were estimated from Cox regression models.

RESULTS

During 107,127 person-years of follow-up, 3440 new cases of uterine myomas confirmed by ultrasound (n = 2774) or surgery (n = 666) were reported. All IRRs for "lifetime" and "everyday" experiences of racism were above 1.0. Using a summary variable that averaged the responses from 5 "everyday" racism items, multivariable IRRs comparing quartiles 2, 3, and 4 to quintile 1 (lowest) were 1.16 (95% CI = 1.04-1.29), 1.19 (1.06-1.32), and 1.27 (1.14-1.43), respectively. Multivariable IRRs comparing women who reported 1, 2, or 3 lifetime occurrences of major discrimination (ie, job, housing, or police) relative to those who reported none were 1.04 (0.96-1.13), 1.17 (1.07-1.28), and 1.24 (1.10-1.39), respectively. Results did not vary according to case definition (ultrasound vs. surgery) or health care utilization. Associations were weaker among foreign-born women and among women with higher coping skills.

CONCLUSIONS

Perceived racism was associated with an increased risk of uterine myomas in US-born black women.

Cortisol, dehydroepiandrosterone, and estradiol measured over 24 hours in women with childhood sexual abuse-related posttraumatic stress disorder

Preclinical studies have shown long-term alterations in several hormonal systems including cortisol, dehydroepiandrosterone (DHEA) and DHEA-Sulfate, and estradiol. The purpose of this study was to assess cortisol, DHEA, and estradiol over a 24-hour period in women with early childhood sexual abuse and posttraumatic stress disorder (PTSD); with early abuse and without PTSD; and women without early abuse or PTSD. Forty-three women with early childhood sexual abuse and PTSD, early abuse without PTSD, and without abuse or PTSD, underwent a comprehensive assessment of hormones in plasma at multiple time points over a 24-hour period. Abused women with PTSD had lower concentrations of cortisol during the afternoon hours (12-8 p.m.) compared with women with abuse without PTSD and women without abuse or PTSD. DHEA-Sulfate was elevated throughout the 24-hour period in PTSD women, although this was of marginal statistical significance. There were no differences between groups in DHEA or estradiol. PTSD women also had increased cortisol pulsatility compared with the other groups. These findings suggest that a resting hypocortisolemia in the afternoon hours with increased cortisol pulsatility is associated with childhood abuse-related PTSD in women.

Self-reported stress and risk of endometrial cancer: a prospective cohort study

OBJECTIVES

To assess a possible relationship between perceived stress and first-time incidence of primary endometrial cancer. Psychological stress may affect the synthesis and metabolism of estrogens and thereby be related to risk of endometrial cancer.

METHODS

The 6760 women participating in the Copenhagen City Heart Study were asked about their stress level at baseline from 1981 to 1983. These women were prospectively followed up in the Danish nationwide cancer registry until 2000 and <0.1% were lost to follow-up. Cox proportional hazard models were used to analyze data.

RESULTS

During follow-up, 72 women were diagnosed with endometrial cancer. For each increase in stress level on a 7-point stress scale, there was a lower risk of primary endometrial cancer (hazard ratio (HR) = 0.88; 95% confidence interval (CI), 0.76-1.01). This inverse association was particularly strong in women who received hormone therapy (HR = 0.77; 95% CI, 0.61-0.96) and in normal-weight women (HR = 0.73; 95% CI, 0.58-0.91).

CONCLUSIONS

Stress may affect gonadal synthesis of estrogens and alter the sensitivity of the uterus toward estrogen stimulation. These mechanisms may explain the lower risk of endometrial cancer observed among stressed women in this study. Despite these results, stress may still be a risk factor for a range of other diseases and should therefore not be considered a healthy response.

