427 MUTUAL INTERDEPENDENCE OF BNP, PLASMA VOLUME, RENAL FUNCTION AND LVEF IN HEALTHY SUBJECTS


 
 
 Natriuretic peptides play an important role in cardiovascular control, stimulating diuresis and vasodilatation and suppressing the renin-angiotensin-aldosterone system. They are also pivotal markers in diagnosis, prognosis and therapy of heart failure (HF), specially BNP and its precursor pro-hormone Nt-proBNP. .Many factors can affect BNP levels in HF patients, potentially reducing its diagnostic accuracy. The main important ones include left ventricular ejection fraction (LVEF), glomerular filtration rate (GFR) and plasma volume (PV). Though the mutual relationship between BNP levels and these drivers is well studied in HF patients, paradoxically little is known about this relationship in physiological conditions in healthy subjects. We tried to elucidate mutual interdependence of BNP, PV, renal function and LVEF in healthy subjects.
 
 
 
 A total of 200 healthy adult males underwent clinical assessment, measurement of serum levels of BNP, creatinine, uricemia, hemochrome and echocardiography for LVEF assessment. GFR was calculated according to EPI-CKD formula. PV was estimated with both the Hakim formula and the Kaplan formula. The ideal PV (iPV) i.e. the normal PV was calculated using body weight and sex: iPV (in ml) = c × body weight (in kg), where c = 39 in males and 40 in females.
 
 
 
 Mean levels of BP, LVEF, BNP, serum creatinine, GFR, uricemia and PV were all within the normal range. PV1 and PV2 were significantly different from each other and both differed from iPV (Friedman ANOVA; | = 28.4; df = 2; P <0.01 for all the comparisons). Nevertheless, the three estimates of PV were all significantly and strictly correlated to each other (Spearman correlation coefficient, Rho >0.82 and P<0.001 for all the correlations). BNP levels were positively correlated with age and inversely with both uricemia and iPV. The latter ones were positively correlated to each other. GFR was inversely correlated with both age and uricemia (but not with PV nor with BNP levels). No correlation was found between LVEF and BNP levels or PV.
 
 
 
 In homeostatic conditions, BNP and PV are inversely correlated in healthy adult males (contrary to the positive correlation existing in HF patients due to the predominant effects of angiotensin II and aldosterone), whereas opposite correlations between uricemia and both PV (positive) and GFR (negative) exist. The positive correlation between uricemia and PV could be explained by the strict dependence of tubular reabsorption of uric acid on serum levels of sodium, which is in turn strictly related to the extracellular fluid volume. The negative correlation between uricemia and GFR can be explained by the mutual influence of these two factors, since hyperuricemia seems to be both a cause and a consequence of chronic kidney disease (CKD).
