Does cortisol acting via the type II glucocorticoid receptor mediate suppression of pulsatile luteinizing hormone secretion in response to psychosocial stress?

Correlation Between Perceived Stress Scores and Menstrual Characteristics in Young Indian Women

INTRODUCTION

Stress is a common causative factor of menstrual irregularities, and the effect is supposed to be mediated by an alteration in normal pulsatile gonadotropin-releasing hormone (GnRH) secretion by stress.

METHODOLOGY

A cohort of 150 apparently healthy young women as volunteers was selected randomly. They were asked to attempt the perceived stress scale-14 (PSS-14) questionnaire, and based upon their scores, 50 women were allocated into group A (score of ≤28) and group B (score of ≥29), by a stratified sampling method. Their menstrual characteristics, including age of menarche, cycle length, duration of menses, any history of heavy menstrual flow (staining/passage of clots), severe debilitating dysmenorrhea, irregularities, and pictorial blood assessment chart (PBAC) scores, were recorded. The chi-square (χ2) test, Student's t-test, and Pearson's correlation coefficient were used to analyze the data using SPSS software version 21.0 (IBM Corp., Armonk, NY).

RESULTS

Group B had higher PBAC scores than group A (110.24±70.00 versus 87.56±38.51; t=2.007 and p=0.047). A history of menstrual irregularity was more common in group B as compared to group A (22% versus 4%; χ2=7.162 and p=0.002), and a history of heavy menstrual flow was also more common in group B as compared to group A (72% versus 44%; χ2=8.046 and p=0.005). In the overall selected population, PSS scores were positively correlated with a history of heavy menstrual flow (r=0.267; p=0.007) and a history of debilitating dysmenorrhea (r=0.246; p=0.014). PBAC scores were positively correlated with menstrual irregularity (r=0.497; p<0.001), the duration of menses (r=0.422; p<0.001), a history of debilitating dysmenorrhea (r=0.212; p=0.034), and a history of heavy menstrual flow (r=0.212; p=0.034). The duration of menses was positively correlated with menstrual cycle length (r=0.287; p=0.004) and a history of debilitating dysmenorrhea (r=0.211; p=0.035). The history of heavy menstrual flow was also positively correlated with the history of debilitating dysmenorrhea (r=0.323; p=0.001).

CONCLUSION

Women suffering from higher perceived stress have higher menstrual blood flow, greater blood loss, and more chances of menstrual irregularities. Perceived stress levels are positively correlated with a history of dysmenorrhea and heavy menstrual flow. Menstrual blood loss is more in women with menstrual irregularities, longer menstrual duration, a history of dysmenorrhea, and heavy menstrual flow. Longer menstrual cycles tend to have longer menstrual duration. Dysmenorrhea is positively correlated with heavier menstrual flow.

Cellular and molecular mechanisms regulating the KNDy neuronal activities to generate and modulate GnRH pulse in mammals

Accumulating findings during the past decades have demonstrated that the hypothalamic arcuate kisspeptin neurons are supposed to be responsible for pulsatile release of gonadotropin-releasing hormone (GnRH) to regulate gametogenesis and steroidogenesis in mammals. The arcuate kisspeptin neurons express neurokinin B (NKB) and dynorphin A (Dyn), thus, the neurons are also referred to as KNDy neurons. In the present article, we mainly focus on the cellular and molecular mechanisms underlying GnRH pulse generation, that is focused on the action of NKB and Dyn and an interaction between KNDy neurons and astrocytes to control GnRH pulse generation. Then, we also discuss the factors that modulate the activity of KNDy neurons and consequent pulsatile GnRH/LH release in mammals.

Chronic elevation of plasma cortisol causes differential expression of predominating glucocorticoid in plasma, saliva, fecal, and wool matrices in sheep

There is increasing interest in using nonblood measures of glucocorticoids to assess the physiological response to chronic stress conditions. In sheep, cortisol has been measured in various matrices including saliva, feces, and wool, but comprehensive studies of the relationship between plasma concentrations of cortisol and concentrations in these nonblood matrices are lacking. Therefore, we tested the hypothesis that administration of cortisol to sheep would result in elevated concentrations of cortisol in blood, saliva, feces, and wool. Merino ewes were administered with saline or 2 mg/kg BW/d hydrocortisone acetate (HCA) by intramuscular (i.m.) injection for 28 d. This treatment was imposed to mimic circulating cortisol concentrations experienced during periods of chronic stress. Cortisol and cortisone were directly measured in plasma, saliva, and wool before, during, and after treatment with saline or HCA. A 14-d pre-treatment and a 14-d post-treatment period were used to measure time taken for glucocorticoid concentrations in each of the matrices to return to baseline levels. Cortisol was also measured in feces before, during, and after treatment. Wool growth was also measured. Before treatment, there was no difference in the concentration of cortisol or cortisone in plasma, saliva, feces, or wool in animals treated with saline or HCA. In contrast, treatment with HCA increased (P < 0.05) concentrations of both cortisol and cortisone in plasma, saliva, and wool and of cortisol in feces. In plasma, cortisol concentrations were higher than cortisone (P < 0.05), whereas saliva cortisol and cortisone concentrations did not differ significantly. In wool, the concentration of cortisone was about 19-fold higher than that of cortisol during treatment and post-treatment periods. Treatment with HCA inhibited wool growth. These results demonstrate that an increase in glucocorticoids in the blood of sheep is reflected in increases in saliva (after 7 d of treatment), feces (21 d), and wool (14 d). Therefore, measures of glucocorticoids in these matrices may provide a measure of activation of the adrenal glands over time in sheep, thereby providing a retrospective indicator of chronic stress. With respect to wool, it appears that cortisol is predominantly metabolized to cortisone in the skin or wool follicle and is stored as cortisone. Therefore wool cortisone may also provide an important measure in quantifiying chronic stress in sheep.

Chronic stress increases the tyrosine phosphorylation in female reproductive organs: An experimental study

BACKGROUND

Changes in tyrosine-phosphorylated (TyrPho) protein expressions have demonstrated stress in males. In females, chronic stress (CS) is a major cause of infertility, especially anovulation. However, the tyrosine phosphorylation in the female reproductive system under stress conditions has never been reported.

OBJECTIVE

To investigate the alteration of TyrPho protein expression in ovary, oviduct, and uterus of CS rats.

MATERIALS AND METHODS

In this experimental study, 16 female Sprague-Dawley rats (5 wk: 220-250 gr) were divided into control and CS groups (n = 8/group). Every day, the CS animals were immobilized within a restraint cage and individually forced to swim in cold water for 60 consecutive days. Following the stress induction, the ovary, oviduct, and uterus of all rats were observed for their morphologies. The total protein profiles of all tissues were revealed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) before detecting TyrPho proteins using western blot. Intensity analysis was used to compare the expression of proteins between groups.

RESULTS

The results showed that the morphology and weights of ovary and oviduct in the CS group were not different from control. In contrast, the CS significantly increased the uterine weight as compared to control. Moreover, the expressions of TyrPho proteins in the ovary (72, 43, and 28 kDas), oviduct (170, 55, and 43 kDas), and uterus (55, 54, and 43 kDas) were increased in CS group as compared to those of control.

CONCLUSION

The increased expressions of TyrPho proteins in ovary, oviduct, and uterus could be potential markers used to explain some machanisms of female infertility caused from chronic stress.

