RIAKEY hGH IRMA is an in vitro diagnostic assay for the quantitative determination of human growth hormone in serum.
Human Growth Hormone (hGH, somatotropin) is the most abundantly secreted, circulating pituitary hormone. It is synthesized by the alpha cells of the anterior pituitary, with molecular weight of about 21.5 kDa. It is composed of a polypeptide chain of 191 amino acids with two disulfide bonds. Endogenous circulating hGH has a short half-life (20-30 minutes) and its serum levels are influenced by several factors: hypoglycemia, exercise and some amino acids (arginine) result in increased hGH levels, while glucose and cortisol tend to inhibit circulating hGH. Somatotropin activity is not directed towards a specific target organ, although hGH receptors have been demonstrated both on liver cells and on lymphocyte membranes. Human Growth Hormone has a direct anti-insulin action, by facilitating amino acid transport as well as free fatty-acid release in muscle tissue. Growth in children is mediated by hGH, which stimulates the liver to produce somatomedins (or insulin-like growth factors, IGF). IGFs are low molecular weight hormones (about 7 kDa) sharing structural homology with pro-insulin. IGFs mostly circulate bound to carrier proteins, which prolong their half-life and make their serum concentrations relatively stable. Quantitative hGH testing is a necessary diagnostic tool for pathologies such as: acromegaly, gigantism, hyposomatism and hypopituitary syndromes. Basal hGH levels are of little relevance, while useful information can be obtained with several dynamic tests like: provocation with arginine, insulin, L-dopa or glucagon, and inhibition by oral glucose intake.
The present method is based upon two anti-hGH monoclonal antibodies recognizing two different epitopes of the molecule. One antibody is adsorbed the solid phase (coated tube), the other - labeled with Iodine 125 - is used as conjugate. During the incubation, the sample to be tested and the labeled antibody are incubated simultaneously in the coated tube forming a "sandwich". At the end of the incubation, the unbound material is removed by an aspiration/washing cycle. The radioactivity in the tubes is measured in a gamma counter.