The dynamics of the steroidogenic response of perifused Xenopus ovarian explants to gonadotropins.

Steroid release before and during maturation was studied in Xenopus ovarian follicles under various conditions of stimulation of LH in a perifusion system. Acute stimulation by 15 micrograms of LH induces a 10-fold increase in the androgen (testosterone and androstenedione) level which reaches a maximum 4 hr later and then slowly decreases until the 25th hour. Repeated stimulations every 2 or 4 hr are followed by the same androgen increase during the first 8 or 10 hr and then by a slow decrease in the secretion despite new LH injections. A significant increase in progesterone secretion is seen only after at least two stimulations (8 hr). Estradiol secretion slowly increases to a moderate level during the first 5 hr and then remains stable whatever the stimulation. During continuous stimulation (LH 0.5 microgram/ml) androgen levels reach an initial maximum after 4 hr and then fluctuate with a 2-hr period. Addition of theophyllin to the medium enhances these fluctuations. After 12 hr when the progesterone has increased, androgen secretion diminishes to reach a basal level without fluctuations. Germinal vesicle breakdown occurs only in follicles that have been appropriately stimulated to secrete androgens and progesterone during the required time.