Endocrine Metabolism V: Reproductive System
(S y n th e tic )
F I G U R E 3 4 -7
Structures of estrogens and selective estrogen receptor modifiers.
Biological Effects of Progesterone
The human progesterone receptor (PR) gene on chromo-
some 11 encodes a single PR protein that is homologous to
the other steroid hormone receptors but that binds proges-
F I G U R E 3 4 - 8
Structures of phytoestrogens. These are diphenolic compounds found in
plants, such as soybeans, sprouts of cloves, and alfalfa.
terone preferentially. Like the ER, PR is predominantly
found in the nucleus; however, it shuttles between the nu-
cleus and the cytoplasm. PR exists in a stable form bound
to heat-shock proteins (hsp), but is activated when proges-
terone (P) displaces the hsp and binds to the hormone bind-
ing domain. The P-PR complex dimerizes and binds to two
half-sites of progesterone response elements (PREs) in
chromatin; this promotes transcription of a progesterone-
sensitive gene. The PRE is identical to the glucocorticoid
response element and androgen response element, but the
significance of three hormones sharing the same response
element in DNA is not known. PR production is stimu-
lated by estrogen and in some tissues is downregulated by
Following adequate priming of the en-
dometrium by estradiol, progesterone increases glycogen
deposition in the glandular epithelium and stimulates se-
cretory function of the glands from about day 4 after ovu-
lation. Progesterone also stimulates fluid accumulation in
the endometrial stroma, with maximal edema occurring
at about the time of implantation (day 7). Progesterone
promotes the decidual reaction in the stroma in response
to the implanting blastocyst and stimulates the production
of decidual prolactin (dPRL) by the decidual cells. In the
absence of conception, progesterone causes predecidual-
ization of the stroma from about day 9 in a process of
terminal (irreversible) differentiation that leads to degen-
eration of the tissue when progesterone levels decline.
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