The ovaries, testes, and adrenal glands produce sex hormones. The follicle-stimulating hormone (FSH), luteinizing hormone (LH), and gonadotropin-releasing hormone are all involved in controlling the reproductive cycle as well as the secretion of sex steroids from the sex glands. GnRH is secreted by the hypothalamus as a peptide, whereas gnrh1 and gnrh2 are neurotransmitters/peptides found throughout various tissues, with numerous varied effects. In humans, gnrh1 and gnrh2 mRNAs have been identified in the gastrointestinal tract, while GnRH has been discovered in both submucosal and myenteric neurons. Some researchers claim to have found GnRHa-encoding mRNA and a fully expressed peptide in rat intestinal neurons, while others don’t. In one research, rodents were found to express mRNA encoding GnRH receptors but not a full receptor.
GnRH analogs are clinically utilized in the treatment of diseases dependent on sex hormones, such as endometriosis and malignant neoplasms, as well as a preliminary preparation for in vitro fertilization. Peristalsis and gastrointestinal tract secretion are affected by GnRH.
With this therapy, there was a reduction in the number of intestinal neurons and IgM antibodies against GnRH and progonadoliberin-2 (GNRH2 precursor) with a clinical picture of gastrointestinal motility disorders, as well as the formation of an animal model for intestinal neurodegeneration after administration of buserelin. Patients with gastrointestinal motility and/or autonomic dysfunction, such as irritable bowel syndrome, intestinal motor disorders, diabetes mellitus, and primary Sjogren syndrome have been shown to have elevated serum IgM antibodies to GnRH1, progonadoliberin-2, and GnRH receptors. As a result of this, along with the control of reproduction and sex hormone production, GnRH is also involved in the ENS’s functions in both normal and disease states. The goal of this paper was to examine the function of GnRH in the ENS.
Gonadotropin-Releasing hormone, a family
GnRH was first discovered in porcine and ovine hypothalamic extracts, leading to the widespread belief that a single type of GnRH (mammalian GnRH) controls the hypothalamic-pituitary-gonadal axis in all mammals. How does one GnRH regulate the release of two gonadotropins, LH and FSH? Although there have been several different theories proposed over time, questions still remain, and these have fueled continued research into a distinct FSH-releasing factor or new GnRH isoform.
According to some studies, at least two distinct GnRH isoforms are present in the brain of a single vertebrate species. Current thinking is that one form (type GnRH-I) of GnRH (subclass Hormone) acts as a neurohormone regulating the pituitary gland’s release of gonadotropin. The second form (subclass Hormone) has been linked to neurotransmitters or neuromodulators and is generally found in the midbrain and adjacent areas. Chicken GnRH-II is the second GnRH isoform to be discovered in mammalian species. The discovery of additional GnRH forms outside of mammal GnRH in mammals is supported by the identification of three species’ complementary DNAs for chicken GNRHa: the tree shrew, guinea pig, and human. In the guinea pig, a preproGNHRH encodes for a distinct form of guinea pig gonadotropin. Most recently, two genes for mammal and chicken GnRH were found in humans.
In rodents, a restricted selection of species, monotremes, marsupials, rats, and primitive eutherians have been studied for variant GnRH forms through immunocytochemistry (ICC), high-performance liquid chromatography (HPLC), and radioimmunoassay (RIA) using specific antibodies to various GnRH types. Chicken GnRH-II was found to be present everywhere in the majority of the species looked at. In rats, lamprey GnRH-III neurons have been found in areas that control FSH production, as well as in places that primarily regulate LH release, according to recent studies utilizing a double-labeled immunocytochemical technique. These investigations employed indirect methods with various heterologous antibodies. Immunoreactive (ir) GnRH will require confirmation by identification of these ir-variant GnRH forms through protein purification or molecular cloning followed by extensive biological activity trials.
