サイロキシン結合蛋白の臨床的意義

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The PBI, the resin uptake of 131I-T3, total TBG and endogenous binding TBG have been determined in a total of 134 patients (28 clinically healthy, 13 of them male, 15 female, 25 prengnat, 27 hyperthyroid, 13 hypothyroid, 7 nephrotic, 35 simple goiter and 8 hepatic cirrhosis). Maximum TBPA capacity and serum free thyroxine were also determined in 86 cases of these patients. When γ-resorcylic acid which may inhibit binding of thyroxine to TBPA was added to serum, the resin uptake of 131I-T4 increased more markedly in hyperthyroid than in normal subjects, compared with control resin uptake of 131I-T4, but no elevation in the resin uptake of 131I-T4 after γ-resorcylic acid addition was found in hypothyroid. In this country, dietary iodine is difficult to be restricted. Therefore, slightly elevated PBI level may be caused in high iodine diet, as suspected by the fact that 24-hour stable urinary iodine excretion values are remarkably higher than those reported in foreign countries. Clark's free thyroxine index was influenced by slightly elevated PBI, and there was an increased percent of patients falling outside of the normal range in the euthyroid sick group. Clark's index was evaluated. Free thyroxine index derived from free TBG values reflected better thyroid status, and had a highly significant correlation (r=0.95) with serum free thyroxine. The ratio of the free 131I-T4 to the protein-bound (F/B) which was separated on microcolumn of Sephadex G-25, showed highly significant differences between the normal and hyperthyroid or hypothyroid, but there was no significant difference between the normal and pregnant. Free thyroxine values by gel filtration and equilibrium dialysis showed significant good correlation (r=0.97); no significant difference was found between them. The remarkble reduction in maximum TBPA capacity in the hyperthyroid and euthyroid severely sick patients, and marked elevation in total TBG capacity in the hyperthyroid, pregnant and some patients who had hepatic cirrhosis, were observed. Results are summarized as follows : 1) In the PBI, the resin uptake of 131I-T3, total TBG capacity and freethy roxine, there was no significant difference between the normal male and female, but in the latter a significant reduction in TBPA capacity was observed. These results suggest that the reduction in TBPA capacity within physiologic changes may give no significant influence upon serum free thyroxine. 2) Correlation between F/B and endogenous binding TBG/free TBG was highly significant. It is suggested that free thyroxine percent was not dependent upon increase or decrease of free TBG, but closely upon the ratio of endogenous binding TBG/free TBG. Its ratio was very consonant with thyroid status. 3) Maximum TBG or TBPA capacity showed significant reverse relation to serum free thyroxine. The reduction in TBG or TBPA capacity may result in the increase of serum free thyroxine. 4) Endogenous thyroxine binding to TBPA had close relation with endogenous distribution in TBG in each group. It is suspected that dissociation of free thyroxine from thyroxine-binding TBPA in response to a demand in peripheral tissues would be followed by dissociation of free thyroxine from bound thyroxine to TBG, and that the ratio of bound form to free TBPA would change maintaining a constant equilibrium in proportion to the ratio of bound to free TBG. 5) The author's free thyroxine index was more consonant with thyroid status than Clark's, the former had highly significant correlation with serum free thyroxine.
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サイロキシン結合蛋白の臨床的意義

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