Trophoblastic giant cells in placentas of rats and mice and their probable role in steroid-hormone production.

Abstract

Implantation sites of rats (pregnant 10 to 21 days) and of mice have been assayed for Δ5-3β-hydroxysteroid dehydrogenase activity by histochemical and biochemical methods. Histochemically, activity was limited to the peripheral giant trophoblasts of the fetal placenta. In rats, enzymic activity was found by both methods to rise to a peak at about 13 to 15 days of gestation and thereafter to decline. This enzyme is required for oxidation of C19 and C21 Δ5-3β-hydroxysteroids to Δ4-3-ketosteroids and thus plays a key role in the biosynthesis of the active steroid hormones. Other features of the giant cells indicating their function in the production of steroid hormones are a conspicuous amount of cytoplasmic lipid and a high capacity for making reduced triphosphopyridine nucleotide (TPNH) as a result of oxidation of glucose-6-phosphate. Some confirmatory evidence has also been presented for local erosive activity and trophic-hormone production by the giant cells. The attributes of the giant cells in rat and mouse placentas are reviewed.