Vasopressin mediates hypoglycemia-induced inhibition of luteinizing hormone secretion in the ovariectomized rhesus monkey

Neuropeptides as regulators of the hypothalamus-pituitary-gonadal (HPG) axis activity and their putative roles in stress-induced fertility disorders

Neuropeptides being regulators of the hypothalamus-pituitary-adrenal (HPA) axis activity, also affect the function of the hypothalamus-pituitary-gonadal (HPG) axis by regulating gonadotrophin-releasing hormone (GnRH) secretion from hypothalamic neurons. Here, we review the available data on how neuropeptides affect HPG axis activity directly or indirectly via their influence on the HPA axis. The putative role of neuropeptides in stress-induced infertility, such as polycystic ovary syndrome, is also described. This review discusses both well-known neuropeptides (i.e., kisspeptin, Kp; oxytocin, OT; arginine-vasopressin, AVP) and more recently discovered peptides (i.e., relaxin-3, RLN-3; nesfatin-1, NEFA; phoenixin, PNX; spexin, SPX). For the first time, we present an up-to-date review of all published data regarding interactions between the aforementioned neuropeptide systems. The reviewed literature suggest new pathophysiological mechanisms leading to fertility disturbances that are induced by stress.

A Clinician's Guide to Functional Hypothalamic Amenorrhea

Patients and clinicians alike want to know if stress causes infertility. Stress could impair with reproductive function by a variety of mechanisms, including compromise of ovarian function, spermatogenesis, fertilization, endometrial development, implantation, and placentation. Herein we focus on the pathogenesis and treatment of stress-induced anovulation, which is often termed functional hypothalamic amenorrhea (FHA), with the objective of summarizing the actual knowledge as a clinical guide. FHA is a reversible form of anovulation due to slowing of gonadotropin-releasing hormone pulse frequency that results in insufficient pituitary secretion of gonadotropins to support full folliculogenesis. Importantly, FHA heralds a constellation of neuroendocrine alterations with health concomitants. The activity of the hypothalamic-pituitary-adrenal axis is increased in women with FHA and this observation supports the notion that stress is the cause. The extent of reproductive suppression relates to individual endocrinological and physiological sensitivity to stressors, both metabolic and psychogenic, and chronicity.

Deciphering the Contributions of CRH Receptors in the Brain and Pituitary to Stress-Induced Inhibition of the Reproductive Axis

Based on pharmacological studies, corticotropin-releasing hormone (CRH) and its receptors play a leading role in the inhibition of the hypothalamic–pituitary–gonadal (HPG) axis during acute stress. To further study the effects of CRH receptor signaling on the HPG axis, we generated and/or employed male mice lacking CRH receptor type 1 (CRHR1) or type 2 (CRHR2) in gonadotropin-releasing hormone neurons, GABAergic neurons, or in all central neurons and glia. The deletion of CRHRs revealed a preserved decrease of plasma luteinizing hormone (LH) in response to either psychophysical or immunological stress. However, under basal conditions, central infusion of CRH into mice lacking CRHR1 in all central neurons and glia, or application of CRH to pituitary cultures from mice lacking CRHR2, failed to suppress LH release, unlike in controls. Our results, taken together with those of the earlier pharmacological studies, suggest that inhibition of the male HPG axis during acute stress is mediated by other factors along with CRH, and that CRH suppresses the HPG axis at the central and pituitary levels via CRHR1 and CRHR2, respectively.

