THE METABOLIC RESPONSE TO THYROID DEPRESSANT DRUGS IN ANIMALS MAINTAINED IN A COLD ENVIRONMENT

Abstract

Female rats of the hooded var. were placed in a refrigerator and the temp. slowly lowered from 5 to 0cC over the course of 10 days and maintained at this level throughout the expt. Metabolism was followed by determining the oxygen consumption by means of the multiple chamber apparatus, and the oxygen consumed recorded on kymograph drums. Most normal rats showed a 23% increase in oxygen consumption, although one group showed only 13% increase during refrigeration . The findings suggest that failure to adapt to the elevated metabolism, rather than failure of the metabolism per se, is the essential factor in the mortality of thyroidectomized rats exposed to low temps. Although the thyroid is apparently not essential for the metabolic response to acute cold, medical thyroidectomy (thiouracil) abolished the response to chronic cold. Iodine therapy moderately depresses oxygen consumption in chronically refrigerated rats. No anti-thyroxine properties could be demonstrated with the use of a tyroxine analogue, p-nitrobenzyl ether of N-acetyl-3, 5-di-iodo-L-tyrosine.