Accelerated female differentiation of the gonad by inhibition of steroidogenesis in amphibia

Abstract

Larvae of toad ( Bufo bufo) and frog ( Rana dalmatina) were treated with 17 β C (androsten-3 one 17 β-carbossilic acid) at early stages of development in order to inhibit the activity of 5-α-reductase and to reduce the level of dehydrotestosterone, die active form of the male hormone. The effects of drug treatment on larval ovarian differentiation were analyzed at different stages in the rostral portion of the gonad of Bufo (Bidder's organ, a rudimentary ovary) and at early stages of metamorphosis in the female gonads of Rana. The Bidder's organ of experimental Bufo larvae were characterized by a considerable increase in volume and an anticipated differentiation of germ cells. In fact, oocytes of these specimens were present at earlier stages and increased in size at a faster rate than controls. The gonads of female larvae of Rana showed a much higher number of oocytes, which were also considerably larger in size. As a working hypothesis, we suggest that cells present in the larval androgenic component of the gonad may synthesize small amounts of dehydrotestosterone acting locally by diffusion upon the gynogenic component destined to produce an ovary. This hormone would inhibit ovarian development in genetic males and would regulate the time table of differentiation in genetic females. Hence the exuberant ovarian development in specimens with an induced lower level of dehydrotestosterone.