Molecular and Neuroendocrine Approaches to Understanding Trade-offs: Food, Sex, Aggression, Stress, and Longevity-An Introduction to the Symposium

Life history strategies are composed of multiple fitness components, each of which incurs costs and benefits. Consequently, organisms cannot maximize all fitness components simultaneously. This situation results in a dynamic array of trade-offs in which some fitness traits prevail at the expense of others, often depending on context. The identification of specific constraints and trade-offs has helped elucidate physiological mechanisms that underlie variation in behavioral and physiological life history strategies. There is general recognition that trade-offs are made at the individual and population level, but much remains to be learned concerning the molecular neuroendocrine mechanisms that underlie trade-offs. For example, we still do not know whether the mechanisms that underlie trade-offs at the individual level relate to trade-offs at the population level. To advance our understanding of trade-offs, we organized a group of speakers who study neuroendocrine mechanisms at the interface of traits that are not maximized simultaneously. Speakers were invited to represent research from a wide range of taxa including invertebrates (e.g., worms and insects), fish, nonavian reptiles, birds, and mammals. Three general themes emerged. First, the study of trade-offs requires that we investigate traditional endocrine mechanisms that include hormones, neuropeptides, and their receptors, and in addition, other chemical messengers not traditionally included in endocrinology. The latter group includes growth factors, metabolic intermediates, and molecules of the immune system. Second, the nomenclature and theory of neuroscience that has dominated the study of behavior is being re-evaluated in the face of evidence for the peripheral actions of so-called neuropeptides and neurotransmitters and the behavioral repercussions of these actions. Finally, environmental and ecological contexts continue to be critical in unmasking molecular mechanisms that are hidden when study animals are housed in enclosed spaces, with unlimited food, without competitors or conspecifics, and in constant ambient conditions.

Neurokinin B signaling in the female rat: a novel link between stress and reproduction

Acute systemic stress disrupts reproductive function by inhibiting pulsatile gonadotropin secretion. The underlying mechanism involves stress-induced suppression of the GnRH pulse generator, the functional unit of which is considered to be the hypothalamic arcuate nucleus kisspeptin/neurokinin B/dynorphin A neurons. Agonists of the neurokinin B (NKB) receptor (NK3R) have been shown to suppress the GnRH pulse generator, in a dynorphin A (Dyn)-dependent fashion, under hypoestrogenic conditions, and Dyn has been well documented to mediate several stress-related central regulatory functions. We hypothesized that the NKB/Dyn signaling cascade is required for stress-induced suppression of the GnRH pulse generator. To investigate this ovariectomized rats, iv administered with Escherichia coli lipopolysaccharide (LPS) following intracerebroventricular pretreatment with NK3R or κ-opioid receptor (Dyn receptor) antagonists, were subjected to frequent blood sampling for hormone analysis. Antagonism of NK3R, but not κ-opioid receptor, blocked the suppressive effect of LPS challenge on LH pulse frequency. Neither antagonist affected LPS-induced corticosterone secretion. Hypothalamic arcuate nucleus NKB neurons project to the paraventricular nucleus, the major hypothalamic source of the stress-related neuropeptides CRH and arginine vasopressin (AVP), which have been implicated in the stress-induced suppression of the hypothalamic-pituitary-gonadal axis. A separate group of ovariectomized rats was, therefore, used to address the potential involvement of central CRH and/or AVP signaling in the suppression of LH pulsatility induced by intracerebroventricular administration of a selective NK3R agonist, senktide. Neither AVP nor CRH receptor antagonists affected the senktide-induced suppression of the LH pulse; however, antagonism of type 2 CRH receptors attenuated the accompanying elevation of corticosterone levels. These data indicate that the suppression of the GnRH pulse generator by acute systemic stress requires hypothalamic NKB/NK3R signaling and that any involvement of CRH therewith is functionally upstream of NKB.

Sense and nonsense in metabolic control of reproduction

An exciting synergistic interaction occurs among researchers working at the interface of reproductive biology and energy homeostasis. Reproductive biologists benefit from the theories, experimental designs, and methodologies used by experts on energy homeostasis while they bring context and meaning to the study of energy homeostasis. There is a growing recognition that identification of candidate genes for obesity is little more than meaningless reductionism unless those genes and their expression are placed in a developmental, environmental, and evolutionary context. Reproductive biology provides this context because metabolic energy is the most important factor that controls reproductive success and gonadal hormones affect energy intake, storage, and expenditure. Reproductive hormone secretion changes during development, and reproductive success is key to evolutionary adaptation, the process that most likely molded the mechanisms that control energy balance. It is likely that by viewing energy intake, storage, and expenditure in the context of reproductive success, we will gain insight into human obesity, eating disorders, diabetes, and other pathologies related to fuel homeostasis. This review emphasizes the metabolic hypothesis: a sensory system monitors the availability of oxidizable metabolic fuels and orchestrates behavioral motivation to optimize reproductive success in environments where energy availability fluctuates or is unpredictable.

