Urinary excretion of 3-methylhistidine and creatinine and plasma concentrations of amino acids in hyperthyroid patients following preoperative treatment with antithyroid drug or beta-blocking agent: results from a prospective, randomized study.

The aim of this investigation was to compare the effects of a beta 1-selective adrenoceptor blocking agent and an antithyroid drug on urinary excretion of creatinine (Cr) and 3-methylhistidine (3-MH) and plasma concentrations of amino acids in hyperthyroid patients. beta-adrenoceptor blocking agents are increasingly used in the treatment of hyperthyroid patients, and the effects on clinical signs and symptoms mainly reflect beta 1-adrenoceptor blockade. The consequences of this treatment on metabolic alterations in hyperthyroidism are not fully known. In the present study, 30 hyperthyroid patients were randomized to preoperative treatment with the antithyroid drug methimazole + thyroxine (group I) or the beta 1-selective adrenoceptor blocking agent metoprolol (group II). Urinary excretion of Cr and 3-MH and plasma concentrations of amino acids were measured at the time of diagnosis, following preoperative treatment and 6 months postoperatively. Serum triiodothyronine (T3) was comparably elevated in the two groups of patients at the time of diagnosis and was normalized during preoperative treatment in group I but remained elevated during preoperative treatment in group II. Urinary excretion of creatinine was lower at the time of diagnosis than postoperatively, suggesting reduced muscle mass during hyperthyroidism. Urinary excretion of Cr increased during preoperative treatment in group I but was not significantly altered during treatment with metoprolol. The 3-MH/Cr ratio, which was higher at the time of diagnosis than postoperatively, indicating accelerated protein breakdown in skeletal muscle during hyperthyroidism, was reduced during preoperative treatment in group I but not in group II.(ABSTRACT TRUNCATED AT 250 WORDS)