Regulation of Thyroid Hormone Gatekeepers by Thyrotropin in Tanycytes

Background: Tanycytes are specialized glial cells within the mediobasal hypothalamus that have multiple functions, including hormone sensing and regulation of hypophysiotropic hormone secretion. There are ongoing discussions about the role of tanycytes in regulating the supply of hypothalamic thyroid hormones (THs) through the expression of TH transporters (Slc16a2, Slco1c1) and deiodinases (Dio2, Dio3). In this study, we investigated the potential feedback effect of thyrotropin (TSH) on the transcription of these gatekeeper genes on tanycytes. Methods: We analyzed the changes in the expression of TH-gatekeeper genes, in TSH-stimulated primary tanycytes, using quantitative polymerase chain reaction (qPCR). We also used RNAScope® in brain slices to further reveal the local distribution of the transcripts. In addition, we blocked intracellular pathways and used small-interfering RNA (siRNA) to elucidate differences in the regulation of the gatekeeper genes. Results: TSH elevated messenger RNA (mRNA) levels of Slco1c1, Dio2, and Dio3 in tanycytes, while Slc16a2 was mostly unaffected. Blockade and knockdown of the TSH receptor (TSHR) and antagonization of cAMP response element-binding protein (CREB) clearly abolished the increased expression induced by TSH, indicating PKA-dependent regulation through the TSHR. The TSH-dependent expression of Dio3 and Slco1c1 was also regulated by protein kinase C (PKC), and in case of Dio3, also by extracellular signal-regulated kinase (ERK) activity. Importantly, these gene regulations were specifically found in different subpopulations of tanycytes. Conclusions: This study demonstrates that TSH induces transcriptional regulation of TH-gatekeeper genes in tanycytes through the Tshr/Gαq/PKC pathway, in parallel to the Tshr/Gαs/PKA/CREB pathway. These differential actions of TSH on tanycytic subpopulations appear to be important for coordinating the supply of TH to the hypothalamus and aid its functions.

Hypothalamic CRF neurons facilitate brain reward function

Aversive stimuli activate corticotropin-releasing factor (CRF)-expressing neurons in the paraventricular nucleus of hypothalamus (PVNCRF neurons) and other brain stress systems to facilitate avoidance behaviors. Appetitive stimuli also engage the brain stress systems, but their contributions to reward-related behaviors are less well understood. Here, we show that mice work vigorously to optically activate PVNCRF neurons in an operant chamber, indicating a reinforcing nature of these neurons. The reinforcing property of these neurons is not mediated by activation of the hypothalamic-pituitary-adrenal (HPA) axis. We found that PVNCRF neurons send direct projections to the ventral tegmental area (VTA), and selective activation of these projections induced robust self-stimulation behaviors, without activation of the HPA axis. Similar to the PVNCRF cell bodies, self-stimulation of PVNCRF-VTA projection was dramatically attenuated by systemic pretreatment of CRF receptor 1 or dopamine D1 receptor (D1R) antagonist and augmented by corticosterone synthesis inhibitor metyrapone, but not altered by dopamine D2 receptor (D2R) antagonist. Furthermore, we found that activation of PVNCRF-VTA projections increased c-Fos expression in the VTA dopamine neurons and rapidly triggered dopamine release in the nucleus accumbens (NAc), and microinfusion of D1R or D2R antagonist into the NAc decreased the self-stimulation of these projections. Together, our findings reveal an unappreciated role of PVNCRF neurons and their VTA projections in driving reward-related behaviors, independent of their core neuroendocrine functions. As activation of PVNCRF neurons is the final common path for many stress systems, our study suggests a novel mechanism underlying the positive reinforcing effect of stressful stimuli.

Study on the mechanism of regulating the hypothalamic cortical hormone releasing hormone/corticotropin releasing hormone type I receptor pathway by vibro-annular abdominal massage under the brain-intestine interaction in the treatment of insomnia

BACKGROUND

Insomnia is a common disease associated with different nervous system stress response and endocrine disorders. It has been reported previously that abdominal vibration and ring massage therapy can significantly improve the symptoms of insomnia patients, enhance the activity of neurons. In addition, functional MRI (resting state brain functional magnetic resonance imaging [Rs_fMRI]) of the resting state brain test has proved that the functional connection between hypothalamus and parahippocampal gyrus could be significantly enhanced after abdominal massage treatment. It has been confirmed that there is possible involvement of brain-gut interaction effect in the treatment of insomnia, but there is a lack of research to elucidate the possible mechanisms of brain-gut interaction in the treatment of insomnia. The purpose of this study is to investigate the relationship between the hypothalamus and intestinal interaction in the treatment of insomnia by abdominal massage.

METHODS AND DESIGN

A single blind randomized controlled trial will be conducted. Sixty chronic insomnia volunteers and 30 healthy volunteers will be recruited for this study. Sixty insomnia volunteers will be randomly divided into a drug group and a massage group, and 30 healthy volunteers will be assigned to the healthy group. The manipulation of the treatment group will be mainly carried out through abdominal rubbing and vibration massage, once a day, 30 min/time, 5 days for a course of treatment, and a total of 4 intervention courses will be carried out. Patients in the drug group will be given orally spleen-invigorating bolus, twice a day, 1 pill in the morning and 1 pill in the evening. The course of treatment will be carried for 5 days, and a total of 4 courses of treatment will be administered.The massage group will be compared with the healthy group and the drug group by Pittsburgh Sleep Index scale (PSQI), Hyperarousal scale (HAS), Hamilton Depression scale (HAMD), Fatigue scale-14 (FS-14), and Wechsler Adult Memory scale (WAIS) scales using to observe the sleep quality. Rs-fMRI will be used to observe various BOLD signals in the brain and compare the values of Reho, fALFF, and FC. MRS technology will be used to observe the contents of GABA and 5-HT in the hypothalamus. Additionally, the contents of cortical hormone releasing hormone (CRH), adrenocorticotropic hormone (ACTH), COR, GABA, NE, PGE2, and 5-HT in the serum will be also detected. The serum of each group will be taken for 1H nuclear magnetic resonance (1HNMR) metabolomics study to analyze the various common metabolites, differential metabolites, potential metabolic biomarkers, and metabolic pathways among the 3 groups. Finally, in combination with the brain functional imaging and brain spectrum, the potential mechanism of abdominal vibration and ring massage will be discussed.

DISCUSSION

The results of this study will be used to possibly elaborate the various mechanisms of brain and intestine interaction in the treatment of insomnia by employing abdomen ring rubbing.

Role of hypothalamic corticotropin-releasing factor in mediating alcohol-induced activation of the rat hypothalamic-pituitary-adrenal axis

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis through brain-based mechanisms in which endogenous corticotropin-releasing factor (CRF) plays a major role. This review first discusses the evidence for this role, as well as the possible importance of intermediates such as vasopressin, nitric oxide and catecholamines. We then illustrate the long-term influence exerted by alcohol on the HPA axis, such as the ability of a first exposure to this drug during adolescence, to permanently blunt neuroendocrine responses to subsequent exposure of the drug. In view of the role played by CRF in addiction, it is likely that a better understanding of the mechanisms through which this drug stimulates the HPA axis may lead to the development of new therapies used in the treatment of alcohol abuse, including clinically relevant CRF antagonists.

HANS SELYE AND THE STRESS RESPONSE: FROM "THE FIRST MEDIATOR" TO THE IDENTIFICATION OF THE HYPOTHALAMIC CORTICOTROPIN-RELEASING FACTOR

Selye pioneered the stress concept that is ingrained in the vocabulary of daily life. This was originally build on experimental observations that divers noxious agents can trigger a similar triad of endocrine (adrenal enlargement), immune (involution of thymus) and gut (gastric erosion formation) responses as reported in a letter to Nature in 1936. Subsequently, he articulated the underlying mechanisms and hypothesized the existence of a "first mediator" in the hypothalamus able to orchestrate this bodily changes. However he took two generations to identify this mediator. The Nobel Laureate, Roger Guillemin, a former Selye's PhD student, demonstrated in 1955 the existence of a hypothalamic factor that elicited adrenocorticotropic hormone release from the rat pituitary and named it corticotropin releasing factor (CRF). In 1981, Wylie Vale, a former Guillemin's Ph Student, characterized CRF as 41 amino acid and cloned the CRF1 and CRF2 receptors. This paves the way to experimental studies establishing that the activation of the CRF signaling pathways in the brain plays a key role in mediating the stress-related endocrine, behavioral, autonomic and visceral responses. The unraveling of the biochemical coding of stress is rooted in Selye legacy continues to have increasing impact on the scientific community.