Corticotrophin-releasing factor and stress-induced inhibition of the gonadotrophin-releasing hormone pulse generator in the female

It is well established that stress activates the hypothalamo-pituitary-adrenal (HPA) axis and suppresses the hypothalamo-pituitary-gonadal (HPG) axis. A large literature dealing with various stressors that regulate gonadotrophin-releasing hormone (GnRH) secretion in a variety of species (including nonhuman primates, sheep, and rats) provides evidence that stress modulates GnRH secretion by activating the corticotrophin-releasing factor (CRF) system and sympathoadrenal pathways, as well as the limbic brain. Different stressors may suppress the HPG axis by activating or inhibiting various pathways in the CNS. In addition to CRF being the principal hypophysiotropic factor driving the HPA axis, it is a potent inhibitor of the GnRH pulse generator. The suppression of the GnRH pulse generator by a variety of stressful stimuli can be blocked by CRF antagonists, suggesting a pivotal role for endogenous CRF. The differential roles for CRF receptor type 1 (CRF-R1) and CRF-R2 in stress-induced suppression of the GnRH pulse generator add to the complexity of CRF regulation of the HPG axis. Although the precise sites and mechanisms of action remain to be elucidated, noradrenergic and gamma-amino-butyric acid (GABA) neurones are implicated in the system's regulation, and opioids and kisspeptin in the medial preoptic area (mPOA) and hypothalamic arcuate nucleus (ARC) may operate downstream of the CRF neuronal system.

Hyperglycaemic hyperosmolar nonketotic state as a cause of low gonadotrophin levels in postmenopausal diabetic women: a role for severe hypernatraemia

Hypogonadotrophic hypogonadism is associated with uncontrolled diabetes mellitus. Hyperglycaemia is a unique metabolic abnormality of the hyperglycaemic hyperosmolar nonketotic state (HHNKS) and, as glucose availability regulates gonadotrophin release, we investigated whether gonadotrophin release is inhibited in diabetic women with HHNKS, and whether hyperglycaemia, hypernatraemia or both inhibit in vitro gonadotrophin-releasing hormone (GnRH) expression in GT1-7 neurones. Three groups of postmenopausal women were studied: nine diabetics with HHNKS, nine hospitalised ill nondiabetics and 15 healthy women. In addition, the effects of glucose (5.55, 33.3, 66.6 mmol/l) and sodium chloride (150 and 170 mmol/l) on GnRH expression were investigated using GT1-7 neurones. Postmenopausal diabetics with HHNKS showed a decrease in serum levels of luteinising hormone (diabetic HHNKS 2.2 +/- 0.9 IU/l versus ill nondiabetic 21.0 +/- 2.3 IU/l and healthy controls 20.9 +/- 2.8 IU/l, P < 0.01), follicle-stimulating hormone (diabetic HHNKS 8.2 +/- 2.1 IU/l versus ill nondiabetic 50.4 +/- 9.1 IU/l and controls 60.2 +/- 6.9 IU/l, P < 0.01) and free 3,5,3'-triiodothyronine (diabetic HHNKS 1.48 +/- 0.57 pmol/l versus ill nondiabetic 4.28 +/- 0.26 pmol/l and controls 3.88 +/- 0.11 pmol/l, P < 0.01). The plasma cortisol level was higher in both diabetic (985 +/- 130 nmol/l) and ill nondiabetic (726 +/- 52 nmol/l) women than in healthy women (512 +/- 47 nmol/l), but no differences were observed in plasma oestradiol, thyroid-stimulating hormone or free thyroxine. In vitro GT1-7 neurones expressed three-fold less GnRH at 170 mmol/l than at 150 mmol/l NaCl, whereas changing glucose concentrations in the culture medium did not affect GnRH expression. In conclusion, postmenopausal diabetic women with HHNKS show decreased serum gonadotrophin levels, and severe hypernatraemia may participate in the hypogonadotropism observed in HHNKS.

