The effect of vasopressin on hormone secretion and blood flow from the thyroid vein in sheep with exteriorized thyroids.

1. Vasopressin has been shown to activate the thyroid in some species, and also to be released into the bloodstream after emotional and other stresses.2. Emotional stimuli applied to sheep have previously been shown to increase thyroid secretion and the possible influence of vasopressin in this process has been investigated. Sheep bearing exteriorized thyroid glands were used, so that thyroid vein blood could be collected in undisturbed conscious animals.3. (125)I or (131)I (50 muc) was injected I.M. into the sheep; 4-7 days later, samples of thyroid vein blood were collected at 10 min intervals for 4 hr, and the concentration of total and protein bound (125)I or (131)I was measured. Intravenous infusions of 0.3, 3.0 or 31 m-u./min arginine or lysine vasopressin, or close arterial infusions of 3.0 or 31 m-u./min arginine vasopressin were administered 1.5 hr after commencement of blood sampling. Blood flow from the thyroid was measured by a plethysmographic technique during similar experiments.4. No significant changes in thyroid hormone secretion were observed as a result of vasopressin infusion, and it was concluded that vasopressin release does not play a part in the activation of the thyroid resulting from emotional stimulus in the sheep.