ABSTRACT
An important action of thyroxine is to augment the response of adrenergic effectors to the catecholamines. An increased basal metabolic rate (BMR) accords with hyperthyroidism, but could also be a manifestation of the calorigenic action of excess catecholamines. Generalized hypermetabolism produced by excess thyroxine causes autoregulatory vasodilation to increase blood flow to tissues, producing a lowered diastolic pressure, an increased cardiac output, and a wide pulse pressure. Patients with pheochromocytoma, in contrast, would be expected to have elevated diastolic pressures.