Molecular genetics of the developing neuroendocrine hypothalamus

Formation of the mammalian endocrine system and neuroendocrine organs involves complex regulatory networks resulting in a highly specialized cell system able to secrete a diverse array of peptide hormones. The hypothalamus is located in the mediobasal region of the brain and acts as a gateway between the endocrine and nervous systems. From an endocrinology perspective, the parvicellular neurons of the hypothalamus are of particular interest as they function as a control centre for several critical physiological processes including growth, metabolism and reproduction by regulating hormonal signaling from target cognate cell types in the anterior pituitary. Delineating the genetic program that controls hypothalamic development is essential for complete understanding of parvicellular neuronal function and the etiology of congenital disorders that result from hypothalamic-pituitary axis dysfunction. In recent years, studies have shed light on the interactions between signaling molecules and activation of transcription factors that regulate hypothalamic cell fate commitment and terminal differentiation. The aim of this review is to summarize the recent molecular and genetic findings that have advanced our understanding of the emergence of the known important hypophysiotropic signaling molecules in the hypothalamus. We have focused on reviewing the literature that provides evidence of the dependence on expression of specific genes for the normal development and function of the cells that secrete these neuroendocrine factors, as well as studies of the elaboration of the spatial or temporal patterns of changes in gene expression that drive this development.

Cells expressing RFamide-related peptide-1/3, the mammalian gonadotropin-inhibitory hormone orthologs, are not hypophysiotropic neuroendocrine neurons in the rat

An RFamide peptide named gonadotropin-inhibitory hormone, which directly inhibits gonadotropin synthesis and secretion from the anterior pituitary gland, has recently been discovered in the avian hypothalamus. It is not known whether the mammalian orthologs of gonadotropin-inhibitory hormone and RFamide-related peptide (RFRP)-1 and -3 act in the same way. We used a newly generated antibody against the rat RFRP precursor combined with retrograde tract tracing to characterize the cell body distribution and fiber projections of RFRP-1 and -3 neurons in rats. RFRP-1/3-immunoreactive cell bodies were found exclusively within the dorsomedial hypothalamus. Immunoreactive fibers were observed in the septal-preoptic area, hypothalamus, midbrain, brainstem, and hippocampus but not in the external zone of the median eminence. Intraperitoneal injection of the retrograde tracer Fluoro-Gold in rats resulted in the labeling of the majority of GnRH neurons but essentially no RFRP-1/3 neurons. In contrast, intracerebral injections of Fluoro-Gold into the rostral preoptic area and CA2/CA3 hippocampus resulted in the labeling of 75 +/- 5% and 21 +/- 8% of RFRP-1/3 cell bodies, respectively. To assess actions at the pituitary in vivo, RFRP-3 was administered as an iv bolus to ovariectomized rats and plasma LH concentration measured at 0, 2.5, 5, 10, and 30 min. RFRP-3 had no effects on basal secretion, but GnRH-stimulated LH release was reduced by about 25% at 5 min. Together these observations suggest that RFRP-3 is not a hypophysiotropic neuroendocrine hormone in rats.

Minireview: Thyrotropin-releasing hormone and the thyroid hormone feedback mechanism

Thyroid hormone (TH) plays a critical role in development, growth, and cellular metabolism. TH production is controlled by a complex mechanism of positive and negative regulation. Hypothalamic TSH-releasing hormone (TRH) stimulates TSH secretion from the anterior pituitary. TSH then initiates TH synthesis and release from the thyroid gland. The synthesis of TRH and TSH subunit genes is inhibited at the transcriptional level by TH, which also inhibits posttranslational modification and release of TSH. Although opposing TRH and TH inputs regulate the hypothalamic-pituitary-thyroid axis, TH negative feedback at the pituitary was thought to be the primary regulator of serum TSH levels. However, study of transgenic animals showed an unexpected, dominant role for TRH in regulating the hypothalamic-pituitary-thyroid axis and an unanticipated involvement of the thyroid hormone receptor ligand-dependent activation function (AF-2) domain in TH negative regulation. These results are summarized in the review.

Regulation of hypophysiotrophic corticotrophin-releasing hormone- and thyrotrophin-releasing hormone-synthesising neurones by brainstem catecholaminergic neurones

Hypophysiotrophic corticotrophin-releasing hormone (CRH)- and thyrotrophin-releasing hormone (TRH)-synthesising neurones are the principal hypothalamic regulators of glucocorticoid and thyroid hormone secretion, respectively. These two neuroendocrine cell populations are closely situated in the hypothalamic paraventricular nucleus and are targets of neuronal afferent pathways that convey important signals for adapting the neurosecretory activity of CRH and TRH neurones to actual demands. The catecholaminergic afferents of CRH and TRH neurones originate from both noradrenaline- and adrenaline-synthesising cell groups located in the brainstem, and collectively represent one of the most well studied neural inputs of these neurones. The present review summarises the data obtained in recent years concerning the functional significance of the catecholaminergic innervation of hypophysiotrophic CRH and TRH neurones in rats.

Neuroendocrine control of food intake

Appetite is regulated by a complex system of central and peripheral signals which interact in order to modulate the individual response to nutrient ingestion. Peripheral regulation includes satiety signals and adiposity signals, while central control is accomplished by several effectors, including the neuropeptidergic, monoaminergic and endocannabinoid systems. Satiety signals, including cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), originate from the gastrointestinal (GI) tract during a meal and, through the vagus nerve, reach the nucleus tractus solitarius (NTS) in the caudal brainstem. From NTS afferents fibers project to the arcuate nucleus (ARC), where satiety signals are integrated with adiposity signals, namely leptin and insulin, and with several hypothalamic and supra-hypothalamic inputs, thus creating a complex network of neural circuits which finally elaborate the individual response to a meal. As for the neuropeptidergic system, ARC neurons secrete orexigenic substances, such as neuropeptide Y (NPY) and agouti-related peptide (AGRP), and anorexigenic peptides such as pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART). Other brain areas involved in the control of food intake are located downstream the ARC: among these, the paraventricular nucleus (PVN), which produces anorexigenic peptides such as thyrotropin releasing hormone (TRH), corticotrophin releasing hormone (CRH) and oxytocin, the lateral hypothalamus (LHA) and perifornical area (PFA), secreting the orexigenic substances orexin-A (OXA) and melanin concentrating hormone (MCH). A great interest in endocannabinoids, important players in the regulation of food intake, has recently developed. In conclusion, the present work reviews the most recent insights into the complex and redundant molecular mechanisms regulating food intake, focusing on the most encouraging perspectives for the treatment of obesity.

Chronology of Advances in Neuroendocrine Immunomodulation

This review documents the remarkable progress over the last 50 years of our knowledge of the control of anterior pituitary hormone release and synthesis by a family of peptidic releasing and inhibiting hormones, synthesized in hypothalamic neurons and released into the hypophysial portal vessels. These vessels transport them to the anterior pituitary, where they stimulate release and synthesis of pituitary hormones or inhibit these processes. In general, there are at least two hypothalamic hormones for each pituitary hormone-vasopressin and corticotrophin-releasing hormone (CRH) for adrenocorticotropin hormone (ACTH) and growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GIH) for growth hormone (GH). Some of these hormones have extrapituitary action: for example, luteinizing hormone-releasing hormone (LHRH) stimulates mating behavior. High doses of LHRH have an inhibitory action on the growth of prostate cancer. Proinflammatory and anti-inflammatory cytokines act not only in the brain, but also on the pituitary and peripheral tissues. All of these transmitters are controlled by neuronal transmitters. We anticipate further rapid progress and clinical application of these transmitters and the discovery of new ones.