Influence of estradiol on adrenal activity in ovariectomized cows during acute stress

Stress-dependent activation of the hypothalamo-pituitary-adrenal axis (HPA) can compromise reproductive function in animals and humans. In addition, it has been shown that estrogens are also capable of influencing the activity of the adrenal cortex. The objective of this study was to evaluate the effect of estradiol (E2) on adrenocortical secretion of cortisol and progesterone as well as on pituitary LH-release in cows during stress. Five ovariectomized Brown Swiss cows were exposed to acute restraint stress (2-h immobilization in a trimming chute), either with or without E2 treatment. Blood samples were taken every 15 min during a 5-h period for determination of cortisol progesterone and LH. Our results demonstrate that during the 2-h stress period mean cortisol concentrations significantly (P < 0.05) increased in all cows independent of E2 treatment. Mean progesterone concentrations also increased during stress, but the effect was only significant in E2-untreated cows. In contrast to cortisol and progesterone, mean LH values decreased in all animals during stress, but the decline was not significant. However, significantly lower mean LH values were seen at the end of the stress period comparing to values before stress. In cows without stress, E2 treatment had no significant effect on mean values of all three hormones analyzed. From our results it can be concluded that in ovariectomized cows (a) acute stress increases cortisol and progesterone secretion but decreases LH release and (b) the stress induced adrenocortical and pituitary responses were clearly attenuated under the influence of estradiol.

Maintenance of gonadotropin secretion by glucocorticoids under stress conditions through the inhibition of prostaglandin synthesis in the brain

We have previously reported that glucocorticoids counteract the suppressive effects of tumor necrosis factor-alpha on both pulsatile and surge secretion of LH. This suggests that glucocorticoids have a protective effect on reproductive function under infectious stress. In the present study, we examined whether glucocorticoids maintain pulsatile LH secretion under various conditions of acute stress and the possible involvement of prostaglandins (PGs) in glucocorticoid actions. Three different types of stressors, namely infectious (lipopolysaccharide, 0.5 microg/kg), hypoglycemic (2-deoxy-D-glucose, 100 mg/kg), and restraint stress (1 h) were applied to ovariectomized rats. In ovariectomized rats, LH pulses were partially suppressed by restraint, but not by lipopolysaccharide or 2-deoxy-D-glucose. On the other hand, adrenalectomy (ADX) significantly enhanced the suppressive effects of all the stressors applied on LH pulses. Treatment with both corticosterone (25 mg/kg) and indomethacin (10 mg/kg) in ADX rats significantly attenuated the suppressive effects of these stressors on LH pulses. In addition, the immunoreactivity of cyclooxygenase-2, a PG-synthesizing enzyme, in the brain under stress conditions was much enhanced by ADX, and this was counteracted by corticosterone treatment. Similarly, an increase in body temperature under restraint stress was enhanced by ADX and suppressed by corticosterone. These results suggest that suppression of LH pulsatility by stress is mediated by PGs in the brain, and that increased release of endogenous glucocorticoids in response to stress counteracts this suppression by inhibiting PG synthesis, and thereby maintains reproductive function regardless of the nature of the stressor.

Stress model for research into preterm delivery among black women

The disparity between black and white infant mortality rates increased over the last decade, despite overall improvement in infant survival. Because most black infant deaths are related to preterm delivery, the discovery of the cause of premature birth in general and excess premature birth for black infants in particular is of paramount importance for reproductive health research. Substantial theoretic support exists for maternal stress as a risk factor for preterm birth. Traumatic events early in life may sensitize the adult to contemporary stresses and increase her vulnerability to stress-induced neuroendocrine or infection/inflammatory pathways to early parturition. In addition, an individual may prematurely age as a result of cumulative stress or a major traumatic event. This "stress age," which is synonymous with the concept of weathering and similar to the concept of allostatic load, may affect parturition through chronic conditions (such as hypertension) and in poorly understood pathophysiologic mechanisms that are related to increased chronologic age. One potential measure of stress age is maternal serum dehydroepiandrosterone sulfate. Maternal stress is a potential explanatory factor for excess preterm delivery among black women because of their exposure to racism-associated stress. However, few studies have addressed this question, and results are mixed. Future etiologic research must take into account the complexities of the measurement of stress age and past and current exposures to stress, which includes internalized racism and interpersonal racism.

Effects of Gamisoyosan onin vitro fertilization and ovulation of stressed mice by electric shock

Exposure to stress is known to precipitate or exacerbate many reproductive dysfunctions such as dysmenorrhea and infertility. Abnormalities of the reproductive system, as shown by reduced ovulation, fertilization and early embryonic development, are frequently seen in dysmenorrhea and infertility. It has been generally accepted that Gamisoyosan (GSS) is a useful prescription for treating insomnia, dysmenorrhea and infertility induced by a stress. Also GSS has been used traditionally to improve systemic circulation and biological energy production. Based on these, this study investigates whether GSS improved ovarian dysfunction caused by stress in mice. Mice were subjected to stress by electric shock on the foot for 30 min daily for a week and treated with GSS at 500 / body weight per day for one week. Thereafter, changes body weight, adrenal weight, ovulation rate, in vitro and in vivo fertilization, embryonic development and estradiol concentrations were measured. GSS markedly increased the body weight of mice with stress, but not normal mice. The administration of GSS caused a reduction in adrenal weight in stressed mice. GSS also had significant positive effects on ovulation rate, estradiol production, in vivo and in vitro fertilization rates and embryonic development. These results indicate that GSS can improve the reproductive dysfunctions caused by stress, and these may production biological energy.

