Abstract
Since a Fundamental Action of thyroid is an increase in the metabolic rate, it might be supposed that such metabolic stimulation might be responsible for the well known acceleration of Metamorphosis in tadpoles. 1 If this were true, the rate ofmetamorphosis might be increased by dinitrophenol (1-2-4), which has been shown to increase mammalian metabolism to a remarkable degree. 2 However, the results of this study indicate that, in this respect, these 2 metabolic stimulants differ, as indeed they do also clinically. 3
Tadpoles of Bufo halophilus from the same and neighboring egg strings and in the same stage of development were selected at random from a swarm of about 1,000 and divided into 13 groups of 10 each. Two groups were used as untreated controls, 3 for various concentrations of thyroxin, and 8 for various concentrations of alph-dinitrophenol (1-2-4). Each group of 10 was kept in 200 cc. of tap water which contained a clump of green algae and about 5 cc. of pond water. The solutions and algae were changed every second day. Later in the experiment, 1 cc. of raw minced liver was fed each group every second day, about an hour before changing the solutions. Solutions of crystalline thyroxin (E. R. Squibb and Sons) were added to the baths to give final concentrations ranging between 1:150,000 and 1:2,000,000 and of dinitrophenol to give final concentrations ranging from 1:5,000 to 1:4,000,000. The pH of all the final solutions, including the controls, was between 7.21 and 7.47. This close similarity in the pH values is important, since Zondek and Ucko 4 have shown that the increase in rate of metamorphosis in tadpoles by thyroid extract is modified by the H-ion concentration of the medium. The experiments were made at a fairly constant room temperature of about 22°. and in dull sunlight. Records of the growth and development were made at frequent intervals and accurate measurements of length were made by photographing the tadpoles against a millimeter scale.
Conclusions. 1. Toad tadpoles were found to metamorphose no more rapidly in up to lethal concentrations of dinitrophenol than in the absence of medication, whereas the usual acceleration of metamorphosis was demonstrated in tadpoles on thyroxin. This difference in action agrees with clinical differences in human subjects. 2. Although dinitrophenol can cause increases in metabolism comparable to those of thyroxin, it appears to lack the power of thyroxin to accelerate developmental processes. Apparently, the effect of thyroxin on metamorphosis is not the direct result of increased metabolism, but presumably an independent action. 3. Accordingly, dinitrophenol lacks the hormonal actions of thyroid, and should probably not be used therapeutically to replace the gland in true thyroid deficiencies.
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