Prolactin
Identifiers
Symbol	PRL
Entrez	5617
HUGO	9445
OMIM	176760
RefSeq	NM_000948
UniProt	P01236
Other data
Locus	Chr. 6 p22.2-p21.3

Prolactin (PRL) is a peptide hormone primarily associated with lactation. The Entrez Global Query Cross-Database Search System is a powerful Federated search engine or Web portal that allows users to search many discrete Health sciences The Human Genome Organisation (HUGO is an organization involved in the Human Genome Project, a project about mapping the human genome The Mendelian Inheritance in Man project is a Database that catalogues all the known Diseases with a genetic component, and—when possible—links them The National Center for Biotechnology Information ( NCBI) is part of the United States National Library of Medicine (NLM a branch of the National Institutes Swiss-Prot is a manually curated Biological database of Protein sequences In the fields of Genetics and Evolutionary computation, a locus (plural loci) is a fixed position on a Chromosome such as the position of a Chromosome 6 is one of the 23 pairs of Chromosomes in Humans People normally have two copies of this chromosome Peptide hormones are a class of peptides that are secreted into the blood stream and have Endocrine functions in living animals Lactation describes the secretion of Milk from the Mammary glands the process of providing that milk to the young and the period of time that a Mother In breastfeeding, the act of an infant suckling the nipple stimulates the production of prolactin, which fills the breast with milk via a process called lactogenesis, in preparation for the next feed. In its most general form a nipple is a Structure from which a fluid emanates The breast is the upper Ventral region of an animal’s Torso, particularly that of Mammals including Human beings. Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. Mammary glands are the organs that in Mammals produce Milk for the sustenance of the young Oxytocin, another hormone, is also released, which triggers milk let-down. Oxytocin ( IPA: /ˌɔksɪˈtoʊsɪn/ (Greek "quick birth" is a Mammalian Hormone that also acts as a Neurotransmitter in the

Contents 1 Production and regulation 2 Effects 3 Variance in levels 4 Structure 5 Prolactin receptor 6 Diagnostic use 6.1 Conditions causing elevated prolactin secretion 6.2 Conditions causing decreased prolactin 7 Use of breastfeeding as contraceptive 8 See also 9 References 10 External links

Production and regulation

Prolactin is synthesised and secreted by lactotrope cells in the adenohypophysis (anterior pituitary gland). Lactotrophs (also known as lactotrope mammatroph mammotroph epsilon acidophil prolactin cell and lactotropic cell are cells in the Anterior pituitary which produce The anterior pituitary (also called the adenohypophysis, from Greek adeno, "gland" hypo, "under" physis, "growth" The pituitary gland, or hypophysis, is an Endocrine gland about the size of a Pea. It is also produced in other tissues including the breast and the decidua. The breast is the upper Ventral region of an animal’s Torso, particularly that of Mammals including Human beings. Decidua is the term for the uterine lining ( Endometrium) during a Pregnancy, which forms the maternal part of the placenta

Pituitary prolactin secretion is regulated by neuroendocrine neurons in the hypothalamus, the most important ones being the neurosecretory dopamine neurons of the arcuate nucleus, which inhibit prolactin secretion. Neuroendocrine cells are cells that receive neuronal input (neurotransmitters released by nerve cells and as a consequence of this input release message molecules (hormones to the blood The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis Dopamine is a Hormone and Neurotransmitter occurring in a wide variety of animals including both vertebrates and invertebrates The arcuate nucleus (or infundibular nucleus is an aggregation of Neurons in the mediobasal Hypothalamus, adjacent to the Third ventricle and the Median Thyrotropin-releasing factor has a stimulatory effect on prolactin release. Thyrotropin-releasing hormone ( TRH) also called thyrotropin-releasing factor ( TRF) thyroliberin or protirelin, is a tropic

Vasoactive intestinal peptide and peptide histidine isoleucine help to regulate prolactin secretion in humans, but the functions of these hormones in birds can be quite different. Vasoactive intestinal peptide ( VIP, also polypeptide) is a Peptide hormone containing 28 Amino acid residues and is produced in many Peptide PHI (or peptide Histidine Isoleucine) is a Peptide which functions as a Hormone. ^[1]

