Digitoxigenin, a digitalis steroid, induces meiotic maturation of Xenopus laevis oocytes

Digitoxigenin, a C23 digitalis steroid induces meiotic maturation of Xenopus oocyte. The dose of digitoxigenin which induces half maximal response is 3.3 +/- 2.10(-5)M. In contrast the conjugated digitalis steroid, digitoxin (digitoxigenine + 3 digitoxoses) never triggered maturation at any of the doses tested. These experiments which show that only free digitoxigenin mimics progesterone action, suggest that both digitoxigenin and progesterone possess a common initial site of action which is not localized at the level of the outer leaflet of the oocyte plasma membrane.