Renal concentrating ability in cirrhosis. 3. Failure of hypertonic saline to increase reduced T C H 2 O formation

Vasopressin release and water metabolism in patients with cirrhosis

Water retention is a complication in many patients with cirrhosis, usually attributed to excessive release of arginine vasopressin. To investigate the responsiveness of arginine vasopressin to osmotic and non-osmotic stimuli and its relationship to free water excretion, we studied 19 patients with cirrhosis under three different conditions: 45 min with legs raised to 60 degrees, to expand the central blood volume; infusion of 1000 ml of 0.45% saline solution to reduce plasma osmolality; and rapid injection of 50 ml of 2 M NaCl to increase plasma osmolality. Both expansion of central blood volume and decrease of plasma osmolality significantly reduced plasma vasopressin levels (from 2.1 +/- 0.6 to 1.39 +/- 0.3 pg/ml, p < 0.04; and from 1.09 +/- 0.25 to 0.41 +/- 0.13 pg/ml, p < 0.0001). The changes in free water excretion differentiated two subgroups of patients during each test: excretors and non-excretors. In the excretors, increased free water excretion was associated with suppressed vasopressin levels (below 0.5 pg/ml) and normal renal function. In the non-excretors, inability to improve free water excretion was associated with high vasopressin levels or with reduced distal delivery of the glomerular filtrate, except in some cases where vasopressin levels had fallen below 0.5 pg/ml and renal function was normal. For these cases the presence of other vasopressin-independent antidiuretic mechanisms is conceivable. The injection of hypertonic saline solution caused significant rises in plasma osmolality (from 287 +/- 1.9 to 292 +/- 1.6 mmol/kg, p < 0.05) and in plasma vasopressin levels (from 1.13 +/- 0.29 to 2.86 +/- 0.52 pg/ml, p < 0.05). These results suggest that vasopressin release in patients with cirrhosis is normally responsive to osmotic and non-osmotic stimuli, although our results show a lower theoretical osmolar threshold for suppression of vasopressin release in non-excretors than in excretors (276 vs 284 mmol/kg).

Hepatorenal syndrome: a disease mediated by the intrarenal action of renin

The functional renal failure accompanying advanced liver disease is characterized by azotemia, a urine of very low sodium concentration and systemic hypotension with decreased renal perfusion and high renal vascular resistance. Patients with this disorder have a markedly reduced ability to excrete free water and develop hyponatremia, ascites and edema. It is postulated that this renal dysfunction is due to hepatic failure to make renin substrate. Renin released from the kidney is thus unable to exert its pressor effect. The resultant hypotension and renal hypoperfusion continue to stimulate excessive synthesis and release of renin. It is postulated that the overdriven renal renin system increases renovascular resistance at the level of the glomerular arterioles. This causes decreased renal blood flow and decreased glomerular filtration rate leading to salt and water retention and azotemia. Since no renin substrate is available for human infusion, this hypothesis could be tested either by infusion of angiotensin II to restore systemic blood pressure and renal perfusion or by beta adrenergic blockade with propranolol to attempt to decrease the intrarenal effects of renin, restore glomerular blood flow and filtration and thus return of renal function.