Reabsorption of sodium in the proximal renal tubule in cirrhosis of the liver

Multiparametric renal function assessment in cirrhotic patients shows high prevalence of medically actionable changes in multiple modules

AIM

Renal dysfunction is a common complication of cirrhosis, occurring either as part of multiorgan involvement in acute illness or secondary to advanced liver disease. To date, no study has comprehensively assessed multiple renal function parameters in hospitalized patients with cirrhosis through a multiparametric analysis of renal biochemistry markers.

METHODS

We conducted a retrospective, observational study including all consecutive patients hospitalized with cirrhosis who underwent a 43-multiparametric renal function assessment between January 1, 2021, and June 30, 2023.

RESULTS

All patients showed at least one of the following renal abnormalities: Kidney Disease: Improving Global Outcomes stage G2 or higher, sodium and/or chloride excretion fraction <1%, electrolyte-free water clearance <0.4 mL/min, or tubular maximum phosphate reabsorption capacity <0.8 mmol/L. The estimated glomerular filtration rate equations significantly overestimated the measured creatinine clearance with median differences of +14 mL/min/1.73 m2 (95% CI 6-29) and +9 mL/min/1.73 m2 (95% CI 2-15) for European Kidney Function Consortium equations, respectively. Notably, 54% and 39% of patients demonstrated estimated glomerular filtration rates exceeding 30% of the measured creatinine clearance when the Chronic Kidney Disease - Epidemiology Collaboration and European Kidney Function Consortium formulas were employed, respectively. Substantial discrepancies in Kidney Disease: Improving Global Outcomes stage assignments were observed between the estimated glomerular filtration rate- and measured creatinine clearance-based assessments.

CONCLUSIONS

This study underscores the value of a multiparametric renal function assessment as a routine tool for evaluating renal function in patients with cirrhosis. A high prevalence of medically actionable renal abnormalities spanning multiple renal function modules, including alterations in glomerular function, salt and solute-free water excretion, and proximal tubule phosphate reabsorption, has been demonstrated in hospitalized patients with cirrhosis.

Use, misuse and abuse of diuretics

Resolution of edema requires a correct interpretation of body fluids-related renal function, to excrete the excess volume while restoring systemic hemodynamics and avoiding renal failure. In heart failure, the intensive diuresis should be matched by continuous fluids refeeding from interstitium to plasma, avoiding central volume depletion. The slowly reabsorbed ascites cannot refeed this contracted volume in cirrhosis: the ensuing activation of intrathoracic receptors, attended by increased adrenergic and Renin release, causes more avid sodium retention, producing a positive fluid and Na balance in the face of continuous treatment. High-dose-furosemide creates a defect in tubular Na causing diuresis adequate to excrete the daily water and electrolyte load in Chronic Renal Failure. Diuretic treatment requires care, caution and bedside "tricks" aimed at minimizing volume contraction by correctly assessing the homeostatic system of body fluids and related renal hemodynamics.

Blunted natriuretic response to low-dose brain natriuretic peptide infusion in nonazotemic cirrhotic patients with ascites and avid sodium retention

Patients with cirrhosis and ascites have high plasma levels of atrial (ANP) and brain (BNP) natriuretic peptides, two cardiac hormones released by the atria and ventricles, respectively. We evaluated renal hemodynamics, sodium excretion, and intrarenal sodium handling (lithium clearance method) in seven cirrhotic patients with ascites and avid sodium retention before, during, and after the infusion of synthetic human BNP, at the dose of 4 pmol/kg.min for 1 hour, which has been shown to increase renal plasma flow, glomerular filtration rate (GFR), and sodium excretion in healthy subjects without affecting systemic hemodynamics. Plasma BNP levels were 7.31 +/- 0.85 pmol/L in baseline conditions, and increased to 33.60 +/- 2.96 pmol/L at the end of the infusion (P < .01 vs. baseline). Urinary excretion of guanosine 3',5'-cyclic monophosphate (cGMP) also significantly increased during the infusion, indicating stimulation of natriuretic peptide receptors by BNP. BNP administration did not modify renal plasma flow, GFR, sodium excretion or tubular sodium reabsorption to any appreciable extent. Arterial pressure heart rate, plasma norepinephrine, and plasma renin activity (PRA) where also unchanged, whereas plasma aldosterone concentration showed a significant, 35% reduction at the end of the postinfusion period, ruling out the possibility that BNP-induced vasodilation might be responsible for failure of the peptide to induce a natriuretic response. Overactivity of antinatriuretic factors is probably the main determinant of the blunted natriuretic effect of BNP in these patients.

