THE UPTAKE OF I¹³¹ BY THE THYROID GLAND OF TURTLES AFTER TREATMENT WITH THIOUREA

¹ Department of Biology, The Catholic University of America, Washington, D. C.

1. The painted turtle, Chrysemys picta (Schneider), was treated with a 0.1 per cent solution of thiourea by means of subcutaneous injections, then injected with radioiodine in order to determine the correlation of percentage epithelium and colloid level with radioiodine uptake. The data obtained in this study were analyzed statistically in terms of length of treatment and the time of the year during which the work was carried out.

2. From the point of view of length of treatment, the correlations between the uptake of I¹³¹ and colloid level or per cent epithelium were very poor, due to the high degree of variability.

3. When these results were analyzed from the point of view of seasonal cyclic activity, the correlations were decidedly improved.

4. The best correlations were obtained in the fall group, where the percentage epithelium of experimental and control aninials was more closely related; the range of variation was decidedly lower, and the correlation between colloid level and uptake of radioiodine much better than in the other series.

5. Further evidence in favor of the seasonal cyclic activity was found in the uptake per milligram dry weight, and in the thyroid/serum ratio.

6. This seasonal factor appears to be genetic in nature since it exerts its control independently of the environmental temperature and the effects of the drug.