Plasma levels of NT-pro-brain natriuretic peptide in patients with overt and subclinical hyperthyroidism and hypothyroidism

BACKGROUND

Several studies have assessed natriuretic peptides in patients with thyroid disorders, and these studies have provided contrasting results. This difference may be partially explained by the presence of concomitant disorders of the cardiovascular system in participants.

MATERIAL AND METHODS

The study included 101 patients free of any cardiovascular disorder, who, on the basis of plasma levels of TSH and thyroid hormones, were divided into patients with overt hyperthyroidism, patients with subclinical hyperthyroidism, patients with overt hypothyroidism, patients with subclinical hypothyroidism, and control subjects with normal thyroid profile. Hyperthyroidism was induced either by nodular thyroid disease or by Graves' disease, while hypothyroidism was secondary to autoimmune thyroiditis or surgery.

RESULTS

Compared to control subjects, hyperthyroid patients were characterised by higher plasma levels of NT-pro-BNP. This increase was particularly pronounced in cases of overt disease. On the other hand, neither clinical nor subclinical hypothyroidism was associated with any significant changes in this peptide. Plasma levels of NT-pro-BNP did not differ between patients with Graves' disease and toxic nodular goitre nor between patients with autoimmune hypothyroidism and hypothyroidism secondary to thyroidectomy. Only L-thyroxine substitutions, but not hyperthyroidism treatment, caused changes in plasma concentration of NT-pro-BNP.

CONCLUSIONS

Hyperthyroidism and hypothyroidism induce changes of the plasma concentration of NT-pro-BNP. Although both exogenous L-thyroxine and antithyroid drugs restored thyroid function, only the former drug changed plasma NT-pro-BNP content. The thyrometabolic state of a patient should always be taken into consideration when NT-pro-BNP is assessed as a marker of cardiac dysfunction.

[Natriuretic peptides: their role in diagnosis and therapy]

Cardiac natriuretic peptide hormones, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), are synthesized and secreted by the heart, producing several biological effects, such as natriuresis, vasorelaxation and hypotension. During the last decade these peptides, especially BNP, have received increasing attention as potential markers of cardiovascular disease. Their measurements can be used to diagnose heart failure, including diastolic dysfunction, and using them has been shown to save money. BNP levels can enable the differentiation between dyspnoic patients secondary to ventricular dysfunction and subjects with primary respiratory disorders. Moreover, there is good evidence that natriuretic peptides may have a diagnostic role in arterial hypertension, acute coronary syndromes, pulmonary hypertension, some valvular heart disease and some disorders affecting other systems (diabetes or thyroid disorders). In this paper we discuss the clinical utility of assessment of natriuretic peptide hormones in the diagnosis of various clinical conditions and their use as pharmacological agents.

[Thyroid hormones and the cardiomyocytes]

The authors present the current knowledge on the intracellular mechanisms of thyroid hormone action in the cardiomyocytes. Many of the clinical manifestations of thyroid diseases are due to the ability of thyroid hormone to alter cardiovascular hemodynamics. Triiodothyronine affects the hemodynamic state mainly by its influence on the expression of cardiomyocyte genes. These genes encode both structural and regulatory proteins in the heart (myosin heavy chains, sarcoplasmic reticulum calcium-activated ATP-ase, phospholamban). The impaired myocardium contractile activity in hypothyreosis reminds findings in heart failure and may warrant further exploration of therapeutic approaches using thyroid hormone to improve cardiac function in heart failure.