View source for Human placental lactogen

{{Infobox protein
| Name = chorionic somatomammotropin hormone 1 (human placental lactogen)
| caption = Crystal Structure of Human Placental Lactogen.<ref name="pmid16546209">{{PDB|1Z7C}}; {{cite journal |vauthors=Walsh ST, Kossiakoff AA | title = Crystal structure and site 1 binding energetics of human placental lactogen | journal = J. Mol. Biol. | volume = 358 | issue = 3 | pages = 773–84 |date=May 2006 | pmid = 16546209 | doi = 10.1016/j.jmb.2006.02.038 | url = | issn = }}</ref>
| image = 1Z7C.pdb.png
| HGNCid = 2440
| Symbol = CSH1
| AltSymbols = 
| EntrezGene = 1442
| OMIM = 150200
| RefSeq = NM_001317
| UniProt = Q6PF11
| PDB = 
| ECnumber = 
| Chromosome = 17
| Arm = q
| Band = 22
| LocusSupplementaryData = -q24
}}
{{infobox protein
| Name = chorionic somatomammotropin hormone 2
| caption = 
| image = 
| width = 
| HGNCid = 2441
| Symbol = CSH2
| AltSymbols = 
| EntrezGene = 1443
| OMIM = 118820
| RefSeq = NM_020991
| UniProt = P01243
| PDB = 1Z7C
| ECnumber = 
| Chromosome = 17
| Arm = q
| Band = 22
| LocusSupplementaryData = -q24
}}

'''Human placental lactogen''' ('''hPL'''), also called '''human chorionic somatomammotropin''' ('''HCS'''), is a [[polypeptide]] [[placenta]]l hormone, the human form of [[placental lactogen]] ([[chorionic]] somatomammotropin). Its structure and function are similar to those of human [[growth hormone]]. It modifies the metabolic state of the mother during [[pregnancy]] to facilitate the energy supply of the [[fetus]]. hPL has anti-[[insulin]] properties. hPL is a hormone secreted by the [[syncytiotrophoblast]] during pregnancy.  Like [[human growth hormone]], hPL is encoded by genes on [[chromosome 17]]q22-24. It was identified in 1963.<ref name="pmid14068826">{{cite journal |vauthors=Josimovich JB, Atwood BL, Goss DA | title = Luteotrophic, Immunologic and Electrophoretic Properties of Human Placental Lactogen | journal = Endocrinology | volume = 73 | issue = | pages = 410–20 |date=October 1963 | pmid = 14068826 | doi = 10.1210/endo-73-4-410 }}</ref>

==Structure==
hPL [[molecular mass]] is 22,125 and contains single chain consisting of 191 [[amino acid]] residues that are linked by two [[disulfide bonds]] and the structure contains 8 helices.  A crystal structure of hPL was determined by [[X-ray diffraction]] to a resolution of [[Angstrom|2.0 Å]].<ref name="pmid16546209"/>

==Levels==
hPL is present only during pregnancy, with maternal serum levels rising  in relation to the growth of the fetus and placenta. Maximum levels are reached near term, typically to 5&ndash;7&nbsp;mg/L (5-7 micrograms/ml)<ref>{{Cite web|url=https://www.medscape.com/viewarticle/408910_2|title=Medscape Log In|website=www.medscape.com|access-date=2018-03-23}}</ref>.  Higher levels are noted in patients with [[multiple gestation]]. Little hPL enters the fetal circulation. Its [[biological half-life]] is 15 minutes.

==Physiologic function==
hPL affects the metabolic system of the maternal organism in the following manners:

* In a [[bioassay]], hPL mimics the action of [[prolactin]], yet it is unclear whether hPL has any role in human [[lactation]].
* Metabolic:
** ↓ maternal [[insulin]] sensitivity, leading to an increase in maternal blood glucose levels. 
** ↓ maternal glucose utilization, which helps ensure adequate fetal nutrition (the mother responds by increasing beta cells). Chronic [[hypoglycemia]] leads to a rise in hPL.
** ↑ [[lipolysis]] with  the release of [[free fatty acid]]s.  With fasting and release of hPL, free fatty acids become available for the maternal organism as fuel,  so that relatively more [[glucose]] can be utilized by the fetus. Also, [[ketone]]s formed from free fatty acids can cross the [[placenta]] and be used by the fetus.
These functions help support fetal nutrition even in the case of maternal [[malnutrition]].