The first study to show that a lamprey-like GnRH was present in the human hypothalamus and median eminence combined ICC, HPLC, and RIA. In these same studies, the hypothalamic location of immunopositive lamprey-like GnRH neurons was comparable to that seen in humans. It has subsequently been shown that chicken GnRH-II-like molecules were discovered in stump tail and rhesus monkeys, but just a few of their chicken GnRH-II cells were located in the posterior basal hypothalamus; The majority of the immunopositive neurons were found to be in the midbrain in these studies. This research did not look for other types of GnRH, such as lamprey GnRH forms, and their data suggest that chicken GnRH-II is a neurohormone. As a result, there is uncertainty about the nature of Primate Rhs hormones because there is missing and conflicting information. Confirmation of the precise nature of a second or maybe a third form of primate or other mammal GnRH will require isolation, sequencing analysis, localization assessment, and biological function research.
GnRH directly inhibits multiple beneficial functions of endometrial stem cells in vitro
We first isolated endometrial stem cells from human endometrial tissue and then characterized their biological characteristics by utilizing a range of negative and positive stem cell surface markers such as CD34, CD44, CD45, CD73, CD105, CD140B, CD146, and W5C5. Adipogenic and osteogenic differentiation were induced to evaluate the capacity of endometrial stem cells to differentiate into several lineages. We investigated whether GnRH inhibits the various beneficial activities of endometrial stem cells in vitro since GnRH may act as an exogenous agent that damages the endometrium.
We discovered that endometrial stem cells have a reduced proliferative response to GnRH and exhibit decreasing growth rates in vitro when treated with the hormone. In addition, in vitro endometrial stem cell migration and wound healing assays revealed an inhibitory effect of GnRH on the migratory capability of these cells. To further verify the inhibitory action of GnRH on endometrial stem cell migration, Western blotting was performed to analyze the levels of matrix metalloproteinase 2 (MMP-2) and MMP-9, which regulate cellular mobility.
We previously discovered that the actin cytoskeleton is involved in cell migration by pushing or pulling the substrate near the plasma membrane. Phalloidin staining of actin filaments revealed a significant positive correlation between GnRH treatment and greater actin cytoskeleton disorder, suggesting that reduced migratory capability of GnRH-treated stem cells may be linked to actin cytoskeleton disorder. GnRH treatment upregulates the expression of pro-apoptotic member caspase 3, resulting in DNA damage. Furthermore, GnRH significantly decreased the multi-lineage differentiation potential of mesenchymal stem cells toward osteoblasts in vitro. In fact, FSH administration during in vitro fertilization therapy serves to stimulate follicle development by downregulating pituitary production with a GnRH agonist.
To further evaluate whether our in vitro findings may be translated to the clinical setting, we investigated whether FSH affects GnRH-induced endometrial stem cell activities. The decrease of stem cells proliferation, apoptosis, pluripotency-associated gene expression levels, and mobility induced by GnRH was only marginally influenced by F saliva co-treatment in vitro. In conclusion, these findings suggest that GnRH inhibits various beneficial functions of endometrial stem cells in vitro, such as proliferative, migratory, and multilineage differentiation potential.
We investigated whether this effect is restricted to endometrial stem cells or if it occurs in other types of stem cells by isolating and treating human adipose tissue stem cells with several doses of GnRH. We obtained stem cells from human fat tissues using our standard technique, then examined the biological characteristics of these stem Cells using a range of positive and negative stem cell surface markers. Adipose-derived stem cells were shown to be able to differentiate into various tissue lineages in vitro by inducing osteoblast and adipocyte differentiation.
GnRH dosage also inhibited bone formation in mice, consistent with the findings with endometrial stem cells. Those utilizing human adipose tissue-derived progenitor cells showed that GnRH inhibits a variety of beneficial activities including proliferation, differentiation, and migration.
GnRH neurons: the central neural regulators
In general, the GnRH neurons are essential central regulators of reproductive function. Their cell bodies are found in the preoptic region, anterior hypothalamic area, and middle basal hypothalamus. It should be mentioned that two distinct genes exist in mammals that encode GnRH: GnRH-I and GnRH-II. It is probable that these distinct populations of GnRH neurons have overlapping but independent roles.
However, since most research on the role of GnRH in ovarian cyclicity is focused on GnRH-I, this part refers to GnRH for simplicity. The median eminence houses the GnRH nerve endings that control anterior pituitary function.
