Stimulation of brain natriuretic peptide release from the heart by thyroid hormone

This study was designed to examine the involvement of thyroid hormone in the release of brain natriuretic peptide (BNP) from the heart. We measured plasma immunoreactive BNP (ir-BNP) concentrations in patients with untreated hyperthyroidism. We also measured BNP values in experimental rats with hyperthyroidism induced by thyroxine (T4) and in rats with hypothyroidism induced by propylthiouracil (PTU). The in vitro effects of triiodothyronine (T3) and T4 on the release of BNP were examined in newborn rat atrial and ventricular myocytes in primary culture. Plasma BNP levels were increased in hyperthyroid patients compared with normal control subjects. Plasma BNP levels were increased in hyperthyroid rats and decreased in hypothyroid rats compared with euthyroid rats. Plasma BNP level was correlated with serum T4 level in hyperthyroid patients and hyperthyroid rats. A major component of ir-BNP in plasma from hyperthyroid patients was human BNP-32 and that in plasma from hyperthyroid rats was rat BNP-45. T4 and T3 stimulated release of ir-BNP from both cultured atrial and ventricular myocytes in a dose-dependent manner. Plasma BNP concentration is frequently increased in hyperthyroidism, and thyroid hormone may regulate BNP release from both atrial and ventricular myocytes.