Effects

Prolactin has many effects:

• To stimulate the mammary glands to produce milk (lactation): Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and increases the production of milk. Mammary glands are the organs that in Mammals produce Milk for the sustenance of the young Lactation describes the secretion of Milk from the Mammary glands the process of providing that milk to the young and the period of time that a Mother Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female Mammary glands are the organs that in Mammals produce Milk for the sustenance of the young However, the high levels of progesterone during pregnancy act directly on the breasts to stop ejection of milk. Progesterone is a C-21 Steroid Hormone involved in the Female Menstrual cycle, Pregnancy (supports Gestation It is only when the levels of this hormone fall after childbirth that milk ejection is possible. Sometimes, newborn babies (males as well as females) secrete a milky substance from their nipples. In its most general form a nipple is a Structure from which a fluid emanates This substance is commonly known as Witch's milk. Witch's milk or neonatal milk is Milk secreted from the Breasts of some Newborn infants It is the result of influence by the mother's Hormones This is caused by the fetus being affected by prolactin circulating in the mother just before birth, and usually stops soon after birth.

• To provide the body with sexual gratification after sexual acts: The hormone represses the effect of dopamine, which is responsible for sexual arousal. An orgasm (sexual climax is the conclusion of the plateau phase of the sexual response cycle, and may be experienced by both males and females Human sexual behavior or different human sexual practices encompass a wide range of activities such as strategies to find or attract partners ( Mating and display Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Dopamine is a Hormone and Neurotransmitter occurring in a wide variety of animals including both vertebrates and invertebrates This is thought to cause the sexual refractory period. In sexuality the refractory period is the recovery phase after Orgasm during which it is physiologically impossible for an individual to have additional orgasms ^[2] The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido (see hyperprolactinemia Symptoms). Libido in its common usage means Sexual desire however more technical definitions such as those found in the work of Carl Jung, are more general referring to libido Hyperprolactinaemia ( BrE) or hyperprolactinemia ( AmE) is the presence of abnormally-high levels of Prolactin in the blood

• To stimulate proliferation of oligodendrocyte precursor cells: These cells differentiate into oligodendrocytes, the cells responsible for the formation of myelin coatings on axons in the central nervous system. Oligodendrocyte precursor cells in nervous tissue cells precede Oligodendrocytes, and may also be able to generate neurons and astrocytes Origin Oligodendroglia arise during development from an Oligodendrocyte precursor cell, which can be identified by its expression of a number of Antigens, including Myelin is an electrically-insulating Dielectric Phospholipid layer that surrounds only the Axons of many Neurons It is an outgrowth An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. ^[3]

• To contribute to surfactant synthesis of the fetal lungs at the end of the pregnancy and immune tolerance of the fetus by the maternal organism during pregnancy

• To decrease normal levels of sex hormones — estrogen in women and testosterone in men. Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive Immune or immunological tolerance is the process by which the Immune system does not attack an Antigen. Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Testosterone is a Steroid hormone from the Androgen group In mammals testosterone is primarily secreted in the testes of males and the Ovaries "^[4]

• Prolactin delays hair regrowth in mice^[5].

• In the rat, Dopamine inhibits plasma Prolactin. Production of prolactin is transiently inhibited by L-dopa. Also plasma prolactin levels are decreased (in 30 mins) and restored (in 3 hours) by L-dopa by a peripheral processes (i. e. , tissues outside pituitary). ^[6]

Variance in levels

There is a diurnal as well as an ovulatory cycle in prolactin secretion. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the Note This article deals primarily with Human ovulation nonhuman Animal ovulation is touched on briefly at the conclusion

During pregnancy, high circulating concentrations of estrogen promote prolactin production. Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, The resulting high levels of prolactin secretion cause further maturation of the mammary glands, preparing them for lactation.

