This is a working overview of selectivity, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-02-22 and is reviewed periodically as new material appears.
Signal transduction begins when the peptide binds GHSR-1a on pituitary somatotrophs. The receptor couples to Gq/11 proteins, activating phospholipase C, which cleaves phosphatidylinositol bisphosphate into inositol trisphosphate and diacylglycerol. Inositol trisphosphate releases calcium from intracellular stores, and the resulting rise in cytosolic calcium drives growth hormone vesicle fusion. Concurrent Gs coupling and cyclic AMP elevation have also been reported, and the relative contribution of each arm to the overall secretory response is not fully settled.
Structural features distinguish the molecule from earlier secretagogues. An alpha-aminoisobutyric acid residue near the N-terminus and a D-naphthylalanine substitution increase receptor affinity, while C-terminal amidation improves resistance to exopeptidases. These modifications are associated with reduced stimulation of appetite and of the hypothalamic-pituitary-adrenal axis compared with hexarelin or growth hormone releasing peptide-6. Whether the same profile applies at every dose level studied is a matter of ongoing investigation rather than settled consensus.
现有文献多来自小规模、短期的研究，涉及生长激素缺乏、术后肠麻痹等方向。长期使用是否导致受体脱敏，以及重复给药后效应是否衰减，仍属开放问题。不同研究之间的剂量、给药途径和受试者特征差异较大，因此结论外推需谨慎。关于临床获益的确切证据尚不充分，需要更大规模的对照试验来澄清。
Ipamorelin 是一种合成五肽，在 20 世纪 90 年代被报道为生长激素促分泌剂。其结构基于胃饥饿素受体激动剂的设计思路，但并非天然激素。早期药理学研究显示，它可刺激垂体释放生长激素，而对应激激素轴的影响相对较小。该化合物常被用作研究生长激素调节通路的工具分子。
在机制层面，ipamorelin 与生长激素促分泌受体 1a 型结合，该受体也介导胃饥饿素的多种效应。受体激活后，细胞内信号促进生长激素从垂体前叶释放。由于对促肾上腺皮质激素和皮质醇的刺激较弱，它被视为选择性较高的促分泌剂。这种选择性在动物模型和少量人体研究中被观察到，但人体数据仍然有限。
| Property | Value | Notes |
|---|---|---|
| Molecular formula | C38H49N9O5 | Reported for the free peptide |
| Molecular mass | 711.85 Da | Monoisotopic value |
| Residue motif | Aib-His-D-2-Nal-D-Phe-Lys-NH2 | Non-natural residues at positions one and three |
| Primary target | GHSR-1a | Ghrelin receptor, G protein coupled |
| Reported plasma half-life | About two hours | Values vary with assay and subject group |
Selectivity is the property most often attached to this peptide. Published animal and early human studies record increases in growth hormone release after administration, with adrenocorticotropic hormone and cortisol responses remaining small by comparison. Effects on appetite-related pathways also appear weaker than those reported for several earlier secretagogues. Reviews that compare members of the growth hormone secretagogue family cite these findings frequently, though the receptor-level explanation for the selectivity continues to be debated rather than settled.
Ipamorelin is a synthetic pentapeptide classified as a growth hormone secretagogue. Its sequence, Aib-His-D-2-Nal-D-Phe-Lys-NH2, combines three non-proteinogenic residues with a C-terminal amide. The N-terminal aminoisobutyric acid unit and the two aromatic D-amino acids distinguish it from peptides assembled only from standard L-amino acids. Its formula is C38H49N9O5, corresponding to an average mass near 711.9 Da. At neutral pH the molecule carries a net positive charge, a property that shapes its behaviour in chromatographic and electrophoretic systems.
At the receptor level, ipamorelin binds GHS-R1a and triggers signaling through Gq-coupled pathways. Activation leads to calcium release and downstream effects in pituitary somatotroph cells. These events promote the release of growth hormone into circulation. The response depends on the presence of the receptor and on the physiological state of the animal or tissue studied. Because the receptor is also found in other tissues, effects beyond the pituitary have been examined in laboratory models, though the extent of those effects remains an area of ongoing study.
