THE SECRETION OF THYROTROPHIN WITH IMPAIRED BIOLOGICAL ACTIVITY IN PATIENTS WITH HYPOTHALAMIC–PITUITARY DISEASE

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Abstract
We describe here two patients with hypothyroidism due to pituitary‐hypothalamic disease in whom basal thyrotrophin (TSH) levels measured by radioimmunoassay (RIA) were elevated yet when measured by a cytochemical bioassay (CBA) were found to be normal. This finding and the absence of the normal rise of thyroid hormones in response to thyrotrophin‐releasing hormone (TRH) mediated release of TSH confirms for the first time the secretion of TSH with impaired biological activity. Primary thyroid disease as a cause for the elevated immunoreactive TSH was excluded by the absence of circulating thyroid antibodies and by a normal thyroidal radioiodine uptake response to exogenous TSH.