AN ATTEMPT TO PRODUCE COMPLETE THYROXINE DEFICIENCY IN THE RAT

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Abstract
Virtually complete thyroxine-deficiency can be produced by feeding young (50 mg.) thyroidectomized rats on low-I, low-thyroxine diet. Although, at 27[degree]C, such animals survived indefinitely, they stopped growing 2-3 weeks after operation and took on an hypothyroid appearance. Beside the lack of general and sexual development, they showed hyperkeratinization of the epidermis, especially in the tail region, exophthalmos and general lethargy. Acidophils were absent in the hypophysis. The thyroidectomized animals given a replacement dose of thyroxine, grew at a normal rate and showed none of these effects. The thyroxine requirement was increased by exposure of otherwise similarly-treated animals to a moderately cool temp. satisfactory for the growth of intact animals (16[degree]C). In addition to similar symptoms as above, around the 4th week after operation, the thyroidectomized animals developed an acute syndrome which is attributed to a sharp fall in body temp. and consists of a progressive muscular paralysis, coma with slow respiratory rate, and death within 1 or 2 days. The failure in the homeothermic mechanism is considered to be the end result of the progressive depletion of thyroxine stores.