1. Previous studies of endogenous atrial natriuretic peptide (ANP) in humans have examined changes in plasma levels, rather than regional secretion and clearance of the peptide. Using arterial and selective venous catheterization and sampling, and measurement of regional organ flow, we measured haemodynamics, cardiac secretion of ANP and renal clearance of ANP in six healthy volunteers at rest, on a normal sodium diet

2. Salt restriction decreases plasma concentrations of ANP. We assessed the contribution of the heart and kidney to this decrease, by measuring cardiac secretion and renal clearance of ANP at the termination of a low salt diet

3. Twenty-four hour urinary sodium excretion fell on the low salt diet from 163 to 29 mmol/day [standard error of the difference (sed) ± 14, P < 0.001]. Body weight decreased on salt restriction from 76.4 to 75.4 kg (sed ± 0.33, P < 0.05). Brachial mean arterial pressure fell by 6% (P < 0.05), but right atrial pressure was unchanged. Renal vein plasma renin activity increased by 56% with sodium restriction (P < 0.01), whereas arterial ANP concentrations fell by 39% (P < 0.05)

4. Coronary sinus ANP levels fell from 417 to 268 pg/ml (sed ± 74, P < 0.05), whereas renal vein concentrations were unaltered. There was a 47% decrease in cardiac secretion of ANP in the low salt state (P < 0.05). Net extraction of ANP across the kidney (about two-thirds) and renal clearance of ANP were unchanged on the low salt diet. Thus decreased plasma ANP with sodium restriction is due to reduced cardiac secretion.

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