[Clinical studies on regulatory system of thyroid hormone secretion and serum triiodothyronine. Part. I. Solid-state radioimmunoassy for human serum TSH and its clinical application (author's transl)].

A solid-state RIA method using a plastic microtiter plate for human TSH was developed: 1) The choice of carrier protein for standard TSH was critical in this method and pooled sera from untreated Graves patients was found to be suitable for this purpose. The mean lowest detectable TSH level was 0.2 muU/assay, which was almost equal to those reported by other methods. This method is superior in simple assay procedure, especially in the separation of bound and free TSH and in the shorter incubation time required in the double antibody method. 2) Serum TSH concentration in 22 normal subjects, 17 patients with Graves' disease, 35 Hashimoto's thyroiditis, 18 primary hypothyrodism, 16 simple goiter, 4 nodular goiter and 7 secondary hypothyroidism was estimated as 4.7 +/- 2.0 muU/ml (mean +/- s.d.), 2.1 +/- 0.2 mu/U/ml, 14.1 +/- 26.5 muU/ml, 211 +/- 177 muU/ml, 3.6 +/- 2.4 muU/ml, 3.2 +/- 2.4 muU/ml and 2.6 +/- 1.0 muU/ml, respectively. 3) A statistically significant and hyperbolic inverse correlation (r= --0.37, N=90) was found between TSH and T4 levels. Some cases with normal T4 level were found to be high in TSH levels. It was also noted that 36 of 65 euthyroid cases (55.4%) who had been treated with 131I for Graves' disease showed elevated TSH levels. 4) After intravenous injection of 500 mug TRH, TSH level reached its peak value of 8 to 32 muU/ml at 15 to 45 minutes in normal subjects. Low to no response was found in patients with Graves' disease. An exaggerated response in patients with primary hypothyroidism to TRH was observed and an inhibitory process in TSH production at the pituitary level was suggested in patients with Cushing syndrome. Hypothyroid patients with pituitary lesion showed low or no response, on the other hand some hypothyroid patients with lesions around the pituitary and hypothalamus showed high basal TSH and exaggerated response to TRH.