THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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197J-; Rayford et al | !9721 . Consistent hrith this, no ovarian
uptake of tritiurn-Labeled alpha or beta subuniÈs is found
in vívo (Braunstein et a1 , L972b) and neither subunit significantly
inhibits hCG in vitro (Lee and Ryan, 1972; Catt et aJ-, 1973).
Holr¡ever, the clissociated subunits can be recombíned when
incubated in equimolar concentrations in solution to form
native hCG with the same el-ectrophoretic mobility and got of
the original biological activity (Canfield et a1 , 1971, Morgan
et al, I97l; Pierce et al , 197I; Bahla, I972a; Rathnam et al ,
L972¡ ùllorgan et al, 19741 . Two possible reasons for the
lack of in vivo biological activity of the isoLated subunit.s
are that they do no survive long enough to reach their target
cells and that they bind poorly to receptors on target cell
membranes. In connect.ion with the former, Braunstein et al_.
(L972bl report a much shorter half-Iife for dissociated hCG
subunits compared r^rith the undíssociated hormone when injected
into fernale rats. The initiaÌ half-life of hcc-alpha in Èhe
plasma was 6 minutes, hcc-beta was lI minutes, and the half*
Iife of intact hCG vùas l4l" minutes. In addition to shortened
survival, Kammerman et aI . (1972) found that, the subunits
did not bind to target cells ín vitro.
b- Removal of Carbohydrates-
The biological specific activity of hCG preparations
decreases hrith progressive removal of sialíc acid, notably
on loss of the terminal sialic acid resÍdues in the molecule
(Goverde et aI., 1968¡ Van HeIL et a1, 1970t Braunstein et aL,
1971; Brossner et al, 197I¡ craesslin et al, L9?2) with l_ess