The pulsation of GnRH secretion into the portal vasculature is well established, and changes in GnRH pulse frequency have significant effects on the amounts of LH and FSH released from the pituitary. One of the neuroendocrinology’s most enduring Mysteries is the nature of the GnRH pulse generator. The majority view at present is that pulsatility is an inherent property of the GnRH neuron.
However, since GnRH neurons are not concentrated in specific regions, coordination between them is required. Although several neurotransmitters and neuromodulators have been identified that act at the level of GnRH cell bodies or nerve endings, the mechanism by which this occurs is unknown. It’s generally acknowledged that norepinephrine, glutamate, γ-aminobutyric acid (GABA), neuropeptide Y, opioids, and GnRH all have significant effects on GnRH neuronal activity and appear to target these cells directly.
Other key regulators of GnRH include estradiol and progesterone, both of which have both negative and positive feedback effects. The mechanisms by which they work in contrast remain unknown, but the detrimental and beneficial responses of steroids on GnRH, LH, and FSH are important regulatory mechanisms that underpin the ovarian cycle.
Kisspeptin, a new hypothalamic neuropeptide system that controls GnRH neuron activity, has been identified in recent research. Kisspeptin neurons are found in the arcuate nucleus and anteroventral periventricular nucleus of the hypothalamus and are regulated differently by ovarian hormones. It’s been suggested that kisspeptin neurons in the arcuate nucleus function in the negative feedback effects of steroids to inhibit GnRH neurons, while kisspeptin neurons in the anteroventral periventricular nucleus are activated by high estrogen levels and may contribute to the GnRH/LH rise at ovulation.
Endocrinology, brain, and pituitary gland
GnRH is secreted in pulses every hour or so into the hypophyseal portal system rather than continuing from the hypothalamus. In response, the pituitary gonadotropes secrete FSH and LH in a pulsating manner. The pulsatile pattern of GnRH release is critical for gonadotropin secretion, which explains why it is so important for sexual function. It was formerly thought that simply administering GnRH agonists would cure infertility in men and women. Surprisingly, these agonists no longer worked after being first stimulated with FSH and LH. Only when GnRH agonists are given in natural bursts via an intravenous pump is normal gonadotropin secretion restored. It’s been suggested that continual exposure to GnRH causes pituitary cell receptors or the GnRH signaling pathway to downregulate.
The GnRH-producing cells are mostly found in the HTA in humans, though they may be detected all through the hypothalamus. This nucleus is positioned near the median eminence at the base of the brain and includes ordinary neurons that synapse with GnRH neurons. The activity of cells in this region controls the pulsatile secretion of GnRH. GnRH neurons have an inherent pulsating property, and their frequency and amplitude can be changed by synapses with regular neurons. The hypothalamus houses neurons that actively control the release of GnRH. Kisspeptins, a group of peptides secreted by adjacent nerve cells to GnRH neurons, appear to activate GnRH neuron secretion directly. Glutamate and even GnRH have been proposed as regulators of GnRH secretion. In humans, another neuropeptide, gonadotropin-inhibitory hormone (GnIH), limits GonRHa through inhibiting GnRH cell function and the gonadotrope response to GnRHa. Although its role in people is unknown, it has been shown to negatively regulate GonRHa by preventing GnRH cell activity and stimulating ovulation in rodents.
Neuroendocrinology of reproduction
The decapeptide GnRH has the amino acid structure (pyro)Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly. Although the central Tyr-Gly -Leu -Arg segment varies slightly among vertebrate species, the amino acids of GnRH are quite conserved across vertebrates. The GnRH-1 gene is located on the human chromosome and encodes a 92-amino acid precursor peptide called pre-pro-GnRH, which contains a 23-amino acid signal sequence (GnRH), GnRH (10 amino acids), a proteolytic processing site (3 amino acids), and GnRH-associated peptide (56 amino acids). The latter protein may stimulate gonadotropin secretion while also inhibiting prolactin release, although its physiological significance if any, is uncertain. GnRH’s effects are controlled by the GnRH type I receptor.