One distinguishing feature reported in animal studies is selectivity. Ipamorelin stimulated growth hormone release with limited elevation of adrenocorticotropic hormone or cortisol compared with earlier secretagogues such as GHRP-6. This pattern has been described as more selective for the growth hormone axis. The finding comes mainly from preclinical work, and the degree to which it holds across species and doses is not fully settled. Reports also describe effects on gastric motility in animal models, suggesting activity outside the pituitary, though the clinical relevance of this observation is uncertain.
Ipamorelin is a synthetic pentapeptide that acts on the growth hormone secretagogue receptor, also known as the ghrelin receptor. Its sequence contains five amino acid residues, including a non-natural residue that increases stability against enzymatic breakdown. The compound was developed in the 1990s as part of research into small peptides that stimulate pituitary hormone release. Unlike larger protein hormones, it can be produced by solid-phase peptide synthesis and characterized by standard analytical methods.
The lignans are a large group of low molecular weight polyphenols found in plants, particularly seeds, whole grains, and vegetables. The name derives from the Latin word for "wood". Lignans are precursors to phytoestrogens. They may play a role as antifeedants in the defense of seeds and plants against herbivores.
Ohmefentanyl (also known as β-hydroxy-3-methylfentanyl, OMF and RTI-4614-4) is an extremely potent opioid analgesic drug which selectively binds to the μ-opioid receptor. There are eight possible stereoisomers of ohmefentanyl. These stereoisomers are among the most potent μ-opioid receptor agonists known, comparable to super-potent opioids such as carfentanil and etorphine which are only legally used for tranquilizing large animals such as elephants in veterinary medicine. In mouse studies, the most active stereoisomer, 3R,4S,βS-ohmefentanyl, was 28 times more powerful as a painkiller than fentanyl, the chemical from which it is derived, and 6300 times more powerful than morphine. Ohmefentanyl has three stereogenic centers and eight stereoisomers, which are named F9201–F9208. Researchers are studying the different pharmaceutical properties of these isomers. The 4″-fluoro analogue (i.e., substituted on the phenethyl ring) of the 3R,4S,βS isomer of ohmefentanyl is one of the most potent opioid agonists yet discovered, possessing an analgesic potency approximately 18,000 times that of morphine. Other analogues with potency higher than that of ohmefentanyl itself include the 2′-fluoro derivative (i.e., substituted on the aniline phenyl ring), and derivatives where the N-propionyl group was replaced by N-methoxyacetyl or 2-furamide groups, or a carboethoxy group is added to the 4-position of the piperidine ring. The latter is listed as being up to 30,000 times more potent than morphine.
== Medical uses == Metenolone, as its esters, is used almost exclusively in the treatment of anemia due to bone marrow failure. It has also been used to treat wasting syndromes due to major surgery, infection, long-term corticosteroid therapy, malnutrition, or other causes. It has also been used to treat osteoporosis and sarcopenia, to inhibit the natural loss of muscle mass with aging, and to promote weight gain in underweight premature infants and children.
A person with type 1 diabetes should balance insulin delivery to manage their blood glucose level. Occasionally, insufficient insulin can result in hyperglycemia. The appropriate response is to take a correction dose of insulin to reduce the blood sugar level and to consider adjusting the insulin regimen to deliver additional insulin in the future to prevent hyperglycemia. Conversely, excessive insulin delivery may result in hypoglycemia. The appropriate response is to treat the hypoglycemia and to consider adjusting the regimen to reduce insulin in the future. Somogyi and others have claimed that if prolonged hypoglycemia is untreated, then stress due to low blood sugar can result in a high blood glucose rebound. The physiological mechanisms driving the rebound are defensive. When the blood glucose level falls below normal, the body responds by releasing the endocrine hormone glucagon as well as the stress hormones epinephrine, cortisol and growth hormone. Glucagon facilitates release of glucose from the liver that raises the blood glucose immediately; the stress hormones cause insulin resistance for several hours, sustaining the elevated blood sugar.