Alpha-fetoprotein controls female fertility and prenatal development of the gonadotropin-releasing hormone pathway through an antiestrogenic action

It has been shown previously that female mice homozygous for an alpha-fetoprotein (AFP) null allele are sterile as a result of anovulation, probably due to a defect in the hypothalamic-pituitary axis. Here we show that these female mice exhibit specific anomalies in the expression of numerous genes in the pituitary, including genes involved in the gonadotropin-releasing hormone pathway, which are underexpressed. In the hypothalamus, the gonadotropin-releasing hormone gene, Gnrh1, was also found to be down-regulated. However, pituitary gene expression could be normalized and fertility could be rescued by blocking prenatal estrogen synthesis using an aromatase inhibitor. These results show that AFP protects the developing female brain from the adverse effects of prenatal estrogen exposure and clarify a long-running debate on the role of this fetal protein in brain sexual differentiation.

Phenotypic characterization of multi-functional somatotropes, mammotropes and gonadotropes of the mouse anterior pituitary

The existence of bihormonal anterior pituitary (AP) cells co-storing growth hormone and either prolactin (mammosomatotrope) or gonadotropins (somatogonadotrope) has been described. These cells have been proposed to be involved in "paradoxical" secretion [secretion of an AP hormone induced by a non-related hypothalamic releasing factor (HRH) and transdifferentiation (a phenotypic switch between different cell types without cell division]. Here we combine calcium imaging (to assess HRH responsiveness) and multiple sequential immunoassay of the six AP hormones to perform a single-cell phenotypic study of multifunctional somatotropes, mammotropes and gonadotropes in the normal male and female mouse pituitaries. AP cell phenotypes differed from the classic view, showing multiple HRH-receptor expression and/or hormone storage. Mammosomatotropes represented only 5-6% of somatotropes and were poorly responsive to HRHs, suggesting that their contribution to paradoxical secretion should be very limited. Somatogonadotropes were present only in females and contained adrenocorticotropic hormone. They responded to growth hormone-releasing hormone but failed to respond to gonadotropin-releasing hormone (LHRH). Other polyhormonal cells identified include (1) gonadocorticotropes, restricted to females, where they make up more than 50% of all the gonadotropes and contain other AP hormones; (2) gonadomammotropes, which are present preferentially in female cells and respond to LHRH; and (3) gonadothyrotropes, which are present similarly in male and female pituitaries.

Stimulatory effects of gonadotropin-releasing hormone and dopamine on growth hormone release and growth hormone mRNA expression in Epinephelus coioides

Gonadotropin-releasing hormone (GnRH) and dopamine (DA) can stimulate growth hormone (GH) release, but their effects on GH mRNA synthesis are controversial and deficient in fish. Orange-spotted grouper (Epinephelus coioides) is a hermaphroditic marine fish with sex reversal. Few data are available concerning the regulation of GH in grouper. In the present study, the effects of GnRH and DA on GH release and GH mRNA expression were determined using pituitary fragments of orange-spotted grouper under static culture conditions. After incubation from 1 h to 24 h, salmon GnRH (sGnRH, 100 nmol/L) stimulated the release of GH and increased the level of GH mRNA time-dependently. The minimum duration of sGnRH effect was 1 h. Both of sGnRH and mammalian GnRH (mGnRH) augmented the release of GH and the level of GH mRNA in a dose-dependent manner. The potency of sGnRH on both GH release and GH mRNA level was more pronounced than that of mGnRH. The effects of 1 micromol/L APO (Apomorphine), an agonist of D(1)/ D(2) dopamine receptors, significantly stimulated GH release and GH mRNA synthesis after incubation for 12 h. APO stimulated GH release and GH mRNA abundance in a dose-dependent manner. These results demonstrate that both GnRH and DA directly stimulate GH release and GH mRNA expression at the pituitary level, the actions of GnRH are more potent than that of DA in orange-spotted grouper.

Emerging functions for tuberoinfundibular peptide of 39 residues

Tuberoinfundibular peptide of 39 residues (TIP39), a neuropeptide recently purified from the hypothalamus, appears to be an endogenous ligand for the parathyroid hormone 2 (PTH2) receptor. PTH2 receptors are present in several central nervous system and peripheral areas and are particularly concentrated in the hypothalamus, limbic areas and the outer layers of the spinal cord dorsal horn. TIP39-containing neuronal cell bodies have been identified in the subparafascicular area and the medial paralemniscal nucleus, two brainstem regions that project widely through the entire neuraxis. Treatment of hypothalamic explants with TIP39, and intraventricular injection of the peptide, suggest that it might stimulate hypothalamic-releasing factor secretion. Injection of TIP39, and sequestration of endogenous TIP39 by intrathecal injection of an antibody to TIP39, have provided evidence that it is involved in some aspects of pain sensitivity. Thus, TIP39 might be a new neuromodulator.

Transgenic studies on the regulation of the anterior pituitary gland function by the hypothalamus

The anterior pituitary gland is composed of five different cell types secreting hormones whose functions include the regulation of post-natal growth (growth hormone, GH), lactation (prolactin, PRL), reproduction (luteinising hormone, LH, and follicle stimulating hormone, FSH), metabolism (thyroid stimulating hormone, TSH), and stress (adrenocorticotrophic hormone, ACTH). The synthesis and secretion of the anterior pituitary hormones is under the control of neuropeptides released from the hypothalamus into a capillary portal plexus which flows through the external zone of the median eminence to the anterior lobe. This review describes the ways that gene transfer technologies have been applied to whole animals in order to study the regulation of anterior pituitary function by the hypothalamus. The extensive studies on these neuronal systems, within the context of the physiological integrity of the intact organism, not only exemplify the successful application of transgenic technologies to neuroendocrine systems, but also illustrate the problems that have been encountered, and the challenges that lie ahead.

The hypothalamic mechanisms of the hypophysiotropic action of ghrelin

Ghrelin is an endogenous ligand for the growth hormone secretagogue (GHS) receptor, expressed in the hypothalamus and pituitary. Ghrelin, like synthetic GHSs, stimulates food intake and growth hormone (GH) release following systemic or intracerebroventricular administration. In addition to GH stimulation, ghrelin and synthetic GHSs are reported to stimulate the hypothalamo-pituitary-adrenal (HPA) axis in vivo. The aims of this study were to elucidate the hypothalamic mechanisms of the hypophysiotropic actions of ghrelin in vitro and to assess the relative contribution of hypothalamic and systemic actions of ghrelin on the HPA axis in vivo. Ghrelin (100 and 1,000 nM) stimulated significant release of GH-releasing hormone (GHRH) from hypothalamic explants (100 nM: 39.4 +/- 8.3 vs. basal 18.3 +/- 3.5 fmol/explant, n = 49, p < 0.05) but did not affect either basal or 28 mM KCl-stimulated somatostatin release. Ghrelin (10, 100 and 1,000 nM) stimulated the release of both corticotropin-releasing hormone (CRH) (100 nM: 6.0 +/- 0.8 vs. basal 4.2 +/- 0.5 pmol/explant, n = 49, p < 0.05) and arginine vasopressin (AVP) (100 nM: 49.2 +/- 5.9 vs. basal 35.0 +/- 3.3 fmol/explant, n = 48, p < 0.05), whilst ghrelin (100 and 1,000 nM) also stimulated the release of neuropeptide Y (NPY) (100 nM: 111.4 +/- 25.0 vs. basal 54.4 +/- 9.0 fmol/explant, n = 26, p < 0.05) from hypothalamic explants in vitro. The HPA axis was stimulated in vivo following acute intracerebroventricular administration of ghrelin 2 nmol [adrenocorticotropic hormone (ACTH) 38.2 +/- 3.9 vs. saline 18.2 +/- 2.0 pg/ml, p < 0.01; corticosterone 310.1 +/- 32.8 ng/ml vs. saline 167.4 +/- 40.7 ng/ml, p < 0.05], but not following intraperitoneal administration of ghrelin 30 nmol, suggesting a hypothalamic site of action. These data suggest that the mechanisms of GH and ACTH regulation by ghrelin may include hypothalamic release of GHRH, CRH, AVP and NPY.