hPL is a potent [[agonist]] of the [[prolactin receptor]] and a weak agonist of the [[growth hormone receptor]].<ref name="JamesonGroot2015">{{cite book|author1=J. Larry Jameson|author2=Leslie J. De Groot|title=Endocrinology: Adult and Pediatric E-Book|url=https://books.google.com/books?id=xmLeBgAAQBAJ&pg=PA2490|date=25 February 2015|publisher=Elsevier Health Sciences|isbn=978-0-323-32195-2|pages=2490–}}</ref>

===Prolactin-like activity===
hPL has been found to bind to the prolactin receptor with equal [[affinity (pharmacology)|affinity]] to that of prolactin in rabbit milk fat gobule membrane, and hPL and prolactin have been found to possess very similar lactogenic activity ''[[in vitro]]'' in mouse and rat [[mammary gland]] [[explant culture|explant]]s.<ref name="Neville2013">{{cite book|author=Margaret Neville|title=Lactation: Physiology, Nutrition, and Breast-Feeding|url=https://books.google.com/books?id=hNvTBwAAQBAJ&pg=PA150|date=11 November 2013|publisher=Springer Science & Business Media|isbn=978-1-4613-3688-4|pages=150–}}</ref> In addition, hPL has been found to stimulate [[DNA synthesis]] in human mammary [[fibroadenoma]] cells transplanted into mice, which suggests that hPL promotes the growth of the human mammary gland similarly to prolactin.<ref name="Neville2013" /> As hPL circulates at concentrations that are 100-fold higher than those of prolactin during pregnancy, these findings suggest that hPL may play an important role in human [[mammogenesis]] during this time.<ref name="Neville2013" /> However, the relative affinities of hPL and prolactin for the human prolactin receptor have yet to be published and the effects of hPL on normal human mammary epithelial tissue have not yet been investigated, and so a definitive role of hPL in human mammary gland development during pregnancy has not been established at present.<ref name="Neville2013" />

===Growth hormone-like activity===
hPL has weak actions similar to those of [[growth hormone]], causing the formation of [[protein]] [[Tissue (biology)|tissues]] in the same way that growth hormone, but 100 times more hPL than growth hormone is required to promote growth.<ref name="isbn81-8147-920-3">{{cite book |author= Guyton and Hall |title=Textbook of Medical Physiology |edition=11 |publisher=Saunders |location=Philadelphia |year=2005 |origyear= |pages= 1033 |quote= This hormone has weak actions similar to those of [[growth hormone]], causing the formation of [[protein]] [[Tissue (biology)|tissues]] in the same way that growth hormone. |isbn=81-8147-920-3 |oclc= |doi= |url= |accessdate=}}</ref> However, hPL has a blood level of more than 50 times that of hGH<ref>{{Cite journal|date=2016-06-01|title=Growth Hormone: Reference Range, Interpretation, Collection and Panels|url=https://emedicine.medscape.com/article/2089136-overview#a1}}</ref>, hence its effects must not be ignored. An enhancer for the human placental lactogen gene is found 2 kb downstream of the gene and participates in the cell-specific control gene expression.

==Clinical measurement==
While hPL has been used as an indicator of  fetal well-being and growth, other [[fetal testing]] methods have been found to be more reliable.{{citation needed|date=September 2012}} Also, normal pregnancies have been reported with undetectable maternal levels of hPL.

==See also==
*[[Placental lactogen]] in other species 
*[[Somatotropin family]]

==References==
{{reflist}}
* {{cite web |url=http://www.rcsb.org/pdb/explore/explore.do?structureId=1Z7C |title=RCSB Protein Data Bank - Structure Summary for 1Z7C - Crystal Structure of Human Placental Lactogen |format= |work= |accessdate=}}
* {{cite web |url=http://mend.endojournals.org/cgi/content/full/11/9/1223 |title=Human Chorionic Somatomammotropin Enhancer Function Is Mediated by Cooperative Binding of TEF-1 and CSEF-1 to Multiple, Low-Affinity Binding Sites  |format= |work= |accessdate=}}

== Further reading ==
* {{cite book |vauthors=Speroff L, Glass RH, Kase NG | title = Clinical gynecologic endocrinology and infertility | edition = Sixth | language = | publisher = Lippincott Williams & Wilkins | location = Hagerstwon, MD | year = 1999 | origyear = | pages = | quote = | isbn = 0-683-30379-1 | oclc = | doi = | url = | accessdate = }}

==External links==
*{{MeshName|Human+Placental+Lactogen}}

{{Hormones}}
{{Signaling peptide/protein receptor modulators}}
{{GH/IGF-1 axis signaling modulators}}

[[Category:Peptide hormones]]
[[Category:Hormones of the placenta]]
[[Category:Hormones of the pregnant female]]
[[Category:Human female endocrine system]]