Use of cognitive behavior therapy for functional hypothalamic amenorrhea

Behaviors that chronically activate the hypothalamic-pituitary-adrenal (HPA) axis and/or suppress the hypothalamic-pituitary-thyroidal (HPT) axis disrupt the hypothalamic-pituitary-gonadal axis in women and men. Individuals with functional hypothalamic hypogonadism typically engage in a combination of behaviors that concomitantly heighten psychogenic stress and increase energy demand. Although it is not widely recognized clinically, functional forms of hypothalamic hypogonadism are more than an isolated disruption of gonadotropin-releasing hormone (GnRH) drive and reproductive compromise. Indeed, women with functional hypothalamic amenorrhea display a constellation of neuroendocrine aberrations that reflect allostatic adjustments to chronic stress. Given these considerations, we have suggested that complete neuroendocrine recovery would involve more than reproductive recovery. Hormone replacement strategies have limited benefit because they do not ameliorate allostatic endocrine adjustments, particularly the activation of the adrenal and the suppression of the thyroidal axes. Indeed, the rationale for the use of sex steroid replacement is based on the erroneous assumption that functional forms of hypothalamic hypogonadism represent only or primarily an alteration in the hypothalamic-pituitary-gonadal axis. Potential health consequences of functional hypothalamic amenorrhea, often termed stress-induced anovulation, may include an increased risk of cardiovascular disease, osteoporosis, depression, other psychiatric conditions, and dementia. Although fertility can be restored with exogenous administration of gonadotropins or pulsatile GnRH, fertility management alone will not permit recovery of the adrenal and thyroidal axes. Initiating pregnancy with exogenous means without reversing the hormonal milieu induced by chronic stress may increase the likelihood of poor obstetrical, fetal, or neonatal outcomes. In contrast, behavioral and psychological interventions that address problematic behaviors and attitudes, such as cognitive behavior therapy (CBT), have the potential to permit resumption of full ovarian function along with recovery of the adrenal, thyroidal, and other neuroendocrine aberrations. Full endocrine recovery potentially offers better individual, maternal, and child health.

Hypotensive hypovolemia and hypoglycemia activate different hindbrain catecholamine neurons with projections to the hypothalamus

To better understand the involvement of hindbrain catecholamine neurons in hypovolemia-induced secretion of AVP, we injected antidopamine beta-hydroxylase saporin (DSAP) or unconjugated saporin (SAP) control solution into the hypothalamic paraventricular nucleus (PVH) of anesthetized rats to retrogradely lesion catecholamine neurons innervating magnocellular areas of the hypothalamus. Subsequently, hypotensive hypovolemia was induced by remote blood withdrawal (4.5 ml, 1 ml/min) using an intra-atrial catheter. Blood was sampled at 2, 5, 20, and 50 min after onset of blood withdrawal. The AVP response was severely impaired by DSAP. Peak responses at 50 min were 51 pg/ml in SAP control and 17 pg/ml in DSAP-lesioned rats, indicating the importance of catecholamine neurons for this response. We also measured AVP responses to osmotic challenge induced by administration of hypertonic saline (1 M, 15 ml/kg, sc) and to insulin-induced hypoglycemia. Osmotic challenge increased AVP levels, but the response was not impaired by DSAP, indicating that AVP neurons were not damaged by the DSAP injection. Insulin-induced hypoglycemia did not increase AVP levels in either DSAP- or SAP-treated rats. However, the same dose of insulin increased food intake and corticosterone secretion in SAP controls, and these responses were profoundly impaired by DSAP. Thus catecholamine neurons are required for both the AVP response to hypotensive hypovolemia and for feeding and corticosterone responses to hypoglycemia. Lack of an AVP response to insulin-induced hypoglycemia in intact rats therefore indicates that responses to hypovolemia and hypoglycemia are mediated by different catecholamine neurons under distinct sensory controls.

