Cardiac and plasma catecholamine response to dynamic exercise in hyperthyroidism

: To investigate cardiac and sympathoadrenal responses to dynamic exercise, heart rate, systolic blood pressure, serial plasma norepinephrine (NE) and epinephrine (E) concentrations during multistage treadmill exercise were measured in 24 hyperthyroid patients (mean age; 42 +/- 16) and 24 age-sex matched control subjects. Eleven patients were re-examined in the euthyroid state after antithyroid therapy. Exercise duration was shorter in patient with hyperthyroidism. Also, the heart rates and systolic blood pressures at rest and in the early stage of exercise were significantly higher in hyperthyroidism. NE at rest (normal vs hyperthyroid: 124 +/- 10 vs 80 +/- 7 pg/ml, p < 0.01) and NE at peak exercise (475 +/- 38 vs 310 +/- 38 pg/ml, p < 0.01) were lower in hyperthyroidism. E at rest (22 +/- 2 vs 29 +/- 4 pg/ml, n.s.) did not differ, however, E during the first stage of exercise (30 +/- 3 vs 69 +/- 12 pg/ml, p < 0.01) was higher in hyperthyroidism. Re-examination for the euthyroid state revealed the decreases in the heart rates and systolic blood pressures at rest and in the early stage of exercise, and the normalization of the NE and E response. Thus, patients with hyperthyroidism was in the hyperdynamic cardiac state at rest and during dynamic exercise, which was accounted for by decreased sympathetic nervous activity and increased adrenomedullary responses. These modifications of sympathoadrenal response seemed reversible when patients were controlled by antithyroid therapy.