出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2014/11/04 14:09:49」(JST)
性腺刺激ホルモン放出ホルモン(Gonadotropin releasing hormone, GnRH)はFSHとLHを下垂体前葉から分泌させるペプチドホルモンである。これは視床下部で合成、分泌される。
GnRH前駆体の遺伝子は第8番染色体に位置する。この前駆体は92のアミノ酸からなり、デカペプチド(10のアミノ酸)のGnRHへ加工される。
GnRHの姿は1977年ノーベル賞受賞者のロジェ・ギルマンとアンドリュー・ウィクター・シャリーにより次の様に明らかにされた:pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly CONH2.
GnRHは特定の神経細胞で産生され、その神経末端から放出される神経ホルモンと考えられている。視床下部のGnRHの産生の主要エリアは視索前野で、そこに殆どのGnRH分泌ニューロンが含まれている。GnRHは正中隆起の高さで門脈血流へ分泌され、性腺刺激ホルモン産生細胞の膜上にある受容体を活性化させる。GnRHはタンパク質分解によって数分の内に分解される。
下垂体ではGnRHはFSHとLHの合成と分泌を刺激し、その過程はGnRHパルスの頻度と強さ、それからアンドロゲンとエストロゲンのフィードバックである。GnRH分泌には性差が存在し、男性ではGnRHは一定の頻度で分泌されるのに対し、女性では月経周期によってその頻度が異なり、排卵前にGnRHが急激に高まる。GnRHの拍動性は全ての脊椎動物において見られ、正しい生殖機能を確実にするのに不可欠である。従って雌ではホルモンであるGnRHが単独で卵胞成長、排卵、黄体の保持という複合した過程、そして雄では精子形成をコントロールする。
GnRHの活性は子供のうちは非常に低い。繁殖年齢ではパルス活性は複数のフィードバックによりコントロールされた順調な繁殖機能へ重大な意味をもつ。しかしながら、妊娠するとGnRH活性は要求されなくなる。パルス活性は視床下部・下垂体どちらかでの不全(即ち視床下部抑制)または器官の傷害(外傷、腫瘍)により乱される。プロラクチンの上昇によりGnRH活性は低下する。対照的に高インスリン血症ではパルス活性を上昇させ、多嚢胞性卵巣症候群(PCOS)で見られる様なLHとFSHの活性の障害へ導く。GnRHの形成はカルマン症候群では先天的に存在しない。ドーパミンはGnRH活性を低下させるらしい。
GnRHは視床下部と下垂体以外の例えば胎盤や性腺にも見られ、そこでの役割はよく判っていない。
GnRHはゴナドレリン塩酸塩(Factrel)として注射して使われる。研究によって、これが注入ポンプシステムを通して視床下部性性腺機能低下症の患者へ排卵を誘発させる事が明らかになった。
GnRHが合成され手に入るようになった一方で、短い半減期の所為でそれを医療へ用いるには注入ポンプを要する。GnRHのデカペプチド構造の改変により性腺刺激ホルモンへ刺激(GnRHアゴニスト)または抑制(GnRHアンタゴニスト)の作用をする類似体の薬物に行き着いた。重要なことに、ダウンレギュレーションを通してアゴニストはまた延長された抑制効果を行使することができる。
|
Gonadotropin-releasing hormone 1 (luteinizing-releasing hormone) | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
from PDB 1YY1 |
|||||||||||||
Identifiers | |||||||||||||
Symbols | GNRH1 ; GNRH; GRH; HH12; LHRH; LNRH | ||||||||||||
External IDs | OMIM: 152760 MGI: 95789 HomoloGene: 641 GeneCards: GNRH1 Gene | ||||||||||||
|
|||||||||||||
RNA expression pattern | |||||||||||||
More reference expression data | |||||||||||||
Orthologs | |||||||||||||
Species | Human | Mouse | |||||||||||
Entrez | 2796 | 14714 | |||||||||||
Ensembl | ENSG00000147437 | ENSMUSG00000015812 | |||||||||||
UniProt | P01148 | P13562 | |||||||||||
RefSeq (mRNA) | NM_000825 | NM_008145 | |||||||||||
RefSeq (protein) | NP_000816 | NP_032171 | |||||||||||
Location (UCSC) | Chr 8: 25.28 – 25.28 Mb |
Chr 14: 67.75 – 67.75 Mb |
|||||||||||
PubMed search | [1] | [2] | |||||||||||
This box:
|
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2013) |
Gonadotropin-releasing hormone (GnRH), also known as Luteinizing-hormone-releasing hormone (LHRH) and luliberin, is a trophic peptide hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is synthesized and released from GnRH neurons within the hypothalamus. The peptide belongs to gonadotropin-releasing hormone family. It constitutes the initial step in the hypothalamic–pituitary–gonadal axis.
