THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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on the role af PL in the fetus. Studies in our laboratory have shown
that oPL binds to ovine feta'l ljver menbranes and oGH competes
for the same receptor sites as shown in Figure 21. This suggests
that oPL may act as a GH in early gestatÍon in the fetus. At later
stages fetal pituitary GH may resume that role.
The presence of oPL in allantoic fluids is unexpected.
The peak levels of oPL in allantoic and amniotic fìuid are
coincident with the transient peaks of estrogen-suì fate ln ann.iotic
fluid( private conmunications lvith Dr. H.A. Robertson). l.lhether
this relationship is merely fortuitous or is related to steroldogenesis
and placental attachment requires further examination.
2. Ovine Placental Lactogen in the Maternal and Fetaì Cotyìedons
It has been shown that the sheep corpus luteum (CL)
is necessary for the maintenance of pregnancy durìng the first 50
days of gestati on ( Denamur et a1 ,1955). The embryo also ¡u, been
shown to be essential for the maintenance of the CL of pregnancy
after day 12 ( Moore et al ,1966). The ernbryo may secrete a
luteotropic substance which extends the l.ife span of the CL rather than
stimulating its secretory activity, especiaì1y as there is
no evidence that the secretory activity of the CL increases
durlng the first 50 days of pregnancy (Bassett et al ,1969; Flylling,
1970). llhether the sìgna'l arislng from the embryo is luteotropic
or antiluteoìytic is unknown. By RIA, oPL is detectabìe in the
fetal chorionic membranes as ear]y as 16-lB days of gestation. Thus.