THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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Ordêr Rodêhtia (Tat, nicê, rolê, hirmster and guihêA pig):
(Í) Rat:
Lyons in l-944 shovred that rat. placental extracts
are capable of synêrgizing with ovari.an steroids to induce
manmary l-obulo-alveooar grorÁrth and also early indication
of lactat,ion. tater Ray eÈ al (1955) demonstrated by means
of assay of its varlous components that the most potent.
mammotropic activity was found in the trophoblastic tissue
from day 12 placênta.
In rats, removal of fetuses plus fetal and placent.al
tissue on day l-2 or 16 of pregnancy reduced the weight of
the mammary glands to control, non-pregnant levels by day 2I
(Desjardin et al, 1968). Removal of the fetus alone on day
16 had no significant effect on mamnary weight, DNA, or RNA
content. on day 21. Relnoval of the fetus on day 12 depressed
all these parameters to some ext,ent but considerable mamrnary
development had nevertheless occurred between day 12 and 2I.
The placenta, therefore, appears to mahe some hormonal
cont.ributions to mammary development, bef ore mid-pregnancy
and provides the major stimulus in the second half of
pregnan cy.
Current investigation using radi oreceptoras says
for prolactin (RR.A,-PRL) by Shiu et al (1973) shohred that
two peaks of serurn rat placental lactogen (rpl) $rere
observed during pregnancy. The first peak of rpt occurred
at mid-pregnancy and the second peak occurred near t.erm.
Upon Sephadex G-l-00 fractionation of day 17 pregnancy rat
serum, all the lactogenÍc activity is found in fractions