THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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addition of CAMP (Handwerger et aI , L973¡ Hussa et aI, 1924;
Story et aL, 1-9741 . Furthermore, Bolander et aL (1928) using
culture explants from near term placental tissue shovred that
the secretion of hCG into the medÍum increased 7-8 fold durinq
the second to forth day of i.ncubation, suggesting that the
synthesis of hCG from the term placenta is subject, to an
inhibitory influence which declines with time in culture.
A new and significant factor in the control of
hCG secretion may have energed ri,rith the clai¡n to have identified
luteotropin-releasing factor (LRF) activity in the placenta
(Gilbons et al , 1975). Since LRF secreted by the hypothalamus
regulated output of the corresonding gonadotropin tH from the
pituitary gland, this observation suggests that con¿rol of
hCG nay occur through LRF made in the placenta, possibly in
the cytotrophoblast. There, CAMP $¡ould Èhen be formed and
cause hCG output to be st.imulated. This theory is compatible
with the synthesis of hCG by the slno¡Èiotrophoblast., but. not
cytotrophobLast, and. the increased release of hCG by cAIr'lP
noted above for iel.ls in culture. The formation of LRE
may. decline in later pregnancy and explain the dectine in
hcc formation. Although Gilbo¡srs hypothesis is interest,ing,
there are no further studies to confirm his claims.
v) Secretion and Metabol ism of hCG:
Using a variety of biologícal and inununological
assay procedures, numerous I-nvestigators have reported on
the conaentrations of hCG in the urine and serum of pregnant.