Estradiol Enables Chronic Corticosterone to Inhibit Pulsatile Luteinizing Hormone Secretion and Suppress Kiss1 Neuronal Activation in Female Mice

INTRODUCTION

Two common responses to stress include elevated circulating glucocorticoids and impaired luteinizing hormone (LH) secretion. We have previously shown that a chronic stress level of corticosterone can impair ovarian cyclicity in intact mice by preventing follicular-phase endocrine events.

OBJECTIVE

This study is aimed at investigating if corticosterone can disrupt LH pulses and whether estradiol is necessary for this inhibition.

METHODS

Our approach was to measure LH pulses prior to and following the administration of chronic corticosterone or cholesterol in ovariectomized (OVX) mice treated with or without estradiol, as well as assess changes in arcuate kisspeptin (Kiss1) neuronal activation, as determined by co-expression with c-Fos.

RESULTS

In OVX mice, a chronic 48 h elevation in corticosterone did not alter the pulsatile pattern of LH. In contrast, corticosterone induced a robust suppression of pulsatile LH secretion in mice treated with estradiol. This suppression represented a decrease in pulse frequency without a change in amplitude. We show that the majority of arcuate Kiss1 neurons contain glucocorticoid receptor, revealing a potential site of corticosterone action. Although arcuate Kiss1 and Tac2 gene expression did not change in response to corticosterone, arcuate Kiss1 neuronal activation was significantly reduced by chronic corticosterone, but only in mice treated with estradiol.

CONCLUSIONS

Collectively, these data demonstrate that chronic corticosterone inhibits LH pulse frequency and reduces Kiss1 neuronal activation in female mice, both in an estradiol-dependent manner. Our findings support the possibility that enhanced sensitivity to glucocorticoids, due to ovarian steroid milieu, may contribute to reproductive impairment associated with stress or pathophysiologic conditions of elevated glucocorticoids.

Neural and endocrine mechanisms underlying stress-induced suppression of pulsatile LH secretion

Stress is well-known to inhibit a variety of reproductive processes, including the suppression of episodic Gonadotropin releasing hormone (GnRH) secretion, typically measured via downstream luteinizing hormone (LH) secretion. Since pulsatile secretion of GnRH and LH are necessary for proper reproductive function in both males and females, and stress is common for both human and animals, understanding the fundamental mechanisms by which stress impairs LH pulses is of critical importance. Activation of the hypothalamic-pituitary-adrenal axis, and its corresponding endocrine factors, is a key feature of the stress response, so dissecting the role of stress hormones, including corticotrophin releasing hormone (CRH) and corticosterone, in the inhibition of LH secretion has been one key research focus. However, some evidence suggests that these stress hormones alone are not sufficient for the full inhibition of LH caused by stress, implicating the additional involvement of other hormonal or neural signaling pathways in this process (including inputs from the brainstem, amygdala, parabrachial nucleus, and dorsomedial nucleus). Moreover, different stress types, such as metabolic stress (hypoglycemia), immune stress, and psychosocial stress, appear to suppress LH secretion via partially unique neural and endocrine pathways. The mechanisms underlying the suppression of LH pulses in these models offer interesting comparisons and contrasts, including the specific roles of amygdaloid nuclei and CRH receptor types. This review focuses on the most recent and emerging insights into endocrine and neural mechanisms responsible for the suppression of pulsatile LH secretion in mammals, and offers insights in important gaps in knowledge.

The effect of chronic and acute stressors, and their interaction, on testes function: an experimental test during testicular recrudescence

Organisms are expected to invest less in reproduction in response to a stressor, but theory predicts that this effect should depend on the frequency and duration of stressors in the environment. Here, we investigated how an acute stressor affected testes function in a songbird, and how chronic stressors influenced the acute stress response. We exposed male dark-eyed juncos (Junco hyemalis) either to chronic or minimal (control) disturbance during testicular recrudescence, after which we measured baseline testosterone, testosterone after an acute handling stressor, and capacity to produce testosterone after hormonal stimulation. In a 2×2 design, we then killed males from the two chronic treatment groups either immediately or after an acute stressor to investigate the effect of long- and short-term stressors on the testicular transcriptome. We found that chronically disturbed birds had marginally lower baseline testosterone. The acute stressor suppressed testosterone in control birds, but not in the chronic disturbance group. The ability to elevate testosterone did not differ between the chronic treatments. Surprisingly, chronic disturbance had a weak effect on the testicular transcriptome, and did not affect the transcriptomic response to the acute stressor. The acute stressor, on the other hand, upregulated the cellular stress response and affected expression of genes associated with hormonal stress response. Overall, we show that testicular function is sensitive to acute stressors but surprisingly robust to long-term stressors, and that chronic disturbance attenuates the decrease in testosterone in response to an acute stressor.

Social and ecological drivers of reproductive seasonality in geladas

Many nonseasonally breeding mammals demonstrate some degree of synchrony in births, which is generally associated with ecological factors that mediate fecundity. However, disruptive social events, such as alpha male replacements, also have the potential to affect the timing of female reproduction. Here, we examined reproductive seasonality in a wild population of geladas (Theropithecus gelada) living at high altitudes in an afro-alpine ecosystem in Ethiopia. Using 9 years of demographic data (2006-2014), we determined that, while females gave birth year-round, a seasonal peak in births coincided with peak green grass availability (their staple food source). This post-rainy season "ecological peak" in births meant that estimated conceptions for these births occurred when temperatures were at their highest and mean female fecal glucocorticoid concentrations were at their lowest. In addition to this ecological birth peak, we also found a separate birth peak that occurred only for females in groups that had experienced a recent replacement of the dominant male (i.e., a takeover). Because new dominant males cause abortions in pregnant females and kill the infants of lactating females, takeovers effectively "reset" the reproductive cycles of females in the group. This "social birth peak" was distinct from the ecological peak and was associated with higher rates of cycling and conceptions overall and higher glucocorticoid levels immediately following a takeover as compared to females that did not experience a takeover. These data demonstrate that social factors (in this case, male takeovers) can contribute to population-level reproductive seasonality above and beyond group-level reproductive synchrony.

Estradiol-Dependent Stimulation and Suppression of Gonadotropin-Releasing Hormone Neuron Firing Activity by Corticotropin-Releasing Hormone in Female Mice

Gonadotropin-releasing hormone (GnRH) neurons are the final central regulators of reproduction, integrating various inputs that modulate fertility. Stress typically inhibits reproduction but can be stimulatory; stress effects can also be modulated by steroid milieu. Corticotropin-releasing hormone (CRH) released during the stress response may suppress reproduction independent of downstream glucocorticoids. We hypothesized CRH suppresses fertility by decreasing GnRH neuron firing activity. To test this, mice were ovariectomized (OVX) and either implanted with an estradiol capsule (OVX+E) or not treated further to examine the influence of estradiol on GnRH neuron response to CRH. Targeted extracellular recordings were used to record firing activity from green fluorescent protein-identified GnRH neurons in brain slices before and during CRH treatment; recordings were done in the afternoon when estradiol has a positive feedback effect to increase GnRH neuron firing. In OVX mice, CRH did not affect the firing rate of GnRH neurons. In contrast, CRH exhibited dose-dependent stimulatory (30 nM) or inhibitory (100 nM) effects on GnRH neuron firing activity in OVX+E mice; both effects were reversible. The dose-dependent effects of CRH appear to result from activation of different receptor populations; a CRH receptor type-1 agonist increased firing activity in GnRH neurons, whereas a CRH receptor type-2 agonist decreased firing activity. CRH and specific agonists also differentially regulated short-term burst frequency and burst properties, including burst duration, spikes/burst, and/or intraburst interval. These results indicate that CRH alters GnRH neuron activity and that estradiol is required for CRH to exert both stimulatory and inhibitory effects on GnRH neurons.

