Plasma concentrations of atrial natriuretic peptide in hypothyroidism

We studied a group of 15 patients in whom clinical and biochemical hypothyroidism had been newly diagnosed (mean age 49, range 23-73) and a group of 21 healthy normal subjects (mean age 43, range 27-86). In addition, 10 patients were restudied after treatment with thyroxine for six to 12 weeks. None had signs of heart failure, valvular heart disease, or hypertension (blood pressure > 150/90 mm Hg). Venous blood from the forearm was drawn between 0900 and 1100 after 30 minutes of quiet sitting and placed into cooled tubes containing sequestrene and aprotinin. On the same day the peptide was extracted from plasma with octadecyl silica and methanol.4 The mean recovery was 70%, and the results are given uncorrected for the losses. The concentration of atrial natriuretic peptide was measured with a previously described radioimmunoassay using a polyclonal antibody to the carboxy terminus of atrial natriuretic factor 99-126 (Peninsula Laboratories) and an iodine-125 label (Amersham).4 Intraassay and interassay variations were 10% and 12% respectively, and samples from before and after treatment were measured in the