Discussion
hyperthyroidism, cardiopulmonary disease, Hyperthyroidism, hyperthyroid
THYROID STORM, CARDIOPULMONARY DISEASE, HYPERTHYROIDISM, HYPERTHYROID, COLD, HYPERTHYROIDISM
Hyperthyroidism elevates patients’ REE and significantly increases their oxygen consumption. Especially in the setting of thyroid storm or in patients with concomitant cardiopulmonary disease it is highly desirable to acutely reduce REE. Beta-adrenergic blockade with propranolol or other β-blockers is recommended to quickly alleviate the symptoms of hyperthyroidism (Theoretically the amount of propranolol given in our study could have been insufficient. In a previous trial propranolol effectively reduced REE when given to patients suffering from hyperthyroidism for a period of four weeks. Patients received a cumulative daily amount of 160 mg to 320 mg, divided into four single doses which translates into similar plasma levels as a single dose of 80 mg (Patients underwent calorimetry in a fasted state and predominantly metabolized fatty acids (FAs) as indicated by a respiratory quotient (RQ) close to 0.7. During the control visit the RQ declined further, in line with increased use of FAs. However, after intake of propranolol, the RQ remained stable implying that propranolol slowed lipolysis by blocking βBAT is a major target of TH and metabolically active in hyperthyroidism even in the absence of a cold stimulus (TH are crucial for BAT differentiation and activity and are required for mitochondriogenesis and the regulation of UCP1 in response to cold exposure (Recent data from experiments in rodents indicate that the increase in REE and body temperature induced by high levels of thyroxine are centrally mediated and independent of UCP1 (βIn addition, increased metabolism within the liver may contribute to the elevation of REE in hyperthyroidism. Investigations in isolated hepatocytes from hyperthyroid rats revealed an increased mitochondrial proton leak as well as a higher ATP consumption as a source of stimulated thermogenesis (Although skin temperature in the supraclavicular region where BAT is mainly located (β-blockers and especially propranonol can have a direct effect on TH metabolism, especially by the conversion of T4 to T3 (Our study is the first to evaluate the effects of propranolol on REE in hyperthyroid patients. Strengths of our study comprise a prospective design and a cohort representing the clinical reality of hyperthyroid patients. Our conclusions on the effect of propranolol on BAT activity are limited by the fact that we did not employ 