Effect of active and passive immunization of male and female rats with a recombinantly expressed bonnet monkey pituitary GnRH receptor fragment

Gonadotropin releasing hormone (GnRH) exerts its action by binding to the specific receptor which belongs to the family of G-protein coupled receptors that are characterized by the presence of seven transmembrane domains linked together by extracellular and intracellular loops. A fragment of the pituitary receptor of the bonnet monkey (Macaca radiata) corresponding to amino acids 164-266 was cloned and expressed in Escherichia coli. This was used to raise antibodies to the receptor in rabbits. Active and passive immunization studies in both male and female rats were carried out using, both the 'overexpressed' fragment, as well as antibodies raised to the receptor fragment. Both active, as well as passive immunization in the male rats brought about an agonistic effect in terms of increase in serum LH level, as well as increase in serum and testicular testosterone levels. However, in the female rats, active immunization with the receptor fragment did not have any effect on the gonadal steroid levels but had a selective effect on the uterine morphology.

Physiological neuroendocrinology of peptides, steroids and other hormones in cerebrospinal fluid

Cerebrospinal fluid acts as a conduit in neuroendocrine regulation. Valid assessment of normal cerebrospinal fluid levels of peptides, steroids and other hormones requires clarification of reference concentrations in control patients and normal volunteers. Awareness of factors which may alter neuronal activity and, in turn, the relative composition of cerebrospinal fluid constituents is essential to the accurate sampling and hormonal analysis of cerebrospinal fluid.

Effects of thyrotropin-releasing hormone on the sleep EEG and nocturnal hormone secretion in male volunteers

Various peptides including corticotropin-releasing hormone (CRH) exert selective effects on sleep structure and noctural secretions of cortisol and growth hormone (GH). In animal studies analeptic effects and sleep disturbances after thyrotropin-releasing hormone (TRH) administration have been observed; studies of endocrine function in depressed patients suggest a pathological activity of CRH and TRH as compared with that in healthy volunteers. As the role of TRH in the regulation of the sleep endocrine pattern in humans has not yet been clarified, we performed a study to examine the effects of pulsatile administration of TRH on the sleep EEG pattern and the nocturnal secretions of cortisol and GH in 7 healthy male subjects. The sleep EEG was recorded from 23.00 to 07.00 h, and blood samples were collected every 20 min from 20.00 to 07.00 h for the analysis of GH and cortisol concentrations during intravenous administration of placebo or 4 x 50 microgram TRH at 22.00, 23.00, 24. 00, and 01.00 h. In contrast to the well-known effects of CRH on the sleep endocrine pattern, TRH exerts only a weak effect on the sleep EEG which is reflected in a slight decrease in sleep efficiency associated with a trend to wakefulness during the night. Furthermore, after TRH administration, the cortisol rise appeared earlier, and a nonsignificant tendency to an increased secretion of cortisol during the first half of the night was found. The GH secretion did not differ significantly after application of TRH or placebo. The activating, albeit weak, effect of TRH on the sleep EEG and nocturnal cortisol secretion in healthy volunteers confirms and adds to the results previously observed in animals. On the basis of these findings, we surmise that TRH may contribute to the disturbed sleep continuity seen in depressed patients, probably acting as a cofactor of CRH in a synergistic manner.

Endocrine function in multiple sclerosis

In 31 patients with multiple sclerosis (MS) the endocrine functions of the hypothalamus, the pituitary and several peripheral endocrine glands were assessed with a combined pituitary test; 3/31 patients had an endocrine disease: one primary hypothyroidism, one primary amenorrhea and one primary male hypogonadism. We found no patient with endocrine disease of the hypothalamus, the pituitary or the adrenals. However, the poststimulatory secretion of cortisol, growth hormone or thyroid-stimulating hormone was impaired in 7/31 patients, suggesting a possible preclinical endocrine insufficiency in these patients.

Fetal development and regulation of pituitary cell types

The ontogenesis of the pituitary gland is considered from anatomical and functional points of view. Embryogenesis of the hypothalamo-pituitary unit involving development of the hypothalamo-hypophyseal portal system is complete during early life as shown in several mammalian species. The ultrastructural characteristics of the different cell types during development are described according to observations made by using immunochemical techniques. The patterns of differentiation of the cell types are reviewed according to studies of pituitary glands from human anencephalic fetuses and encephalectomized rat fetuses as well as in vitro studies of cultured pituitary primordia in synthetic media. The maturation of the neuroendocrine mechanisms controlling the secretion of fetal hormones is also analyzed. During fetal life, the factors implicated in the regulation of pituitary hormone secretion are generally the same as in adults, but the intensity of the response of pituitary cells to their action is variable according to the species, thus reflecting an immaturity in the functioning of certain cell types.

Hypothalamic regulatory peptides and their receptors: cytochemical studies of their role in regulation at the adenohypophyseal level

Hypothalamic regulatory peptides bind to specific receptors on target cells in the pituitary and control secretion. They in turn can be regulated at the pituitary level by steroid and peptide modulators. Affinity cytochemical techniques are important tools for the identification of specific target binding sites for these regulatory peptides. This presentation reviews the work in which potent, biotinylated ligands of gonadotropin releasing hormone (bio-GnRH), corticotropin releasing hormone (bio-CRH), and arginine vasopressin (bio-AVP) were applied to study the target cell responses. Bio-GnRH, bio-CRH, and bio-AVP bind to membrane receptors on specific anterior pituitary cells. Dual labeling for either gonadotropin or adrenocorticotropin (ACTH) antigens further identified the target cells. After 1-3 minutes, the label was in patches or capped on the surface. After 3 minutes, it was internalized in small vesicles and sent to receptosomes and vacuoles in the Golgi complex. Eventually the biotinylated peptides, or a metabolite, was found in the lysosomes (multivesicular bodies) and a subpopulation of secretory granules. The route and rate of uptake was similar to that described for the classical receptor-mediated endocytosis process. In contrast, intermediate lobe corticotropes internalized the bio-CRH in less than 1 minute. The route through the Golgi complex appeared to be bypassed. Instead the labeled peptide was in vesicles, on the membranes of scattered vacuoles, and in multivesicular bodies. Modulation of ligand binding by steroids showed that changes in receptor numbers correlated with changes in the number of cells that bound the ligand. In male rats, dihydrotestosterone reduced the percentage of GnRH-bound cells by 50%. Most of the reduction appeared in cells that stored luteinizing hormone (LH) antigens. In diestrous female rats, estradiol increased the percentage of bio-GnRH-bound cells. However, the steroid decreased the percentage of GnRH-bound cells in cells from proestrous rats. Glucocorticoids decreased the percentage of CRH-bound corticotropes in as little as 10 minutes. Potentiation of secretion by these ligands was correlated with increases in the percentage of ligand-bound cells. AVP pretreatment of corticotropes increased the percentage of cells that bound bio-CRH. It also increased the rate of receptor-mediated endocytosis of CRH and changed the route so that the Golgi complex was bypassed. This effect could be mimicked by activation of its second messengers (calcium and protein kinase C). Similarly, CRH pretreatment increased the percentage of corticotropes that bound AVP. Thyrotropin releasing hormone (TRH) pretreatment also increased the percentage of thyrotropes that bound AVP.(ABSTRACT TRUNCATED AT 400 WORDS)

Secretory patterns of LH and FSH during development and hypothalamic and hypophysial characteristics following development of steroid-induced ovarian follicular cysts in dairy cattle