The gene, GNRH1, for the GnRH precursor is located on chromosome 8. In mammals, the linear decapeptide end-product is synthesized from a 92-amino acid preprohormone in the preoptic anterior hypothalamus. It is the target of various regulatory mechanisms of the hypothalamic–pituitary–gonadal axis, such as being inhibited by increased estrogen levels in the body.
The identity of GnRH was clarified by the 1977 Nobel Laureates Roger Guillemin and Andrew V. Schally:
pyroGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2
As is standard for peptide representation, the sequence is given from amino terminus to carboxyl terminus; also standard is omission of the designation of chirality, with assumption that all amino acids are in their L- form. The abbreviations appearing are to standard proteinogenic amino acids, except for pyroGlu, which refers to pyroglutamic acid, a derivative of glutamic acid. The NH2 at the carboxyl terminus indicates that rather than terminating as a free carboxylate, it terminates as a carboxamide.
GnRH is considered a neurohormone, a hormone produced in a specific neural cell and released at its neural terminal. A key area for production of GNRH is the preoptic area of the hypothalamus, which contains most of the GnRH-secreting neurons. GnRH neurons originate in the nose and migrate into the brain, where they are scattered throughout the medial septum and hypothalamus and connected by very long >1-millimeter-long dendrites. These bundle together so they receive shared synaptic input, a process that allows them to synchronize their GnRH release.[1]
GnRH is secreted in the hypophysial portal bloodstream at the median eminence. The portal blood carries the GnRH to the pituitary gland, which contains the gonadotrope cells, where GnRH activates its own receptor, gonadotropin-releasing hormone receptor (GnRHR), a seven-transmembrane G-protein-coupled receptor that stimulates the beta isoform of Phosphoinositide phospholipase C, which goes on to mobilize calcium and protein kinase C. This results in the activation of proteins involved in the synthesis and secretion of the gonadotropins LH and FSH. GnRH is degraded by proteolysis within a few minutes.
At the pituitary, GnRH stimulates the synthesis and secretion of the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH). These processes are controlled by the size and frequency of GnRH pulses, as well as by feedback from androgens and estrogens. Low-frequency GnRH pulses lead to FSH release, whereas high-frequency GnRH pulses stimulate LH release.[2]
There are differences in GnRH secretion between females and males. In males, GnRH is secreted in pulses at a constant frequency; however, in females, the frequency of the pulses varies during the menstrual cycle, and there is a large surge of GnRH just before ovulation.[citation needed]
GnRH secretion is pulsatile in all vertebrates [there is no evidence that this is correct -- the only empirical evidence to date is for a handful of mammals], and is necessary for correct reproductive function. Thus, a single hormone, GnRH1, controls a complex process of follicular growth, ovulation, and corpus luteum maintenance in the female, and spermatogenesis in the male.
GnRH activity is very low during childhood, and is activated at puberty or adolescence. During the reproductive years, pulse activity is critical for successful reproductive function as controlled by feedback loops. However, once a pregnancy is established, GnRH activity is not required. Pulsatile activity can be disrupted by hypothalamic-pituitary disease, either dysfunction (i.e., hypothalamic suppression) or organic lesions (trauma, tumor). Elevated prolactin levels decrease GnRH activity. In contrast, hyperinsulinemia increases pulse activity leading to disorderly LH and FSH activity, as seen in polycystic ovary syndrome (PCOS). GnRH formation is congenitally absent in Kallmann syndrome.
