Interrelationships Between the Thyroid Gland and Adrenal Cortex During Fear, Cold and Restraint in the sheep

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Abstract
To examine the relationship between the functioning of the adrenal and thyroid glands in sheep, plasma cortisol concentration, concentration of protein-bound 1251 from thyroid vein plasma, heart rate and blood pressure were measured in ewes bearing exteriorized thyroid glands. During these measurements stresses were imposed on the animals: fear induced by pistol shots or by a barking dog, cold by cooling and wetting, and physical restraint by a loose harness. Increases in plasma cortisol concentration of 2-6 jlg/lOO ml were observed with each type of stressor, the response rapidly decreasing with habituation of the animal. Increases in the concentration of protein-bound 1251 from thyroid vein plasma were also observed repeatedly during cooling and wetting, occasionally after the introduction of a barking dog, and during continued restraint. Cooling and wetting was the only stress causing consistent parallel activation of the adrenal cortex and thyroid gland; the other stressors resulted in independent fluctuations of secretions, as indicated by plasma cortisol concentration and concentration of protein-bound 1251 from thyroid vein plasma. No reciprocal relationship between thyroid gland and adrenal cortex activity was detected.