Linking Stress and Infertility: A Novel Role for Ghrelin

Infertility affects a remarkable one in four couples in developing countries. Psychological stress is a ubiquitous facet of life, and although stress affects us all at some point, prolonged or unmanageable stress may become harmful for some individuals, negatively impacting on their health, including fertility. For instance, women who struggle to conceive are twice as likely to suffer from emotional distress than fertile women. Assisted reproductive technology treatments place an additional physical, emotional, and financial burden of stress, particularly on women, who are often exposed to invasive techniques associated with treatment. Stress-reduction interventions can reduce negative affect and in some cases to improve in vitro fertilization outcomes. Although it has been well-established that stress negatively affects fertility in animal models, human research remains inconsistent due to individual differences and methodological flaws. Attempts to isolate single causal links between stress and infertility have not yet been successful due to their multifaceted etiologies. In this review, we will discuss the current literature in the field of stress-induced reproductive dysfunction based on animal and human models, and introduce a recently unexplored link between stress and infertility, the gut-derived hormone, ghrelin. We also present evidence from recent seminal studies demonstrating that ghrelin has a principal role in the stress response and reward processing, as well as in regulating reproductive function, and that these roles are tightly interlinked. Collectively, these data support the hypothesis that stress may negatively impact upon fertility at least in part by stimulating a dysregulation in ghrelin signaling.

Exposure to Acute Psychosocial Stress Disrupts the Luteinizing Hormone Surge Independent of Estrous Cycle Alterations in Female Mice

The disruptive effects of severe stress on reproductive function are well documented, but surprisingly few studies exist that demonstrate milder psychosocial stressors interfere with the ovarian cycle in females. We hypothesized repeated application of psychosocial stress would disrupt estrous cycles in mice. Mice were transferred to a new cage, transported to a new room, and restrained (2 hours) for 21 consecutive days. Contrary to our hypothesis, this paradigm did not affect estrous cycles. We next tested the hypothesis that a single exposure to mild stress disrupts a specific aspect of the cycle: the proestrous luteinizing hormone (LH) surge. We developed a model of acute, layered psychosocial stress (sequential application of new cage, transport to new room, restraint and predator cues lasting 5 hours total) that consistently increased circulating corticosterone. Application of this stress paradigm on midmorning of proestrus disrupted the LH surge measured near lights out in 14 of 24 mice; there was no evidence for a 24-hour delay of the surge. Following stress, mice continued to have normal estrous cycles, even when the LH surge was disrupted. Stressed mice failing to exhibit an LH surge had uterine masses suggesting the proestrous estradiol rise occurred. To test specifically whether the layered stress paradigm blocks estradiol-dependent positive feedback mechanisms, we examined the estradiol-induced LH surge. Stress blocked the estradiol-induced LH surge in all mice. These results suggest exposure to mild, acute psychosocial stress on proestrus can severely disrupt the generation of the LH surge in mice without affecting the overall estrous cycle.

A novel non genomic glucocorticoid signaling mediated by a membrane palmitoylated glucocorticoid receptor cross talks with GnRH in gonadotrope cells

Glucocorticoid hormones (GC) are the main stress mediators associated with reproductive disorders. GC exert their effects through activation of the glucocorticoid receptor (GR) principally acting as a transcription factor. Beside well-established GR-mediated genomic actions, several lines of evidence suggest a role for rapid membrane-initiated GC signaling in gonadotrope cells triggered by a membrane-associated GR. Herein, we demonstrate the existence of a specific membrane-initiated GC signaling in LβT2 gonadotrope cells involving two related phosphoproteins: Ca²⁺/Calmodulin-dependent protein kinase II (CaMKII) and synapsin-I. Within 5 min, LβT2 cells treated with stress range of 10⁻⁷ M Corticosterone or a membrane impermeable-GC, BSA-conjugated corticosterone, exhibited a 2-fold increase in levels of phospho-CaMKII and phospho-synapsin-I. Biochemical approaches revealed that this rapid signaling is promoted by a palmitoylated GR. Importantly, GC significantly alter GnRH-induced CaMKII phosphorylation, consistent with a novel cross-talk between the GnRH receptor and GC. This negative effect of GC on GnRH signaling was further observed on LH release by mouse pituitary explants. Altogether, our work provides new findings in GC field by bringing novel understanding on how GR integrates plasma membrane, allowing GC membrane-initiated signaling that differs in presence of GnRH to disrupt GnRH-dependent signaling and LH secretion.

New concepts of the central control of reproduction, integrating influence of stress, metabolic state, and season

Gonadotropin releasing hormone is the primary driver of reproductive function and pulsatile GnRH secretion from the brain causes the synthesis and secretion of LH and FSH from the pituitary gland. Recent work has revealed that the secretion of GnRH is controlled at the level of the GnRH secretory terminals in the median eminence. At this level, projections of kisspeptin cells from the arcuate nucleus of the hypothalamus are seen to be closely associated with fibers and terminals of GnRH cells. Direct application of kisspeptin into the median eminence causes release of GnRH. The kisspeptin cells are activated at the time of a natural "pulse" secretion of GnRH, as reflected in the secretion of LH. This appears to be due to input to the kisspeptin cells from glutamatergic cells in the basal hypothalamus, indicating that more than 1 neural element is involved in the secretion of GnRH. Because the GnRH secretory terminals are outside the blood-brain barrier, factors such as kisspeptin may be administered systemically to cause GnRH secretion; this offers opportunities for manipulation of the reproductive axis using factors that do not cross the blood-brain barrier. In particular, kisspeptin or analogs of the same may be used to activate reproduction in the nonbreeding season of domestic animals. Another brain peptide that influences reproductive function is gonadotropin inhibitory hormone (GnIH). Work in sheep shows that this peptide acts on GnRH neuronal perikarya, but projections to the median eminence also allow secretion into the hypophysial portal blood and action of GnIH on pituitary gonadotropes. GnIH cells are upregulated in anestrus, and infusion of GnIH can block the ovulatory surge in GnRH and/or LH secretion. Metabolic status may also affect the secretion of reproduction, and this could involve action of gut peptides and leptin. Neuropeptide Y and Y-receptor ligands have a negative impact on reproduction, and Neuropeptide Y production is markedly increased in negative energy balance; this may be the cause of lowered GnRH and gonadotropin secretion in this state. There is a complex interaction between appetite-regulating peptide neurons and kisspeptin neurons that enables the former to regulate the latter both positively and negatively. In terms of how GnRH secretion is reduced during stress, recent data indicate that GnIH cells are integrally involved, with increased input to the GnRH cells. The secretion of GnIH into the portal blood is not increased during stress, so the negative effect is most likely effected at the level of GnRH neuronal cell bodies.