A number of animal species, including humans, have been shown to possess a form of GnRH and its receptor. GnRH-2 is a decapeptide with the following structure: (pyro)Glu-His-Trp-Ser-His-Gly-Trp-Tyr-Pro (italicized amino acids indicate differences from GnRH1). However, in people, the gene for GnRH2 is located on chromosome 20. In many animals, especially those that reproduce sexually or viviparously, such as cattle and sheep, it may contribute to reproductive behavior regulation. GnRH-2 receptors have also been found in lower animals, including humans. GnRH-2 works by binding to its own receptor, which is structurally and functionally distinct from the GnRH type I receptor. Although a homologue of the Gnrh-2 receptor gene has been discovered in people, it contains a frameshift and an early stop codon. As a result, the physiological significance of GnRH-2 in humans is uncertain.
Isolation and culture of human endometrial stem cells
Human endometrial stem cells were obtained from uterine fibroid patients at Hallym University Kangnam Sacred Heart Hospital with written informed consent and the approval of the Hallym University Kangnam Sacred Heart Hospital Institutional Review Board. All of Gachon University’s human-related studies were authorized and conducted in accordance with its institutional review board. Fresh, undiluted whole endometrial tissue was minced into tiny pieces and then digested in DMEM with 10% FBS and 250 U/ml types I collagenase for 5 hours at 37°C in a rotating shaker. The digestion solution was filtered through a 40-micrometer cell strainer to remove stromal-like stem cells from epithelial gland fragments and undigested tissue. Cells were cultured in EBM-2 medium (Lonza) supplemented with EGM-2 at 37°C and 5% CO2 after isolation.
Cell proliferation assay
According to the manufacturer’s instructions, the anti-proliferative capability of GnRH was evaluated using the MTT assay. Cells (1 x 104 cells per well) were seeded in 96-well plates. After 24 hours of incubation, the cells were treated with GRS or vehicle for 72 hours. The living cells were quantified at 570 nm using a VersaMax microplate reader after 72 hours of treatment with GRS or vehicle.
In vitro cell migration assay
In each well of a 24-well plate, 1 × 104 cells were plated in 200 μL medium in the upper chambers of transwell permeable supports to observe cell migration. The transwell chambers had 8.0-mm pores and used a 6.5-mm diameter polycarbonate membrane. Noninvasive cells on the upper surface of each membrane were removed with laboratory paper by scrubbing the higher surface of each membrane. Migrated cells on the lower surface of each membrane were stained with hematoxylin for 15 minutes before being fixed with 4% paraformaldehyde for 5 minutes. The number of migrated cells was counted in three randomly chosen fields of the wells under a light microscope at 50x power later. The number of cells that migrated in response to GnRH treatment was divided by the total number of spontaneously migrating cells to calculate the chemotactic index.
Scratch test assay
The cell monolayers were scratched with a sterile pipette tip to produce a 12-mm-wide area without cells. The cell surface was then washed 3 times with PBS to remove detritus. Cells were cultured in the presence or absence of GnRH for 24 hours. Cells were fixed with 4% paraformaldehyde for 15 minutes and washed twice with PBS before being imaged at 0 and 24 hours after the scratch was made.
Neurology and pregnancy
GnRH is produced in hypothalamic GnRH neurons and released into the hypophyseal portal circulation. The synthesis and release of pituitary gonadotropins, FSH and LH, are controlled by the GnRH release pattern (Schally et al., 1971). It has been suggested that it works in an autocrine and paracrine manner in various tissues (e.g., ovary, placenta), as well as playing significant roles in other physiologic processes such as implantation.
GnRH is a decapeptide when it enters the portal circulation, but it is the cleavage product of the repro-GnRH precursor peptide, which has 92 amino acids. The human chromosome contains the GnRH gene. The repro-GnRH peptide comprises GnRH (10 amino acids), GnRH-associated peptide (56 amino acids), signal sequence (23 amino acids), and a proteolytic processing site (3 amino acids). Gonadotropin release can be stimulated by GnRH-associated peptides. The term “hypothalamic GnRH pulse generator” derives from the pulsatile pattern of hypothalamic GnRH release. The infundibular (arcuate) nucleus and the medial preoptic area of the hypothalamus are rich in GnRH neurons, which are functionally integrated and have extensive connections with other neuronal groups. Note that the olfactory neurons that travel to the hypothalamus from the olfactory placode require GnRH. Failure of migration is one of the primary causes of natural HH in both men and women.
