Abstract
SUMMARY: The placenta and the foetal membranes of rats (pregnant 5–21 days) have been assayed by histochemical methods for 3β-hydroxysteroid dehydrogenase (3β-HSDH), NAD-dependent, and 17α- and 17β-hydroxysteroid dehydrogenases (17α- and 17β-HSDH), both NAD and NADP-dependent. 3β-HSDH was limited to the trophoblastic giant cells of the first generation, whereas 17α- and 17β-HSDH were present in both the first- and second-generation giant cells and also in the endodermal cells of the inverted yolk sac placenta.