HGH (human growth hormone)
HGH (somatotropin) is essential in the growth process, and in adults it plays an important role in metabolic activities. It is synthesized in the acidophilic cells of the anterior pituitary, and its secretion from the intracellular deposit granules is regulated by the hypothalamic hormones (growth hormone-reileing hormone) and SRIF (somatotropin relay-inhibiting factor); Their synthesis depends on neurotransmitters, such as serotonin, dopamine, norepinephrine and growth release peptides. It is also secreted in response to effort, stress, deep sleep, hypoglycemia, glucagon, insulin, thyroid hormones, estrogen, testosterone and vasopressin. In plasma there are in several monomeric isoforms and oligomeri («Big Gh» and «Big Big Gh»). Circulates tied to Gh-Binding Protein, which is similar to the extramembrane domain of the tissue receiver of HGH 5 .
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HGH stimulates RNA production, protein synthesis, mobilizes fatty acids from deposits and has transient effects antagonistic insulin; Increased levels for a long time can induce alteration of glucose tolerance 5 .
HGH secretion is pulsatile, but in adults plasma concentrations are stable, HGH oscillations are attenuated by GHBP. The plasma half -life is 20 minutes 5 .
If the pituitary pituitary or excessively HGH secretes in different stages of growth, it will cause nanism and gigantism respectively. An excess of growth hormone in adults will generate acromegaly.
The test is useful for confirming hypo- or hyperpituitarism so that adequate therapy can be initiated as soon as possible.
The determination of the hormone can be done both under basal conditions and after stimulation (physical exertion, arginine, glucagon or insulin) or suppression (after administration of 100 g glucose).
The absence of the response or an inadequate response to stimulation tests is associated with hypopituitarism.
In case of gigantism or acromegaly, the lack of suppression or incomplete suppression after glucose administration is recorded. Moreover, patients with acromegaly may have paradoxical HGH increases in suppression test 1 .
Recommendations for Determining HGH – Diagnosis of hypothalamic disorders, hypopituitarism, acromegaly and HGH ectopic production 4 .
Patient preparation – à jeun (on non -tin) and after at least 30 minutes of rest, to determine the basal concentration 3; 4 .
Specimen harvested – venous blood 3 .
Harvesting container – Vacutainer without anticoagulant, with/without separator gel 3 .
Processing required after harvesting – the serum is separated by centrifugation; the serum is worked immediately; If this is not possible, the serum is frozen 3; 4 .
Sample volume – Minimum 0.5 ml serum 3 .
Causes of rejection of the sample – Intense hemalized specimen 3 .
Proof stability – 2 months at -20 ° C; Do not defrost/reconcile 3 .
Method – immunoenzyme 3 .
Reference values – are dependent on age and sex 3:
Conversion factor: NG/ml = μg/l.
Detection limit – 0.01ng/ml 3 .
limitation and interference
A single determination of HGH has a limited value, due to the fluctuations marked in the serum concentration. Stimulation or suppression tests provide much more information.
Increased levels can be encountered postprandially, after physical activities, deep sleep, stress, anxiety, sexual hormones deficiency, especially androgens, hypo-, hyperthyroidism, adrenal hyperfunction, increased levels of free fatty acids; Low levels can occur in hunger, cachexia, protein deficits, metabolic imbalance 5 .
increasing: amino acids, clomipramine, clonidine, oral contraceptives, diazepam, etinil estradiol, phenytoin, indomethacin, insulin, interferon, methamphetamine, metoclopramide, propranolol, vasopressin 2 .
Decreases : valproic acid, bromocriptine, chlorpromazine, corticosteroids, hydrocortisone, medroxiprogesterone, methyldopa, prednisone, propantine 2 .
Patients under treatment with growth hormone may develop antibodies against this hormone, antibodies that may interfere with the test leading to false values.
Heterophilous antibodies present in patients can interact with immunoglobulins included in the kit components altering results 3 .
1. Frances Fischbach. Chemistry Studies. In a manual of laboratory and diagnosis tests. Lippincott Williams & Wilkins, USA, 8 ED., 2009, 394-396.
2. Frances Fischbach. Effects of the Most Commonly Used Drugs On Frequently Ordered Laboratory Tests. In a manual of laboratory and diagnosis tests. Lippincott Williams & Wilkins, USA, 8 ED., 2009, 1242.
3. Synevo laboratory. References specific to work technology used. 2015. Ref Type: Catalog.
4. Laboratory Corporation of America. Directory of Services and Interpretive Guide. Growth Hormone, Serum. www.labcorp.com 2015. Ref Type: Internet Communication.
5. Lothar Thomas. Growth Disorders. In Clinical Laboratory Diagnostics-Rese and Assessment of Clinical Laboratory Results. Th -books Verlagsgesellschaft Mbh, Frankfurt /Main, Germany, 1 Ed., 1998, 1073-1074.