Pituitary-thyroid axis in Himalayan endemic goitre

Abstract

26 patients from the Himalayan endemic-goitre area were studied. Circulating levels of thyroid hormone were assessed by measuring serum-thyroxine (T4) by the 'Thyopac-4' method, and the effective-thyroxine ratio (E.T.R.), and serum-triiodothyronine (T3) by radioimmunoassay. Serum-thyroid-stimulating-hormone (T.S.H.) levels were measured by radioimmunoassay, and pituitary T.S.H. reserve was determined by the T.S.H. response to thyrotrophin-releasing hormone (T.R.H.). Basal T.S.H. levels and peak T.S.H. in response to T.R.H. were greater in the patients than in the controls and were related to goitre size. Serum T4 and E.T.R. values fell with increasing goitre size, whereas serum-T3 levels, although higher than in controls, bore no relation to goitre size. There was a significant direct relation between basal T.S.H. and peak T.S.H. and an inverse relation between basal T.S.H. and T4, peak T.S.H. and T4, and peak T.S.H. and E.T.R. There was no relation between basal or peak T.S.H. and T3. Although none of the patients was clinically hypothyroid, 20 had increased basal T.S.H. levels and could therefore be classified as having subclinical hypothyroidism.