After childbirth, prolactin levels fall as the internal stimulus for them is removed. Childbirth (also called labour, birth, partus or parturition) is the culmination of a Human Pregnancy or Sucking by the baby on the nipple then promotes further prolactin release, maintaining the ability to lactate. The sucking activates mechanoreceptors in and around the nipple. These signals are carried by nerve fibers through the spinal cord to the hypothalamus, where changes in the electrical activity of neurons that regulate the pituitary gland cause increased prolactin secretion. The hypothalamus links the Nervous system to the Endocrine system via the Pituitary gland (hypophysis The suckling stimulus also triggers the release of oxytocin from the posterior pituitary gland, which triggers milk let-down: Prolactin controls milk production (lactogenesis) but not the milk-ejection reflex; the rise in prolactin fills the breast with milk in preparation for the next feed. Oxytocin ( IPA: /ˌɔksɪˈtoʊsɪn/ (Greek "quick birth" is a Mammalian Hormone that also acts as a Neurotransmitter in the The posterior pituitary (or neurohypophysis) comprises the Posterior lobe of the Pituitary gland and is part of the Endocrine system.

In usual circumstances, in the absence of galactorrhea, lactation will cease within one or two weeks of the end of demand breastfeeding. Galactorrhea or galactorrhoea is the spontaneous flow of Milk from the Breast, unassociated with Childbirth or nursing Breastfeeding is the feeding of an Infant or young Child with Breast milk directly from human Breasts, not from a Baby bottle or other

High prolactin levels also tend to suppress the ovulatory cycle by inhibiting the secretion of both follicle-stimulating hormone (FSH) and gonadotropic-releasing hormone (GnRH). Gonadotropin-releasing hormone ( GNRH) also known as Luteinizing-hormone releasing hormone ( LHRH) is a tropic Peptide Hormone

Prolactin levels peak during REM sleep, and in the early morning. Levels can rise after exercise, meals, sexual intercourse, or minor surgical procedures. ^[7]

Structure

Prolactin is a single-chain polypeptide of 199 amino acids with a molecular weight of about 24,000 daltons. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this The unified atomic mass unit ( u) or Dalton ( Da) or sometimes universal mass unit, is an unit of Mass used to express Its structure is similar to that of growth hormone and placental lactogen. Growth hormone ( GH) is a Peptide hormone that stimulates growth and cell reproduction in humans and other animals Placental lactogen is a Polypeptide Placental Hormone. Its structure and function is similar to that of Growth hormone. The molecule is folded due to the activity of three disulfide bonds. In Chemistry, a disulfide bond is a single Covalent bond derived from the coupling of Thiol groups Significant heterogeneity of the molecule has been described, thus bioassays and immunoassays can give different results due to differing glycosylation, phosphorylation, sulfation, as well as degradation. Bioassay is a shorthand commonly used term for biological assay and is a type of scientific Experiment. An immunoassay is a Biochemical test that measures the Concentration of a substance in a biological liquid typically serum or Urine, using the Glycosylation is the enzymatic process that links Saccharides to produce glycans, either free or attached to Proteins and Lipids This enzymatic Phosphorylation is the addition of a Phosphate (PO4 group to a Protein molecule or a small molecule Sulfation refers to the process whereby a Lead-acid battery (such as a Car battery) loses its ability to hold a charge after it is kept in a discharged state too long The non-glycosylated form of prolactin is the dominant form of prolactin that is secreted by the pituitary gland. The pituitary gland, or hypophysis, is an Endocrine gland about the size of a Pea.

Little prolactin is apparently the result of removal of some amino acids, whereas big prolactin can be the product of interaction of several prolactin molecules.

Pit-1 is a transcription factor that binds to the prolactin gene at several sites to allow for the production of prolactin in the pituitary gland. In the field of Molecular biology, a transcription factor (sometimes called a sequence-specific DNA binding factor is a Protein that binds to specific sequences A key regulator of prolactin production is estrogens that enhance growth of prolactin-producing cells and stimulate prolactin production directly, as well as suppressing dopamine. Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Dopamine is a Hormone and Neurotransmitter occurring in a wide variety of animals including both vertebrates and invertebrates

Human prolactin receptors are insensitive to mouse prolactin^[8].

