Effects of thyroid hormone withdrawal on natriuretic peptides during radioactive iodine therapy in female patients with differentiated thyroid cancer

Objective: We aimed to investigate the effects of thyroid hormone withdrawal on N-terminal prohormone forms of atrial natriuretic peptide (NT-proANP) and brain natriuretic peptide (NT-proBNP) during radioiodine therapy in female patients with differentiated thyroid cancer (DTC).Methods: Serum concentrations of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), NT-proANP and NT-proBNP were measured in 51 female patients with DTC (48.74.2 years) at three time-points: day of radioiodine therapy (t1 - under acute hypothyroidism), 5 days after radioiodine (t2 - under acute hypothyroidism) and 3 months after radioiodine (t3 - under TSH suppression). Thirty healthy euthyroid women served as controls (42.85.6 years).Results: At t1/t2/t3, median NT-proANP was 5.2/1.7/487pmol/L vs. 297.7pmol/L in control group (p<0.001), median NT-proBNP was 50.1/36.5/79.5pmol/L vs. 64.5pmol/L (p<0.001) and median NT-proANP/NT-proBNP ratios was 0.20/0.18/4.81 vs. 4.14 (p<0.001). In acute hypothyroidism, FT3 levels were positively correlated with NT-proANP (r=0.38, p=0.005), NT-proANP/NT-proBNP ratios (r=0.47, p=0.001), heart rate (r=0.39, p=0.005), and negatively with mean arterial blood pressure (r=-0.58, p<0.001).Conclusions: Our results indicate that NT-proANP reflects more accurately direct thyroid hormone effects than NT-proBNP. Thyroid hormone-dependent hemodynamic effects seem to be overlapped on the direct stimulatory effect of thyroid hormones on NT-proANP secretion by cardiac myocytes.