The effect of change in chemical structure of some thyroxine analogues on the metamorphosis of Rana pipiens tadpoles.

Forty-three different substances structurally related to tliyroxine were assayed for their metamorphosing effect on Rana pipiens tadpoles. Triiodinated compounds with iodines at the 3,3′,5 positions were found more active than tetraiodinated compounds. The 3,5- and 3,3′ diiodinated compounds tested also had some activity except for the 3,5 diiodothyroformic acid. None of the monoiodinated compounds assayed showed biological activity. The most active compound studied was 3,3′,5-triiodothyropropionic acid which was 300 times more potent that ?-thyroxine. IN 1912 Gudernatsch (1) showed that tadpole metamorphosis was under the control of the thyroid gland. Since these original observations, many iodinated compounds have been reported capable of inducing amphibian metamorphosis. Recently the relationship of thyroxine-like metamorphosing activity and chemical structure of some compounds has been studied by Roche et al.(2) and reviewed by Bruice et al. (3). The recent discovery of naturally occurring thyroxine-l...