CASE FILES: BIOCHEMISTRY
A nsw ers
A. Hyperandrogenism is primarily ovarian in origin in PCOS women,
although a minor contribution from the adrenal gland may occur.
Hyperinsulinemia is the primary stimulus. Fat cells convert androgens
to estrogens. This may explain the late menopause in this case. In nor-
mal postmenopausal women, ovarian production of testosterone con-
tinues and this provides the main source of circulating estrogen.
Typically an LH/FSH ratio of at least 2.5 is associated with PCOS.
B. Increased levels of FSH and LH result from decreased estrogen
levels and release of feedback inhibition. Androgen secretion contin-
ues although diminished. Osteoblast activity decreases, eventually
leading to risk of osteoporosis. Progesterone levels decrease, and GnRH
C. Progesterone is secreted by the corpus luteum under the influence
of LH. Together with estrogen, it promotes the thickening and main-
tenance of the endometrium. Progesterone inhibits GnRH release,
uterine contraction, and follicle development.
B IO C H E M IS T R Y PE A R L S
Puberty is initiated by the pulsatile release of gonadotropin-
releasing hormone (GnRH) from the hypothalamus.
GnRH binds to plasma membrane receptors in its target cells in the
anterior pituitary and triggers activation of the phosphatidylinos-
itol signaling pathway, stimulating the release of both follicle-
stimulating hormone (FSH) and luteinizing hormone (LH) from
the same cell.
FSH binds its plasma membrane receptor in the ovarian follicle to
stimulate, via adenylate cyclase activation, cyclic AMP produc-
tion, and protein kinase, increasing the ovarian synthesis and
secretion of 17-P-estradiol, the female sex hormone.
Follicular atresia is
the cause of hypoestrogenemia in the
menopause, which is associated with elevated gonadotropin lev-
els (FSH and LH).
Litwack G, Schmidt TJ. Biochemistry of hormones I: polypeptide hormones. In:
Devlin TM, ed. Textbook of Biochemistry with Clinical Correlations, 5th ed.
New York: Wiley-Liss, 2002.
Pathophysiology of the endocrine system. An online textbook from Colorado State