THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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Gusdon et al (1920)using . haernagglutinat.ion
inhj,bition test also reported that crude ovine placental
extracts cross-teact with anti-hpl antiserum. Lat,erf
Forsyth (1974) confirmed the presence of placental lactogen
in the sheep by us-ing co-cuJ.ture experiments.
Usíng radioreceptorassays for prolactin and. for
grovrth hormone, Kelly et al (1974) were the first to
quantitate the plasma levels of opL in the sheep during
pregnancy. By day 60 of gestation and thereafter placental
lactogen concentrations increase as pregnancy advances,
reaching peak concentrations of 1to 2 yg /mL (opRL equivalent
in the RRA-PRL) on days 95 to 1L4 of gestation. After the
init.ial peak there is generalJ_y a decline in placental
Lactogen concentration followed by anothêr peak before
párturition opI, concentrations slovùly declined from
approximatel-y I pg,/ml to less than 500 ng,/mJ_ by 12 hours
before parturition and then decreased quite rapidLy post_
partla. By re-assaying t,he serum samples during pregnancy
with a radioreceptorassay for growth hormone (RR.å,-GH) ,
simil-ar results were obtained. However, the se^¡m concentration
of gro$rth hormone-like activity is much lovrer t,han prolactin_
l-ike acÈivity, the ratio of pRL,/cH is approximately
3 or 5 to I, r¡rhereas in placental extracts, the ratio of
PRL,/GH activity Ís about 1:L. This may suggest that serum
cont,ains substances that interfer.e in t,he RRA-PRL more t,han
vr'ith RRA-GH. oPL r,ras demonstrated (as-sayed by RR.A,-PRL )
in the trophoblasts as early as day 16-17 of pregnancy