Abstract
Abstract The effect of thyroid hormones on blood flow alterations produced by norepinephrine, epinephrine, angiotensin, and vasopressin has been investigated. Dogs and cats were divided into several groups according to the different thyroid preparation which they received for a period of 2 weeks. Control groups were given lactose. Heart rate, blood pressure, body weight, electrocardiogram, serum cholesterol, and, in some animals, oxygen consumption were recorded before and after treatment. The vasoactive drugs were infused into the femoral artery while blood flow of the hind limb was recorded by venous occlusion plethysmography both before and after thyroid administration. Contrary to expectation, both epinephrine and norepinephrine produced significantly less vasoconstriction following the administration of thyroid hormones. There was no significant alteration in the effect of angiotensin or vasopressin. Nethalide, a selective beta adrenergic blocking agent, restored vasoconstriction produced by epinephrine or norepinephrine in animals treated by thyroid preparations. It is suggested that in hyperthyroidism there may be an increased sensitivity of the beta receptors rather than a general increased sensitivity to catecholamines.
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