Plasma catecholamine concentrations in hyperthyroidism and hypothyroidism.

Using a modification of the fluorometric method of Anton and Sayre, we have measured the plasma epinephrine (E) and norepinephrine (NE) concentrations in patients with thyroid dysfunction. There was no significant difference in plasma E in hyperthyroid or hypothyroid subjects, the values being similar to those observed in normal subjects. There was a striking relationship between age and plasma NE in the euthyroid individuals (r = 0.685, p less than 0.001, n = 41). Observed plasma NE concentrations were similar in control subjects (21.05 +/- 1.6 ng/100 ml; mean +/- SEM) and hyperthyroid patients (22.33+/- 2.0 ng/100 ml). However, plasma NE was significantly increased in hypothyroidism (35.46 +/- 3.9 ng/100 ml; p less than 0.01) and remained statistically different when the age factor was excluded (31.31 +/- 2.67 ng/100 ml; p less than 0.025). There was no correlation between plasma NE and serum thyroxine (T4), free thyroxine (FT4), or triiodothyronine (T3), in any of the three groups studied. These data indicate that hyperthyroidism is accompanied by normal plasma NE concentrations and that hypothyroidism is associated with significantly increased plasma NE concentrations, possible in an attempt to compensate for the lack of thyroid hormones.