Corticosterone Blocks Ovarian Cyclicity and the LH Surge via Decreased Kisspeptin Neuron Activation in Female Mice

Stress elicits activation of the hypothalamic-pituitary-adrenal axis, which leads to enhanced circulating glucocorticoids, as well as impaired gonadotropin secretion and ovarian cyclicity. Here, we tested the hypothesis that elevated, stress-levels of glucocorticoids disrupt ovarian cyclicity by interfering with the preovulatory sequence of endocrine events necessary for the LH surge. Ovarian cyclicity was monitored in female mice implanted with a cholesterol or corticosterone (Cort) pellet. Cort, but not cholesterol, arrested cyclicity in diestrus. Subsequent studies focused on the mechanism whereby Cort stalled the preovulatory sequence by assessing responsiveness to the positive feedback estradiol signal. Ovariectomized mice were treated with an LH surge-inducing estradiol implant, as well as Cort or cholesterol, and assessed several days later for LH levels on the evening of the anticipated surge. All cholesterol females showed a clear LH surge. At the time of the anticipated surge, LH levels were undetectable in Cort-treated females. In situ hybridization analyses the anteroventral periventricular nucleus revealed that Cort robustly suppressed the percentage of Kiss1 cells coexpressing cfos, as well as reduced the number of Kiss1 cells and amount of Kiss1 mRNA per cell, compared with expression in control brains. In addition, Cort blunted pituitary expression of the genes encoding the GnRH receptor and LHβ, indicating inhibition of gonadotropes during the blockage of the LH surge. Collectively, our findings support the hypothesis that physiological stress-levels of Cort disrupts ovarian cyclicity, in part, through disruption of positive feedback mechanisms at both the hypothalamic and pituitary levels which are necessary for generation of the preovulatory LH surge.

Role of cortisol and superoxide dismutase in psychological stress induced anovulation

Stress has been identified as a potential trigger for reproductive dysfunctions, but the psycho-physiological pathway behind the effect of stress on ovulation remains unexplored. The present research work highlights the plausible mechanism of psychological stress on ovulation in mice by targeting superoxide dismutase (SOD), an enzyme involved in ovulation. For this, three consecutive studies were carried out. The first study aimed to determine the effect of psychological stress induced change in cortisol level, behavioral parameters and normal estrous cyclicity. The effect on mRNA expression of SOD subtypes, follicular growth in histological sections of ovaries and the difference in oocyte quality and number, upon superovulation were assessed in the subsequent studies. The results indicate that psychological stress model causes an increase in cortisol level (p⩽0.05) with development of anhedonia, depression and anxiety. An irregular estrous cycle was observed in stressed mice with an upregulation in mRNA expression of SOD subtypes. Histological sections revealed an increase in atretic antral follicle with an impaired follicular development. Moreover, immature oocytes were obtained from superovulated stressed mice. The study concludes that psychological stress results in anovulation which may be due to increase in cortisol level and SOD activity in stressed mice.

The effect of fluphenazine decanoate on glucocorticoid production, reproductive cyclicity, and the behavioral stress response in the Persian onager (Equus hemionus onager)

Artificial insemination, performed to maximize genetic diversity in populations of zoo-housed animals, requires intensive management and has been associated with low success rates in fractious species. In these species, stressors, such as frequent handling, may impact fertility. Long-acting neuroleptic pharmaceuticals (LANs) can attenuate the stress response to handling, but may also disrupt ovulation in some species, compromising their use for artificial insemination. Therefore, the goal of this study was to determine whether LANs may be used to mitigate stress during reproductive management in wild equids without inhibiting ovulation. Six female Persian onagers (Equus hemionus onager) were treated with fluphenazine decanoate (FD; 0.1 mg/kg IM) or saline control in a random crossover design study. Urinary cortisol, progesterone, estrogen metabolites and behavior were monitored, and follicular dynamics were examined using ultrasonography until ovulation. Onagers demonstrated significantly lower cortisol concentrations (P = 0.03) when treated with FD (6.61 ± 3.26 ng/mg creatinine) compared to saline (9.73 ± 3.19 ng/mg creatinine). Overall, there were no differences in peak estrogen (P = 0.51) or progesterone (P = 0.38) concentrations between the two groups, and all animals ovulated within the expected time frame following FD treatment. However, some onagers exhibited only minor reductions in cortisol secretion and one treated female demonstrated a suppressed luteal progesterone peak, indicating a possible reproductive cost to FD administration. While FD may be useful for highly fractious equids for which the stress of handling delays or inhibits ovulation, these results warrant further investigation of dosing.

Nursing regimens: effects on body condition, return to postpartum ovarian cyclicity in Santa Ines ewes, and performance of lambs

The effects of nursing regimens on the body condition, onset of ovarian cyclicity postpartum and weaning weight of lambs were assessed in Santa Ines ewes. Thirty-two ewes were blocked according to parity, number of lambs, and body weight at lambing and within each block randomly allocated to treatments: continuous nursing (CN), controlled nursing (CN2) with two daily feedings for an hour after the 10th day postpartum, or early weaning (EW) with total separation from the lambs after the 10th day. The animals were evaluated from the 12th day postpartum until the first estrus or until 60th day. The dry matter and nutrients intake did not differ among treatments (P>0.05) but did differ over time (P<0.01). The weight, body condition score, serum concentrations of non-esterified fatty acids and prolactin, the percentages of ewes in estrus, of ewes that ovulated within 60th day and had ovulation silent, the period from lambing to estrus, ovulation and follicle with a diameter ≥5mm and the maximum follicular diameter did not differ (P>0.05) among the treatments. The percentage of ovulation until 30th day was greater (P<0.05) in the EW group. The percentage of short luteal phases was higher in the CN2 and EW groups (P=0.07) and normal luteal phases were higher in the CN group (P=0.01). Lamb weight weaning was lower in the EW group (P<0.05). It is possible to use CN to obtain lambing periods less than eight months in Santa Ines ewes, with the advantages of simpler management and higher lamb weaning weights.

A comparison of methods for analyzing time series of pulsatile hormone data

Many endocrine systems are regulated by pulsatile hormones - hormones that are secreted intermittently in boluses rather than continuously over time. To study pulsatile secretion, blood is drawn every few minutes for an extended period. The result is a time series of hormone concentrations for each individual. The goal is to estimate pulsatile hormone secretion features such as frequency, location, duration, and amount of pulsatile and non-pulsatile secretion and compare these features between groups. Various statistical approaches to analyzing these data have been proposed, but validation has generally focused on one hormone. Thus, we lack a broad understanding of each method's performance. By using simulated data with features seen in reproductive and stress hormones, we investigated the performance of three recently developed statistical approaches for analyzing pulsatile hormone data and compared them to a frequently used deconvolution approach. We found that methods incorporating a changing baseline modeled both constant and changing baseline shapes well; however, the added model flexibility resulted in a slight increase in bias in other model parameters. When pulses were well defined and baseline constant, Bayesian approaches performed similar to the existing deconvolution method. The increase in computation time of Bayesian approaches offered improved estimation and more accurate quantification of estimation variation in situations where pulse locations were not clearly identifiable. Within the class of deconvolution models for fitting pulsatile hormone data, the Bayesian approach with a changing baseline offered adequate results over the widest range of data.

Neuroendocrine recovery initiated by cognitive behavioral therapy in women with functional hypothalamic amenorrhea: a randomized, controlled trial

OBJECTIVE

To determine whether cognitive behavior therapy (CBT), which we had shown in a previous study to restore ovarian function in women with functional hypothalamic amenorrhea (FHA), could also ameliorate hypercortisolemia and improve other neuroendocrine and metabolic concomitants of in FHA.

DESIGN

Randomized controlled trial.

SETTING

Clinical research center at an academic medical university.

PATIENT(S)

Seventeen women with FHA were randomized either to CBT or observation.

