Thyroid hormone levels during glucose tolerance test in euthyroid subjects.

Twelve normal, healthy, clinically and biochemically proven euthyroid volunteer subjects (age 19-35) were administered a standard glucose tolerance test (100 g glucose orally) and thyroxine (T4), triiodothyronine (T3) and reverse triiodothyronine (rT3) levels were determined by specific radioimmunoassays to determine the acute effect of glucose and insulin on peripheral monodeiodination of thyroxine. The fasting levels of T4, T3, rT3 and free thyroxine were 82.4 nmol/l, 1.7 nmol/l, 0.52 nmol/l, and 0.22 nmol/l, respectively, and these levels were unchanged during the 3 hours post-glucose load. The rise and fall of glucose and insulin levels were typical of the standard responses normally observed in the glucose tolerance test. The variations in insulin and glucose levels were not correlated with thyroid hormone concentrations at any interval during the test. It is therefore concluded that dietary glucose does not acutely cause shifts in peripheral monodeiodination of thyroxine in healthy euthyroid subjects.