Two experiments were conducted to (1) investigate developmental endocrinology of ovarian follicular cysts (cysts) in cattle and (2) evaluate effects of cysts on hypothalamic and hypophysial characteristics. Cysts were induced with oestradiol-17 beta (15 mg) and progesterone (37.5 mg) dissolved in alcohol and injected s.c. twice daily for 7 days. Cysts were defined as the presence of follicular structures (which may or may not have been the same structure) of 2.0 cm in diameter or greater that were present for 10 days without ovulation and corpus luteum development. In Exp. 1,22 non-lactating, non-pregnant Holstein cows were allocated to 3 groups. Beginning on Day 5 (oestrus = Day 0) of the oestrous cycle, 7 cows (Controls) were treated with twice daily s.c. injections of ethanol (2 ml/injection) for 7 days. Luteolysis was then induced with PGF-2 alpha and blood samples were collected daily every 15 min for 6 h from the morning after the PGF-2 alpha injection (Day 13) until oestrus. Steroids to induce cysts were injected as previously described into the remaining cows (N = 15). Three blood samples were collected at 15-min intervals every 12 h throughout the experimental period. Additional blood samples were collected every 15 min for 6 h on a twice weekly basis. After steroid injections, follicular and luteal structures on ovaries were not detected via rectal palpation for a period of 36 +/- 4 days (static phase). Then follicles developed which ovulated within 3-7 days (non-cystic; N = 7) or increased in size with follicular structures present for 10 days (cystic; N = 8). Mean (+/- s.e.m.) concentrations of LH, FSH, oestradiol-17 beta and progesterone in serum remained low and were not different during the static phase between cows that subsequently developed cysts or ovulated. During the follicular phase, mean serum concentration of LH (ng/ml) was higher (P less than 0.1) in cows with cysts (2.9 +/- 0.2) than in cows without cysts (1.1 +/- 0.1) or control cows (1.4 +/- 0.2). In addition, LH pulse frequency (pulses/6 h) and amplitude (ng/ml) were higher (P less than 0.1) in cows with cysts (3.6 +/- 0.3 and 2.2 +/- 0.3, respectively) than in non-cystic (2.3 +/- 0.2 and 1.0 +/- 0.2, respectively) and control (1.8 +/- 0.1 and 1.1 +/- 0.2, respectively) groups during the follicular phase. There were no differences in the FSH, oestradiol-17 beta or progesterone characteristics in cows of any of the 3 groups during the follicular phase.(ABSTRACT TRUNCATED AT 400 WORDS)

[Effect of delayed-action Mirenil (Polfa) on the hypothalamic function in patients with schizophrenia]

Hormonal tests--TRH, ITT and L-RH--were performed in 10 cases of paranoid schizophrenia before the paranoid deterioration and after--on average--ten months of treatment with fluphenazine depot injection. The drug did show a clear modulating effect on the mechanisms regulating secretion of gonadotrophins and prolactin --it did not effect the secretion of thyrotropin , thyroxine, triiodothyronine, cortisol, growth hormone or insulin .

Degradation of gonadotropin-releasing hormones in the gilthead seabream, Sparus aurata. I. Cleavage of native salmon GnRH and mammalian LHRH in the pituitary

The pattern and kinetics of degradation of native salmon gonadotropin-releasing hormone (sGnRH) and mammalian leuteinizing hormone-releasing hormone (LHRH) by pituitary bound enzymes were studied in the gilthead seabream, Sparus aurata. sGnRH and LHRH were incubated for different periods of time with membrane or cytosolic fractions of pituitary homogenates. At the end of the incubation, the degradation mixture was fractionated on reverse-phase high-pressure liquid chromatography. The degradation products were identified by comparing their retention times to those of synthesized GnRH fragments and by analyzing their amino acid composition. The main GnRH degradative activity resides in the cytosolic fraction of the pituitary homogenate. Both sGnRH and LHRH are rapidly degraded by pituitary cytosol, with 78.3 and 87.7% of the peptides, respectively, cleaved after 3 hr of incubation. Maximal degradation of sGnRH occurred at a pH range of 7 to 8. The main initial products of degradation of sGnRH and LHRH are the 1-5, 6-10, and 1-9 fragments. This suggests the involvement of two site-specific peptidases, a Tyr5-Gly6 endopeptidase and a Pro9-Gly10NH2 peptidase or postproline cleaving enzyme. While the 1-6 and 1-9 fragments undergo rapid secondary degradation, the 1-5 is relatively stable. Competition experiments suggest that the endopeptidase cleaving the sGnRH at the Tyr5-Gly6 bond is not specific to the neuropeptide and is probably a general proteolitic enzyme. However, the cleavage at the 9-10 bond has a high degree of specificity to the Pro9-Gly10NH2 sequence found in sGnRH. The two proposed pituitary peptidases of S. aurata have some characteristics similar to those of rat hypophyseal and hypothalamic GnRH cleaving enzymes. No differences are found in hypophyseal GnRH degradative activity between females with occytes undergoing previtellogenesis or advanced stages of vitellogenesis.

Degradation of gonadotropin-releasing hormones in the gilthead seabream, Sparus aurata. II. Cleavage of native salmon GnRH, mammalian LHRH, and their analogs in the pituitary, kidney, and liver

The pattern and kinetics of degradation of native salmon gonadotropin-releasing hormone (sGnRH), mammalian luteinizing hormone-releasing hormone (LHRH), and some of their analogs by cytosolic enzymes of pituitary, kidney, and liver were studied in the gilthead seabream, Sparus aurata. The native peptides sGnRH and LHRH are rapidly degraded by all three tissues, LHRH being degraded faster than sGnRH. The kinetics of production of the peptide fragments suggest that initial cleavage of sGnRH and LHRH in the three studied tissues occurs at the 5-6 and 9-10 bonds. This indicates the initial activity of a Tyr5-Gly6 endopeptidase and a Pro9-Gly10NH2 peptidase or postproline cleaving enzyme. Secondary degradation of the main initial fragments (1-5, 6-10, and 1-9) is more intensive in the kidney than in the pituitary or liver. Substitution of the position 6 amino acid glycine by a dextrorotatory (D) amino acid such as in the D-Trp6-LHRH renders the 5-6 bond resistant to cleavage. However, whereas [D-Trp6]-LHRH is intensively cleaved at the Pro9-Gly10NH2 bond by the pituitary, its cleavage at this site by the kidney and liver is slow. This suggests a low activity of the Pro9-Gly10NH2 peptidase in the kidney and liver as compared to the pituitary. When, in addition to the position 6 substitution, the carboxy terminus Pro9-Gly10NH2 is modified to Pro9NET, such as in the [D-Ala6-Pro9NET]-LHRH and the [D-Arg6-Pro9NET]-sGnRH, the 9-10 cleavage site is also blocked, resulting in GnRH analogs highly resistant to degradation. The relationships between susceptibility of the different forms of GnRH to enzymatic degradation by the pituitary, kidney, and liver and their relative biological activities in S. aurata are discussed. We conclude that increased resistance of GnRH analogs to enzymatic degradation contributes to their superactivity.

Role of voltage-sensitive calcium channels in [Ca2+]i and secretory responses to activators of protein kinase C in pituitary gonadotrophs

The gonadotropin secretory response of anterior pituitary cells to phorbol esters includes both extracellular Ca2(+)-dependent and -independent components (Stojilković et al, 1988; J. Biol. Chem. 263, 17301-17306, 1988). In cultured pituitary cells, measurements of [Ca2+]i using Fura-2 and of LH release during cell perifusion studies revealed that the initial effects of phorbols and permeant diacylglycerols on these responses are extracellular Ca2(+)-dependent and are mediated through activation of voltage- and dihydropyridine-sensitive calcium channels. On the other hand, pretreatment with phorbol esters for 30 to 60 min inhibited subsequent [Ca2+]i responses to diacylglycerols and phorbols and significantly reduced agonist-induced biphasic [Ca2+]i responses, with no change in the number of GnRH receptors. These findings demonstrate that protein kinase C exerts both positive and negative control of [Ca2+]i, and indicate that the calcium, phospholipid dependent enzyme participates in the activation of voltage-sensitive calcium channels and hormone secretion in pituitary gonadotrophs.

The effects of gonadotrophin releasing hormone analogues in prostate cancer are mediated through specific tumour receptors

We have investigated the possibility of a direct regulatory effect of gonadotrophin releasing hormone (GnRH) analogues on prostatic cancer cell growth. Here we report high affinity binding (Kd = 50 nM) of a GnRH analogue resulting in biphasic growth modulation of the human androgen-sensitive prostatic cancer cell line LNCaP. In contrast, the human androgen-insensitive prostatic cancer cell line DU145 showed low-affinity (Kd = 10 microM) binding without any biological response to the GnRH analogue. A GnRH-specific radioimmunoassay demonstrated GnRH-like immunoreactivity in the concentrated culture medium from both cell lines. Seventy-six human benign and malignant tumours were assayed following surgical resection. Nineteen of 22 (86%) malignant tumours and 49 of 54 (91%) benign tumours, exhibited high affinity GnRH-analogue binding. Fourteen of 19 (74%) malignant tumours and 17 of 49 (35%) benign tumours exhibiting high affinity binding contained GnRH-like immunoreactivity, suggesting that this system may be involved in prostatic epithelial cell growth in vivo.