The GnRH neurons are regulated by many different afferent neurons, using several different transmitters (including norepinephrine, GABA, glutamate). For instance, dopamine appears to stimulate LH release (through GnRH) in estrogen-progesterone-primed females; dopamine may inhibit LH release in ovariectomized females.[3] Kisspeptin appears to be an important regulator of GnRH release.[4] GnRH release can also be regulated by estrogen. It has been reported that there are kisspeptin-producing neurons that also express estrogen receptor alpha.[5]
GnRH is found in organs outside of the hypothalamus and pituitary, and its role in other life processes is poorly understood. For instance, there is likely to be a role for GnRH1 in the placenta and in the gonads. GnRH and GnRH receptors are also found in cancers of the breast, ovary, prostate, and endometrium.[6]
GnRH production/release is one of the few confirmed examples of behavior influencing hormones, rather than the other way around.[citation needed] Cichlid fish that become socially dominant in turn experience an upregulation of GnRH secretion whereas cichlid fish that are socially subordinate have a down regulation of GnRH secretion.[7] Besides secretion, the social environment as well as their behavior affects the size of GnRH neurons. Specifically, males that are more territorial have larger GnRH neurons than males that are less territorial males. Differences are also seen in females, with breeding females having smaller GnRH neurons than controls females.[8] These examples suggest that GnRH is a socially regulated hormone.
GnRH activity influences a variety of sexual behaviors. Increased levels of GnRH facilitate sexual displays and behavior in females. GnRH injections enhance copulation solicitation (a type of courtship display) in white-crowned sparrows.[9] In mammals, GnRH injections facilitate sexual behavior of female display behaviors as shown with the musk shrew’s (Suncus murinus) reduced latency in displaying rump presents and tail wagging towards males.[10]
An elevation of GnRH raises males’ testosterone capacity beyond a male’s natural testosterone level. Injections of GnRH in male birds immediately after an aggressive territorial encounter results in higher testosterone levels than what is observed naturally during an aggressive territorial encounter.[11]
A compromised GnRH system has aversive effects on reproductive physiology and maternal behavior. In comparison to female mice with a normal GnRH system, female mice with a 30% decrease in GnRH neurons are poor caregivers to their offspring. These mice are more likely to leave their pups scattered rather than grouped together, and will take significantly longer to retrieve their pups.[12]
GnRH is available as gonadorelin hydrochloride (Factrel®) and gonadorelin diacetate tetrahydrate (Cystorelin®) for injectable use. It has a chemical composition and structure identical to the natural hormone, identified from porcine or ovine hypothalami. It is currently used for evaluating hypothalamic-pituitary gonadotropic function. Studies have described it being used via an infusion pump system to induce ovulation in patients with hypothalamic hypogonadism.
It is also used in veterinary medicine as a treatment for cattle with cystic ovarian disease.
Its analogue Leuprolide is used for continuous infusion, to treat Breast carcinoma, endometriosis, prostate carcinoma, and following research in the 1980s by researchers, including Dr. Florence Comite of Yale University, it was used to treat precocious puberty.[13][14] The analogue Deslorelin is used in veterinary reproductive control through a sustained-release implant.
While GnRH has been synthesized and become available, its short half-life requires infusion pumps for its clinical use. Modifications of the decapeptide structure of GnRH have led to GnRH1 analog medications that either stimulate (GnRH1 agonists) or suppress (GnRH antagonists) the gonadotropins. It is important to note that, through downregulation, agonists are also able to exert a prolonged suppression effect.
