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Alkaline phosphatase

" Abstracted from Vorherr, H. (1972). To breast-feed or not to breast-feed. Postgrad. Med. J. 51, 127-139.

" Abstracted from Vorherr, H. (1972). To breast-feed or not to breast-feed. Postgrad. Med. J. 51, 127-139.

villus core, and the fetal capillary endothelium (see Figures 14-4A,B).

b. Chorionic Gonadotropin

Human chorionic gonadotropin, hCG, is a hetero-dimeric glycoprotein of 57 kDa consisting of a noncova-lently bound a (92 amino acids) and a distinctive {i (134 amino acids) subunit. There is one gene for the a-subunit located on chromosome 6q21.1-23; this a-subunit is also very similar to the TSH, LH, and FSH a-subunits. Chromosome 19 has a cluster of six genes for the hCG /3-subunit and one gene for the LH /3-subunit.

Table 14-2 summarizes the structural homology of several of the released pituitary and placental hormones. The fi-CG has an 80% homology to the 121-amino acid subunit of the LH /3-subunit.

hCG is produced by the syncytiotrophoblast and thus, technically, hCG is produced by the fetus. The rate of production of hCG is maximal by the 10th week of pregnancy, and then it falls slowly to a nadir at 17 weeks and remains at a low but readily measurable level for the duration of the pregnancy.

The major biological function of CG is to function as a luteotropin, that is, to stimulate the production of progesterone by the corpus luteum. This ensures a continual supply of ovarian progesterone until the placenta has developed to the point (usually at 6-8 weeks) when it can generate adequate quantities of progesterone; at this time the corpus luteum atrophies. By anal-

GESTATION (wk)

figure 14-7 Temporal changes during human pregnancy in the serum concentrations of several hormones. Abbreviations: hPL, human placental lactogen; hCG, human chorionic gonadotropin; PRL, prolactin. Modified from Aragona, C., and Friesen, H. G. (1979). Lactation and galactorrhea. In "Endocrinology" (L. J. DeGroot, G. F. Cahill, L. Martin, D. H. Nelson, W. D. Odell, J. T. Potts, E. Steinberger, and A. I. Winegrad, eds.), Vol. 3, pp. 1614-1617. Grune & Stratton, New York.

GESTATION (wk)

figure 14-7 Temporal changes during human pregnancy in the serum concentrations of several hormones. Abbreviations: hPL, human placental lactogen; hCG, human chorionic gonadotropin; PRL, prolactin. Modified from Aragona, C., and Friesen, H. G. (1979). Lactation and galactorrhea. In "Endocrinology" (L. J. DeGroot, G. F. Cahill, L. Martin, D. H. Nelson, W. D. Odell, J. T. Potts, E. Steinberger, and A. I. Winegrad, eds.), Vol. 3, pp. 1614-1617. Grune & Stratton, New York.

ogy with LH (Chapter 13), the /3-subunit of hCG is believed to interact specifically with a membrane receptor to stimulate the production of progesterone from cholesterol.

Human CG is the first hormone to be produced in significant quantities by the conceptus; accordingly, a radioimmunoassay for hCG has been developed as a means of diagnosing pregnancy even before the men strual period has been missed. The hCG is believed to be produced by the syncytiotrophoblast cells of the villi (see Figures 14-1 and 14-3).

c. Chorionic Somatomammotropin

Human chorionic somatomammotropin (hCS), which was formerly referred to as human placental lactogen (hPL), is a 190-amino acid polypeptide (single

figure 14-8 Model for hormone production by paracrine interaction of the cytotrophoblast and syncytiotrophoblast cells. (See also Figures 14-1 and 14-3 for anatomical details.) The syncytiotrophoblasts produce chorionic somatomammotropin (CS), chorionic gonadotropin (CG), and proopiomelanocortin (POMC) polypeptide hormones. Abbreviations: NPY, neuropeptide Y; ACTH, adrenocorticotropic hormone; GHRH, growth hormone-releasing hormone; SRIF, somatostatin; GnRH, gonadotropin-releasing hormone; MSH, melanocyte-stimulating hormone. Modified with permission from Jaffe, R. B. (1991). "Reproductive Endocrinology" (S. S. C. Yen, and R. B. Jaffe, eds.), 3rd ed. W.B. Saunders, Philadelphia, PA.

Cytotrophoblast figure 14-8 Model for hormone production by paracrine interaction of the cytotrophoblast and syncytiotrophoblast cells. (See also Figures 14-1 and 14-3 for anatomical details.) The syncytiotrophoblasts produce chorionic somatomammotropin (CS), chorionic gonadotropin (CG), and proopiomelanocortin (POMC) polypeptide hormones. Abbreviations: NPY, neuropeptide Y; ACTH, adrenocorticotropic hormone; GHRH, growth hormone-releasing hormone; SRIF, somatostatin; GnRH, gonadotropin-releasing hormone; MSH, melanocyte-stimulating hormone. Modified with permission from Jaffe, R. B. (1991). "Reproductive Endocrinology" (S. S. C. Yen, and R. B. Jaffe, eds.), 3rd ed. W.B. Saunders, Philadelphia, PA.

Hormones, Second Edition TABLE 14-2 Structural Homology of Pituitary and Placental Hormones

Hormone

Molecular mass (kDa)

Number of amino acids in the chains a p

Carbohydrate containing

Produced by

Pituitary

Placenta

Glycoproteins

FSH (follicle-stimulating

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