INTERVENTION(S)

CBT versus observation.

MAIN OUTCOME MEASURE(S)

Circulatory concentrations of cortisol, leptin, thyroid-stimulating hormone (TSH), total and free thyronine (T(3)), and total and free thyroxine (T(4)) before and immediately after completion of CBT or observation. (Each woman served as her own control.)

RESULT(S)

Cognitive behavior therapy but not observation reduced cortisol levels in women with FHA. There were no changes in cortisol, leptin, TSH, T(3), or T(4) levels in women randomized to observation. Women treated with CBT showed increased levels of leptin and TSH, but their levels of T(3) and T(4) remained unchanged.

CONCLUSION(S)

In women with FHA, CBT ameliorated hypercortisolism and improved the neuroendocrine and metabolic concomitants of FHA while observation did not. We conclude that a cognitive, nonpharmacologic approach aimed at alleviating problematic attitudes not only can restore ovarian activity but also improve neuroendocrine and metabolic function in women with FHA.

CLINICAL TRIAL REGISTRATION NUMBER

NCT01674426.

Genetic selection for temperament affects behaviour and the secretion of adrenal and reproductive hormones in sheep subjected to stress

We investigated the effect of genetic selection for temperament on the way that stressors affect the behaviour and the adrenal and reproductive axes of sheep. We tested three hypotheses: (i) isolation would increase cortisol secretion and decrease luteinising hormone (LH) secretion more in nervous sheep than in calm sheep; (ii) isolation combined with simulated human presence would increase cortisol secretion and decrease LH secretion more in nervous sheep than in calm sheep and (iii) isolation combined with stressors that were not specific to the selection process (i.e. non-selection stressors) would increase cortisol secretion and decrease LH secretion equally in calm and nervous sheep. Isolation alone increased cortisol secretion and decreased LH secretion in nervous sheep but not in calm sheep. Compared to calm sheep, nervous sheep were more agitated during the first 2 h of isolation but not during the second 2 h of isolation. Exposure to non-selection stressors increased cortisol secretion, decreased LH pulse amplitude and the mean plasma concentrations of LH in both calm and nervous sheep. We conclude that genetic selection for temperament affects the behavioural expression of the stress response and the secretion of adrenal and reproductive hormones during isolation, but has less impact on their reactivity to non-selection stressors.

Chronic unpredictable stress decreases expression of brain-derived neurotrophic factor (BDNF) in mouse ovaries: relationship to oocytes developmental potential

Background

Brain-derived neurotropic factor (BDNF) was originally described in the nervous system but has been shown to be expressed in ovary tissues recently, acting as a paracrine/autocrine regulator required for developments of follicles and oocytes. Although it is generally accepted that chronic stress impairs female reproduction and decreases the expression of BDNF in limbic structures of central nervous system, which contributes to mood disorder. However, it is not known whether chronic stress affects oocytes developments, nor whether it affects expression of BDNF in ovary.

Methods

Mice were randomly assigned into control group, stressed group, BDNF-treated group and BDNF-treated stressed group. The chronic unpredictable mild stress model was used to produce psychosocial stress in mice, and the model was verified by open field test and hypothalamic-pituitary-adrenal (HPA) axis activity. The methods of immunohistochemistry and western blotting were used to detect BDNF protein level and distribution. The number of retrieved oocytes, oocyte maturation, embryo cleavage and the rates of blastocyst formation after parthenogenetic activation were evaluated.

Results

Chronic unpredictable stress decreased the BDNF expression in antral follicles, but didn’t affect the BDNF expression in primordial, primary and secondary follicles. Chronic unpredictable stress also decreased the number of retrieved oocytes and the rate of blastocyst formation, which was rescued by exogenous BDNF treatment.

Conclusion

BDNF in mouse ovaries may be related to the decreased number of retrieved oocytes and impaired oocytes developmental potential induced by chronic unpredictable stress.

Stress levels of glucocorticoids inhibit LHβ-subunit gene expression in gonadotrope cells

Increased glucocorticoid secretion is a common response to stress and has been implicated as a mediator of reproductive suppression upon the pituitary gland. We utilized complementary in vitro and in vivo approaches in the mouse to investigate the role of glucocorticoids as a stress-induced intermediate capable of gonadotrope suppression. Repeated daily restraint stress lengthened the ovulatory cycle of female mice and acutely reduced GnRH-induced LH secretion and synthesis of LH β-subunit (LHβ) mRNA, coincident with increased circulating glucocorticoids. Administration of a stress level of glucocorticoid, in the absence of stress, blunted LH secretion in ovariectomized female mice, demonstrating direct impairment of reproductive function by glucocorticoids. Supporting a pituitary action, glucocorticoid receptor (GR) is expressed in mouse gonadotropes and treatment with glucocorticoids reduces GnRH-induced LHβ expression in immortalized mouse gonadotrope cells. Analyses revealed that glucocorticoid repression localizes to a region of the LHβ proximal promoter, which contains early growth response factor 1 (Egr1) and steroidogenic factor 1 sites critical for GnRH induction. GR is recruited to this promoter region in the presence of GnRH, but not by dexamethasone alone, confirming the necessity of the GnRH response for GR repression. In lieu of GnRH, Egr1 induction is sufficient for glucocorticoid repression of LHβ expression, which occurs via GR acting in a DNA- and dimerization-independent manner. Collectively, these results expose the gonadotrope as an important neuroendocrine site impaired during stress, by revealing a molecular mechanism involving Egr1 as a critical integrator of complex formation on the LHβ promoter during GnRH induction and GR repression.

Inhibition of follicular development induced by chronic unpredictable stress is associated with growth and differentiation factor 9 and gonadotropin in mice

Chronic psychosocial stress negatively affects ovarian function. Ovarian follicular development is regulated by both pituitary-derived gonadotropins and intraovarian regulatory factors. To date, the suppressive effects of chronic stress on the ovary have been observed to be manifested mainly as an inhibition of gonadotropin release. It is not clear whether there are any other intraovarian regulatory mechanisms involved in this process. Growth and differentiation factor 9 (GDF9) is an important, oocyte-specific paracrine regulator required for follicular development. In this study, the chronic unpredictable mild stress model was used to produce psychosocial stress in mice. The number of different developmental stages of follicles was counted on ovarian sections stained with hematoxylin and eosin. Real-time PCR and Western blotting were used to detect the mRNA and protein levels, respectively, of GDF9. The results show that chronic unpredictable stress inhibits follicular development, increases follicular atresia, and suppresses GDF9 expression. Exogenous gonadotropin treatment partly restores the repressed antral follicular development, but has no effect on the repressed secondary follicular development associated with chronic stress. Treatment with recombinant GDF9 restores secondary follicular development. Cotreatments with GDF9 and gonadotropins restore both secondary and antral follicular development in stressed mice. These findings demonstrate that inhibition of follicular development induced by chronic unpredictable stress is associated with GDF9 and gonadotropin.

