Radioimmunoassay of Human Plasma Thyrotropin*

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Abstract
A method for the radioimmunoassay of human plasma thyrotropin (HTSH) has been developed. Purified HTSH was for immunization of rabbits, radio-iodination and immunoassay standard. Unlabeled HTSH inhibited the binding of HTSH-I131 by anti-HTSH serum so that 1. 5 m[mu]g (. 015 m [mu]) HTSH/ml plasma was detectable. Chromatoelectrophoresis was used to separate free and antibody bound HTSH-I131. No HTSH was detected in plasma from various animals, in plasma from hypopituitary patients, or in bovine or ovine pituitary TSH preparations. Plasma HTSH ranged from undetectable to 15m[mu]g/ml (0.15 mU/ml) in normal subjects and from 18 to 180 m[mu]g/ml (0.18 to 1.8 mU/ml) in patients with primary hypothyroidism. In hyperthyroid patients, plasma HTSH was undetectable in 75% of cases. No change in plasma HTSH followed insulin hypoglycemia or hyperglycemia and no diurnal variation was found. In hypothyroid patients, initially elevated plasma HTSH values all fell to normal during replacement therapy, the rapidity of response being determined both by the type and dosage of thyroid hormone given.