THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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conponents I the.faster haying a half-Iife of 5-15 hours
and the slor'er half-life of, ZO^37 hours (Faiman et aL, 1969;
Yen et a1, 1g6g; Rizkallah et al, Lg6g). others (parloîr and
vtard, Ì961; Midgley and Jaff,e, 1_968¡ v,Iide et a1 , 1968) have
recognized only one component. Geiger (1923) has tried to
reconcile these differences by suggesting that the half-life
of hCc changes sharply in the early puerperium. Clearance
of hCG in the urine has been esÈimated variously from 0.4 to
6 mJ-/nin., without any alterat,ion in crearance rate reÌated to
the stage of pregnancy (par1or,{ et. a1 , 196l; Rizkallah et al ,
1969). This implies that changes in hCG .Ievels in the blood
during pregnancy must be due to alteration in secretion rate,
not in clearance and degradat,ion. About 5-25t of the
circuJ-ating hormone appears in the uríne.
Finally, t-here is evidence that hCG varies quaLitatively
during the course of pregnancy. Early in pregnancy, the
carbohydrate content of the hormone and its biol0gical activity
are higher than in J_ater pregnancy, although the immunological
propert.ies of the molecule remain unchanged (VaitukaÍtis,
1976'). Free alpha-subunits increase in concentration during
pregnancy to about, 300 ng/rnl of serum whereas beta-subunits remain
at about 50 ng/nl throughout pregnancy, which can be compared
with concentrations of intact hCG of 6 Uçr/mt at its peak value
(10 weeks) and about I pgrlml during the latter part of pregnancy.
However, these concentrations may represent considerably
greater synthesis of free al.pha and beta-subunits, since the
half life of the subunits after injection into female rats is