Changes in LH pulsatility profiles in dairy heifers during exposure to oestrous urine and vaginal mucus

Difficulty in observing oestrus is a problem for many dairy farmers performing AI. Finding ways to synchronize oestrous cycles or strengthen display of oestrus without hormonal treatments would be of great interest because many consumers object to the use of exogenous hormones on healthy animals. Modification of reproductive cycles through chemical communication has been reported in several species including cattle. LH is an important regulator of the follicular phase and could possibly be subject to pheromonal influence. This study focuses on the effect of volatile compounds from oestrous substances on LH pulsatility preceding the preovulatory LH surge in cattle. Four heifers of the Swedish Red breed were kept individually in isolation. Exposure to water during the control cycle (CC), and bovine oestrous urine and vaginal mucus during the treated cycle (TC), started simultaneously with induction of oestrus. Blood sampling at 15-min intervals started 37 h after administration of PGF_2α and continued for 8 h. Monitoring of reproductive hormones, visual oestrus detection and ultrasonographic examination of the ovaries continued until ovulation had occurred. The mean concentration of LH at pulse nadir was significantly higher during TC (2.04 ± 0.18 ng/ml) than during CC (1.79 ± 0.16 ng/ml), and peak amplitude was significantly higher during CC (Δ1.03 ± 0.09) than during TC (Δ0.87 ± 0.09). No other parameters differed significantly between the two cycles. We conclude that the difference in LH pulsatility pattern may be an effect of exposing heifers to oestrous vaginal mucus and/or urine and that the mechanism behind this needs further investigation.

The role of GABAergic signalling in stress-induced suppression of gonadotrophin-releasing hormone pulse generator frequency in female rats

Stress exerts profound inhibitory effects on reproductive function by suppressing the pulsatile release of gonadotrophin-releasing hormone (GnRH) and therefore luteinising hormone (LH). This effect is mediated in part via the corticotrophin-releasing factor (CRF) system, although another potential mechanism is via GABAergic signalling within the medial preoptic area (mPOA) because this has known inhibitory influences on the GnRH pulse generator and shows increased activity during stress. In the present study, we investigated the role of the preoptic endogenous GABAergic system in stress-induced suppression of the GnRH pulse generator. Ovariectomised oestradiol-replaced rats were implanted with bilateral and unilateral cannulae targeting toward the mPOA and lateral cerebral ventricle, respectively; blood samples (25 μl) were taken via chronically implanted cardiac catheters every 5 min for 6 h for the measurement of LH pulses. Intra-mPOA administration of the specific GABA(A) receptor antagonist, bicuculline (0.2 pmol each side, three times at 20-min intervals) markedly attenuated the inhibitory effect of lipopolysaccharide (LPS; 25 μg/kg i.v.) but not restraint (1 h) stress on pulsatile LH secretion. By contrast, restraint but not LPS stress-induced suppression of LH pulse frequency was reversed by application of the selective GABA(B) receptor antagonist, CGP-35348, into the mPOA (1.5 nmol each side, three times at 20-min intervals). However, intra-mPOA application of either bicuculline or CGP-35348 attenuated the inhibitory effect of CRF (1 nmol i.c.v.) on the pulsatile LH secretion. These data indicate a pivotal and differential role of endogenous GABAergic signalling in the mPOA with respect to mediating psychological and immunological stress-induced suppression of the GnRH pulse generator.

Acute and chronic stress-like levels of cortisol inhibit the oestradiol stimulus to induce sexual receptivity but have no effect on sexual attractivity or proceptivity in female sheep

Stress-like levels of cortisol inhibit sexual receptivity in ewes but the mechanism of this action is not understood. One possibility is that cortisol interferes with the actions of oestradiol to induce sexual receptivity. We tested this hypothesis in 2 experiments with ovariectomised ewes that were artificially induced into oestrus by 12 days of i.m. injections of progesterone followed by an i.m. injection of oestradiol benzoate (ODB) 48 h later. In Experiment 1, ewes were randomly allocated to the following groups: saline infusion+25 μg ODB, saline infusion+50 μg ODB, cortisol infusion+25 μg ODB or cortisol infusion+50 μg ODB (n=5 per group). Saline or cortisol was infused i.v. for 40 h beginning at the ODB injection. In Experiment 2, ewes were infused with saline or cortisol (n=5 per group) for 5h beginning 1h before ODB injection. In both experiments, ewe sexual behaviour (attractivity, proceptivity and receptivity) was quantified every 6h. Blood samples were also collected. The cortisol infusion yielded plasma concentrations of cortisol similar to those seen during psychosocial stress. In both experiments, cortisol suppressed receptivity index (number of immobilisations by ewe/courtship displays by ram) and the number of times ewes were mounted but had no effect on attractivity or proceptivity, irrespective of the dose of ODB (Experiment 1). Cortisol also suppressed LH pulse amplitude. These results suggest that both an acute (5h) and chronic (40 h) infusion of cortisol inhibit oestradiol-induced sexual receptivity in ewes and that increasing the dose of ODB does not overcome the inhibitory effects of cortisol.

Exercise affects both ovarian follicular dynamics and hormone concentrations in mares

The objectives were to evaluate the effects of exercise on ovarian folliculogenesis and related hormones in mares. Mares (n = 11) were randomly assigned into a control (non-exercised) or treatment (exercised) group. Treatment mares (n = 5) were moderately exercised for 30 min, 6 d/wk. All mares underwent daily transrectal ultrasonographic examinations and ovarian follicles > 6 mm were measured. Blood samples were collected during the first (Cycle 1) and last (Cycle 4) cycle, and serum concentrations of cortisol, LH, and FSH were determined. Mean cortisol concentrations were elevated (P < 0.05) in exercised mares, 6.29 ± 0.22 compared with 5.62 ± 0.16 ng/dL (mean ± SEM), 30 min post exercise. There were no significant differences between groups in mean FSH concentrations; however, exercised mares had lower (17.3 ± 6.4 vs 41.1 ± 5.5 ng/mL; P < 0.05) peak LH concentrations. Furthermore, exercised mares experienced a longer (24.7 ± 0.8 vs 22.2 ± 0.8 d; P < 0.05) mean interovulatory interval for all cycles combined, fewer (P < 0.05) follicles 6 to 20 mm in diameter, and an increased (P < 0.05) number of follicles >20 mm following deviation. The dominant and largest subordinate follicle in exercised mares had a greater (P < 0.05) mean diameter on the day of deviation, suggesting delayed deviation. Exercised mares also tended (P = 0.06) to have an increased number of cycles with at least two dominant follicles compared to control (62 vs 36%, respectively), indicating a decreased ability of the largest follicle to assert dominance. Under the conditions of this study, moderately exercising mares induced higher cortisol concentrations, lowered peak LH concentrations, and altered ovarian follicular dynamics.

Evidence that RF-amide related peptide-3 is not a mediator of the inhibitory effects of psychosocial stress on gonadotrophin secretion in ovariectomised ewes

It is well known that stress inhibits normal reproductive function, including gonadotrophin secretion; however, the mechanisms and mediators involved are largely unknown. Stress impairs the secretion of luteinising hormone (LH), and it has been suggested that the RF-amide gonadotrophin-inhibitory hormone (GnIH), known as RF-amide related peptide-3 (RFRP-3) in mammalian species, may mediate this inhibitory effect of stress. If this is the case, the GnIH/RFRP system would likely be up-regulated during stress. We tested this hypothesis in ovariectomised ewes using a psychosocial stressor: isolation/restraint. Ewes were randomly allocated to control or stress (n=5 per group). Isolation/restraint stress was imposed for 90 min after control sampling for 4 h, whereas control ewes were sampled continuously for 5.5 h. All ewes were then euthanased and brains were collected. As expected, plasma concentrations of cortisol were increased significantly (P<0.05) by stress and plasma concentrations of LH were significantly (P<0.05) reduced. Immunohistochemistry and in situ hybridisation were conducted for RFRP-3 peptide and RFRP mRNA expression, respectively, in the paraventricular nucleus/dorsal medial hypothalamus region of the hypothalamus. There was no significant effect of stress on RFRP-3 peptide or mRNA levels, with no differences between control or stress ewes. Furthermore, there was no difference in the number of RFRP-3 cells double-labelled for Fos between control and stress ewes and there was no difference in the cellular expression of RFRP mRNA between groups. These results indicate that the GnIH/RFRP system is not activated by psychosocial stress in ewes, suggesting that it is an unlikely mediator of the effects of stress on LH secretion.

