Abstract
Relationship between serum TSH response to TRH and serum thyroid hormone levels was studied in 8 patients with single hyperfunctioning nodule of thyroid. The results were variable. No or low response to 500μg TRH was observed in 6 subjects, 3 of whom were associated with evevated T4 and T3, one with normal T4 and elevated T3 and two with normal T4 and T3. Normal response was shown in other 2 subjects with normal T4 and T3. Following administration of 2, 000μg TRH to 3 subjects with absence of response to 500μg TRH, 2 subjects with elevated T4 and T3 showed no response, but one with normal T4 and T3 showed low but definite response. After removal of the nodule, TSH response to TRH was increased in 3 subjects. Two of them was associated with decreased T4 and T3 but another one showed negligible changes in T4 and T3. These findings may indicate that responsiveness of TSH to TRH in these patients is not solely dependent on circulating thyroid hormone levels.
