THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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diffusion teÊt. Josi¡novich and Maclâren (1962) suggested that
hPL and hGH have tr,ro to three antigenic Aroups, respectively,
onl-y one of whÍch is common to both proteins. This difference
in antÍgenic sites is cJ.earJ-y shown by guantitative precípÍt,in
tests (ti, L972'). Af,ter rnodification of the tryptophan residue,
hPL vras unable to react with its homologous antiserum, but.
retained a limited capacity to bind anti-hcH, indicating thaÈ
the tryptophan, residue is not part of the antigenic determinants
shared by the tr4ro hormones (Neri et al, 1923).
The primary structures of hpt and hGH are also very
similar to that of ovine prolactin, which exhibits lactogenic
but, not. somatotropic activity (Li et al , 1969 , ]-g7O1 Behrley
and Li, 1970, L97Lr. Nlalì et al(1971) have suggested rhat. these
biologically related hormones arose from a co¡nmon ancestor,
a shorter prinordiat peptide, by gene reduplication. Similarly,
the structure of ovine growth hormone, which possesses growth-
stimulating but not lactogenic activity, is partÍally homologous
to that of hcH and hpl, (Bewley and Li, l-974a Lí et al , L9721 .
v) Cell-origin of hpl.:
Using both direct and indirect immunofluorescence
t.echníques, Sciarra et, al (1963) Iocated hpL in the cytoplasm
of the syncytiotrophoblast of chorionic vi1Li, but failed to
detect any specific immunofluorescence in the cytotrophoblast.
This observat.ion has been confirmed by others (crurnbach and
Kapl"an, 1964; Currie et al| 1966t Beck et a1 , 1969¡ Ikonikoff
et al ' I97L). Ikonikof,f (1973) has dêmonstratect the ultrastructural
location of hPL by rneans of a peroxidase-labeÌed