Thyroid hormones and pericardial effusion may influence plasma levels of atrial natriuretic peptide (ANP) in humans.

Fluid and electrolyte homeostasis is impaired in patients suffering from hypothyroidism and myxedema because myxedema induces retention of salt and water. We have measured plasma levels of human atrial natriuretic peptide (hANP) in 8 female patients who had been totally thyroidectomized because of thyroid carcinoma. Estimations of the hormone were done 4 weeks after diagnostic withdrawal (searching for iodine retaining metastases) and after 2 weeks and 4 weeks of reinitiation of thyroid suppressive therapy by L-thyroxine. hANP levels, although within the normal range (10-80 ng/l) throughout the study, were positively linked to the amount of pericardial effusion (determined by echocardiography), which was highest initially and decreased or vanished with duration of L-thyroxine therapy. Additionally, a positive correlation between thyroid hormone levels and hANP was obtained when the counteracting effect of pericardial effusion was allowed for by partial correlation analysis. Our findings might facilitate explanation of mild polyuria in hyperthyroidism and impaired water excretion in hypothyroidism.