THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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stimulating activityf is found in patients with molar preg_.
nancies and choriocarcinomas (Dowling, 1960; OdelL et aI ,
1963t Koch et al , 1g66¡ Mann et al , 1g67; cohen et aI, 1g70;
calton et al_, 197I; Tojo et aL, 19.73) t as wel-l as other
nonchorionic cancers (Hennen, 1956a, bt Lg74,t and is
unresponsive to TRH (Miyai et al , 1966). The thyrotropin
extracted from tumor tissue (Hennen, 1966a, b, L967¡ Hershman
et al , 1970) ttiffers from hCT in molecular size and immuno_
logical properties. Recent evidence (Nisula and Ketekserger,
1974; Kenimer et al, 1975) suggests that a major substance
in hydatidiform moles is chorionic Aonadotropin. Hobrever,
this nay not be an adequate explanation of the thyrotropic
action of these trophoblastic tumors, since the levels of
hCT and hCG in plasma decline at quite different rates
following r:emoval of the trophoblastic disease (Tojo et
al , 1973). Tn addition, although Nisula et aI (l-924)
reported that purified hcc has thyroid_stimulating activity,
Saida et al (197?) has shown that, !ìrhereas their hCT preparation
stimulates cAMp formation in slices of guinea pig thyroid
gland, purifed hCG does not,. Nevertheless, the qucstion of e:levated. thyrotropic
activity during pregnancy is due to an intrinsic activity of hCG(and hLH)
or due to hCT remains unclear.