|date=
(help)
|
|
|
|
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
国試過去問 | 「111G020」「101B097」「109G033」 |
リンク元 | 「試験」「下垂体前葉ホルモン」「無月経」「高プロラクチン血症」「視床下部ホルモン」 |
拡張検索 | 「GnRHレセプター」「GnRH試験」「GnRH antagonist」 |
E
※国試ナビ4※ [111G019]←[国試_111]→[111G021]
A
※国試ナビ4※ [101B096]←[国試_101]→[101B098]
BE
※国試ナビ4※ [109G032]←[国試_109]→[109G034]
名称 | 構造 | 分泌細胞 | 下垂体前葉細胞 全細胞に対する 産生細胞の割合 |
染色性 | サブユニット | 残基数 (aa.) |
分子量 (kDa) |
その他 | ||
成長ホルモン | GH | ペプチド | somatotroph | 40-50% | 好酸性 | 1 | 191 | 22 | ||
プロラクチン | PRL | mammotroph | 10-25% | 好酸性 | 1 | 199 | 23 | |||
副腎皮質刺激ホルモン | ACTH | corticotroph | 0.1 | 好塩基性 | 嫌色素性 | 1 | 39 | 4.5 | POMC由来 | |
甲状腺刺激ホルモン | TSH | 糖タンパク | thyrotroph | 0.05 | 好塩基性 | 2 | α: 92, β:118 | 28 | αサブユニットは共通 | |
卵胞刺激ホルモン | FSH | gonadotroph | 10-15% | 好塩基性 | 2 | α: 92, β:111 | 32.6 | |||
黄体形成ホルモン | LH | 好塩基性 | 2 | α: 92, β:121 | 29.4 |
Table 333-1 Anterior Pituitary Hormone Expression and Regulation | |||||
Cell | corticotrope | somatotrope | lactotrope | thyrotrope | gonadotrope |
Tissue-specific transcription factor | T-Pit | Prop-1, Pit-1 | Prop-1, Pit-1 | Prop-1, Pit-1, TEF | SF-1, DAX-1 |
Fetal appearance | 6 weeks | 8 weeks | 12 weeks | 12 weeks | 12 weeks |
Hormone | POMC | GH | PRL | TSH | FSH LH |
Chromosomal locus | 2p | 17q | 6 | -6q; -1p | -11p; -19q |
Protein | ポリペプチド | 糖タンパク | |||
Amino acids | 266 (ACTH 1–39) | 191 | 199 | 211 | 210 204 |
Stimulators | CRH, AVP, gp-130 cytokines | GHRH, ghrelin, bromocriptine(1) | estrogen, TRH, VIP | TRH | GnRH, activins, estrogen |
Inhibitors | glucocorticoids | somatostatin, IGF-I | dopamine | T3, T4, dopamine, somatostatin, glucocorticoids | sex steroids, inhibin |
Target gland | adrenal | liver, other tissues | breast, other tissues | thyroid | ovary, testis |
Trophic effect | steroid production | IGF-I production, growth induction, insulin antagonism | milk production | T4 synthesis and secretion | sex steroid production, follicle growth, germ cell maturation |
原発性無月経 | 続発性無月経 | |
視床下部性無月経 | カルマン症候群 | 視床下部の機能障害 |
フレーリッヒ症候群 | 神経性食思不振症 | |
ローレンス・ムーン・ビードル症候群 | 体重減少性無月経 | |
プラダー・ウィリー症候群 | 高プロラクチン血症 | |
Chiari-Frommel症候群 | ||
Argonz-del Castillo症候群 | ||
下垂体性無月経 | 先天性ゴナドトロピン欠損症 | Sheehan症候群 |
empty sella症候群 | 下垂体腺腫 | |
Forbes-Albright症候群 | ||
Simmonds病 | ||
卵巣性無月経 | 性腺形成不全 | 早発卵巣機能不全 |
ターナー症候群 | 多嚢胞性卵巣症候群 | |
卵巣摘出 | ||
卵巣の放射線障害 | ||
子宮性無月経 | ロキタンスキー・キュスター・ハウザー症候群 | アッシャーマン症候群 |
子宮奇形 | 子宮内膜炎 | |
処女膜閉鎖 | 子宮摘出術後 | |
膣性無月経 | 処女膜閉鎖症 | |
膣閉鎖症 | ||
その他 | 半陰陽(先天性副腎過形成、アンドロゲン不応症) | Cushing症候群 |
Addison病 | ||
Basedow病 | ||
甲状腺機能低下症 | ||
糖尿病 | ||
生理的 | 妊娠、産褥、授乳、閉経 |
成長ホルモン放出ホルモン | somatotrpin-releasing hormone | SRH | GH分泌↑ |
ソマトスタチン | growth hormone-inhibiting factor / somatostatin | GIF | GH分泌↓ |
甲状腺刺激ホルモン放出ホルモン | thyroid-stimulating hormone-relaing hormone | TRH | TSH分泌↑ |
副腎皮質刺激ホルモン放出ホルモン | corticotropin-releasing hormone | CRH | ACTH分泌↑ |
ゴナドトロピン放出ホルモン | gonadotropin-releasing hormone | GnRH | FSH分泌↑、LH分泌↑ |
プロラクチン放出因子 | prolactin-releasing factor | PRF | prolactin分泌↑ |
プロラクチン抑制因子 | prolactin-inhibiting factor | PIF | prolactin分泌↓ |
.