Projections to the preoptic area from the paraventricular nucleus, arcuate nucleus and the bed nucleus of the stria terminalis are unlikely to be involved in stress-induced suppression of GnRH secretion in sheep

Stress compromises reproductive function and the major physiological system activated during stress is the hypothalamo-pituitary-adrenal axis. Corticotrophin-releasing hormone and arginine vasopressin (AVP), which are produced in neurones of the paraventricular nucleus (PVN), drive the hypothalamo-pituitary-adrenal axis and are also implicated in the suppression of the reproductive axis. We used retrograde tracing and Fos labelling to map the projections from the PVN to the preoptic area (POA) where most gonadotrophin releasing hormone (GnRH) neurones are found. Fluorogold (FG) injections were made into the POA of gonadectomised male and female sheep (n = 5/sex), the animals were stressed and the brains recovered for histochemistry. All animals responded to stress with an increase in the number of Fos-labelled nuclei in the PVN. Few retrogradely labelled cells of the PVN were activated by stress. Dual labelling showed that very few FG-labelled cells also stained for corticotrophin-releasing hormone, none for AVP or enkephalin. Dual labelling for FG and Fos in the bed nucleus of the stria terminalis (BNST) and the arcuate nucleus showed that no FG-labelled cells in the BNST and only few in the ARC were activated by stress. No sex differences were observed in the activation of FG-labelled cells in any of the nuclei examined. We conclude that, although cells of the PVN, BNST and/or arcuate nucleus may affect reproduction via the GnRH cells of the POA, this is unlikely to involve direct input to the POA. If cells of these regions are involved in GnRH suppression during stress, this may occur via interneuronal pathways.

Co-localization and distribution of corticotrophin-releasing hormone, arginine vasopressin and enkephalin in the paraventricular nucleus of sheep: A sex comparison

The paraventricular nucleus (PVN) is integral to regulation of the hypothalamo-pituitary-adrenal (HPA) axis and contains cells producing corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and enkephalin. We used immunohistochemistry to map these peptides and to resolve the extent of co-localization within PVN cells in intact and gonadectomized male and female sheep. Immunoreactive (ir) CRH, AVP and enkephalin cells were mapped in two rams and two ewes at 180 mum intervals throughout the rostro-caudal extent of the PVN. Similar distributions of AVP-ir cells occurred in both sexes whereas CRH-ir and enkephalin-ir cells extended more rostrally in rams. In groups (n=4) of intact and gonadectomized sheep of both sexes, co-localization and distribution of neuropeptides was influenced by sex and gonadectomy. Males had more AVP and CRH cells than females. Intact animals had more AVP cells than gonadectomized animals. There were no differences between groups in the number or percentage of cells that stained for both CRH and AVP or in the number of cells that stained for both CRH and enkephalin. Differences were observed in the percentage of enkephalin cells that contained CRH with males having a greater percentage of co-localized cells than did females. Differences were also observed in the number and percentage of cells that stained for both enkephalin and AVP; the number of cells that stained for both neuropeptides was greater in males than in females and greater in intact animals than in gonadectomized animals. Differences were observed in the percentage of AVP cells that contained enkephalin, and in the percentage of enkephalin cells that contained AVP with males having a greater percentage of co-localized cells than did females. We conclude that sex and gonadal status affect peptide distribution in the PVN of the sheep which may provide an anatomical basis for sex differences in HPA axis responses to stress.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Immunocytochemical localization of vasopressin v1a receptors in the rat pituitary gonadotropes

Immunocytochemical labeling using a specific antibody against vasopressin V1a receptor allowed the localization of this receptor within a subset of cells from male rat anterior pituitary. The presence of transcripts of the corresponding gene in the anterior pituitary was confirmed by RT-PCR. Multiple immunocytochemical labeling combined with confocal microscopy allowed the identification of the V1a-labeled cells as gonadotropes. At the subcellular level, the vasopressin V1a receptor was mainly associated with cytoplasmic vesicles dispersed throughout the cell, which were not the secretory granules storing LH or FSH. In addition to effects exerted by vasopressin via central targets involved in the reproductive pathways, the presence of vasopressin V1a receptors on gonadotropes supports the controversial hypothesis of a local direct action of the neuropeptide on this cell type.

