Estrogen placental

Estrogens, placental (U) (as estriol) Depends on period of gestation mg/24 h 3.468 Depends on period of gestation Mmol/d XXX 1 Minol/d... 

Chen Z, Zheng H, Dong KW (2001) Identification of negative and positive estrogen response elements in human GnRH upstream promoter in the placental JEG-3 cells. Mol Cell Endocrinol 184 125-134... 

Dong KW, Chen ZG, Cheng KW, Yu KL (1996) Evidence for estrogen receptor-mediated regulation of human gonadotropin-releasing hormone promoter activity in human placental cells. Mol Cell Endocrinol 117 241-246... 

Estriol is also produced by another pathway in the syncytiotrophoblast cells of the placenta DHEAS from fetal adrenal is converted to 16a-hydroxydehydroepiandrosterone sulfate in the fetal liver, followed by removal of the sulfated chain to produce 16a-hydroxy-dehydroepiandrosterone, which is then aromatized to estriol. Estriol is the predominant estrogen produced during pregnancy, and almost all of tiie estriol and estradiol produced by the placental syncytiotrophoblast enters the maternal circulation. By the 7th week of gestation, the placenta produces the majority of the estrogen in the maternal circulation. 

The mammary gland consists of the external nipple and the system of ducts from the alveoli to the skin surface. The alveoli do not fully develop until a female experiences pregnancy and lactation. Cortisol, insulin and placental lactogen contribute to alveolar development, but estrogen and progesterone are most important. The cells that line the alveoli synthesize milk, and they are surrounded by a layer of myoepithelial cells that eject the milk. 

Estriol (estra-1,3,5(10)-trien-3,16-a,17-8 -triol) is the major estrogen metabolite found in the urine. It is excreted in the form of its conjugate with glucuronic acid. The determination of this steroid as an index of placental function has become one of the most widely used endocrine determinations. As pregnancy progresses, the excretion increases and reaches very high levels near term. In abnormal fetoplacental function, the levels of estriol will fall in some cases. The fall is usually progressive, and, because of this, serial determinations of urinary estriol must be carried out. The drop in estriol can be taken as evidence of placental insufficiency, and close watch by the physician is indicated, as a continued drop may necessitate Cesarean section to save the life of the infant. 

Chlorobenzilate did not inhibit human placental CYP 19 aromatase activity and did not express estrogen receptor activation in vitro. 

Oral contraceptives have been used widely by women since the 1960s and most contraceptive pills contain various ratios of estrogenic and progestomi-metic substances. Hormone replacement therapy (HRT) has evolved considerably in the composition and doses utilized in the treatment of postmenopausal women, during the past four decades. While pharmaceutical compounds exhibiting estrogen mimicry are structurally diverse, they share common properties such as their retention in body fat deposits, their ability to cross the placental barrier, their transport in blood usually bound to serum proteins, and their affinity for the estrogen receptor protein. 

Placental synthesis of estrogens. The placenta lacks the key enzyme necessary for formation of estrogens from cholesterol (CYP 17) and relies on androgenic precursors from the maternal and fetal compartments. The major androgen used comes from the fetal zone of the fetal adrenal this is DHEAS, which is also taken up and metabolized by fetal liver into Iba-hydroxy-DHEAS. The placenta converts DHEAS into estrone (E ) and estradiol (E2) and proces.ses 16a-hydroxy-DHEAS into estriol (Ej). Estrogens enter the maternal circulation and appear in maternal urine as conjugated estrogens. 

D4. Diczfalusy, E., In vivo biogenesis and metabolism of estrogens in the foeto-placental unit. Proc. 2nd Intern. Congr. Endocrinol. London, 1964 Vol. 2, p. 732. Exoerpta Med. Found., Amsterdam, 1965. 

Caspi, E., T. Arunachalam, and P.A. Nelson (1983). Biosynthesis of estrogens The steric mode of the initial C-19 hydroxylation of androgens by human placental aromatase. J. Am. Chem. Soc. 105, 6987-6989. 

Cole, P.A. and C.H. Robinson (1990). Conversion of 19-oxo[2b-2H]androgens into estrogens by human placental aromatase. An unexpected stereochemical outcome. Biochem. J. 268, 553-561. 

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