THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

?08
whether oPL is mammotropic in the ewe,. desp ite
the fact that earlier experìments performed by other investigators
have suggested that the sheep placenta may secrete a manrnotropic
subs tance ( Denamur et at ,196] ) .
Propertjes of oPL-receptors
Effect of protein, time and temperature on the binding of oPL to
ovine liver, adipose tissue, ovary, corpus luteum, non-pregnant
uterus, and feta'l ¡iys¡- Like the binding of oPRL to rabbit mar nary
gland (100,000 x g fractìons)(Sniu et al ,l974), the binding of
oPL to its receptors are proteinn time and temperature dependent.
At 37 C, binding of oPL to the liver, adipose tissue, corpus luteum,
nonpregnant uterus, and fetal ìiver reaches its maximum within 'l hr.
Iri the case of the ovary; the ndximal bìnding of opl is not reached until
after 24 hr incubation at 37 C. At the present, we have no good
expl anati ons for this discrepancy.
Specificity of oPl-receptors- It is interestlng that in the radio-
receptor assay for oPL using either ovine 1iver, adipose tissue,
ovary, corpus 'luteum, uterus, or fetal liver 100'000 x g fractions'
only oGH lnhibited the binding of 1251-oPL in a para'llel manner
but exhlbited on'ly 1/2 to ì/5 the potency of oPL, whereas oPRL and
oLH failed to inhibit. These findings suggest that, functionally,
the activity of oPL may be more closely linked with GH-like actions