ACTH IRMA
產品名稱：ACTH IRMA
產 地：Demeditec
產品貨號：DE4735
產品規格：96 Tests
產品說明：
Special remarks:
Biological Activity
Adrenocorticotropic hormone (ACTH or corticotrophin) is a polypeptide hormone synthesised (from POMC, pro-opiomelanocortin) and secreted from corticotropes in the anterior lobe of the pituitary gland in response to the hormone corticotrophin-releasing hormone (CRH) released by the hypothalamus. It consists of 39 amino acids with a molecular weight of 4540 Da. ACTH regulates steroid synthesis by the adrenal cortex. ACTH stimulates the secretion of cortisol from the adrenal glands. Cortisol and other glucocorticoids increase glucose production, inhibit protein synthesis and increase protein breakdown, stimulate lipolysis, and affect immunological and inflammatory responses. Cortisol induces thymus involution which is a decline in normal thymus function that in part accounts for its ability to decrease immune system response. Glucocorticoids help maintain blood pressure and from an essential component of the body’s response to stress. ACTH secretion is regulated by corticotrophin- releasing hormone (CRH) and vasopressin (ADH). Cortisol feeds back to the pituitary and hypothalamus to suppress levels of ACTH and CRH. Under basal (non-stress) conditions, cortisol is secreted with a pronounced circadian rhythm, with higher levels early in the morning and low levels late in the evening. Under stressful conditions, the circadian variation is blunted. Non-adrenal gland mediated effects : ACTH stimulates the release of MSH (melanotropic hormone) and GH (growth hormone), increases lipolysis in fat cells (adipocytes), and induces neurological effects (such as stretching and yawning). Much of this is related to its origin from POMC. Lipolysis by ACTH is much weaker than that of lipotropin (LPH). ACTH is a precursor of ?-MSH. In the adrenal cortex, there are two types of ACTH receptors, one with a KD = 1nM, but only about 60 per cell while the other has a KD = 300nM, but with about 600,000 per cell. The presence of high and low affinity receptors for ACTH means that tissues are sensitive not only to the presence of ACTH, but to its concentration.
Clinical Application
Too much ACTH can result in overproduction of cortisol which can cause Cushing’s syndrome. Too much ACTH can be caused by benign pituitary adenoma. Other causes of Cushing’s syndrome (too much cortisol) include ectopic production of ACTH as encountered in some lungs tumors and benign and malignant adrenal tumors. The most common cause of Cushing’s syndrome is exogenous ingestion of glucorticoids. Symptoms of Cushing’s syndrome include truncal obesity, extremity wasting, moon face, buffalo hump, thinning skin, easy bruising, muscular weakness, hypertension, artherosclerosis, congestive heart failure, edema, menstral irregularities, psychological disturbances, osteoporosis, increased infections, and poor wound healing. Reduced secretion of ACTH by the pituitary gland is called secondary adrenal insufficiency. Tertiary adrenal insufficiency is caused by failure of the hypothalamus to produce corticotrophin-releasing hormone (CRH) while primary adrenal insufficiency is defined as loss of adrenocortical hormones due to destruction or impairment of the adrenal cortex. All patients with adrenal insufficiency show weight loss. Secondary and tertiary adrenal insufficiency is in part diagnosed by ACTH (Cortrosyn) injection to look for simulation of cortisol production.
PRINCIPLES OF THE METHOD
The Demeditec ACTH-IRMA is a two-step immunoradiometric assay based on coated-tube separation. It allows the determination of intact human adrenocorticotropic hormone (ACTH) in EDTA plasma. Monoclonal antibodies specific to the 1-24 ACTH fragment (N-terminal fragment) are attached to the lower and inner surface of the plastic tubes. Calibrators or samples are added to the tubes. After 2 hour incubation, washing removes the occasional excess of antigen, mid-regional and C-terminal fragments. 125I labelled polyclonal antibodies specific to the 24-39 ACTH fragment (C-terminal fragment) are added. After 1 hour incubation and washing the remaining radioactivity bound to the tube reflects the intact ACTH concentration.
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