THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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circulationand alìantoic f'lulds throughout gestat.lon with high
lévels during early pregnancy. opL is not detectable in amniotic
fluid and maternal y¡i¡g. oPL is detectable in extracts of chorio-
al lantoic membranes and materna'l caruncles as early as ì6 days of
gestation with higher concentrations in fetal mernbranes.The concentra-
tion and content of oPL in placentomes reaches peak leVels around day g0.
When oPRL and oGH were measured by speclfic RIA ln the maternal
circulation during pregnancy, the secretory pattern of opRL is
inversely related to that oPL secretion whereas there is no
signlflcant varìation of oGH levels. Th.is finding suggests that opl
might be the hormone that suppresses ôPRL secrètion during pregnancy.
The haif-time disappearance rate (tå) of opl in the sheep Ís
approximately 60 minutes. This indicates that the daiìy production
of oPL during late gestational period is approximately 90-'100 mg.
Furthermore, biosynthesis studies showed that opl is synthesfzed
and secreted by the chorioallantoic membrane as ear'ly as day 22.
This study demonstrates
origin.
that oPL ls of embryoni c
In bioassays, we are able to demonstrate that opl
is able to stimu'late growth of epiphyseal carti'lage of ,
hyooohyòectorn i zed rats . hle are abJe to demonstrate
that adminlstration of oPL lnto pseudopregnant rats prevents the
loss of LH-receptors in the corpora lutea and fall of progesterone
caused bV PGF'". These studies suggest that the roles of
placental lactogen during pregnancy is to act as the "growth hormone,,
of pregnancy and to maintain the integrity of LH-receptors in the C.1..