GnRH is secreted from the hypothalamus and other tissues in several steps. The release of pulsatile GnRH into the portal circulation is necessary for anterior pituitary gonadotropin production, which is essential for fertility and reproduction. Mice with GnRH-1 gene mutations become hypogonadal, and treatment with either GnRH-1 gene therapy or transplantation of GnRH neurons can restore their testosterone levels. Defective or absent GnRH secretion in humans is associated with hypogonadotropic hypogonadism (HH), which results in delayed puberty and infertility. Pulsatile GnRH therapy restores puberty and reproductive function by replacing the missing or defective hormone. A genetic defect has been linked to early activation of the GnRH pulse generator, which causes central precocious puberty in boys and girls. The lack of the protein product is caused by a change in the imprinted gene MKRN3. GnRH secretion is regulated by a variety of factors, including psychological stress, sex steroids, and energy balance; behavioral variables are regarded as functional rather than organic modulators of the GnRH function.
The actions of GnRH are controlled by its receptors. Two types of GnRH receptors have been discovered: one named GnRH type I (GnRH-1) and the other GnRH type II (GnRH-2). The two receptors are structurally and functionally different. GnRH type I receptor is responsible for the pituitary activity induced by GnRH. Another form of GnRH, known as GNH-2, has been identified in animals and is located on chromosomes. There is a lot of GnRH-2 expression in the brain and extra-CNS tissues, which means it may play a role in reproductive action regulation. The physiologic significance of human GnRH-2 activity is unknown.
The human placenta produces two GnRH isomers, termed GnRH-I and -II, which are produced from the same precursor molecule (GnRH). Both are activated by the activation of G protein-coupled receptors on cytotrophoblasts, syncytiotrophoblast, and decidua. Levels of GnRH are constantly high throughout pregnancy, although the placenta expresses the same quantity of βhCG as the hypothalamus. Activin A, depolarizing and cAMP-stimulatory agents, and estrogen promote placental GnRH secretion in a manner similar to that seen in the hypothalamus. Placental GnRH 1 is a significant regulator of βhCG. In early pregnancy, because it induced apoptosis in human decidua stromal cells and altered EVT invasion via modulation of matrix metalloproteinases (MMPs), GnRH may play a role in decidualization.
Gonadotropin-Releasing Hormone is a hormone that is responsible for the release of other hormones, like follicle-stimulating hormone and luteinizing hormone. These two hormones are responsible for testosterone production in males and progesterone production in females. GnRH also regulates reproductive behavior. Defects or absent secretion of GnRH can lead to infertility. GnRH is also expressed by the placenta and may have a role in decidualization and early pregnancy.
WHO releases gonadotropin-releasing?
Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus. It stimulates the production and release of the gonadotropins luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. These hormones in turn stimulate the ovaries or testes to produce the sex hormones.
What are gonadotropins?
Gonadotropins are a group of hormones that control reproduction by regulating the development, growth, and function of the reproductive system. They stimulate cells in the testicles (in men) or ovaries (in women) to make sperm or eggs. The two main gonadotropins in the body are LH and FSH.
What triggers gonadotropin-releasing?
GnRH is released in a “pulse” pattern. This means that it is released in bursts rather than constantly. The pulses are regulated by many different factors, including stress, sex hormones, and energy balance. Some of these factors are behavioral, such as psychological stress. Others are physiological, such as the presence of certain sex hormones in the blood.
What are gonadotropins used for?
Gonadotropin hormones (FSH and LH) help to regulate your sex organs and reproductive cycles. FSH causes follicle growth in girls, while LH stimulates egg maturation in girls. In boys, FSH helps with sperm production, while LH triggers testosterone production. Testosterone is important for male reproductive functions, including sperm production and sex drive. LH also helps to maintain the corpus luteum in the ovaries, which is responsible for producing progesterone after ovulation. Progesterone helps to prepare the uterus for a fertilized egg. If fertilization does not occur, progesterone levels will drop and menstruation will begin.
What is the difference between GnRH-I and -II?
GnRH-I is the main form of GnRH that regulates reproduction. GnRH-II is a newer version of GnRH that has been discovered in animals. Its role in humans is not yet clear. GnRH-II may be involved in reproduction, stress, and other functions.