Stimulation of Vitellogenin Uptake in Stage IV Xenopus Oocytes by Treatment with Chorionic Gonadotropin in vitro

Ovarian fragments from Xenopus laevis were incubated with various concentrations of human chorionic gonadotropin (hCG) and Stage IV oocytes were subsequently tested for their ability to incorporate vitellogenin. Such oocytes displayed incorporation rates up to 350% greater than controls. This was accompanied by increased endocytotic activity. hCG-stimulated uptake is dose dependent and reaches a maximum at 100 IU/ml, at which concentration ovulation also occurs. At 100 IU/ml of hCG, there is a lag period of at least 12 h between gonadotropin treatment and increased vitellogenin incorporation. Because hCG has little effect on isolated (dissected) cultured Stage IV oocytes which have lost their follicle cells, it is postulated that intact follicle cells are required for the induction of vitellogenin uptake.