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Prolactin

Function and Effects: – Stimulates mammary glands for milk production during pregnancy – Influences lipid synthesis in mammary and adipose cells – Inhibits sex hormone […]

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Function and Effects:
– Stimulates mammary glands for milk production during pregnancy
– Influences lipid synthesis in mammary and adipose cells
– Inhibits sex hormone levels
– Acts as a weak gonadotropin in humans
– Enhances testosterone secretion in males
– Stimulates maternal behavior
– Impacts lipid synthesis differently in mammary and adipose cells
– Suppresses gonadotropin-releasing hormone secretion
– Enhances luteinizing hormone-receptors in Leydig cells
– Promotes proliferation of oligodendrocyte precursor cells
– Regulates reproductive functions in fish
– Controls hair growth and moulting in skin
– Regulates feather moulting in birds
– Initiates pseudopregnancy in rodents

Regulation:
– Produced in various human tissues
– Controlled by Pit-1 transcription factor
– Inhibited by dopamine and stimulated by estrogens
– Interaction with neuropeptides is under active research
– Specific prolactin-releasing hormone not identified
– Mice react to VIP and TRH, but details are still under research
– Extrapituitary prolactin is controlled by a superdistal promoter
– Progesterone upregulates prolactin synthesis in the endometrium
– Breast and other tissues may express the Pit-1 promoter
– Prolactin levels peak during REM sleep and in the early morning
– High estrogen and progesterone levels during pregnancy increase prolactin levels
– Sucking on the nipple triggers prolactin secretion and oxytocin release
– Prolactin levels can rise after exercise, high-protein meals, and stress

Structure and Isoforms:
– Prolactin has significant structural heterogeneity
– Three sizes of prolactin: little prolactin, big prolactin, big big prolactin
– Non-glycosylated form is predominant
– Levels of larger variants higher in early postpartum period
– Other variants exist with molecular masses of 14, 16, and 22 kDa

Prolactin Receptor:
– Present in various tissues including mammillary glands, ovaries, and skeletal muscle
– Prolactin binding causes receptor dimerization and activation of Janus kinase 2
– Human prolactin receptors are insensitive to mouse prolactin
– Activation leads to the JAK-STAT pathway and other kinase activations

Diagnostic Use and Clinical Implications:
– Prolactin levels checked in sex hormone workups
– Elevated levels associated with hypogonadism and erectile dysfunction
– Differentiates epileptic seizures from psychogenic non-epileptic seizures
– Upper normal thresholds: 25µg/L for women, 20µg/L for men
– Diagnosing deficiency: below 3µg/L in women, 5µg/L in men
– Hyperprolactinemia disrupts the hypothalamic-pituitary-gonadal axis

Prolactin (Wikipedia)

Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. Prolactin is secreted from the pituitary gland in response to eating, mating, estrogen treatment, ovulation and nursing. It is secreted heavily in pulses in between these events. Prolactin plays an essential role in metabolism, regulation of the immune system and pancreatic development.

PRL
Available structures
PDBOrtholog search: PDBe RCSB
Identifiers
AliasesPRL, GHA1, prolactin
External IDsOMIM: 176760 MGI: 97762 HomoloGene: 732 GeneCards: PRL
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_000948
NM_001163558

NM_001163530
NM_011164

RefSeq (protein)

NP_000939
NP_001157030

NP_001157002
NP_035294

Location (UCSC)Chr 6: 22.29 – 22.3 MbChr 13: 27.24 – 27.25 Mb
PubMed search
Wikidata
View/Edit HumanView/Edit Mouse

Discovered in non-human animals around 1930 by Oscar Riddle and confirmed in humans in 1970 by Henry Friesen, prolactin is a peptide hormone, encoded by the PRL gene.

In mammals, prolactin is associated with milk production; in fish it is thought to be related to the control of water and salt balance. Prolactin also acts in a cytokine-like manner and as an important regulator of the immune system. It has important cell cycle-related functions as a growth-, differentiating- and anti-apoptotic factor. As a growth factor, binding to cytokine-like receptors, it influences hematopoiesis and angiogenesis and is involved in the regulation of blood clotting through several pathways. The hormone acts in endocrine, autocrine, and paracrine manners through the prolactin receptor and numerous cytokine receptors.

Pituitary prolactin secretion is regulated by endocrine neurons in the hypothalamus. The most important of these are the neurosecretory tuberoinfundibulum (TIDA) neurons of the arcuate nucleus that secrete dopamine (a.k.a. Prolactin Inhibitory Hormone) to act on the D2 receptors of lactotrophs, causing inhibition of prolactin secretion. Thyrotropin-releasing hormone has a stimulatory effect on prolactin release, although prolactin is the only anterior pituitary hormone whose principal control is inhibitory.

Several variants and forms are known per species. Many fish have variants prolactin A and prolactin B. Most vertebrates, including humans, also have the closely related somatolactin. In humans, 14, 16, and 22 kDa variants exist.

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