[Increase of circulating thyroid hormones following oral administration of TRH in preclinical hyperthyroidism. Biological efficacy of minimal TSH stimulation].

In patients with multinodular goiter and preclinical hyperthyroidism (euthyroid values of free T4-index, free T3-index, free T4, absent TSH response to oral TRH (40 mg), i.e. TSH after TRH less than 1.0 microU/ml) a statistical increase in the serum-T3 (free T3-index), serum-T4 (free T4-index) and free T4 was observed after oral TRH. No thyroid response to oral TRH occurred in multinodular goiter patients with hyperthyroidism or in preclinically hyperthyroid +athyrotic patients under T4. The thyroid response in patients with a preclinically hyperthyroid goiter was significantly lower than the response in goiter patients with a normal TSH reserve and in controls. The results demonstrate that (1) in euthyroid TRH-TSH unresponsiveness the pituitary TSH-reserve may not be completely suppressed; (2) very small variations in TSH not detectable by the available radioimmunologic assay may be of biological importance. In euthyroid TRH-TSH-unresponsive patients under T4 (simple goiter, differentiated thyroid carcinoma) thyrotropic function may not be completely suppressed. In euthyroid TRH-TSH-unresponsive patients with an autonomously functioning adenoma, additional exogenous suppression should be evaluated for protection of paranodular tissue before ablative radioiodine is given.