Peripubertal changes in the nature of the GnRH response to alpha-adrenoceptor stimulation in vitro and their modulation by testosterone

Adrenergic mechanisms have been widely implicated in the regulation of GnRH secretion in adult rats but their role in young animals, in which the activity of the GnRH neurones is minimal, is unclear. These experiments were done to examine the effects of alpha-adrenoceptor stimulation on the secretion in vitro of GnRH by hypothalami from immature and adult male rats. The alpha 1-adrenoceptor agonist, phenylephrine (10(-9) - 10(-7) M), stimulated release of GnRH from hypothalami from adult (200 g) and peripubertal (150 g) rats but inhibited markedly the secretion of the releasing factor from the limited stores available in hypothalami from immature (50 or 100 g) rats. The stimulatory and inhibitory responses to phenylephrine, evident in adult and younger rats respectively, were concentration-dependent and antagonized readily by the selective alpha 1-adrenoceptor antagonist, alfuzosin (10(-6) M), but not by the beta-adrenoceptor antagonist, propranolol (10(-6) M). Hypothalami from 14-day castrated adult rats, in which the serum LH was elevated and hypothalamic GnRH content reduced, responded to alpha 1-adrenoceptor stimulation in vitro, like those from immature rats, with a marked reduction in GnRH release. In contrast, hypothalami from corresponding castrates bearing testosterone implants, which maintained the hypothalamic GnRH content and serum LH and testosterone concentrations at levels similar to those of intact controls, exhibited the normal 'adult' response to phenylephrine. Studies utilizing 3H-prazosin indicated that the number (Bmax) of hypothalamic alpha 1-adrenoceptor binding sites increases at puberty but that receptor affinity (KD) is unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Immortalization of hypothalamic GnRH neurons by genetically targeted tumorigenesis

By genetically targeting tumorigenesis to specific hypothalamic neurons in transgenic mice using the promoter region of the gonadotropin-releasing hormone (GnRH) gene to express the SV40 T-antigen oncogene, we have produced neuronal tumors and developed clonal, differentiated, neurosecretory cell lines. These cells extend neurites, express the endogenous mouse GnRH mRNA, release GnRH in response to depolarization, have regulatable fast Na+ channels found in neurons, and express neuronal, but not glial, cell markers. These immortalized cells will provide an invaluable model system for study of hypothalamic neurosecretory neurons that regulate reproduction. Significantly, their derivation demonstrates the feasibility of immortalizing differentiated neurons by targeting tumorigenesis in transgenic mice to specific neurons of the CNS.

Chlordimeform-induced alterations in endocrine regulation within the male rat reproductive system

The acaricide chlordimeform has been reported to have adverse effects in mammals that may be mediated by an interaction with alpha-adrenergic receptors. Since the hormonal signals involved in the regulation of reproductive function are themselves under hypothalamic adrenergic control, the present study was designed to investigate the effects of acute exposure to this compound on the hypothalamic-pituitary-testicular axis. Male rats given two intraperitoneal injections of chlordimeform-HCl (20 or 50 mg/kg) spaced 12 hr apart showed 24-hr declines in serum gonadotropins at 50 mg/kg that were paralleled by a drop in testosterone. These changes returned to control levels by 96 hr. Thyroid-stimulating hormone exhibited a dose-response decline that was accompanied by a similar decrease in serum thyroid hormone levels. The norepinephrine-stimulated secretion in vitro of gonadotropin-releasing hormone from hypothalamic explants was suppressed at the higher dose, while LH release from pituitary fragments in culture was unaffected. Although measurements of the in vitro release of other pituitary hormones suggest that there could be some direct pituitary effects of the compound, it appears likely that chlordimeform is able to influence endocrine regulation adversely within the reproductive system by interfering with hypothalamic alpha-adrenergic activity.

Steroidal modulation of pituitary gonadotropin-releasing hormone responsiveness in young turtles, Pseudemys scripta

Steroid-modulated pituitary secretion and glandular content of gonadotropin (Gth: LH and FSH) was studied in young slider turtles. Injection (ip) of both 17 beta-estradiol (E2) and testosterone (T) reduced pituitary content of both Gths and caused significant inhibition of basal LH secretion and gonadotropin-releasing hormone (GnRH)-stimulated LH and FSH secretion measured in vitro. However, gonadectomy did not affect pituitary Gth secretion or response in these juveniles, and anti-estrogen and anti-androgen compounds had some steroid agonistic action on the pituitary gland. Exposure to E2, T, and 5 alpha-dihydrotestosterone (DHT) in vitro for 4, 24, or 48 hr either had no effect or completely inhibited pituitary GnRH responsiveness. Progesterone (P) alone had no effect on pituitary GnRH response and in combination did not alter the typical inhibitory effect of E2. There were several indications of differential effects of steroids on secretion of the two Gths, especially in response to GnRH and tetraethyl chloride (receptor independent) stimulation. The results suggest that steroids may act directly at the pituitary level to alter Gth secretion and that steroidal modulation of pituitary secretion might play a role in differential regulation of LH and FSH in turtles.

Acute administration of estrogen suppresses LH secretion without altering GnRH release in ovariectomized rhesus macaques

The pattern of hypothalamic gonadotropin-releasing hormone (GnRH) release was examined during estrogen (E)-induced suppression of plasma luteinizing hormone (LH) in ovariectomized (OVX) rhesus macaques. In Expt. 1, 4 OVX macaques were fitted with a jugular catheter and a push-pull cannula (PPC) directed into the median eminence (ME). Push-pull perfusion (PPP) was initiated 10 h before and continued for 10 h after subcutaneous estradiol benzoate (EB) injection (42 micrograms/kg b.wt.). In Expt. 2, 4 additional monkeys were subjected to local intrahypothalamic perfusion with estradiol-17 beta (E2, 3 microM) for the last 10 h of a 20-h PPP. In Expt. 2, OVX animals were challenged with 5 micrograms exogenous GnRH 3 h before and 8 h after EB injection to test for changes in altered LH release. Integrated 10-min ME perfusate and intermittent 10- or 60-min peripheral plasma samples were assayed for GnRH and LH by radioimmunoassay and bioassay, respectively. In addition, 2 other OVX macaques that received similar ME-PPC placement were sacrificed 2 days after the completion of a PPP for immunocytochemical labeling of GnRH neurons at the perfusion site. The results show that after EB, hypothalamic GnRH (MBH-GnRH) release remained unaltered while LH levels declined rapidly (Expt. 1). Similarly, intrahypothalamic perfusion of E2 failed to change the pattern of MBH-GnRH release in any of 4 monkeys (Expt. 2). Conversely, plasma LH release in response to exogenous GnRH was greatly reduced after EB (Expt. 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes-induced alterations of reproductive and adrenal function in the female rat

Diabetes interferes with reproductive function in laboratory animals. Previous studies in female diabetic rats have not resolved if the reproductive abnormalities observed are at the hypothalamic, pituitary and/or ovarian level. The interaction of the gonadal and adrenal axes has not been studied in the diabetic female rat. The purpose of this study is twofold: first, to determine the level of dysfunction in the hypothalamic-pituitary axis caused by diabetes in the adult female rat controlling for stage of the estrous cycle, and, second, to evaluate basal corticosterone secretion in female diabetic rats. Sixty cycling 40-day-old female rats were randomly assigned to 3 groups; control (n = 32), diabetic (n = 14), and diabetic insulin-replaced animals (n = 14). The level of hyperglycemia in each group was documented by glycosylated hemoglobin levels and biweekly blood glucoses. Three weeks after induction of diabetes, pituitary luteinizing hormone (LH) responsiveness following an i.v. injection of gonadotropin-releasing hormone (GnRH) was assessed in representative diestrous rats from each group. All animals were sacrificed in either diestrus or proestrus for determination of GnRH concentration in the hypothalamus, LH and follicle-stimulating hormone (FSH) content in pituitary and LH, FSH, estradiol and corticosterone in serum. Uterine weight to body weight ratios (a bioassay for estrogen) were also calculated. Hypothalamic GnRH concentration was significantly lower in diabetic versus control diestrous rats. Basal pituitary and serum gonadotropin levels were not different between any groups. GnRH-stimulated serum LH levels were higher in diabetic vs. control and diabetic insulin-treated animals. LH surges occurred in the control and diabetic insulin-replaced but not the diabetic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of dietary energy intake on prepubertal development of Brahman bulls

