Vasotocin is an oligopeptide homologous to oxytocin and vasopressin found in all non-mammalian vertebrates (including birds, fishes, and amphibians) and possibly in mammals during the fetal stage of development. Arginine vasotocin (AVT), a hormone produced by neurosecretory cells within the posterior pituitary gland (neurohypophysis) of the brain, is a major endocrine regulator of water balance and osmotic homoeostasis and is involved in social and sexual behavior in non-mammalian vertebrates. In mammals, it appears to have biological properties similar to those of oxytocin (stimulating reproductive tract contraction as in egg laying or birth) and vasopressin (diuretic and antidiuretic effects). It has been found to have effects on the regulation of REM sleep.[1] Evidence for the existence of endogenous vasotocin in mammals is limited[2][3] and no mammalian gene encoding vasotocin has been confirmed.
AVT (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Arg-Gly-NH2), which occurs in the lamprey, represents the ancestral form in the phylogeny of the vertebrate neurohypophysial hormones.[4] Gene duplication and point mutation have produced two distinct lineages, one involved in reproduction (oxytocin-like peptides) and the other in osmoregulation (vasopressin-like peptides). These hormones have remained highly conserved throughout evolution. Each is a peptide of nine amino acids derived from a preprohormone precursor by proteolytic cleavage, with an intramolecular disulfide bridge between the cysteine (Cys) residues; the C-terminal glycine (Gly) residue is amidated. Six of the residues have been found to be invariant in homologous peptides from numerous species of vertebrates. The vasopressin-like peptides, which differ in positions 3 and/or 8, include AVT and the mammalian hormones arginine vasopressin (Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-Gly-NH2, with isoleucine-3 of AVT changed to phenylalanine) and lysine vasopressin (isoleucine-3 changed to phenylalanine and arginine-8 changed to lysine). The oxytocin-like peptides, which differ in positions 4 and/or 8, include oxytocin (Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, with arginine-8 of AVT changed to leucine), mesotocin (arginine-8 changed to isoleucine), and isotocin (glutamine-4 changed to serine and arginine-8 changed to isoleucine); they differ from the vasopressin-like peptides in having a neutral amino acid in place of a basic amino acid at position 8. Oxytocin occurs in placental mammals; mesotocin occurs in amphibians, reptiles, and birds, and isotocin occurs in fishes.
Biosynthesis
AVT is synthesized as a preprohormone that includes a second peptide, neurophysin VT (neurophysins are carrier proteins that are secreted along with their passenger hormones); intracellular proteolytic processing generates the mature peptides. In the chicken (Gallus gallus), the 161-amino acid vasotocin-neurophysin VT preprohormone is encoded by the gene AVP, which is considered homologous to the mammalian genes encoding arginine vasopressin.[5] Removal of the 19-amino acid N-terminal signal peptide generates the prohormone, which is hydrolysed to AVT (derived from amino acids 20-28) and neurophysin VT (derived from amino acids 32-161).[6] The existence of two AVT preprohormones with different sequences in fishes (such as chum salmon, Oncorhynchus keta[7]) is evidence for gene duplication.
Physiological effects
AVT combines both antidiuretic and reproductive activities similar to those of oxytocin and vasopressin. The physiological actions of AVT in birds are mediated through diverse receptor subtypes VT1, VT2, VT3 and VT4.[8] AVT and synthetic analogs injected into monkeys cause reabsorption of osmotically free water and changes in excretion of sodium and potassium ions in the kidneys.[9] AVT produces distinct effects on the reproductive functions of male and female domestic chickens. In laying hens, AVT synthesised in magnocellular diencephalic neurons is released into circulation in a highly coordinated manner, contributing to the peripheral control of oviposition. In males, parvocellular AVT cells located in the limbic system (bed nucleus of stria terminalis) express AVT. This expression is sensitive to gonadal steroids and is correlated with sexual differentiation of masculine behavior such as courtship vocalization and copulation.[8]
Behavioral effects
Several animal studies have been conducted that explore the behavioral effects of AVT. The main findings of these studies have revealed that AVT plays an integral role in the pair bonding behavior and social hierarchy in non-mammalian vertebrates.
In a study conducted with zebra finches,[10] increased levels of AVT were linked to an increase in aggressive, competitive behavior in non-paired male finches, but were subsequently related to an increase in defensive behavior after the finches had been paired. However, this study also found that blocking AVT receptors did not directly affect pair bonding ability. The shift in behaviors were explained by the location of the release of AVT in the brain. Competitive aggressive behavior was found to be linked with AVT release in the BSTm, whereas defensive, nest-protecting behavior was linked with AVT release in the neurons of the Hypothalamus and Paraventricular Nucleus.
In a study conducted with male Japanese quail, AVT was found to have an effect on later social interactions amongst the species. Immediately after injection with AVT, the quails displayed less aggressive behavior (pecking). However, the next day, the quail that were injected with AVT displayed more dominant behavior towards familiar birds, but not unfamiliar birds. This study shows that AVT may play a role in establishing social hierarchy.[11]
A study that investigated the role of social construction and AVT compared territorial and non-territorial species of tropical coral reeffish.[12] Experimenters administered Manning compound, an AVT agonist to the fish and found that, after treatment, non-territorial species displayed more territorial behavior whereas territorial species displayed less territorial behavior.
