The Hemodynamic and Metabolic Interrelationships in the Activity of Epinephrine, Norepinephrine and the Thyroid Hormones

Abstract

The hemodynamic and metabolic effects of a total sympathetic block and of the infusion of l -epinephrine or l -norepinephrine were studied in 27 euthyroid dogs and in 31 thyroid-fed dogs. The physiologic changes produced by increased concentrations of the thyroid hormones were abolished by preventing the reflex release of epinephrine and norepinephrine with a total sympathetic block. The inotropic, chronotropic and calorigenic effects of l -epinephrine and of l -norepinephrine were found to be increased by thyroid feeding. It is concluded that there is a dynamic interrelationship between the thyroid hormones and those of the adrenal medulla and sympathetic nerve endings. The hemodynamic and metabolic changes of thyrotoxicosis are not the result of the isolated activity of the thyroid hormones, but rather are due to the physiologic effects of epinephrine and norepinephrine, as augmented by the thyroid hormones. Studies indicate that l -norepinephrine is the predominant mediator of the changes produced by thyroid feeding.