Twelve Brahman bulls (paired by sire, weight and age) were assigned randomly and limit fed to gain either .10 to .25 (moderate gain; MG) or .75 to 1.0 (high gain: HG) kg.hd-1.d-1 to examine the effect of dietary energy on onset of puberty. Hip height (HH), scrotal circumference (SC) and serum samples (20 min for 6 h) were obtained at four times (AGE): 0, 56 and 112 d on feed and after appearance of first motile spermatozoa (FS) in the ejaculate of HG bull of the pair. At FS both bulls of a pair were slaughtered, reproductive tissues were collected and in vitro GnRH release from the median eminence (ME) was measured. Increases in BW, HH and SC were greater (P less than .05) in HG bulls. Basal ME GnRH secretion was greater (P less than .05) in HG bulls. Serum LH concentrations were unchanged by energy level (P greater than .10) but increased (P less than .01) with increasing AGE. AGE and energy level increased (P less than .01) basal, mean and total serum testosterone (T) and these two factors acted synergistically (P less than .01). Height and amplitude of T pulses were increased by energy level (P less than .003) and AGE (P less than .002). Testicular T (P less than .08) and development (P less than .05) were increased in HG bulls. Growth hormone peak height and amplitude concentrations following feeding increased with AGE (P less than .06) but were not altered (P greater than .10) by energy level. Serum triglycerides (P less than .03) and BUN (P less than .003) increased with increasing AGE (P greater than .01). These data indicate that dietary energy level influences onset of puberty most directly at the testicular level.

Luteinizing hormone in nutrient-restricted ovariectomized ewes

This study was designed to evaluate profiles of serum concentrations of LH, pituitary content of LH and GnRH receptors, and hypothalamic content of GnRH in undernourished, ovariectomized ewes. In earlier studies, pulsatile secretion of LH diminished as duration of undernutrition progressed in prepubertal or adult ovariectomized ewes. Ewes having similar body condition scores (CS) of 5 to 9 (1 = extremely thin, 5 = moderate, 9 = obese) were fed maintenance or low-energy diets (100% and 60% of NRC requirements, respectively). Blood samples for analysis of LH were collected at 15-min intervals for 4 h at initiation of the project and immediately prior to slaughter. Serum concentrations of LH did not differ (P greater than .05) among groups at the initial sampling period. At slaughter, ewes with CS less than or equal to 2 (n = 7) had lost 26.8 kg (42% of initial weight). Ewes with CS greater than or equal to 3 (n = 12) had lost an average of 13.7 kg (18% of initial weight). Concentrations of LH in ewes with final CS greater than or equal to 3 was similar (P greater than .05) to that observed during the initial sampling period. However, release of LH was reduced (P less than .01) in ewes with CS less than or equal to 2 compared with ewes with CS greater than or equal to 3 (2.6 vs 9.5 and 3.2 vs 10.5 ng/ml for basal and mean concentrations, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in gonadotropin-releasing hormone immunoactivities in discrete brain areas of male goldfish during spawning behavior

In male goldfish, spawning behavior and gonadotropin (GtH) secretion are stimulated during exposure to females which were induced to perform spawning behavior by treatment with prostaglandin F2 alpha (PG). In this study, exposure to PG-treated females for 1 or 2 h significantly increased serum GtH levels, and GtH-releasing hormone (GnRH) concentrations in the olfactory bulbs, telencephalon and hypothalamus, indicating that spawning behavior can influence cellular events of the brain GnRH neuronal system and pituitary GtH secretion in male goldfish. To study the role of the olfactory system in the hormonal responses to PG-treated females, bilateral sectioning of olfactory tracts (OTX), medial (mOTX) or lateral (lOTX) olfactory tract were carried out in male goldfish. Both OTX and mOTX, but not lOTX, blocked the behavioral response of male goldfish to PG-treated females and abolished the increases in serum GtH and brain GnRH levels, suggesting that alterations in pituitary GtH secretion and brain GnRH levels are associated with a pheromonal activation of spawning behavior through the medial olfactory tracts in male goldfish. This behavioral activation of the GnRH neuronal system provides a useful physiological model for studying the regulation of GnRH system in male goldfish.

Hypothalamic-pituitary axis during reproductive aging in mice

We correlated the content of hypothalamic (HT) GnRH and pituitary (PT) GnRH receptor sites with PT and plasma gonadotropin levels throughout aging in C57BL/6J mice. Female mice of 4-6 months (young), 10-12 months (middle-age) or 15-18 months (old) of age were studied either intact or 15 days post-ovariectomy (OVX) with or without E2 therapy. In intact mice, HT GnRH content increased twofold during aging while GnRH receptor sites in PT remained unchanged. PT content of both FSH and LH gradually rose during aging while plasma concentration rose even more. OVX resulted in a significant decrease in both HT GnRH content and PT receptor sites and no age difference was observed. OVX also resulted in a significant increase in both PT content and plasma levels of gonadotropin in young and middle-age mice while old mice showed a blunted response. After E2 therapy for 7 days, HT GnRH content and PT GnRH receptor sites returned to normal levels in all age groups. By contrast, E2 therapy resulted in no change in PT content of FSH:LH in any age group. Whereas plasma FSH:LH levels returned to intact levels in young mice, they remained elevated to OVX levels in middle-age and old ones. Our results demonstrate an age related dichotomy in the PT production of FSH:LH unrelated to changes in either HT GnRH content or its PT receptor sites, thus suggesting cellular defects in post-receptor binding events within the pituitary.

Reduction in testicular function in rats. I. Reduction by a specific gonadotropin-releasing hormone antagonist in fetal rats

A gonadotropin-releasing hormone (GnRH) antagonist, when injected 24 h before sacrifice to rat fetuses, did not modify plasma testosterone concentrations in males on day 18 of gestation but it did on days 19, 20 and 21. This GnRH antagonist reduced plasma luteinizing hormone (LH) levels and increased pituitary LH content in both male and female 19-day-old fetuses from mothers adrenalectomized on day 14 of gestation. An inverse relationship between plasma testosterone and LH levels was noted in males and females, on days 19 and 21. These data suggest that the hypothalamic control of gonadotropic function is operating by day 19 of fetal life and that a negative feedback of testosterone on LH and probably GnRH release is also operating in rat fetuses on days 19 and 21 of gestation.

A norepinephrine-dependent mechanism in the preoptic/anterior hypothalamic area but not in the mediobasal hypothalamus is involved in the regulation of the gonadotropin-releasing hormone pulse generator in ovariectomized rats

Pulsatile gonadotropin secretion from the pituitary is dependent upon the gonadotropin-releasing hormone (Gn-RH) pulse generator producing intermittent release of the neuropeptide into the portal vessels. Various neurotransmitters seem to be involved in the regulation of pulsatile Gn-RH release. The present study was an attempt to determine in vivo the temporal relation of preoptic/anterior hypothalamic area (PO/AH) norepinephrine (NE) release and pulsatile luteinizing hormone (LH) secretion in ovariectomized rats. To assess whether NE acts in the PO/AH to maintain pulsatile Gn-RH release, we applied locally an alpha 1-receptor antagonist into this structure. Push-pull cannulae (PPC) were implanted into the PO/AH of ovariectomized rats. The contralateral, not PPC-implanted PO/AH was lesioned electrochemically. Another group of ovariectomized rats was implanted with a PPC into the mediobasal hypothalamus. Two experiments were performed: (1) To determine whether the PO/AH or the mediobasal hypothalamus is the site where NE exerts its stimulatory effect on LH secretion, we applied doxazosine, a new specific alpha 1-receptor antagonist, locally into these structures by means of PPC. The effect of this adrenergic drug on the Gn-RH pulse generator was examined by measuring blood LH levels. (2) To study the temporal relation between in vivo release rates of NE and amine metabolites in the preoptic area and pulsatile pituitary LH secretion, preoptic perfusates and blood samples were collected at 5-min intervals. Brain perfusates were subjected to high-performance liquid chromatography-electrochemical analysis. In blood samples LH concentrations were determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction in testicular function in rats. II. Reduction by dexamethasone in fetal and neonatal rats

Chronic administration of dexamethasone in drinking water to maternal rats from days 15 to 21 of gestation (1) reduced plasma testosterone concentrations in male fetuses between days 19 and 21 but not earlier on day 18 and abolished the prenatal peak of plasma testosterone which normally occurs on day 19 of gestation, and (2) suppressed the postnatal surge of plasma testosterone in male newborns 1.5 and 2 h after delivery at term by cesarean section. The administration of dexamethasone to male fetuses at birth induced 1 h later a slight but not significant increase in hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary luteinizing hormone (LH) contents, reduced drastically plasma LH levels and completely prevented the postnatal surge of plasma testosterone which occurred normally in littermate controls. A rise in pituitary LH content, and a sharp reduction in plasma LH and testosterone concentrations were noted in 19-day-old male fetuses whose mothers were acutely treated with dexamethasone on day 18 of gestation. Similar evolutions for LH were observed in littermate females. These results suggest that the inhibitory effects of exogenous glucocorticoids on testosterone secretion could be mediated in both fetuses and newborns at least partially through suppression of the hypothalamic and pituitary secretion of GnRH and LH, respectively, and provide insight how stress or hormone imbalance may affect the development of this neuroendocrine system.

