The correlation of fine structure with endocrine function of ovarian follicle cells in tadpoles

Estradiol secretion by the ovarian tissue, in response to hypophyseal stimulation, during ontogenesis of the bullfrog

Ovaries of tadpoles, froglets, young frogs, and mature frogs of Rana catesbeiana were cut into small pieces. They were incubated for 6 hr in Krebs-Ringer bicarbonate buffer as controls. Another series of ovaries of the same developmental stages were incubated with pituitary extracts in the buffer as experimentals. Media were then analyzed for estradiol secretion by radioimmunoassay. The results showed that estradiol secretion by tadpole ovaries during development was not affected by the addition of pituitary extracts of mature frogs in the media at any stage while those of young and mature frogs with pituitary extracts secreted more estradiol than those without. These findings indicate that tadpole ovaries are unresponsive to pituitary agents to produce estradiol while frog ovaries are dependent on some pituitary hormones to synthesize estradiol. Thus frog ovaries acquire dependence on the pituitary agent only after metamorphosis.

In vitro inhibition of estradiol secretion of tadpole ovaries by cyanoketone

We have demonstrated the presence of delta 5-3 beta-hydroxysteroid dehydrogenase (HSD) activity in tadpole ovaries of Rana catesbeiana. In the present study, we wish to determine whether estradiol (E2) secretion of tadpole ovaries could be influenced by cyanoketone (CK), a specific inhibitor of delta 5-3 beta-HSD. R catesbeina tadpoles at the premetamorphic climax were used, and pooled ovaries were incubated, 30 mg/tube, with CK at dosages of 0, 0.001, 0.01, 0.1, 1, and 10 micrograms/ml of Krebs-Ringer bicarbonate buffer for 6 hr. Media were collected for assay of E2 by radioimmunoassay (RIA). Results showed an inhibition of E2 secretion by CK that was positively correlated with CK dosage, but plateaued at doses of 0.1 microgram/ml and higher. This finding was comparable to that of G.F. Young, H. Kagawa, and Y. Nagahama (1982, Gen. Comp. Endocrinol. 47, 357-360) on adult fish ovaries. However, adult vertebrates depend on gonadotropins to regulate secretion of E2 while tadpoles, being immature, might secrete E2 independently of pituitaries. When the histochemical test for delta 5-3 beta-HSD activity was performed on in vitro CK-treated ovaries, there was a decrease of enzyme activity by CK. The RIA and histochemical findings may contribute to the concept of sex transformation in which a disturbance of steroidogenesis may induce sex reversal from females to males, at least in tadpoles.