Estrogen suppression of preincubated tadpole ovaries in vitro by cyanoketone

In a previous RIA study we found that cyanoketone (CK) inhibited ovarian E2 secretion of tadpoles in vitro and that this inhibition effect was through inactivation of delta 5-3 beta-HSD activity. A complete 100% inhibition was expected at a CK dosage of 0.1 microgram/ml of the medium, but, instead, it was 85%. The discrepancy might be due to the fact that the previous experiments did not preincubate the ovaries with CK in order to get rid of the residual E2. To this end, the present study was designed. Tadpole ovaries of Rana catesbeiana were preincubated with CK of a dosage of 0, 0.001, 0.01, 0.1, 1, or 10 micrograms/ml of the KRbb medium for 30 min. The media were discarded. Fresh media with the same series of CK doses were added to the ovaries and were incubated again for 6 hr. The media were collected for RIA of estrogen. The results showed the same tendency of estrogen inhibition as the previous study. However, a maximal inhibition effect of 95% was obtained at the dose of 0.1 microgram/ml. Therefore, the difference between non-preincubation of the previous experiments and preincubation of the present study does exist as we predicted.