Immunoradiometric assay for quantitative determination of luteinizing hormone (LH) in human serum or plasma
The luteinizing hormone (LH, lutropin) is secreted by the β-cells of the anterior pituitary under the control of hypothalamic gonadotropin releasing hormone (GnRH). Also, LH called interstitial cell stimulating hormone is a glycoprotein hormone with a molecular weight of approximately 30,000 dalton. It is secreted by the gonadotrophic cells of the anterior pituitary gland and biochemically similar to the other glycoprotein hormones, follicle stimulating hormone(FSH), thyroid stimulating hormone(TSH), and human chorionic gonadotropin(HCG). Each of these four hormones is composed of two distinct non-covalently linked polypeptide chains, the alpha (α) and beta (β) subunits. The alpha (α) subunits of LH, FSH, and hCG are biochemically very identical, whereas the beta (β) chains are biochemically unique and confer biological and immunological specificity to each hormone. Bioactivity is also determined by the beta (β) chain. The secretion of LH and FSH is modulated by gonadotropin releasing hormone (GnRH), a ten amino acid peptide produced by the hypothalamus. The secretion of GnRH is pulsatile, which in turn produces pulsatile secretion of LH and FSH. Peaks of LH and FSH in plasma normally occur about every one or two hours. Thus, laboratory results of LH and FSH determinations on single serum samples should be interpreted with caution. Peaks of FSH in serum are less evident because of its longer plasma half-life. LH and FSH secretion is further controlled by both negative and positive feedback effects of ovarian steroids acting at both the hypothalamic and pituitary levels. In postmenopausal women, ovarian function and estradiol secretion are diminished and will eventually cease.
The RIAKEY LH IRMA Tube II is an one step non-competitive Immunoradiometric (IRMA) method (“sandwich”). The method employs two highly specific monoclonal anti-LH antibodies which recognize two different epitopes of the molecule. One antibody is coated on solid phase (coated tube), the other, specific for the LH and labeled with Iodine-125, is used as a tracer. Antibody-coated polystyrene tubes serve as solid phase. The tracer antibody and the coated antibody react simultaneously with the LH antigen present in the standards, control serum and samples. Unbounded material is removed by a washing step. The amount of bound tracer will be directly proportional to the LH antigen concentration and the remaining radioactivity bound to the tubes is measured in a gamma scintillation counter