THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

3. Luteotropic Effect:
234
There aré several pieces of evidence: to
support the vîew that opi- is thê luteoiropín in the
: heep .
Studies on hypophysectomy of pregnant ewes durlng
pregnancy demonstnated that when hypophysectomy was performed in
pregnant ewes before 30 days of gestation, the corpus lutèum reqressed
within l0 days' and the embryo was eventuaty resorbed (Denamur et ar,
1955;.l966;.l922; Amoroso,l952; BJorknan,l965; Davies et al ,.¡965;
Boshier,ì969). 0n the other hand, when the embryo ìs removed before
day l2 of gestation, corpus luteum regressed wlthin 2_3 days (
Moore et at,1966). However, when hypophysectomy was perfonned on
day 60 of gestation, the welght of the corpus luteum examined l2
days later, the weight of corpus luteum remained at 75% of the
controì value, and abortion did not occur. Our studies indicate
oPL isrr'etectable' in uterine vein blood after day 25 0f gestation,
the tJme when the conceptus acqu.ires its luteotroplc properties.
Thus these studies strongìy indicate that the corpus luteum is
necessary for the maintenance of pregnancy during the first fifty
days of gestation, the embryo is essenfiaì for the survival of the
corpus ìuteum of pregnancy after day 12, and opl may be the ruteotropic
hormone during pregnancy.
Another.. prtecq of evirlence suggesting that opl
is the Juteotropic hormone in sheep is derlved from studies on
the binding of opl to ovÍne corpus luteum. l.le have denonstrated that
oPL binds speclfically to sheep corpus luteum. Thus, it ls conceÍvable