Plasma levels of atrial natriuretic peptide (ANP) have been measured in eight sodium-retaining cirrhotic nonascitic rats and eight control animals before and after extracellular volume expansion by isotonic saline infusion (30 ml/kg BW, 20 min). In addition, disappearance of [125I]ANP was studied in six control and six cirrhotic rats. The effect of infusing synthetic rat ANP-(1-28) (1 microgram) on mean arterial pressure and renal function has been also studied. In basal conditions, cirrhotic rats showed higher ANP plasma levels than control animals (71.1 +/- 16.6 vs. 43.9 +/- 5.1 pg/ml; P less than 0.05). After extracellular volume expansion, ANP increased in both control and cirrhotic rats; the increase in cirrhotic was higher than that in control rats (88 +/- 27% vs. 33 +/- 8%; P less than 0.05). Disappearance of iodinated ANP from plasma was identical in control and cirrhotic rats. ANP infusion induced a larger decrease in mean arterial pressure in control (21 +/- 5%) than in cirrhotic rats (9 +/- 2.5%). ANP induced comparable increases in glomerular filtration rate and renal plasma flow in both groups of animals. However, diuretic and natriuretic effects were markedly impaired in cirrhotic animals. Thus, urinary flow increased by 91 +/- 18 microliters/min in control animals, but only by 37 +/- 7 microliters/min in cirrhotic animals. Fractional sodium excretion increased to 1.7 +/- 0.44% in controls and to 0.54 +/- 0.12% in cirrhotic rats (P less than 0.05). It is concluded that the defect in renal handling of sodium in cirrhotic rats is not due to a lack of ANP synthesis or release. In addition, these animals show an impaired renal response to ANP.