Research suggests that the effects of AVT on aggression may be influenced by the social construction of the species. For example, in a study done with Rainbow Trout,[13] increased levels of AVT were associated with more subordinate behavior. It is currently hypothesized that the contrasting effects of AVT are related to the distinction between territorial versus colonial social systems. In a territorial species, such as Rainbow Trout, AVT is linked to less dominant behavior. This may be due to the differences in the distribution of AVT receptors in territorial and colonial species.
Sources
↑ Kales, Anthony (1995). The Pharmacology of sleep. Berlin: Springer-Verlag. ISBN3-540-58961-9.
↑ Ervin MG, Amico JA, Leake RD, Ross MG, Robinson AG, Fisher DA (1988). "Arginine vasotocin and a novel oxytocin-vasotocin-like material in plasma of human newborns". Biol Neonate. 53 (1): 17–22. doi:10.1159/000242757. PMID3355867.
↑ Liu JW, Ben-Jonathan N (January 1994). "Prolactin-releasing activity of neurohypophysial hormones: structure-function relationship". Endocrinology. 134 (1): 114–18. doi:10.1210/endo.134.1.8275925. PMID8275925.
↑ Heierhorst J, Mahlmann S, Morley SD, Coe IR, Sherwood NM, Richter D (January 1990). "Molecular cloning of two distinct vasotocin precursor cDNAs from chum salmon (Oncorhynchus keta) suggests an ancient gene duplication". FEBS Lett. 260 (2): 301–4. doi:10.1016/0014-5793(90)80129-7. PMID2298304.
1 2 Jurkevich A, Grossmann R (2003). Vasotocin and reproductive functions of the domestic chicken. Domest Anim Endocrinol. 25(1):93-9. PMID12963102
↑ Buravkova LB, Larina IM, Korolkov VI, Dobrokhotov IV, Grigorev AI (2003). Bull Exp Biol Med. 142(6):714-6. PMID17603678
↑ Riters LV, and Panksepp J. Effects of vasotocin on aggressive behavior in male Japanese quail. Annals of the New York Academy of Sciences. 2006; 807(1): 478-480.
↑ Semsar K, Kandel FLM, Godwin J. Manipulations of the AVT system shift social status and related courtship behavior in the Bluehead Wrasse. Hormones and Behavior. 2001; 40(1): 21-31.
↑ Backström T, and Winberg S. Arginine vasotocin influence on aggressive behavior and dominance in rainbow trout. Physiology and Behavior. 2009; 96(3): 470-475.
Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travels down the axon terminating in the posterior pituitary, and is released from vesicles into the circulation in response to extracellular fluid hypertonicity (hyperosmolality). AVP has two primary functions. First, it increases the amount of solute-free water reabsorbed back into the circulation from the filtrate in the kidney tubules of the nephrons. Second, AVP constricts arterioles, which increases peripheral vascular resistance and raises arterial blood pressure.
Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to sexual activity and during labour. It is also available in pharmaceutical form. In either form, oxytocin stimulates uterine contractions to speed up the process of childbirth. In its natural form, it also plays a role in bonding with the baby and milk production. Production and secretion of oxytocin is controlled by a positive feedback mechanism, where its initial release stimulates production and release of further oxytocin. For example, when oxytocin is released during a contraction of the uterus at the start of childbirth, this stimulates production and release of more oxytocin and an increase in the intensity and frequency of contractions. This process compounds in intensity and frequency and continues until the triggering activity ceases. A similar process takes place during lactation and during sexual activity.
Peptide hormones are hormones whose molecules are peptide. Peptide hormones have shorter amino acid chain lengths than protein hormones. These hormones have an effect on the endocrine system of animals, including humans. Most hormones can be classified as either amino acid–based hormones or steroid hormones. The former are water-soluble and act on the surface of target cells via second messengers; the latter, being lipid-soluble, move through the plasma membranes of target cells to act within their nuclei.
The supraoptic nucleus (SON) is a nucleus of magnocellular neurosecretory cells in the hypothalamus of the mammalian brain. The nucleus is situated at the base of the brain, adjacent to the optic chiasm. In humans, the SON contains about 3,000 neurons.
Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the gut, muscles, and heart.
Vasoactive intestinal peptide, also known as vasoactive intestinal polypeptide or VIP, is a peptide hormone that is vasoactive in the intestine. VIP is a peptide of 28 amino acid residues that belongs to a glucagon/secretin superfamily, the ligand of class II G protein–coupled receptors. VIP is produced in many tissues of vertebrates including the gut, pancreas, cortex, and suprachiasmatic nuclei of the hypothalamus in the brain. VIP stimulates contractility in the heart, causes vasodilation, increases glycogenolysis, lowers arterial blood pressure and relaxes the smooth muscle of trachea, stomach and gallbladder. In humans, the vasoactive intestinal peptide is encoded by the VIP gene.
