In vitro estradiol synthesis and secretion by tadpole ovaries of different developmental stages.

The tadpole ovaries at TK stage XIX can synthesize and secrete estradiol (E2), yet it is unknown when this ovarian function starts and how it develops. To this end, the present work has been carried out. The ovaries of different developmental stages of tadpoles and young frogs of Rana catesbeiana were taken, cut into small pieces, and incubated for 6 hr at 20 degrees in Krebs-Ringer bicarbonate buffer. The media were then analyzed for E2 by radioimmunoassay. The results indicate that the tadpoles synthesize and release E2 as early as stage X, that E2 increases slowly and gradually through stage XXV, and that E2 increases rapidly in juvenile frogs. This trend of growth of the ovarian function in estradiol secretion in vitro is in accordance with that reported for female chick embryos. There exists the possibility that the growth of E2 secretion could be biphasic, one with slow increment of autonomous E2 secretion at early stages and the other with quick increase due to pituitary stimulation at the stage of metamorphic climax.