BLOOD-PRESSURE AND ENDOCRINE RESPONSES TO CHANGES IN DIETARY-SODIUM INTAKE IN CARDIAC TRANSPLANT RECIPIENTS - IMPLICATIONS FOR THE CONTROL OF SODIUM-BALANCE

Background The role of cardiac extrinsic innervation in the regulation of sodium balance and blood pressure is controversial. Methods and Re sults We performed a double-blind study of endocrine and blood pressur e responses to 5 days of low- (LS, 10 mmol/d) and 5 days of high- (350 mmol/d) sodium intake in 12 cardiac transplant recipients, 12 matched healthy subjects, and 12 matched subjects with untreated essential hy pertension. In transplant recipients on low sodium, supine blood press ure was 137/94+/-8/4 (mean+/-SEM) mm Hg and plasma atrial natriuretic peptide (ANP) was 59.3+/-6.3 pg/mL; on high sodium, blood pressure was 148/97+/-5/3 mm Hg (P<.05 for systolic pressure versus LS), and ANP w as 94.3+/-10.6 pg/mL (P<.01 versus LS), respectively. Plasma ANP for t hose on each diet was significantly higher in the cardiac transplant r ecipients than in healthy or hypertensive controls; relative changes i n plasma ANP in changing from low- to high-sodium diet were similar in each group. Urinary sodium excretion by the fifth day of each diet wa s similar in each group. Suppression of plasma renin activity and aldo sterone by high-sodium diet was blunted in cardiac transplant recipien ts compared with healthy subjects (respectively, plasma renin activity : 1.41+/-0.30 versus 0.68+/-0.21 ng.mL(-1).h(-1), P<.05; aldosterone: 391+/-35 versus 166+/-21 pmol/L, P<.05). Conclusions These results sug gest that extensive denervation of the heart does not result in major abnormalities in regulation of large changes in sodium intake and that intact cardiac innervation is not required for plasma ANP responses t o altered sodium intake. Blood pressure after cardiac transplantation is sensitive to reduced sodium intake.