Stimulation of the estrogen synthesizing system of the immature rat ovary by exogenous and endogenous gonadotropins.

Immature rat ovaries increase their secretion of estradiol (E2) when stimulated by gonadotropins but only after a lag period of several hours. Once established, estrogen secretion can be maintained, or increased, by the continued presence of gonadotropin. A combination of ovine FSH+LH given at 2 hr intervals stimulated the estrogen synthesizing system (ESS) of the ovary and serum E2 showed a pronounced rise between 16 and 20 hrs after the initial injection. When given every 2 hrs for 5 doses (0-8 hrs) serum E2 was undetectable. However, it was increased if 20 IU PMS was injected at the time of the last dose of FSH+LH. Endogenous FSH+LH, increased by hourly injections of LH-releasing hormone for a period of 8 hrs, stimulated the ESS: serum E2 increased at the expected when this treatment was followed by an injection of PMS. Anti-PMS antiserum given 12 hrs after PMS, prevented the expected rise in serum E2 at 24 hrs. However, FSH, LH or a combination of the two given every 2 hrs beginning at the time of the anti-PMS produced an increase in E2 secretion; the combination was more effective than either hormone alone. These results are consistent with the interpretation that a combined FSH-LH action is responsible for induction fo the ESS in the immature rat ovary. The combination of homones is also very effective in maintaining estrogen secretion but some function appears possible with FSH or LH alone.