Biomass is a form of renewable energy useful as fuel and as a source of some chemical products. Relative to coal and petroleum however, the energy content of biomass is low. Compared to traditional fossil fuels, biomass has a high oxygen content. Its carbon is partially combusted, so to speak. One such notable example is the production of bio-ethanol. There is a general classification of biomass that is produced or sourced for conversion processes. Biofuels such as bioethanol and biodiesel, and bioplastics, are typically derived from primary or “first-generation” source energy-dense plants and oils such as rapeseed, sugarcane, or corn. Their high content of sugars and oils makes them ideal as feedstocks, however, there are drawbacks to their use. As well as inflating the price of the chosen crop due to increased demand, arable land that would otherwise be used to grow food for human and animal consumption is rendered unavailable. Secondary or “second-generation” source biomass encompasses a much wider variety of plant and animal matter. It may be derived from a relatively pure source, such as wood chippings or grass, or it may be a less well defined solid waste stream. This type of biomass is far more challenging to work with, as it contains a more varied mixture of compounds that cannot be easily converted into useful products.
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=== Other reactions of biochemical significance === Homocysteine can cyclize to give homocysteine thiolactone, a five-membered heterocycle. Because of this "self-looping" reaction, homocysteine-containing peptides tend to cleave themselves by reactions generating oxidative stress. Homocysteine also acts as an allosteric antagonist at Dopamine D2 receptors. It has been proposed that both homocysteine and its thiolactone may have played a significant role in the appearance of life on the early Earth.
Union leaders in the Congress of Industrial Organizations (CIO) vigorously campaigned for Truman in the 1948 election based upon a (never fulfilled) promise to repeal Taft–Hartley. Truman won, but a union-backed effort in Ohio to defeat Taft in 1950 failed in what one author described as "a shattering demonstration of labor's political weaknesses".
Aphids and other hemipteran insects secrete a sweet liquid called honeydew, when they feed on plant sap. The sugars in honeydew are a high-energy food source, which many ant species collect. In some cases, the aphids secrete the honeydew in response to ants tapping them with their antennae. The ants in turn keep predators away from the aphids and will move them from one feeding location to another. When migrating to a new area, many colonies will take the aphids with them, to ensure a continued supply of honeydew. Ants also tend mealybugs to harvest their honeydew. Mealybugs may become a serious pest of pineapples if ants are present to protect mealybugs from their natural enemies. Myrmecophilous (ant-loving) caterpillars of the butterfly family Lycaenidae (e.g., blues, coppers, or hairstreaks) are herded by the ants, led to feeding areas in the daytime, and brought inside the ants' nest at night. The caterpillars have a gland which secretes honeydew when the ants massage them. The chemicals in the secretions of Arhopala japonica alter the behavior of attendant Pristomyrmex punctatus workers, making them less aggressive and stationary. The relationship, formerly characterized as "mutualistic", is now considered as possibly a case of the ants being parasitically manipulated by the caterpillars. Some caterpillars produce vibrations and sounds that are perceived by the ants. A similar adaptation can be seen in grizzled skipper butterflies that emit vibrations by expanding their wings in order to communicate with ants, which are natural predators of these butterflies.
=== Post mortem or in tissue biopsies === Amyloid beta can be measured semiquantitatively with immunostaining, which also allows one to determine location. Amyloid beta may be primarily vascular, as in cerebral amyloid angiopathy, or in amyloid plaques in white matter. One sensitive method is ELISA which is an immunosorbent assay which utilizes a pair of antibodies that recognize amyloid beta. Atomic force microscopy, which can visualize nanoscale molecular surfaces, can be used to determine the aggregation state of amyloid beta in vitro. Vibrational microspectroscopy is a label-free method that measures the vibration of molecules in tissue samples. Amyloid proteins like Aβ can be detected with this technique because of their high content of β-sheet structures. Dual polarisation interferometry is an optical technique which can measure early stages of aggregation by measuring the molecular size and densities as the fibrils elongate. These aggregate processes can also be studied on lipid bilayer constructs.