Antagonism of central vasopressin receptors blocks hypoglycemic stress induced inhibition of luteinizing hormone release in male rhesus macaques

The first objective of this study was to investigate whether the inhibitory effect of insulin-induced hypoglycemia (IIH) on luteinizing hormone (LH) secretion was the same in unrestrained adult male rhesus macaques as has been previously reported in restrained female macaques. Since IIH did inhibit pulsatile LH secretion in adult male macaques, and some previous studies have implicated arginine vasopressin (AVP) as a central mediator of this inhibition, the second objective was to investigate whether antagonism of AVP action could reverse the IIH-induced inhibition of LH release in males. Ten adult male rhesus macaques (Macaca mulatta) were studied during 15-h periods (07.00-22.00 h), with blood samples collected every 15-min. There were three experimental groups; controls (n = 5), IIH (n = 6) and IIH plus vasopressin antagonist (AVPa; n = 6). During the hypoglycemia studies, the first 5 h served as a control for that occasion and an insulin bolus of 1 U/kg was administered intravenously at 12.00 h. During the IIH plus AVPa, the vasopressin antagonist was infused intravenously from 12.00 h to 17.00 h. LH and testosterone decreased progressively after the insulin bolus in the IIH group reaching a minimum value at 4 h after the infusion. However, compared to the preinfusion levels, secretion of LH and testosterone was not suppressed by hypoglycemia in the group treated with the AVP antagonist. The present study shows that in male macaques not subjected to the psychological stress of restraint, IIH suppresses LH and testosterone secretion. This inhibition of LH release can be blocked in some animals by antagonism of central vasopressin receptors, suggesting that vasopressin is involved in the suppression of gonadotropin releasing hormone/LH release induced by hypoglycemia.

Stress-induced suppression of pulsatile Luteinising hormone release in the female rat: role of vasopressin

Insulin-induced hypoglycaemic (IIH) stress evokes the release of arginine vasopressin (AVP) and suppresses luteinising hormone (LH) pulses in a number of species, a phenomenon augmented by the presence of oestradiol (E2). The aim of this study was to test the hypothesis that AVP not only disrupts pulsatile LH secretion in the female rat, but specifically mediates the effect of IIH stress on suppressing LH release. The role of E2 in augmenting the disruptive effect of AVP on LH secretion was also addressed. Rats were ovariectomized (OVX) and fitted with intracerebroventricular (i.c.v. ) and intravenous (i.v.) cannulae. For experiments requiring comparisons of neuroendocrine responses in the presence and absence of E2, animals were implanted subcutaneously with E2 or oil-filled capsules respectively. AVP (5 microg) administered via the i.c.v. cannula suppressed LH secretion by decreasing LH pulse amplitude without affecting LH pulse frequency, an effect that was blocked by central administration of an AVP antagonist (25 microg). This inhibitory response was evident only in E2-replaced OVX rats, thus suggesting a sensitizing influence of the gonadal steroid. In the AVP-deficient Brattleboro rats, IIH stress did not interrupt pulsatile LH secretion as demonstrated in Long Evans and Wistar controls. While these data might suggest a pivotal role for AVP in stress-induced suppression of LH release, central administration of an AVP antagonist did not prevent the interruption of LH pulses in response to IIH stress. Furthermore, it would appear that AVP is not primarily involved in hypoglycaemic stress-induced suppression of pulsatile LH secretion since central administration of very high doses of AVP resulted in a suppression of LH pulse amplitude and not frequency, while hypoglycaemic stress caused an interruption of LH pulses.

