CARDIAC TRANSPLANTATION AFFECTS VENTRICULAR EXPRESSION OF BRAIN NATRIURETIC PEPTIDE

Objective: The aim was to examine the ventricular expression of brain natriuretic peptide (BNP) in the transplanted human heart. Methods: Serial right ventricular biopsies (n=68) and plasma samples (n=68) were obtained for measurement of BNP and atrial natriuretic peptide (ANP) from 14 orthotopic cardiac transplant recipients from 1-74 weeks after transplantation. Right ventricular specimens (n=10) were also obtained from normal hearts during necropsy as controls. Results: Mean ventricular BNP in cardiac transplant recipients was higher (p<0.05) than in normal hearts, at 13531(SEM 2244) pg.mg-1 soluble protein (range 3232 - 109 448) v 56(11) pg.mg-1 (range 16-91). Ventricular BNP and ANP values were correlated (r=0.57, p<0.05). Plasma BNP concentrations were higher (p<0.05) than plasma ANP concentrations, at 202(16) pg.ml-1 (range 84-655) v 100(12) pg.ml-1 (range 8-484), and were raised (p<0.05) in comparison with normal plasma BNP concentrations of 20(1.8) pg.ml-1 (range 10-23). Mean ventricular BNP was correlated with time after transplant (r=0.72, p<0.05, n=68) and with mean plasma BNP (r=0.80, p<0.05, n=14). There was no significant relationship between BNP levels and intracardiac or systemic blood pressure, or prednisolone dose (0.1-0.3 mg.kg-1.d-1). The increase in ventricular BNP with time after transplant was not explained by cardiac rejection assessed from histology, and plasma BNP was not significantly increased during rejection episodes. Conclusions: High levels of BNP are synthesised and secreted by the transplanted human ventricle, and the transplanted ventricle may be an important source of circulating BNP. The significant positive association between ventricular BNP and time after transplant suggests a possible self compensatory mechanism or functional adaptation of the transplanted heart which may be beneficial to ventricular function.