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The Effects of L-Thyroxine and Cold-Exposure on the Amount of Food Consumed and Absorbed by Male Albino Rats

Department of Physiology, University of Hong Kong, Hong Kong

1. The effects of environmental temperature and daily subcutaneous injection of 20 µg of L-thyroxine on the digestion coefficient (DC) of a standard diet fed to rats was determined by the use of chromic oxide as an index material.

2. At 28°C the DC was about 78.4%. The injection of L-thyroxine resulted in a reduction of the DC to about 71.4%.

3. At 4°C the DC was about 75.8%. The injection of L-thyroxine resulted in a slight, but significant, fall of DC to about 73.8%.

4. Food consumption of rats kept at 28°C increased after daily injections of L-thyroxine for two weeks, but this did not occur when the experiment was repeated at 4°C.

5. It is suggested that L-thyroxine may have had separate effects on food consumption and on the ability of the animals to absorb food. The reduction in DC could have been the result of increased peristaltic activity.

6. For rats weighing about 220 gm the energy requirement for maintenance of body weight at 4°C was about 84.8 Cal./day. The caloric equivalence of the tissues formed was about 5.8 Cal./gm.