Human placental lactogen
Encyclopedia
Human placental lactogen (HPL), also called human chorionic somatomammotropin, is a polypeptide placenta
l hormone. Its structure and function is similar to that 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
17q22-24. It was identified in 1963.
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 2.0 Å.
HPL mimics the action of prolactin
, yet it is unclear whether HPL has any role in human lactation
.
HPL affects the metabolic system of the maternal organism. HPL decreases maternal insulin
sensitivity, and, therefore, raises maternal blood glucose levels, whilst decreasing maternal glucose utilization, which helps ensure adequate fetal nutrition (the mother responds by pancreatic endocrine upregulation; this is thought to represent an evolutionary 'arms-race' resulting from the conflict of interest between mother and fetus). Chronic hypoglycemia
leads to a rise in HPL. HPL induces lipolysis
with the release of free fatty acids. 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.
This hormone has weak actions similar to those of growth hormone
, causing the formation of protein
tissues
in the same way that growth hormone, but 100 times more HPL than growth hormone is required to promote growth.
. 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.
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l hormone. Its structure and function is similar to that of human growth hormone
Growth hormone
Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
. It modifies the metabolic state of the mother during pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
to facilitate the energy supply of the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
. HPL has anti-insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
properties. HPL is a hormone secreted by the syncytiotrophoblast
Syncytiotrophoblast
Syncytiotrophoblast is the epithelial covering of the placenta villous tree. It is a unique tissue in that it is a multi-nucleated, terminally differentiated syncytium, extending to 13m^2...
during pregnancy. Like human growth hormone, HPL is encoded by genes on chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
17q22-24. It was identified in 1963.
Structure
HPL molecular weight is 22,125 and contains one unique chain consisting of 191 amino acidAmino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
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 2.0 Å.
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 5–7 mg/L. Higher levels are noted in patients with multiple gestation. Little HPL enters the fetal circulation. Its biologic half-life is 15 minutes.Function
In a bioassayBioassay
Bioassay , or biological standardization is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants...
HPL mimics the action of prolactin
Prolactin
Prolactin also known as luteotropic hormone is a protein that in humans is encoded by the PRL gene.Prolactin is a peptide hormone discovered by Henry Friesen...
, yet it is unclear whether HPL has any role in human lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
.
HPL affects the metabolic system of the maternal organism. HPL decreases maternal insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
sensitivity, and, therefore, raises maternal blood glucose levels, whilst decreasing maternal glucose utilization, which helps ensure adequate fetal nutrition (the mother responds by pancreatic endocrine upregulation; this is thought to represent an evolutionary 'arms-race' resulting from the conflict of interest between mother and fetus). Chronic hypoglycemia
Hypoglycemia
Hypoglycemia or hypoglycæmia is the medical term for a state produced by a lower than normal level of blood glucose. The term literally means "under-sweet blood"...
leads to a rise in HPL. HPL induces lipolysis
Lipolysis
Lipolysis is the breakdown of lipids and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation. The process produces Ketones, which are found in large quantities in ketosis, a metabolic state that occurs when the liver...
with the release of free fatty acids. With fasting and release of HPL, free fatty acids become available for the maternal organism as fuel, so that relatively more glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
can be utilized by the fetus. Also, ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s formed from free fatty acids can cross the placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
and be used by the fetus. These functions help support fetal nutrition even in the case of maternal malnutrition.
This hormone has weak actions similar to those of growth hormone
Growth hormone
Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
, causing the formation of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
tissues
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
in the same way that growth hormone, but 100 times more HPL than growth hormone is required to promote growth.
. 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.