Neuroendocrine regulation of GnRH release and expression of GnRH and GnRH receptor genes in the hypothalamus-pituitary unit in different physiological states

This review is focused on the relationship between neuroendocrine regulation of GnRH/LH secretion and the expression of GnRH and GnRH receptor (GnRHR) genes in the hypothalamic-pituitary unit during different physiological states of animals and under stress. Moreover, the involvement of hypothalamic GABA-ergic, Beta-endorphinergic, CRH-ergic, noradrenergic, dopaminergic and GnRH-ergic systems in the regulation of expression of the GnRH and GnRHR genes as well as secretion of GnRH/LH is analyzed. It appears that the neural mechanisms controlling GnRH gene expression in different physiological states may be distinct from those regulating GnRH/LH release. The hypothalamic GnRHR gene is probably located in different neural systems and may act in a specific way on GnRH gene expression and GnRH release.

The estrous cycle of the ewe is resistant to disruption by repeated, acute psychosocial stress

Five experiments were conducted to test the hypothesis that psychosocial stress interferes with the estrous cycle of sheep. In experiment 1, ewes were repeatedly isolated during the follicular phase. Timing, amplitude, and duration of the preovulatory luteinizing hormone (LH) surge were not affected. In experiment 2, follicular-phase ewes were subjected twice to a "layered stress" paradigm consisting of sequential, hourly application of isolation, restraint, blindfold, and predator cues. This reduced the LH pulse amplitude but did not affect the LH surge. In experiment 3, different acute stressors were given sequentially within the follicular phase: food denial plus unfamiliar noises and forced exercise, layered stress, exercise around midnight, and transportation. This, too, did not affect the LH surge. In experiment 4, variable acute psychosocial stress was given every 1-2 days for two entire estrous cycles; this did not disrupt any parameter of the cycle monitored. Lastly, experiment 5 examined whether the psychosocial stress paradigms of experiment 4 would disrupt the cycle and estrous behavior if sheep were metabolically stressed by chronic food restriction. Thirty percent of the food-restricted ewes exhibited deterioration of estrous cycle parameters followed by cessation of cycles and failure to express estrous behavior. However, disruption was not more evident in ewes that also encountered psychosocial stress. Collectively, these findings indicate the estrous cycle of sheep is remarkably resistant to disruption by acute bouts of psychosocial stress applied intermittently during either a single follicular phase or repeatedly over two estrous cycles.

Psychological stress enhances the colonization of the stomach by Helicobacter pylori in the BALB/c mouse

Helicobacter pylori infection is a risk factor for development of peptic ulcers, and psychological stress (PS) may have a role in the pathogenesis of this condition. However, no interaction between PS and H. pylori infection (HI) has been established in the development of peptic ulcer, because colonization by H. pylori is the first step in the infection of the gastric mucosa, we examined H. pylori colonization of the stomach in BALB/c mice after PS. The mice were subjected to PS in a communication box test, in which they observed other mice experiencing a physical stressor (electrical) before they were inoculated with H. pylori. We found that the H. pylori colonization in the stomach of psychologically stressed mice was significantly greater than in the control mice (P < 0.05), and histological examination showed that the gastric mucosal injury in the stressed mice was more extensive than in the control mice (P < 0.05). To explore the underlying mechanisms, we administered RU486 (a type II glucocorticoid (GC) receptor antagonist) to antagonize the effect of endogenous corticosterone: this treatment decreased colonization by H. pylori in the psychologically stressed mice. We conclude that HI of the stomach of BALB/c mice is enhanced by PS, and the effect may be mediated by GCs.

Social subordination and polymorphisms in the gene encoding the serotonin transporter enhance estradiol inhibition of luteinizing hormone secretion in female rhesus monkeys

Psychosocial factors, particularly social stress, may compromise reproduction. However, some individuals may be more susceptible to socially induced infertility. The present study used group-housed, adult, ovariectomized rhesus monkeys to test the hypothesis that exposure to psychosocial stress, imposed by social subordination, would enhance estradiol (E2)-negative feedback inhibition of LH. Because polymorphisms in the gene encoding the serotonin transporter (SLC6A4) may contribute to individual differences in response to adverse environments, we determined whether subordinate females with the short-promoter-length allele (s-variant) would show greater suppression of LH. Subordinate females, particularly those with the s-variant SLC6A4 genotype, received significantly higher rates of noncontact aggression from more dominant cage mates and had consistently lower body weights. Serum LH was not influenced by social status in the absence of E2. In contrast, subordinate females were hypersensitive to E2-negative feedback inhibition of LH. Furthermore, serum LH in subordinate females with s-variant SLC6A4 genotype was maximally suppressed by Day 4 of treatment, whereas nadir concentrations were not reached until later in treatment in other females. Finally, pharmacological elevation of serum cortisol potentiated E2-negative feedback inhibition in all females. The current data suggest that infertility induced by psychosocial stressors may be mediated by hypersensitivity to E2-negative feedback and that polymorphisms in the SLC6A4 gene may contribute to differences in reproductive compromise in response to chronic stress.

Role of estradiol in cortisol-induced reduction of luteinizing hormone pulse frequency

Precise control of pulsatile GnRH and LH release is imperative to ovarian cyclicity but is vulnerable to environmental perturbations, like stress. In sheep, a sustained (29 h) increase in plasma cortisol to a level observed during stress profoundly reduces GnRH pulse frequency in ovariectomized ewes treated with ovarian steroids, whereas shorter infusion (6 h) is ineffective in the absence of ovarian hormones. This study first determined whether the ovarian steroid milieu or duration of exposure is the relevant factor in determining whether cortisol reduces LH pulse frequency. Prolonged (29 h) cortisol infusion did not lower LH pulse frequency in ovariectomized ewes deprived of ovarian hormones, but it did so in ovariectomized ewes treated with estradiol and progesterone to create an artificial estrous cycle, implicating ovarian steroids as the critical factor. Importantly, this effect of cortisol was more pronounced after the simulated preovulatory estradiol rise of the artificial follicular phase. The second experiment examined which component of the ovarian steroid milieu enables cortisol to reduce LH pulse frequency in the artificial follicular phase: prior exposure to progesterone in the luteal phase, low early follicular phase estradiol levels, or the preovulatory estradiol rise. Basal estradiol enabled cortisol to decrease LH pulse frequency, but the response was potentiated by the estradiol rise. These findings lead to the conclusion that ovarian steroids, particularly estradiol, enable cortisol to inhibit LH pulse frequency. Moreover, the results provide new insight into the means by which gonadal steroids, and possibly reproductive status, modulate neuroendocrine responses to stress.