On Lee Kuan Yew's death in March 2015, Mahathir wrote an entry on his blog, expressing grief at the news. Although he often disagreed with Lee, Mahathir wrote that he bore him no enmity for the differences of opinion on the direction of Singapore's development, and that ASEAN had lost the strong leadership of both Lee and Suharto of Indonesia, who had died in 2008. Some analysts observed that with Lee's death, Mahathir was the last of the "Old Guard" of Southeast Asia. On the anniversary of Lee's death, Mahathir told the media that Singaporeans must recognise Lee's contributions towards industrialising Singapore. He said that he does not view Lee "as an enemy and all that, but as a Singapore leader who had his own stand that was not the same with the stand of Malaysia".
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=== THC vis-à-vis CBD === During the selective breeding process for medical marijuana, THC:CBD ratios are accounted for and accommodated to the needs of the client's preference/illness. Due to the large genetic diversity and different geographical climates and environments, a wide range of strains and properties exist. THC is associated with the psychoactive high, while CBD is not psychoactive and is purported to have medicinal properties. However, conversion of CBD to THC can occur when CBD is heated to temperatures between 250–300 °C, potentially leading to its partial transformation into THC.
== Diagnosis == In order to qualify a patient's condition as BSS, the bending angle must be greater than 45 degrees. While the presence of the condition is very easy to note, the cause of the condition is much more difficult to discern. Conditions not considered to be BSS include vertebral fractures, previously existing conditions, and ankylosing spondylitis. Lower-back CT scans and MRIs can typically be used to visualize the cause of the disease. Further identification of the cause can be done by histochemical or cellular analysis of muscle biopsy.
Tea plants are native to East Asia and the probable centre of origin of tea is near the source of the Irrawaddy River from where it spread out fan-wise into southeast China, Indo-China and Assam. The natural home of the tea plant is considered to be within the comparatively small fan-shaped area between Nagaland, Manipur and Mizoram along the Burma frontier in the west, through China as far as the Zhejiang Province in the east, and from this line generally south through the hills to Burma and Thailand to Vietnam. The west–east axis indicated above is about 2,400 km long extending from longitude 95°-120°E. The north–south axis covers about 1,920 km, starting from the northern part of Burma, latitude 29°N passing through Yunnan, Tongkin, Thailand, Laos and on to Annan, reaching latitude 11°N. Chinese (small-leaf) type tea (C. sinensis var. sinensis) may have originated in southern China possibly with hybridization of unknown wild tea relatives. Since there are no known wild populations of this tea, its origin is speculative. Given their genetic differences forming distinct clades, Chinese Assam-type tea (C. sinensis var. assamica) may have two parentages – one being found in southern Yunnan (Xishuangbanna, Pu'er City) and the other in western Yunnan (Lincang, Baoshan). Many types of Southern Yunnan Assam tea have been hybridized with the closely related species Camellia taliensis. Unlike Southern Yunnan Assam tea, Western Yunnan Assam tea shares many genetic similarities with Indian Assam-type tea (also C. sinensis var. assamica).
Superoxide (O−2) is produced by reduction of O2. Several grams are produced per day in the human body within the mitochondria. O2 + e− → O−2 Competing with its formation, superoxide is destroyed by the action of superoxide dismutases, enzymes that catalyze its disproportionation:
Sources: en.wikipedia.org
Both molecules activate the same receptor, GHSR-1a, but they share little sequence identity. Ghrelin is a 28-amino-acid hormone carrying a distinctive acyl modification, whereas ipamorelin is a short synthetic peptide. The shared target explains overlapping endocrine effects, while the different structures account for differences in metabolic stability and receptor selectivity.
Early animal and human studies reported growth hormone release at levels that produced small changes in cortisol, prolactin and adrenocorticotropic hormone. That contrast with older secretagogues gave rise to the selectivity label. The observation is consistent across several reports but rests on a limited number of small studies.
Plasma peptidases cleave the molecule into smaller fragments, and reported half-lives in human studies are on the order of a couple of hours. The identity and activity of individual breakdown products have not been fully mapped. Questions about tissue-level clearance remain open.
不是。它属于人工合成的五肽，设计上模拟胃饥饿素受体的部分作用，但不存在于人体天然激素谱中。