THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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'late in pregnancy were used. Again maximar Þinding of opl was obtarned
after incubation at 4 C for 24 h, with the exception of,the ovary,
where blnding of opl at ZZ C oî 37 C was slighily greater. Dur.ing
routine assays, 24 h incubation periods at 4 C were used for all tissue
receptors because this gave the highest level of blnding wlthin a
convenient tirne period.
oPL usl Adipose Ti ssues
Figure 19 shows the competition by pitultary hormones for
oPL binding sites in liver and adìpose tissue obtarned from the non-
pregnant ewe. PituÍtary growth hormones from various specres competed
with oPL for binding sites in liver to varying degrees(fig. tSA).
Human placental lactogen competed only minlmally.and other pituitary
hormones not at all. Similarìy, the results ln Fig. .l9B for adipose
tissue(ì00,000 x g fractions) show that growth honnones inhiblted the
binding of the tracer ìn a paraller manner to that of opl except that
2 to 5 fo]d lncreases in concentration were required. scatchard ana.lysis
of the data obtained with opl are dispìayed in the figure and the
nunber of binding sites (n) and the affinity constant (fa) ot opL for
each ti ssue is indicated_
for oPL usi
Figure 20 shows the inhiblilon of binding of 125I-opL
to the corpus luteum and to the ovary (.|00,000 x g fractions) by opL
and three ovine pituitary hormones (pRL, GH, and LH). Corpora .lutea