Human chorionic gonadotropin Totally Explained

Everything about Human Chorionic Gonadotropin totally explained

,, | Name = Chorionic gonadotropin, beta polypeptide | HGNCid = 1886 | Symbol = CGB | AltSymbols =; CGB3; hCGB; HCG; MGC119822 | OMIM = 118860 | ECnumber = | Homologene = 37338 | MGIid = | Function = | Component = | Process = | Orthologs = }} Human chorionic gonadotropin (hCG) is a peptide hormone produced in pregnancy that's made by the embryo soon after conception and later by the syncytiotrophoblast (part of the placenta). Its role is to prevent the disintegration of the corpus luteum of the ovary and thereby maintain progesterone production that's critical for a pregnancy in humans. hCG may have additional functions; for instance, it's thought that hCG affects the immune tolerance of the pregnancy. Early pregnancy testing, in general, is based on the detection or measurement of hCG. Because hCG is produced also by some kinds of tumor, hCG is an important tumor marker, but it isn't known whether this production is a contributing cause or an effect of tumorigenesis.

Structure

Human chorionic gonadotropin is an oligosaccharide glycoprotein composed of 244 amino acids with a molecular mass of 36.7 kDa. Its total dimensions are 75×35×30 angstroms (7.5×3.5×3 nanometers).
It is heterodimeric, with an α (alpha) subunit identical to that of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and β (beta) subunit that's unique to hCG.

The α (alpha) subunit is 92 amino acids long and has dimensions 60×25×15 angstroms (6×2.5×1.5 nm).

The beta subunit of human chorionic gonadotropin is encoded by six highly-homologous genes that are arranged in tandem and inverted pairs on chromosome 19q13.3 - CGB (1, 2, 3, 5, 7, 8). The two subunits create a small hydrophobic core surrounded by a high surface area-to-volume ratio: 2.8 times that of a sphere. The vast majority of the outer amino acids are hydrophilic.

Function

Human chorionic gonadotropin interacts with the LHCG receptor and promotes the maintenance of the corpus luteum during the beginning of pregnancy, causing it to secrete the hormone progesterone. Progesterone enriches the uterus with a thick lining of blood vessels and capillaries so that it can sustain the growing fetus. Due to its highly-negative charge, hCG may repel the immune cells of the mother, protecting the fetus during the first trimester. It has also been hypothesized that hCG may be a placental link for the development of local maternal immunotolerance. For example, hCG-treated endometrial cells induce an increase in T cell apoptosis (dissolution of T-cells). These results suggest that hCG may be a link in the development of peritrophoblastic immune tolerance, and may facilitate the trophoblast invasion, which is known to expedite fetal development in the endometrium. It has also been suggested that hCG levels are linked to the severity of morning sickness in pregnant women.
Because of its similarity to LH, hCG can also be used clinically to induce ovulation in the ovaries as well as testosterone production in the testes. As the most abundant biological source is women who are presently pregnant, some organizations collect urine from gravidae to extract hCG for use in fertility treatment.
Human chorionic gonadotropin also plays a role in cellular differentiation/proliferation and may activate apoptosis.

Testing

Levels of hCG may be measured in the blood or urine. Most commonly, this is done as a pregnancy test, intended to indicate the presence or absence of an implanted embryo. Testing for hCG may also be done when diagnosing or monitoring germ cell and trophoblastic tumors.
Most tests employ a monoclonal antibody (MAb), which is specific to the β-subunit of hCG (βhCG). This procedure is employed to ensure that tests don't make false positives by confusing hCG with LH and FSH. (The latter two are always present at varying levels in the body, whereas the presence of hCG almost always indicates pregnancy.)

The urine test may be a chromatographic immunoassay or any of several other test formats, home-, physician's office-, or laboratory-based. Published detection thresholds range from 20 to 100 mIU/ml (milli International Units per milli-liter), depending on the brand of test. Early in pregnancy, more accurate results may be obtained by using the first urine of the morning when hCG levels are highest. When the urine is dilute (specific gravity less than 1.015), the hCG concentration may not be representative of the blood concentration, and the test may be falsely negative.

The serum test, using 2-4 mL of venous blood, is typically a chemiluminescent or fluorimetric immunoassay

Production

Like other gonadotropins, hCG can be extracted from urine or by genetic modification. Pregnyl, Follutein, Profasi, and Novarel use the former method, derived from the urine of pregnant women. Ovidrel, on the other hand, is a product of recombinant DNA.

Use with anabolic steroids

In the world of performance enhancing drugs, hCG is increasingly used in combination with various anabolic androgenic steroid (AAS) cycles.
When AAS are put into a male body, the body's natural negative-feedback loops cause the body to shut down its own production of testosterone via shutdown of the hypothalamic-pituitary-testicular axis (HPTA). High levels of AASs that mimic the body's natural testosterone trigger the hypothalamus to shut down its production of gonadotropin-releasing hormone (GnRH) from the hypothalamus. Without GnRH, the pituitary gland stops releasing luteinizing hormone (LH). LH normally travels from the pituitary via the blood stream to the testes, where it triggers the production and release of testosterone. Without LH, the testes shut down their production of testosterone, causing testicular atrophy.
In males, hCG mimics LH and helps restore and maintain testosterone production in the testes. As such, hCG is commonly used during and after steroid cycles to maintain and restore testicular size as well as endogenous testosterone production. However, if hCG is used for too long and in too high a dose, the resulting rise in natural testosterone will eventually inhibit its own production via negative feedback on the hypothalamus and pituitary.

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