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Biology of Reproduction, Vol 12, 351-359, Copyright © 1975 by Society for the Study of Reproduction
5,3
-Hydroxysteroid Dehydrogenase
1 Dept. of Cell Biology, Roche Institute of Molecular Biology, Nutley, New Jersey 07110 Of all embryonic and extraembryonic tissues in midgestation mouse conceptuses, only trophoblast
has significant levels of Blastocyst cultures are capable of converting pregnenolone added to the medium to progesterone. In
this way, 3
5,3
-hydroxysteroid dehydrogenase (3
-HSD) activity as measured by
progesterone production by sensitive biochemical assays. Because of the importance of progesterone in
the maintenance of pregnancy, we have carried out a study of 3
-HSD activity during trophoblast
development in vivo and in vitro. Enzyme activity is first detected in trophoblast homogenates on the
ninth day of gestation, peaks on the eleventh day, and then falls on the twelfth day. The enzyme activity
is almost totally restricted to that fraction of the trophoblast layer containing giant cells. 3
-HSD can
be detected in growths containing trophoblast cells developing from blastocysts implanted in
extrauterine sites. Enzyme activity is also present in cultured blastocysts, and is associated mainly with
trophoblast-containing monolayers rather than with vesicles which are devoid of trophoblast cells.
However, compared to trophoblast developing in utero, 3
-HSD activity is low in ectopic trophoblast,
and very low in trophoblast from blastocyst cultures.
-HSD activity can be measured in small numbers of blastocysts. Using this technique, we
have found that 3
-HSD is detectable in trophoblast cells developing in culture at least as early in
gestation as it is observed in uterine trophoblast homogenates.
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