Sex differences in photoperiodic and stress-induced enhancement of immune function in Siberian hamsters

Siberian hamsters breed during the long days of spring and summer when environmental conditions (e.g., ambient temperatures, food availability) are favorable for reproduction. Environmental conditions may also influence the onset and severity of infection and disease, and photoperiodic alterations in immune function may comprise part of a repertoire of seasonal adaptations to help survive winter. In order to test the hypothesis that animals use day length to anticipate seasonal stressors and adjust immune function, we measured antigen-specific delayed-type-hypersensitivity (DTH) responses in the skin of male and female hamsters during long, "summer-like," or short, "winter-like" days, at baseline and following acute restraint stress. Sex steroid hormones were lower, and cortisol was higher, in males and females during short days. Baseline DTH was enhanced in short- compared to long-day males, and acute stress augmented this effect. In contrast, photoperiod alone did not influence the DTH response in females. As predicted, female hamsters exhibited significantly higher DTH responses than males during long days, but not during short days. However, this enhancement was observed in acutely stressed females only. Cortisol concentrations were significantly higher at baseline in females, and increased more in response to stress, compared to males in both photoperiods. These results suggest that photoperiod provides a useful cue by which stressors in the environment may be anticipated in order to adjust immune function. Furthermore, interactions among reproductive status and stress responses appear to mediate the expression of sex differences in immune responses in hamsters.

Lipopolysaccharide inhibits luteinizing hormone release through interaction with opioid and excitatory amino acid inputs to gonadotropin-releasing hormone neurones in female rats: possible evidence for a common mechanism involved in infection and immobilization stress

Acute immobilization stress suppresses naloxone- and N-methyl-d-aspartate (NMDA)-induced, but not gonadotropin-releasing hormone (GnRH)-induced, luteinizing hormone (LH) release in ovariectomized oestrogen-primed rats. To explore whether a common mechanism may underlie inhibition of gonadotropin secretion by various stressors, we examined in the present study the effect of lipopolysaccharide (LPS) on LH release induced by progesterone, GnRH, naloxone and NMDA. The effect of LPS on Fos expression in GnRH neurones was also examined in association with its effect on steroid-induced LH release. Injection of progesterone (1 mg/rat) at noon induced an LH surge in the afternoon in ovariectomized rats pretreated with oestradiol benzoate. In these rats, the majority of hypothalamic GnRH neurones expressed Fos in the evening. Intravenous (i.v.) administration of LPS (10 micro g/rat) inhibited steroid-induced LH release and also reduced the Fos expression in GnRH neurones. In separate experiments, an i.v. injection of GnRH (50 ng/kg), naloxone (10 mg/kg) or NMDA (20 mg/kg) significantly elevated serum LH concentrations within 10 min. Pretreatment with LPS, which did not affect basal LH release or GnRH-induced LH release, inhibited naloxone-induced and NMDA-induced LH release. These results show that LPS has a suprapituitary site(s) of action to suppress the activity of GnRH neurones in female rats, and suggest that LPS affects the opioid, as well as the excitatory amino acidergic regulation of GnRH neurones. The similarity of effects of LPS and immobilization stress further suggests that a common mechanism is involved in inhibition of GnRH neurones by different stressors.

Gonadal hormones and sex differences in pain reactivity

BACKGROUND

Sex differences in the response threshold to painful stimuli and the higher number of chronic pain syndromes in women than in men have prompted a series of studies on lower animals and humans aimed at clarifying the role of gonadal hormones in pain.

OBJECTIVE

This article examines the morphologic and functional aspects of gonadal hormone systems and the relations between gonadal hormones and pain circuits, to identify areas deserving of increased attention in elucidating the endocrine mechanisms that contribute to abnormal pain states.