Thyroxine-Binding Proteins and Butanol-Extractable Iodine in Sera of Adolescent Males*

Abstract

Serum thyroxine-binding globulin (TBG) and pre-albumin were measured in a clinical study of the thyroid function of 38 normal males 13 to 18 years old. Tris maleate was the buffer for paper electrophoretic estimation of thyroxine-binding proteins (TBP). Simultaneous duplicate determinations of serum butanol-extractable iodine concentration were in the low range reported previously for adolescents. For each subject, sexual development was estimated clinically at the time of physical examination, with observations on facial, axillary, and pubic hair, genital development and signs of gynecomastia. TBG capacities ranged from 14 μg through 28 μg of thyroxine per 100 ml, extending slightly beyond Ingbar's euthyroid range for adults (17 μg to 25 μg of thyroxine per 100 ml of serum). On the other hand, thyroxine- binding pre-albumin (TBPA) varied in relation to maturity. For adults, Ingbar reported TBPA capacities between 80 μg and 150 μg of thyroxine per 100 ml of serum. Twenty-four boys aged 13 to 16 years had TBPA capacities in a lower more variable range (89 μg±19.2) than 14 boys aged 17 to 18 years (115 ±13.8 μg of thyroxine per 100 ml of serum). The significantly lower TBPA capacities coincided with the growth-spurt age and the high metabolic expenditure of oxygen. The accelerated tissue metabolism of hyperthyroidism is frequently but not invariably accompanied by a low TBPA capacity. The significance of low TBPA capacity during adolescence needs evaluation with tissue metabolic activity and also with the effects of male sex hormones.