STUDIES ON THE ORIGIN OF ALTERED THYROID HORMONE LEVELS IN THE BLOOD OF RATS DURING COLD EXPOSURE

Rats were exposed to cold (4°C) for 1 and 4 weeks. The T4plasma concentrations initially declined (24.5 ± 7.7 nmol/l) after 1 week but returned to normal levels after 4 weeks (52.9 ± 14.2 nmol/l). The T3concentrations were elevated after both 1 and 4 weeks at 4°C (1.31 ± 0.21 and 1.38 ± 0.12 nmol/l, respectively). Control values (23°C) for T4were 42.6 ± 10.3 and for T31.11 ± 0.13 nmol/l. Addition of 0.015 g KI/l to the drinking water prevented the T4decrease in plasma after 1 week of cold exposure. No effect of iodide was observed at 23°C. The suppletion of KI did not change pattern of T3increase after cold exposure. After 4 weeks of cold exposure the T4levels of the iodide-supplemented animals did not differ from the non-supplemented group.No evidence was found that increased food intake is a contributory factor in the development leading to increased T3plasma levels during cold exposure.