Neurophysin I is a carrier protein with a size of 10 KDa and contains 90 to 97 amino acids. It is a cleavage product of preprooxyphysin. It is a neurohypophysial hormone that is transported in vesicles with oxytocin, the other cleavage product, along axons, from magnocellular neurons of the hypothalamus to the posterior lobe of the pituitary. Although it is stored in neurosecretory granules with oxytocin and released with oxytocin, its biological action is unclear.
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently used in sociobiology and evolutionary biology circles. The term often implies either a lifelong socially monogamous relationship or a stage of mating interaction in socially monogamous species. It is sometimes used in reference to human relationships.
Vasopressin receptor 1A (V1AR), or arginine vasopressin receptor 1A is one of the three major receptor types for vasopressin, and is present throughout the brain, as well as in the periphery in the liver, kidney, and vasculature.
Vasopressin V1b receptor (V1BR) also known as vasopressin 3 receptor (VPR3) or antidiuretic hormone receptor 1B is a protein that in humans is encoded by the AVPR1B gene.
The oxytocin receptor, also known as OXTR, is a protein which functions as receptor for the hormone and neurotransmitter oxytocin. In humans, the oxytocin receptor is encoded by the OXTR gene which has been localized to human chromosome 3p25.
Neurophysin II is a carrier protein with a size of 19,687.3 Da and is made up of a dimer of two virtually identical chains of amino acids. Neurophysin II is a cleavage product of the AVP gene. It is a neurohypophysial hormone that is transported in vesicles with vasopressin, the other cleavage product, along axons, from magnocellular neurons of the hypothalamus to the posterior lobe of the pituitary. Although it is stored in neurosecretory granules with vasopressin and released with vasopressin into the bloodstream, its biological action is unclear. Neurophysin II is also known as a stimulator of prolactin secretion.
Demoxytocin (INN), also known as desaminooxytocin or deaminooxytocin, as well as 1-(3-mercaptopropanoic acid)oxytocin ([Mpa1]OT), is an oxytocic peptide drug that is used to induce labor, promote lactation, and to prevent and treat puerperal (postpartum) mastitis. Demoxytocin is a synthetic analogue of oxytocin and has similar activities, but is more potent and has a longer half-life in comparison. Unlike oxytocin, which is given via intravenous injection, demoxytocin is administered as a buccal tablet formulation.
Neuromedin S is a 36-amino acid neuropeptide found in the brain of humans and other mammals. It is produced in the suprachiasmatic nucleus of the hypothalamus and is related to neuromedin U. It is thought to be involved in regulation of circadian rhythm and also has appetite suppressant effects, as well as regulating the release of several other peptide hormones including vasopressin, luteinizing hormone, and oxytocin.
The neurohypophysial hormones form a family of structurally and functionally related peptide hormones. Their representatives in humans are oxytocin and vasopressin. They are named after the location of their release into the blood, the neurohypophysis.
α-Endorphin (alpha-endorphin) is an endogenous opioid peptide with a length of 16 amino acids, and the amino acid sequence: Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr. With the use of mass spectrometry, Nicholas Ling was able to determine the primary sequence of a-endorphin.
Copeptin is a 39-amino acid-long peptide derived from the C-terminus of pre-pro-hormone of arginine vasopressin, neurophysin II and copeptin. Arginine vasopressin (AVP), also known as the antidiuretic hormone (ADH), is encoded by the AVP gene and is involved in multiple cardiovascular and renal pathways and abnormal level of AVP are associated with various diseases. Hence measurement of AVP would be useful, but is not commonly carried out in clinical practice because of its very short half-life making it difficult to quantify. In contrast, copeptin can be immunologically tested with ease and therefore can be used as a vasopressin surrogate marker.
Phenypressin (Phe2-Arg8-vasopressin) is an oxytocin neuropeptide belonging to the vertebrae vasopressin family and has similar pharmacological properties as arginine vasopressin. The name phenypressin came about because there is a substitution of phenylalanine that makes it different from arginine vasopressin in the second residue and that is the only difference. It belongs to the family, neurohypophysial hormones, named after the fact that they are secreted by the neurohypophysis which is a neural projection from the hypothalamus. It has mostly been found to be present is some species belonging to the family, Macropodidae, particularly eastern gray kangaroos[3], red kangaroos, tammar wallaby, and the quokka wallaby. In other marsupial families, Phenypressin has not yet specifically been identified, but they do have other vasopressin-like peptides present.
Arginine Vasopressin (AVP) Gene is a gene whose product is proteolytically cleaved to produce vasopressin, neurophysin II, and a glycoprotein called copeptin. AVP and other AVP-like peptides are found in mammals, as well as mollusks, arthropods, nematodes, and other invertebrate species. In humans, AVP is present on chromosome 20 and plays a role in homeostatic regulation. The products of AVP have many functions that include vasoconstriction, regulating the balance of water in the body, and regulating responses to stress. Expression of AVP is regulated by the Transcription Translation Feedback Loop (TTFL), which is an important part of the circadian system that controls the expression of clock genes. AVP has important implications in the medical field as its products have significant roles throughout body.
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