THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

Guinea Pi g:
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Hypophysectomy of the gulnea pig on day 24 to 26 of pregnancy
'leads to resorption of the young withln 2 days. However, by 40 days
pregnancy can continue independentiy of the pituitary and viable young
are born at term, but the manÍnary glands were smaìler than usua.l
(Pencharz et al ,1934). Thus, it is suggested that gufnea plg placenta
may secrete manmotropic substances during pregnancy.
Using radioreceptor assays for prolactin (RRA_PRL) and for
growth honnone (RRA:GH), it is found that the peak level of guinea pig
p]acental 'lactogen occurred at 50-55 days. Furthennore, the relative
ratio of prolactin to growth hormone activity of guinea plg serum pracentaì
lactogen is 1:2 (50-sB .l
days of gestation). Ge.l _f i trati on studies on
guinea pig extracts and serum demonstrated that the guÍnea pig pracentar
lactogen is approximately 22,000. Untiì now, guinea pig placental lactogen
has not been purf f .i ed.
Hamster:
The first report to suggest that hamster placenta nright secrete
placental ìactogen is by Talamantes (ì973). The existence of such a hormone
is further substantiated by the fìnding using RRA-PRL and RRA-GH to measure
the pìacental lactogen levels in the serum and in the p.lacental extracts
of hamsters. Like guinea pigs, serum leve.l of hamster placental lactogen
reaches its peak actìvity before parturition about day .10_lZ (gestational
period is l5), and declines before partur:ition (Kel.ly et at,l976). Molecular
weight determlnatlon by get fittration in Sephadex G-.l00 lndlcates that
it has a morecurar weight of lg,0oo to 23,000. Hamster pracentar ractogen
has not been purlfied yet.