Isolation and characterization of the human gonadotropin-releasing hormone gene in the hypothalamus and placenta

The GnRH gene has been cloned in several species, but the location of the promoter and the exact start of transcription have not previously been determined. To characterize the low abundance human GnRH mRNA in the hypothalamus and placenta, we have employed the polymerase chain reaction. The hypothalamus was found to have a 61-base pair first exon, and its transcriptional start site was determined. The human hypothalamic GnRH cDNAs isolated thus far have all contained a short 5' untranslated region which would correspond to this start site. However, all human placental GnRH cDNAs reported to date have a long 5' untranslated region, which extends more than 140-base pairs 5' to this start site in the hypothalamus, suggesting the utilization of an alternative promoter in the placenta. In addition, the human GnRH gene undergoes differential splicing in these tissues. The first intron is removed from the hypothalamic, but retained in the placental, GnRH mRNA. Thus, the placenta has a very long first exon, while the hypothalamus has a comparatively short first exon, followed by a long first intron. This characterization of the human GnRH gene will now allow hormonal regulatory studies to be performed using gene transfer techniques.

The effect of aging on hypothalamic function in oophorectomized women

To detect age-related changes intrinsic to hypothalamic-pituitary function, we studied plasma gonadotropin levels in 12 oophorectomized women ages 27 to 64 years who were not undergoing hormone replacement therapy. Blood drawn from an indwelling catheter every 10 minutes for 5 hours was assayed for follicle-stimulating hormone, luteinizing hormone, estradiol, and prolactin concentrations. All estradiol levels were less than 20 pg/ml and prolactin values were normal. Mean gonadotropin concentrations, pulse frequency, and pulse amplitude were no different in women aged 27 to 49 years as compared with subjects 52 to 64 years old. When grouped according to gynecologic age (years since puberty) or years after oophorectomy, luteinizing hormone and follicle-stimulating hormone mean concentrations, mean pulse frequency, and mean pulse amplitude were comparable to those grouped according to chronologic age. On the basis of our findings, lack of response from postmenopausal ovaries to endogenous gonadotropin stimulation is a result of primary age-related change in the ovary, not in the hypothalamus.

Progestins modulate the action of estrogen on gonadotropin-releasing hormone, luteinizing hormone and prolactin in the rat

The aim of the present study was to evaluate the effect of progesterone and of various synthetic progestins on hypothalamic gonadotropin-releasing hormone (GnRH) and on pituitary and plasma LH and prolactin (Prl) concentrations in ovariectomized rats. Groups of 6 rats were treated for 2 weeks with a pharmacological dose of progesterone, desogestrel, medroxyprogesterone acetate or norethisterone enanthate (NET). The same treatment was also repeated in association with estradiol benzoate (EB). Groups of ovariectomized rats were also treated with EB only or vehicle. Ovariectomized rats showed hypothalamic concentrations of GnRH significantly higher than control rats. Progesterone and NET significantly increased GnRH concentrations and reversed the EB-induced changes. Rats treated with progesterone and NET also showed reduced pituitary LH concentration, with high plasma LH levels. All progestins blocked the increase of pituitary LH induced by EB, but were inactive in influencing the inhibitory effect of EB on plasma LH levels. The administration of progesterone and progestins did not induce significant changes of pituitary or plasma Prl, but reversed the EB-induced increase. These results showed that progesterone and progestins have a marked effect on hypothalamic and pituitary hormone secretion and that they modulate estrogen-induced effects.

Gonadotropin-releasing hormone receptor expression in Xenopus oocytes

The rodent GnRH receptor was characterized in Xenopus oocytes injected with RNA isolated from rat pituitary and from a gonadotrope cell line, alpha T3, derived from a transgenic mouse. Three to 4 days after 150-200 ng RNA injection, 93% of the oocytes, which were recorded by voltage clamp, responded to 10(-7) M GnRH. The mean inward currents obtained after RNA injection were 620 +/- 88 nA (n = 22) with pituitary RNA and 1415 +/- 598 (n = 4) with alpha T3 RNA. The threshold GnRH concentration able to evoke the dose dependent current after pituitary RNA injection was 3 x 10(-9) M GnRH. The GnRH receptor response of the oocyte was antagonized by [D-Phe2,6,Pro3] GnRH and [N-Ac-D-Na](2)1, D-alpha D-Me, pCl-Phe2, D-Arg6, D-Ala10-NH2]GnRH and could be elicited by D-Ser(But)6,Pro9-N-ethylamide GnRH (buserelin). The reversal potential of the GnRH generated current as determined by voltage-ramp was -22.5 +/- 1.0 mV (n = 7) and -25.6 +/- 3.3 mV (n = 3) in pituitary and cell line RNA-injected oocytes respectively, consistent with the chloride reversal potential. The GnRH receptor response was virtually eliminated by intracellular EGTA injection but was unaffected by ligand application in calcium-free perfusate. The GnRH-evoked response is mimicked by intracellular injection of inositol 1,4,5-trisphosphate. To determine the size of the GnRH receptor mRNA, alpha T3 RNA was size fractionated through a sucrose gradient. The maximal GnRH response was induced by a fraction larger than the 28S ribosomal peak. Thus we find that oocytes injected with RNA from an appropriate source develop an electrophysiological response to GnRH which is dependent on intracellular calcium mobilization, is independent of extracellular calcium, and may be mediated by inositol 1,4,5-trisphosphate.

Cocaine disrupts estrous cyclicity and alters the reproductive neuroendocrine axis in the rat

Although a common drug of abuse, cocaine's effects on cyclic reproductive functions and the neuroendocrine systems regulating these functions have not been studied. Here, we report the effects of cocaine on (1) estrous cyclicity and ovulation rates and (2) the stimulated in vitro release of hypothalamic GnRH and aminergic neurotransmitters directly involved in regulating or modulating GnRH release. Within 7 days of treatment with 10 mg kg-1 day-1 of cocaine HCl subcutaneously, rats demonstrated significant estrous cycle irregularity including repetitive days of estrus and prolonged periods of diestrus. After 6 weeks of treatment, cocaine-treated rats exhibited a 44.3% decrease in ovulation rates. For the in vitro studies, bilaterally ovariectomized rats were injected with cocaine (10 mg kg-1 day-1) or with saline for 2 weeks. Each rat received estradiol benzoate (50 mg kg-1 day-1 s.c.) for 2 days before sacrifice. Hypothalamic slices were prepared, placed in 0.1 ml microchambers and perfused with modified Krebs buffer (pH 7.4) using a programmable perfusion system. Basal release of norepinephrine (NE) and serotonin (5HT) was significantly increased in the cocaine-treated group versus controls. Ten-minute pulses of 10(-7)M progesterone (P4) increase NE and 5HT, but not dopamine (DA), release in the saline-treated group. In contrast, pulses of P4 increased NE, but not 5HT or DA, in the cocaine-treated rats. Ten-minute pulses of 0.1 microM NE increased GnRH release in both saline- and cocaine-treated rats. However, the response to pulsed NE was significantly attenuated in the cocaine-treated group.(ABSTRACT TRUNCATED AT 250 WORDS)