Studies of the Importance of the Thyroid and the Sympathetic System in the Defence to Cold of the Goat

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Abstract
Markedly hypothyroid goats were found to retain the ability to maintain body temperature during acute cold exposure (‐ 3° C), and to react to local cooling of the hypothalamic thermoregulatory “centre” by a rise in body temperature. However, the shivering response to external cold and to hypothalamic cooling was strongly accentuated, and the increase in urinary excretion of cate‐cholamines (especially of adrenaline) was generally much greater than that of the euthyroid goat. In 3 out of 4 hypothyroid goats studied, the catecholamine excretion at room temperature was also higher than that found in euthyroid goats. During acute cold exposures the blood glucose of the hypothyroid goats rose by about 300 per cent as compared to a rise of about 20 per cent in the euthyroid animals. It is concluded that to maintain thermal homeostasis in the cold markedly hypothyroid goats have to compensate the lack of thyroid hormone by a conspicuous increase in adrenaline secretion. Bilateral splanchnicotomy in the euthyroid goat resulted in practically complete absence of adrenaline in the urine, but did not present the rise in body temperature and the shivering seen during local cooling of the anterior hypothalamus. However, the hyper‐glycemic response to hypothalamic cooling was blocked completely.