The effects of estrogen and progesterone on corticotropin-releasing hormone and arginine vasopressin messenger ribonucleic acid levels in the paraventricular nucleus and supraoptic nucleus of the rhesus monkey

Ovarian steroids increase hypothalamic-pituitary-adrenal (HPA) axis activity and sensitize the hypothalamic-pituitary-ovarian (HPO) axis to stress-induced inhibition. The present study investigated the effect of ovarian steroids on CRH and arginine vasopressin (AVP) messenger RNA (mRNA) levels in the rhesus monkey hypothalamus, as both neuropeptides have been shown to stimulate the HPA axis and inhibit the HPO axis in this species. This was accomplished by measuring CRH and AVP mRNA in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) by in situ hybridization histochemistry. Menstrual cycles were simulated in ovariectomized (OVX) rhesus monkeys by sequential addition and removal of SILASTIC brand (Dow Corning Corp.) tubing containing either 17beta-estradiol (E2) or progesterone (P4). On the morning of day 11 of the simulated follicular phase (E2 alone) or day 21 of the luteal phase (E2 + P4), animals were anesthetized, and the brains were perfused with paraformaldehyde via the carotid artery. Coronal sections (30 microm) were cut, and mRNA for CRH and AVP in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) were semiquantified by in situ hybridization. CRH mRNA in the PVN of E2-replaced OVX animals (n = 7) was 2-fold greater than that in untreated OVX controls (n = 4), whereas CRH mRNA after E2 + P4 (n = 4) was no different from that in controls (optical density + SEM, 0.38 +/- 0.06, 0.13 +/- 0.08, and 0.14 +/- 0.09 for OVX + E2, OVX + E2 + P4, and OVX, respectively; P = 0.02). CRH in the SON was undetectable. In contrast to CRH, AVP mRNA in the PVN and the SON was similar in the three treatment groups. We conclude that E2 and E2 + P4 replacement to OVX monkeys exert different effects on CRH and AVP gene expression, as estrogen stimulation of CRH mRNA in the PVN was abrogated by progesterone, whereas no effect of ovarian steroids on AVP mRNA in either the PVN or SON was observed. We postulate that ovarian steroid regulation of CRH synthesis and release may in part explain the central nervous system mechanisms by which ovarian steroids affect the HPA and HPO axes during basal and stress conditions.

Women with functional hypothalamic amenorrhea but not other forms of anovulation display amplified cortisol concentrations

OBJECTIVE

To test the hypothesis that increased cortisol secretion is specific to women with decreased GnRH drive and not found in eumenorrheic women or those with other causes of anovulation.

DESIGN

Cortisol concentrations in blood were determined at 30-minute intervals for 24 hours in three well-characterized groups: women with functional hypothalamic amenorrhea, those with other causes of anovulation, and eumenorrheic women.

SETTING

Academic medical center.

PATIENT(S)

Women aged 20 through 35 years, with well-defined reproductive states.

INTERVENTION(S)

Venous blood samples were obtained from, and psychometric inventories were completed by, the participants.

MAIN OUTCOME MEASURE(S)

Twenty-four-hour cortisol levels, 24-hour LH pulse patterns, and serial P levels were measured in women with functional hypothalamic amenorrhea, eumenorrheic women, and those with other causes of anovulation.

RESULT(S)

Cortisol secretion was higher in women with functional hypothalamic amenorrhea (n = 19) than in those with other causes of anovulation (n = 19) or eumenorrheic women (n = 19). Six women who recovered from functional hypothalamic amenorrhea had cortisol levels comparable to those of eumenorrheic women and those with other causes of anovulation.

CONCLUSION(S)

These data underscore the association between increased hypothalamic-pituitary-adrenal activity and reduced GnRH drive and support the concept that functional hypothalamic amenorrhea develops in response to stress-induced alterations in central neural function that modify hypothalamic function.