| THE HYPOTHALAMO-PITUITARY-GONADAL AXIS
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| Gonadotropin-releasing hormone (GnRH)
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| GnRH is essential for the secretion of intact FSH and LH
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| The hypothalamus has a major role in the control of gonadal function in both males and females. The secretion of GnRH is the first stage in the onset of puberty. GnRH, in turn, influences the relative secretion of pituitary FSH and LH. GnRH is a decapeptide synthesized as a 92-amino-acid precursor by various hypothalamic nuclei and transported to the pituitary via the portal system. It is secreted in a pulsatile fashion and induces the synthesis and secretion of both FSH and LH from the same gonadotroph cell type. GnRH acts through its cell surface receptor to increase intracellular calcium, hydrolyze phosphoinositides, and activate protein kinase C. Through feedback loops, estrogens increase and androgens decrease the number of GnRH receptors. Long-acting GnRH agonists can also cause down-regulation of GnRH receptors and reduced FSH and LH secretion. Such agonists are now used to treat prostate cancer and to prepare infertile women for assisted-conception programs.
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| BIOCHEMICAL CONFIRMATION OF PREGNANCY |
| Biochemical confirmation of pregnancy is now achieved by means of a simple and sensitive test that can give reliable results within 2 weeks of fertilization (i.e. before the next menstrual period). Pregnancy tests may be performed by doctors, nurses, or even the patients themselves since they are readily purchased from pharmacies. |
| Pregnancy tests are immunoassays that measure the production of human chorionic gonadotropin (HCG). A specific two-site immunoassay is employed (see Fig. 37.2). One antibody recognizes the α-subunit of HCG, while the other only binds to the 32-amino-acid segment of the β-subunit that is unique to HCG (see Fig. 37.8). Since nonpregnant women do not normally produce HCG, the detection of even low levels from the first stages of placental development is sufficient to confirm pregnancy. |
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