The paradox of low BNP levels in obesity.

The aim of this review is to analyze in detail some possible pathophysiological mechanisms linking obesity and cardiac endocrine function, in order to try to explain the negative association previously observed between BMI and BNP values in both healthy subjects and patients with cardiovascular diseases. In particular, we discuss the hypothesis that the response of the cardiac endocrine system is the integrated resultant of several and contrasting physiological and pathological interactions, including the effects of peptide and steroid hormones, cytokines, cardiovascular hemodynamics, clinical conditions, and pharmacological treatment. Several studies suggested that gonadal function regulates both body fat distribution and cardiac endocrine function. Visceral fat expansion can increase the clearance of active natriuretic peptides by means of an increased expression of clearance receptors on adipocytes, and in this way, it may contribute to decrease the activity of the cardiac endocrine system. Moreover, obesity is associated with ectopic lipid deposition even in the heart, which may directly exert a lipotoxic effect on the myocardium by secreting in loco several cytokines and adipokines. Obese subjects are frequently treated for hypertension and coronary artery disease. Pharmacological treatment reduces plasma level of cardiac natriuretic peptides, and this effect may explain almost in part the lower BNP levels of some asymptomatic subjects with increased BMI values. At present time, it is not possible to give a unique and definitive answer to the crucial question concerning the inverse relationship between the amount of visceral fat distribution and BNP levels. Our explanation for these unsatisfactory results is that the cardiac endocrine response is always the integrated resultant of several pathophysiological interactions. However, only few variables can be studied together; as a result, it is not possible to perform a complete evaluation of pathophysiological mechanisms under study. We are still not able to well integrate these multiple information together; therefore, we should learn to do it.