Sex reversal in female tadpoles induced by the treatment with methylmercaptoimidazole.

Since Gordon et al.(1943)reported that amphibian metamorphosis is effectively inhibited by thiourea treatment,a considerable number:of studies have been made by many investigators to examine the effects of antithyroidal substances on amphibian larvae.Most of them,however,dealt with only the inhibition of metamorphosis or the dipigmentation,and no description on the gonads of the treated larvae was found out.The author previously reported on the transformation of ovaries to testes(Iwasawa,1955a,b,1958a)and on the precocious germ cell differentiation(Iwasawa,1957a)in thiourea-treated larvae.The drugs used by foreign investigators were mostly thiouracil,propylthiouracil or phenyl-thiourea, and occasionally,thiourea.Consequently there remains some reason to think that the above mentioned changes observed in the gonads of thiourea-treated larvae were not the common effect of antithyroidal substances,but the specific effect of thiourea.Of course there are other important points to be considered as the causes of this difference,that is,type of sex differentiation,correlationship among the endocrine glands,responsibilities of the endocrine organs for antithyroidal substances,and so on.These matters will be discussed in the ensuing papers.l-methyl-2-mercaptoimidazole is a newly discovered antithyroidal substance,and its stronger antithyroidal effect and lesser by-effects in mammals are already recognized.Therefore,in the present paper,the effects of this substance upon the gonadal development of Rhacophorus larvae were dealt with. The author wishes to thank Prof.I.Motomura of the Tohoku University for his valuable suggestion and encouragement.