Enzyme Immunoassay for the Quantitative Determination of LH Concentration in Human Serum.
Introduction
Luteinizing hormone (LH) is secreted in both men and women from the anterior pituitary gland in response to luteinizing hormone-releasing hormone (LH-RH or Gn-RH), which is released by the hypothalamus. LH, also called interstitial cell-stimulating hormone (ICSH) in men, is a glycoprotein with a molecular weight of approximately 30,000 daltons. It is composed of two noncovalently associated dissimilar amino acid chains, alpha and beta. The alpha chain is similar to that found in human thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG). The differences between these hormones lie in the amino acid composition of their beta subunits, which account for their immunological differentiation (Wide et al., 1976).
A lack of secretion by the anterior pituitary may cause lower LH levels. Low LH levels can result in infertility in both males and females. Additionally, low LH levels may be due to the decreased secretion of GnRH by the hypothalamus or a failure of the anterior pituitary to respond to GnRH stimulation. Low LH values may indicate dysfunction of the pituitary or hypothalamus, but the actual source of the problem must be confirmed by other tests (Veldhuis et al., 2008).
In the differential diagnosis of hypothalamic, pituitary, or gonadal dysfunction, assays of LH concentration are routinely performed in conjunction with FSH assays since their roles are closely interrelated. Furthermore, hormone levels are used to determine menopause, pinpoint ovulation, and monitor endocrine therapy (Baird, 1987).
Clinical Significance
LH plays a pivotal role in reproductive health and is essential in regulating the function of gonads. In females, a surge in LH triggers ovulation and the formation of the corpus luteum, which is crucial for the menstrual cycle and fertility. In males, LH stimulates Leydig cells in the testes to produce testosterone, which is necessary for spermatogenesis and secondary sexual characteristics (Marshall & Besser, 1983).
Abnormal LH levels can indicate various medical conditions:
- Elevated LH Levels: May suggest primary gonadal failure, Turner syndrome, Klinefelter syndrome, menopause, or polycystic ovary syndrome (PCOS).
- Decreased LH Levels: Could indicate hypogonadotropic hypogonadism, pituitary dysfunction, or hypothalamic disorders.
Monitoring LH levels is critical in diagnosing and managing conditions such as infertility, delayed puberty, and endocrine disorders.
Principle of the Assay
The LH ELISA test kit is based on a solid-phase enzyme-linked immunosorbent assay. The assay system utilizes one anti-LH antibody for solid-phase (microtiter wells) immobilization and another mouse monoclonal anti-LH antibody in the antibody-enzyme (horseradish peroxidase) conjugate solution. The test sample reacts with the solid-phase antibodies and the enzyme conjugate, forming a sandwich between solid-phase and conjugated antibodies.
After incubation and a wash step, a tetramethylbenzidine (TMB) solution is added and incubated for 15 minutes, resulting in the development of a blue color. The reaction is stopped with the addition of 1M HCl, changing the color to yellow, which is measured spectrophotometrically at 450 nm. The concentration of LH is directly proportional to the color intensity of the test sample.
References
- Baird, D. T. (1987). A model for follicular selection and ovulation: Lessons from superovulation. Journal of Steroid Biochemistry, 27(1-3), 15-23. https://doi.org/10.1016/0022-4731(87)90263-2
- Marshall, J. C., & Besser, G. M. (1983). Clinical aspects of gonadotropin-releasing hormone and its analogues. Clinical Endocrinology, 18(1), 1-21. https://doi.org/10.1111/j.1365-2265.1983.tb03099.x
- Veldhuis, J. D., Roemmich, J. N., & Richmond, E. J. (2008). Endocrine control of puberty. Clinical Endocrinology, 68(3), 343-352. https://doi.org/10.1111/j.1365-2265.2007.03070.x
- Wide, L., Loraine, J. A., & Bell, E. T. (1976). Human pituitary gonadotropins: Hormone assays and their clinical application (4th ed.). Churchill Livingstone.