Pro-A-type and N-terminal pro-B-type natriuretic peptides in different thyroid function states

Questions under study: Natriuretic peptides are produced predominantly in the heart and secreted in response to volume expansion and pressure overload. A wide spectrum of cardiac changes is observed in thyroid dysfunctions. This study investigates mid regional pro A-type (proANP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels in different thyroid states and evaluates the effect of L-thyroxine treatment on natriuretic peptides in patients with subclinical hypothyroidism. Methods: Case-control and double-blind, placebo-controlled trial. Sera from 161 female patients (35 with overt, 63 with subclinical hypothyroldism; 10 with overt, 14 with subclinical hyperthyroidism; 40 euthyroid controls) were analysed. ProANP and NT-proBNP were measured at baseline and 48 weeks after L-thyroxine treatment in subclinical hypothyroidism. Results: Circulating proANP and NT-proBNP levels were higher in hyperthyroid patients than in hypothyroid and euthyroid patients (p < 0.001). Plasma proANP levels tended to be lower in overt hypothyroidism than in subclinlcal hypothyroidism. ProANP and NT-proBNP levels correlated weakly to thyroid stimulating hormone (TSH) (r = -0.3 and -0.2, respectively). The natriuretic peptide levels of subclinical and overt hypothyroid subjects showed no difference with those of euthyroid subjects. L-thyroxine treatment had no effect on natriuretic peptide levels in subclinical hypothyroidism. Conclusion: Natriuretic peptide levels are altered in different thyroid states with a more pronounced effect in hyperthyroidism than in hypothyroidism. Hyperthyroidism should be considered in patients presenting with unclear symptoms and mildly elevated natriuretic peptide levels, as overt hyperthyroidism results in increased serum A- and B-type natriurectic peptide levels, typically seen in mild heart failure.