Pituitary TSH in Normal Subjects and in Patients with Asymptomatic Atrophic Thyroiditis: Evidence for its Immunological Heterogeneity

Abstract

Biological and radioimmunological measurements of pituitary TSH concentration were performed in 22 cases of asymptomatic atrophic thyroiditis and in 18 controls. Whilst bioassay revealed the presence of a greater pituitary TSH concentration in thyroiditis cases, radioimmunoassay failed to confirm such a difference. The reason therefore seems to lie in the presence in thyroiditis pituitaries of a TSH which reacted in the bioassay but showed only a weak affinity for the anti-hTSH antiserum. The slopes of radioimmunological dilution curves of the pituitary extracts were indeed significantly lower with thyroiditis pituitaries than with controls. When the whole population sample was considered, a negative correlation existed between the ratio of biological and radioimmunological TSH determinations (B/I) and the slope of the corresponding dilution curves. Since in radioimmunoassay a low displacement slope is indicative of a weak immunological affinity of the antigen for the antiserum, this demonstrated negative correlation suggests that a poorly immunoreactive TSH may be present together with a high B/I ratio, even in normal people.