Prolactin receptor

See prolactin receptor

Diagnostic use

Prolactin levels may be checked as part of a sex hormone workup, as elevated prolactin secretion can suppress the secretion of FSH and GnRH, leading to hypogonadism, and sometimes causing erectile dysfunction in men. The prolactin receptor —encoded by a gene on Chromosome 5p13-14—interacts with the Prolactin molecule as a Transmembrane receptor. Hypogonadism is a medical term for a defect of the Reproductive system that results in lack of function of the Gonads ( ovaries or testes)

Prolactin levels may be of some use in distinguishing epileptic seizures from psychogenic non-epileptic seizures. An epileptic seizure is caused by excessive and/or hypersynchronous electrical Neuronal activity and is usually self-limiting Psychogenic non-epileptic seizures are a manifestation or a form of Conversion disorder. The serum prolactin level usually rises following an epileptic seizure. ^[9]

Conditions causing elevated prolactin secretion

Hyperprolactinaemia is the term given to having too-high levels of prolactin in the blood. Hyperprolactinaemia ( BrE) or hyperprolactinemia ( AmE) is the presence of abnormally-high levels of Prolactin in the blood

• Prolactinoma
• Excess thyrotropin-releasing hormone (TRH), usually in primary hypothyroidism
• Many anti-psychotic medications
• Emotional stress

Conditions causing decreased prolactin

• Bulimia
• Excess dopamine

Use of breastfeeding as contraceptive

The World Health Organization states that demand breastfeeding is more than 98% effective as a contraceptive in the first six months postpartum. A prolactinoma is a Benign Tumor ( Adenoma) of the Pituitary gland that produces a Hormone called Prolactin. Thyrotropin-releasing hormone ( TRH) also called thyrotropin-releasing factor ( TRF) thyroliberin or protirelin, is a tropic Hypothyroidism is the disease state in humans and animals caused by insufficient production of Thyroid hormone by the Thyroid gland. Antipsychotics are a group of Psychoactive drugs commonly but not exclusively used to treat Psychosis, which is typified by Schizophrenia. Bulimia nervosa is an Eating disorder characterized by recurrent Binge eating, followed by compensatory behaviors referred to as "purging" Dopamine is a Hormone and Neurotransmitter occurring in a wide variety of animals including both vertebrates and invertebrates Birth control, sometimes synonymous with contraception, is a regimen of one or more actions devices or Medications followed in order to deliberately prevent Postnatal ( Latin for 'after birth' from post meaning "after" and natalis meaning "of birth" is the period beginning immediately after This effect is said to be responsible for the natural spacing of children seen in countries where contraception is not widely available, and is thought to be an evolutionary means of ensuring adequate care is provided to each newborn. The 98% effectiveness applies only if three criteria are met:

1. The mother has had no menstrual periods at all (amenorrhea)
2. The baby is exclusively breast-fed
3. It is six months or less since birth. Amenorrhoea ( BE) amenorrhea ( AmE) or amenorrhœa, is the absence of a Menstrual period in a woman of reproductive age

If one or more of these conditions are broken, lactational amenorrhea is no longer a reliable form of birth control. This contraceptive method is highly effective as long as the three conditions stated above are fulfilled. Further, the WHO suggests that a woman that is still amenorrheic has a less-than-5% chance of getting pregnant in the first year of her baby's life, as long as she is still breastfeeding on demand.

See also

• weaning
• breast-feeding
• baby food
• male lactation
• hormones
• Prolactin receptor
• Prolactinoma
• Hyperprolactinaemia
• PRLH
• Psychogenic non-epileptic seizures

References

External links

• Pathophysiology of Endocrine System - Prolactin at colostate.edu
• MedlinePlus Encyclopedia Prolactin
• med/1098 at eMedicine - "Hyperprolactinemia"
• med/1914 at eMedicine - "Prolactin Deficiency"

MedlinePlus, with the MedlinePlus Medical Encyclopedia, is a website network containing Health information from the world's largest medical Library eMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely two medical doctors eMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely two medical doctors

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