ON THE CONCENTRATING DEFECT IN CIRRHOSIS OF THE LIVER

Renal expression of aquaporins in liver cirrhosis induced by chronic common bile duct ligation in rats

Semiquantitative immunoblotting was used to investigate the expression levels of the four major renal aquaporins, the Na-K-2Cl cotransporter of the thick ascending limb, the type 3 Na-H exchanger, and the Na-K-ATPase in kidneys from rats with cirrhosis secondary to common bile duct ligation (CBDL). These rats had significant water retention and hyponatremia. In contrast to models of cirrhosis induced by carbon tetrachloride, aquaporin-2 expression in CBDL-induced cirrhosis was decreased. Thus, these results show that in the setting of extracellular fluid volume expansion, excessive water retention with hyponatremia can occur in the absence of increases in aquaporin-2 abundance. In addition, the expression levels of the two basolateral collecting duct aquaporins (aquaporin-3 and -4) were decreased in CBDL rats relative to sham-operated control rats. Similarly, the Na-K-2Cl cotransporter of the thick ascending limb and the type 3 Na-H exchanger showed decreases in expression. In contrast, the expression levels of aquaporin-1 and the all subunit of the Na-K-ATPase were not decreased. Thus, dysregulation of multiple water channels and ion transporters may play a role in water balance abnormalities associated with CBDL-induced cirrhosis in rats.

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).

Evidence that renal prostaglandins are involved in renal water metabolism in cirrhosis

Plasma antidiuretic hormone (ADH) and urinary prostaglandin E2 excretion (UPGE2V) were measured in basal conditions, after water restriction, and after water-loading in 10 normal subjects (free water clearance after the water load, CH2O, 9.6 +/- 0.8 ml/min) and in 27 patients with cirrhosis and ascites (13 with a positive CH2O: 3.6 +/- 0.5; 14 with a negative CH2O: -0.37 +/- 0.007). Plasma ADH and UPGE2V were significantly increased in patients with a positive CH2O as compared with normal subjects. Patients with a negative CH2O showed a significantly higher plasma ADH and a lower UPGE2V and GFR than did normal subjects and patients with the positive CH2O. In 18 additional subjects (6 normal and 12 with cirrhosis, ascites, and a positive CH2O) submitted to a sustained water overload, the i.v. administration of 450 mg of lysine acetylsalicylate (LAS) induced a marked reduction of UPGE2V, but it had no effect on plasma ADH. LAS did not alter GFR and CH2O in normal subjects; however, it reduced CH2O in all the 12 patients (from 5.1 +/- 0.4 to 0.6 +/- 0.3) and the GFR in only 6 of these patients. These results suggest (a) that renal PGE2 plays an important role in the maintenance of water excretion in cirrhosis with ascites, and (b) that impaired ability to dilute the urine in cirrhosis may be a consequence of the simultaneous occurrence of impaired renal hemodynamics, nonostomic hypersecretion of ADH, and reduced renal production of PGE2.

Polyuria in experimental intrahepatic cholangitis induced by alpha-naphthyl-isothiocyanate

Alpha-naphthyl-isothiocyanate (ANIT)-induced intrahepatic cholangitis was associated with significant polyuria in rats. The urine output in the experimental rats was about two and a half to four fold higher than that in the controls. The polyuria was accompanied by polydypsia and disappeared when water intake was limited and controlled. The glomerular filtration rate and renal histology remained intact. Dilution and concentration capacities were preserved and the response to exogenous anti-diuretic hormone was intact. Following water deprivation, the water and electrolyte contents of the renal medulla and papilla were similar in both experimental and control rats. The excretion of a salt-load in ANIT-treated rats was delayed. It is concluded that the polyuria in ANIT-treated rats is secondary to polydypsia. The finding of preserved dilution and concentration capacities in this experimental model contrasts to that in other experimental models of hepatobiliary disease.

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.

A micropuncture study of renal salt and water retention in chronic bile duct obstruction

The mechanism of sodium retention by the kidney in rats with ligation of the common bile duct was studied with micropuncture techniques. 10-14 days after bile duct ligation, rats showed positive sodium balance and ascites formation. Measurements of renal blood flow and glomerular filtration rate yielded values that were not different from those in normal control animals. Likewise, single nephron filtration rte of surface nephrons was the same in the experimental rats as in the controls. Sodium reabsorption, however, was markedly increased in the proximal convoluted tubule, as well as in segments beyond the proximal convolutions. Single nephron filtration fraction, calculated from measurements of efferent arteriolar and arterial hematocrits, was significantly elevated in the cortical nephrons, even though whole kidney filtration fraction was the same as in normal rats. The calculated protein concentration of cortical peritubular blood was higher in the bile duct-ligated rats than in the normal controls. The observations are consistent with the view that sodium retention is the result of enhanced reabsorption primarily by cortical nephrons. The enhanced reabsorption can be accounted for by relative cortical ischemia due to efferent arteriolar vasoconstriction with the consequent elevation of peritubular colloid oncotic pressure.

Chronic renal homograft function: correlation with histology and lymphocyte antigen matching

Renal function was studied in twenty-nine of thirty-four surviving renal allograft recipients from an initial group of sixty-four patients two years after transplantation. Mean clearances of inulin and PAH were, respectively, greater than and equal to half the donors’ initial predicted clearances. Minimum urine osmolality during water diuresis was greater, and maximum urine osmolality during hydropenia was less than normal, an effect attributable partly to enhanced solute load in a single transplanted kidney.

Patients with compatible donor-recipient lymphocyte antigens demonstrated statistically better function than those with one or more incompatibilities, although there was a definite degree of overlap between the two groups. In contrast, little correlation could be demonstrated between the cumulative histopathology and renal clearances.

Renal function in patients with compatible donors was statistically greater than half the donors’ initial predicted function. Serial increase in renal clearances was documented in one patient with a compatible donor. Serial decreases were demonstrated in two patients with incompatible donors. These findings suggest that hypertrophy of the denervated, transplanted kidney occurs when immune reaction is minimal.