THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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cross^reaction in irnmunoassays for bovine prolactin and
growth hormone.
Matthies (1974 ) atso reporÈed that presence of
placental lactogen in placental extracts r"¡hen bhey hrere
injected directly ínt.o the rat manìmary gl-and causing
proliferation of mammary gland.
Subsequently, several investigators confirmed
the presence of placental lactogen in the cow by using a
RRA-PRL and RRA-GH to detect bovÍne placental lactogen
(felty et al, L976) Unlike the secret.ion of monkey and
human placental lactogen, xelly et al (l_976) found that
the levels of bovine placent.al lactogen remained fairly
constant throughout pregnancy. The low leve1s of bovine
placental lactogen 1À,¿5 unexpected. The reason for this
is still not clear. tt is possible that a tovù secretion
rate in vivo or rapid clearance of hormone from bl-ood
might result in undetectable levels of placental lactogen
in the peripheral circulation. Upon geI-filtration of
serum and placental extracts on Sephadex-G-Ioo, it appears
t.hat the molecular wêight of bpL is approximateJ_y 40,000
to 50,000.
RecentLy, Bolander et al (1925, 1976) have reported
that they have purified bpl from bovine placentat cotyledons u,ith 40_
fold purification. When the growth promotÍñg actívíty of theÍr bpl was
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tested in hypophysectomi zed rats, it was 5% as potent as bovine growth
hormone standard. Fu¡thermore, vrhen' their bpL i,vas tested for its lactogenic