THYROID FUNCTION AS RELATED TO THE GROWTH OF TADPOLES BEFORE METAMORPHOSIS

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Abstract
The thyroid function of premetamorphic Rana clamitans larvae was investigated utilizing antithyroid drugs and thyroxine. Measurements of live wet wts. demonstrated that larvae treated with antithyroid drugs (0.015, 0.030 and 0.045% 2-thiouracil and 0.030% thiourea) grew more rapidly than the untreated controls. These results were the reverse of those obtained by thyroxine treatment (1[mu]g. and 5[mu]/l.). Several additional lines of evidence, based on measurements of dry wt., total N, fat content and O2 consumption, are presented to support the view that the changes observed were due to a change in the rate of the normal growth process rather than a fundamental change in the process itself. Variations in diet and environment tested did not have any effect on the form of the responses measured. All the data presented are interpreted as supporting the general hypothesis that the anuran thyroid gland begins active function by the 3d or 4th week after hatching and that the physiological role of its secretion is to control the rate of the normal growth process.

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