placental hormone
DESCRIPTION
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Placental Hormone The production of steroid and protein
hormones by human trophoblasts is greater in amount and diversity
Human Chorionic Gonadotropin HCG is a glycoprotein with biological
activity similar to luteinizing hormone hCG is produced almost exclusively in
the placenta, low levels are synthesized in the fetal kidney
Other fetal tissues produce either the ß-subunit or intact hCG molecule
Various malignant tumors also produce hCG, sometimes in large amounts—especially trophoblastic neoplasms
The detection of hCG in blood or urine almost always indicates pregnancy
Chemical Characteristics Chorionic gonadotropin is a glycoprotein
with a molecular weight of 36,000 to 40,000 Da
It has the highest carbohydrate—30 percent. The carbohydrate component, and especially the terminal sialic acid, protects the molecule from catabolism
he 36-hour plasma half-life of intact hCG is much longer than the 2 hours for LH.
The hCG molecule is composed of two dissimilar subunits termed a and ß subunits.
his hormone is structurally related to three other glycoprotein hormones—LH, FSH, and TSH
Recombination of an a- and a ß-subunit of the four glycoprotein hormones gives a molecule with biological activity characteristic of the hormone from which the ß-subunit was derived
Concentrations of hCG in Serum and Urine
Regulation of hCG Synthesis and Clearance
Placental gonadotropin-releasing hormone (GnRH) is likely involved in the regulation of hCG formation
Both GnRH and its receptor are expressed by cytotrophoblasts and syncytiotrophoblast
GnRH administration elevates circulating hCG levels, and cultured trophoblast cells respond to GnRH treatment with increased hCG secretion
Pituitary GnRH production also is regulated by inhibin and activin
In cultured placental cells, activin stimulates and inhibin inhibits GnRH and hCG production
Biological Functions of hCG•Both hCG subunits are required for binding to the LH-hCG receptor in the corpus luteum and the fetal testis.
•Function of hCG is the so-called rescue and maintenance of corpus luteum function—that is, continued progesterone
•he maternal thyroid gland is also stimulated by large quantities of hCG
Abnormally High or Low hCG Levels
There are several higher maternal plasma hCG levels are found:multifetal pregnancy erythroblastosis fetalis associated
with fetal hemolytic anemiagestational trophoblastic disease
Human Placental Lactogen hPL was concentrated in
syncytiotrophoblast hPL detected as early as the second
or third week after fertilization. hPL is demonstrated in
cytotrophoblasts before 6 weeks (Maruo, 1992).
Chemical Characteristics and Synthesis
Human placental lactogen is a single, nonglycosylated polypeptide chain with a molecular weight of 22,279 Da.
Within 5 to 10 days after conception, hPL is demonstrable in the placenta and can be detected in maternal serum as early as 3 weeks.
Maternal plasma concentrations are linked to placental mass, and they rise steadily until 34 to 36 weeks’gestation.
Metabolic Actions1. hPL promotes maternal lipolysis with
increased circulating free fatty acid levels.
2. hPL may aid maternal adaptation to fetal energy requirements.
3. hPL is a potent angiogenic hormone. It may serve an important function in fetal vasculature formation
Other Placental Protein Hormones
Chorionic Adrenocorticotropin (ACTH) Growth Hormone Variant Hypothalamic-Like Releasing Hormones:
- Gonadotropin-Releasing Hormone (GnRH)-Corticotropin-Releasing Hormone (CRH)-Growth Hormone-Releasing Hormone (GHGH)
Relaxin Parathyroid Hormone–Related Protein (PTH-rP) Leptin Neuropeptide Y Inhibin and Activin
Placental Progesterone Production
Placental Estrogen Production The placenta produces huge amounts
of estrogens using bl oodborne steroidal precursors from the maternal and fetal adrenal glands
At 2 to 4 weeks of pregnancy, rising hCG levels maintain production of estradiol in the maternal corpus luteum
Estrogen is produced during the follicular and luteal phases through the interaction of theca and granulosa cells
Dehydroepiandrosterone (dhea) and its sulfate (DHEA-S) are C 19-steroids can also serve as estrogen precursors
FETAL ADRENAL GLAND–PLACENTALINTERACTIONS At term, the fetal adrenal glands weigh
the same as those of the adult Daily steroid production of fetal adrenal
glands near term is 100 to 200 mg/day It is compared with resting adult steroid
secretion of 30-40 mg/day.
Placental Estriol Synthesis he estrogen products released
from the placenta are dependent on the substrate available from the developing fetus
Estradiol is the primary placental estrogen secretori product at term.
Fetal Adrenal Steroid Precursor The precursor for fetal adrenal
steroidogenesis is cholesterol Plasma cholesterol and its esters are
present in the form of very-low-density lipoprotein (VLDL), LDL, and HDL
LDL was most efective, HDL was much less, and VLDL was devoid of stimulatory activity
Fetal Conditions That Affect Estrogen Production
Fetal Demise Fetal Anencephaly Fetal Adrenal Hypoplasia Fetal-Placental Sulfatase Deficiency Fetal-Placental Aromatase Deficiency Trisomy 21—Down Syndrome Deficiency in Fetal LDL Cholesterol
Biosynthesis Fetal Erythroblastosis
Maternal Adrenal Dysfunction Maternal Ovarian Androgen-
Producing Tumors Gestational Trophoblastic Disease
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