Psychosocial stress inhibits amplitude of gonadotropin-releasing hormone pulses independent of cortisol action on the type II glucocorticoid receptor

Our laboratory has developed a paradigm of psychosocial stress (sequential layering of isolation, blindfold, and predator cues) that robustly elevates cortisol secretion and decreases LH pulse amplitude in ovariectomized ewes. This decrease in LH pulse amplitude is due, at least in part, to a reduction in pituitary responsiveness to GnRH, caused by cortisol acting via the type II glucocorticoid receptor (GR). The first experiment of the current study aimed to determine whether this layered psychosocial stress also inhibits pulsatile GnRH release into pituitary portal blood. The stress paradigm significantly reduced GnRH pulse amplitude compared with nonstressed ovariectomized ewes. The second experiment tested if this stress-induced decrease in GnRH pulse amplitude is mediated by cortisol action on the type II GR. Ovariectomized ewes were allocated to three groups: nonstress control, stress, and stress plus the type II GR antagonist RU486. The layered psychosocial stress paradigm decreased GnRH and LH pulse amplitude compared with nonstress controls. Importantly, the stress also lowered GnRH pulse amplitude to a comparable extent in ewes in which cortisol action via the type II GR was antagonized. Therefore, we conclude that psychosocial stress reduces the amplitude of GnRH pulses independent of cortisol action on the type II GR. The present findings, combined with our recent observations, suggest that the mechanisms by which psychosocial stress inhibits reproductive neuroendocrine activity at the hypothalamic and pituitary levels are fundamentally different.

Cortisol reduces gonadotropin-releasing hormone pulse frequency in follicular phase ewes: influence of ovarian steroids

Stress-like elevations in plasma glucocorticoids suppress gonadotropin secretion and can disrupt ovarian cyclicity. In sheep, cortisol acts at the pituitary to reduce responsiveness to GnRH but does not affect GnRH pulse frequency in the absence of ovarian hormones. However, in ewes during the follicular phase of the estrous cycle, cortisol reduces LH pulse frequency. To test the hypothesis that cortisol reduces GnRH pulse frequency in the presence of ovarian steroids, the effect of cortisol on GnRH secretion was monitored directly in pituitary portal blood of follicular phase sheep in the presence and absence of a cortisol treatment that elevated plasma cortisol to a level observed during stress. An acute (6 h) cortisol increase in the midfollicular phase did not lower GnRH pulse frequency. However, a more prolonged (27 h) increase in cortisol beginning just before the decrease in progesterone reduced GnRH pulse frequency by 45% and delayed the preovulatory LH surge by 10 h. To determine whether the gonadal steroid milieu of the follicular phase enables cortisol to reduce GnRH pulse frequency, GnRH was monitored in ovariectomized ewes treated with estradiol and progesterone to create an artificial follicular phase. A sustained increment in plasma cortisol reduced GnRH pulse frequency by 70% in this artificial follicular phase, in contrast to the lack of an effect in untreated ovariectomized ewes as seen previously. Thus, a sustained stress-like level of cortisol suppresses GnRH pulse frequency in follicular phase ewes, and this appears to be dependent upon the presence of ovarian steroids.

Cortisol interferes with the estradiol-induced surge of luteinizing hormone in the ewe

Two experiments were conducted to test the hypothesis that cortisol interferes with the positive feedback action of estradiol that induces the luteinizing hormone (LH) surge. Ovariectomized sheep were treated sequentially with progesterone and estradiol to create artificial estrous cycles. Cortisol or vehicle (saline) was infused from 2 h before the estradiol stimulus through the time of the anticipated LH surge in the artificial follicular phase of two successive cycles. The plasma cortisol increment produced by infusion was approximately 1.5 times greater than maximal concentrations seen during infusion of endotoxin, which is a model of immune/inflammatory stress. In experiment 1, half of the ewes received vehicle in the first cycle and cortisol in the second; the others were treated in reverse order. All ewes responded with an LH surge. Cortisol delayed the LH surge and reduced its amplitude, but both effects were observed only in the second cycle. Experiment 2 was modified to provide better control for a cycle effect. Four treatment sequences were tested (cycle 1-cycle 2): vehicle-vehicle, cortisol-cortisol, vehicle-cortisol, cortisol-vehicle. Again, cortisol delayed but did not block the LH surge, and this delay occurred in both cycles. Thus, an elevation in plasma cortisol can interfere with the positive feedback action of estradiol by delaying and attenuating the LH surge.

Psychosocial stress suppresses attractivity, proceptivity and pulsatile LH secretion in the ewe

Various stressors suppress pulsatile secretion of luteinizing hormone (LH) in ewes and cortisol has been shown to be a mediator of this effect under various conditions. In contrast, little is known about the impact of stress and cortisol on sexual behavior in the ewe. Therefore, we tested the hypothesis that both psychosocial stress and stress-like levels of cortisol will reduce the level of attractivity, proceptivity and receptivity in addition to suppressing LH secretion in the ewe. In Experiment 1, a layered stress paradigm of psychosocial stress was used, consisting of isolation for 4 h with the addition of restraint, blindfold and noise of a barking dog (predator stress) at hourly intervals. This stress paradigm reduced LH pulse amplitude in ovariectomized ewes. In Experiment 2, ovariectomized ewes were artificially induced into estrus with progesterone and estradiol benzoate treatment and the layered stress paradigm was applied. LH was measured and sexual behavior was assessed using T-mazes and mating tests. Stress reduced pulsatile LH secretion, and also reduced attractivity and proceptivity of ewes but had no effect on receptivity. In Experiment 3, ewes artificially induced into estrus were infused with cortisol for 30 h. Cortisol elevated circulating plasma concentrations of cortisol, delayed the onset of estrus and resulted in increased circling behavior of ewes (i.e. moderate avoidance) during estrus and increased investigation and courtship from rams. There was no effect of cortisol on attractivity, proceptivity or receptivity during estrus. We conclude that psychosocial stress inhibits LH secretion, the ability of ewes to attract rams (attractivity) and the motivation of ewes to seek rams and initiate mating (proceptivity), but cortisol is unlikely to be the principal mediator of these effects.

Insight into the neuroendocrine site and cellular mechanism by which cortisol suppresses pituitary responsiveness to gonadotropin-releasing hormone

Stress-like elevations in plasma glucocorticoids rapidly inhibit pulsatile LH secretion in ovariectomized sheep by reducing pituitary responsiveness to GnRH. This effect can be blocked by a nonspecific antagonist of the type II glucocorticoid receptor (GR) RU486. A series of experiments was conducted to strengthen the evidence for a mediatory role of the type II GR and to investigate the neuroendocrine site and cellular mechanism underlying this inhibitory effect of cortisol. First, we demonstrated that a specific agonist of the type II GR, dexamethasone, mimics the suppressive action of cortisol on pituitary responsiveness to GnRH pulses in ovariectomized ewes. This effect, which became evident within 30 min, documents mediation via the type II GR. We next determined that exposure of cultured ovine pituitary cells to cortisol reduced the LH response to pulse-like delivery of GnRH by 50% within 30 min, indicating a pituitary site of action. Finally, we tested the hypothesis that suppression of pituitary responsiveness to GnRH in ovariectomized ewes is due to reduced tissue concentrations of GnRH receptor. Although cortisol blunted the amplitude of GnRH-induced LH pulses within 1-2 h, the amount of GnRH receptor mRNA or protein was not affected over this time frame. Collectively, these observations provide evidence that cortisol acts via the type II GR within the pituitary gland to elicit a rapid decrease in responsiveness to GnRH, independent of changes in expression of the GnRH receptor.