THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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H. POSSIBLE ROLT OF OVINE PLACENTAL LACTOGEN IN THT SHEEP
The role played by opl in the sheep during
pregnancy is not understood. However, experimenta'l evidence
from sevenal studies suggest that opl may have three major roles
in the sheep durlng pregnancy.
l. Manmotropic Effect:
The earliest experimentaì observation Ìndlcatìng that
a placental hormone, possibly opL,and progeste rone ,were lnvolved
in mammary gland development þras réported by
Denamur et al(1961). They found that hypophysectomy of pregnant
ewes after 50 days of gestation did not affect the normal course
of pregnancy. Although the manna ry gland was not so weil devetoped
as ln intact controì, nevertheless sone development did occur and
' transient 'lactation took p'race. Later, Dj iane and associates,found
that when pregnant ewes were rendered hypopro.l acti naemi c by
adninistratlon of ergocryptine, marmogenesfs was still normal
(ojiane et a'l ,.l975; Martal et aì,1977). These stud.les suggest that
the placenta night secrete a proractin-rike substance which is
responsible for the normal mamnogenesls in the ewes.
0vine pL. has .been shown,to have potent lactogenic
äctfvity by its effects on the hÍstolrbsy of marmary gìand tissue
of pseudopregnant rabbits, on Jactose synthetase act.lVity and on
casefn synthesis (Martal et al ,19Z6; Chan et aì,1926). Furthennore,the