Evidence for macromolecular synthesis in stimulation of the estrogen synthesizing system of the immature rat ovary by PMS.

Exposure of immature rat ovaries to pregnant mare's serum gonadotropin (PMS) results in a prompt increase in testosterone and progesterone output but synthesis of estradiol (E2) increases only after a lag period of several hours. Actinomycin D (Act-D) given with PMS did not inhibit testosterone or progesterone production but the estrogenic response was prevented. Delay in administration of the Act-D until 12 hr after PMS resulted in a transient increase in E2 secretion lasting less than 12 hrs. When Act-D was given 12, 16 or 20 hrs after PMS, and ovarian steroid production measured by a one hr incubation, no inhibition of progesterone, testosterone or E2 was found; the synthesis of the latter two steroids was increased by the drug. Cycloheximide, on the other hand, was most effective at inhibiting testosterone and E2 production when it was given at 12 hrs; the drug was progressively less effective in lowering production of these steroids when it was given at 16 or 20 hrs. Cycloheximide did not alter progesterone production unless it was given at the same time as PMS. The results are consistent with the view that the induction of the estrogen synthesizing system of the immature rat ovary by gonadotropin involves, during the first 12 hrs, production of a material sensitive to Act-D inhibition (mRNA?) and then production of a material sensitive to cycloheximide inhibition (protein-enzymes?). The continued production of both of these materials appears to require the continual presence of gonadotropin.