Abstract
The distribution of hydroxysteroid dehydrogenase (HSD) was examined histochemically in the placenta and ovary of the cat at 14 gestational stages to discuss the possibility of steroidogenesis in the cat placenta. The enzymes investigated in this study were Δ5-3β-HSD, 17β-HSD, 20α-HSD, 20β-HSD and G-6-PDH. The activity of Δ5-3β-HSD was detected in the trophoblast of placental labyrinth and junctional zone. The activity of Δ5-3β-HSD was weak at the early stage of gestation, but being gradually increased with the progress of gestation. The activity was strongest at the stage of an 88-mm fetus in CRL (day 45), then decreased slightly toward term. No activity of 17β-HSD was detected in the trophoblast, but a weak activity was detected in the glandular epithelium, persisting throughout pregnancy. In the corpus luteum, the activity of Δ5-3β-HSD was strong or moderate until the stage of an 80-mm fetus (day 43), then abruptly decreased toward term. These results suggested that the conversion of pregnenolone into progesterone may proceed in the trophoblast of the cat placenta and support the fact that ovariectomy after day 45 or 49 of gestation did not interrupt pregnancy.
