CDP is a benign, often familial, condition in which puberty onset is significantly delayed, but eventually occurs and then proceeds normally. Measurement of free alpha-subunit after GnRH-stimulation testing can also be useful in the differential diagnosis of constitutional delay of puberty (CDP) versus hypogonadotrophic hypogonadism (HH). Stimulation testing with hypothalamic releasing factors (eg, gonadotropin releasing hormone: GnRH or thyrotropin-releasing hormone:TRH) may result in further elevations, disproportionate to those seen in individuals without tumors. Overall, depending on cell type and tumor size, 5% to 30% of pituitary adenomas will produce sufficient free alpha-subunits to result in elevated serum levels, which usually fall with successful treatment. Although most commonly associated with gonadotroph- or thyrotroph-derived tumors, alpha-subunit secretion has also been observed in corticotroph, lactotroph, and somatotroph pituitary adenomas. In particular, some pituitary adenomas may overproduce alpha subunits. However, under certain conditions, coordinated production of intact glycoprotein hormones may be disturbed and disproportionate quantities of free alpha-subunits are secreted. Under physiological conditions, alpha- and beta-chain synthesis and secretions are tightly coupled, and only small amounts of monomeric subunits are secreted. By contrast, all the different beta-subunits are transcribed from separate genes, show less homology, and convey the receptor specificity of the dimeric hormones. The alpha-subunits are essential for receptor transactivation. The alpha-subunits of all 4 hormones are essentially identical (92 amino acids molecular weight of the "naked" protein:10,205 Da), being transcribed from the same gene and showing only variability in glycosylation (MW of the glycosylated proteins:13,000-18,000 Da). Each is composed of an alpha- and a beta-subunit, coupled by strong noncovalent bonds. They signal through G-protein-coupled receptors, regulating the hormonal activity of their respective endocrine target tissues. The 3 human pituitary glycoprotein hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH), and the placenta-derived chorionic gonadotropin (hCG), are closely related tropic hormones.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |