Circulating atrial natriuretic peptide (ANP) and central blood volume (CBV) in cirrhosis

Endogenous alpha-atrial natriuretic peptide (ANP) in plasma is elevated in various hypervolaemic conditions. Possible relationships between circulating immunoreactive ANP and cardiovascular and splanchnic haemodynamics were therefore studied in patients with cirrhosis (n = 16) and controls (n = 12). Arterial plasma concentration of ANP in supine patients was (mean +/- SEM) 33 +/- 4 vs 41 +/- 10 pg/ml (9.9 +/- 1.2 vs 12.3 +/- 3.0 fmol/l) in controls (n.s.), and there was a weak direct correlation with right atrial pressure (r = 0.36, P = 0.05). There was no relationship with the presence of ascites or diuretic treatment. Central blood volume (CBV, i.e. the blood volume in the heart cavities, lungs, and aorta), determined from the mean transit time of 125I-labelled of 125I-labelled albumin and cardiac output, was significantly reduced in cirrhotics compared to controls (1.45 +/- 0.12 vs. 1.83 +/- 0.10 l, P less than 0.02) and inversely correlated with portal pressure (r = 0.42, P less than 0.05), whereas total plasma volume was somewhat increased (3.51 +/- 0.2 vs. 3.19 +/- 0.2, 0.05 less than P less than 0.1). A high arterio-venous extraction of ANP was found in the splanchnic system (extraction ratio 0.44 vs 0.28), kidney (0.45 vs 0.54), lower limb (0.53 vs 0.40), and forearm (0.27 vs 0.18) in patients and controls, respectively (n.s.). Our results suggest that the lack of elevation of circulating ANP in cirrhosis, even in the presence of actual fluid retention, may be explained by central hypovolaemia in these patients. Turnover and degradation of ANP is rapid and normal, as evaluated from the tissue extraction ratios.