THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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antibody. The peptide hormone was found on the ribosomes
and in the cisternae of the rough endopLasmic ret.iculum
and on the maternal surface of the plasma membrane of the
synq¿t.iaI microvilli. None rn¡as found on the colgi apparatus
or the nitochondria of the syncyt.ium.
Thus, in the case of both pept.ide hormones, the
syncyt,iotrophoblast appears to be the site of synthesis,
in agreement lvith the structural features of this tissue,
which are characteristic of a protein-secreting organ.
vi) Biosynthesis of hpL:
Studies on isolated pLacental preparat,ions
have established certain features of hpL production. crumbach
and Kapl"an (1964) fÍrst demonstrated synthesis of hpt by
fragments of first and third trimester placentas, and
incorpo::ation of labeled amino acid inÈo hpl, under these
conditions has been observed (cudson and. yen, 1967) even as
early as day 29 of pregnancy (Gitlin and Biasucci, 1969).
Friesen et al (1969) have concluded from studies on slices
on human placenta with tritium-l-eucine that hpl, is the major
protein synthesized at term, and accounts for 5-10t of all
proteins released from slices of human term placentas
(Su$ra et al , 1969a , b) .
The properties of the lactogenic protein synthesized
in vitro has been examined. Fol1ovùing incubation of human
placental tissue, Friesen and coworkers (Suwa et aI , 1969a,b¡
Friesen et al , 1972) found the predominant protêin in the
incubation medium to be identical to native hpL (M.!{. 21,600),