Plasma renin activity in alcoholic liver disease

PURPOSE AND PATIENTS AND METHODS

The relationship of plasma renin activity (PRA) to indices of circulatory filling and other possible determinants of renin secretion was studied in 31 men with alcoholic liver disease. Characteristics of patients with normal and increased PRA values were examined. Significant differences guided subsequent simple and multiple regression analysis.

RESULTS

Supine PRA was increased (greater than 2.4 ng/mL/h on a 200 mEq/d intake of sodium, ranging as high as 33 ng/mL/h) in 14 of 57 studies. Nonascitic patients with elevated PRA values were significantly younger than those with normal PRA values. Among patients without ascites, the plasma atrial natriuretic factor concentration correlated inversely with PRA. Ascitic patients with elevated PRA values had a significantly reduced serum sodium concentration, urinary sodium excretion, creatinine clearance, and arterial pressure. Systemic vascular resistance, plasma norepinephrine and caffeine concentrations, and left atrial volume were similar in patients with and without increased PRA values. Univariate followed by multiple regression analysis identified age and plasma atrial natriuretic factor concentration as significant independent correlates of PRA in patients without ascites (R2 = 0.54). Serum sodium concentration and urinary sodium excretion were significant correlates of PRA in patients with ascites (R2 = 0.80).

CONCLUSION

The associates of PRA in alcoholic liver disease are diverse and potentially complex. Age and plasma atrial natriuretic factor concentration are important in patients without ascites. In patients with ascites, tubular delivery of sodium to the macula densa, as modified by the filtered load and proximal reabsorption, appeared to be a principal association of PRA. Indices of circulatory filling did not emerge as clearly independent associations of PRA. Increased PRA values in patients with ascites may be an effect of sodium retention rather than part of its cause.

Abnormal sympathetic and renal response to sodium restriction in compensated cirrhosis

It has been proposed that in liver cirrhosis portal hypertension causes splanchnic vasodilation and this induces blood volume expansion to maintain blood pressure. The current study was designed to explore the homeostatic response to sodium restriction, a maneuver aiming to contract blood volume, in compensated cirrhosis. Mean blood pressure, sympathetic nervous activity, and proximal sodium reabsorption were evaluated in 16 healthy control and 21 nonazotemic cirrhotic patients (11 without ascites and 10 with ascites) under two experimental conditions: after 4 days on a free sodium diet (basal condition) and after 4 days on a restricted sodium diet (40 mmol/day). No differences were observed in basal conditions in the above parameters between control and cirrhotic patients without ascites. However, cirrhotic patients with ascites showed lower basal values of mean blood pressure and higher basal levels of both plasma norepinephrine and fractional proximal sodium reabsorption than controls. Neither control nor cirrhotic patients with ascites showed significant changes in the measured parameters after sodium restriction. In contrast, in nonascitic patients, this maneuver induced an elevation in plasma norepinephrine concentration (164.4 +/- 24.6 vs. 270.1 +/- 24.9 pg/mL; mean +/- SEM; P less than 0.005) and in fractional proximal sodium reabsorption (86.4 +/- 2.1 vs. 91.8% +/- 0.5%; P less than 0.01). In addition, the nonascitic cirrhotic patients became hypotensive compared with controls (80.9 +/- 1.6 vs. 88.5 +/- 4.8 mm Hg; P less than 0.05) when subjected to the low-sodium diet. In patients without ascites, under conditions of sodium restriction, the decrease in mean arterial pressure correlated inversely with the increase in plasma norepinephrine concentration (r = -0.713; P less than 0.05), whereas the levels of plasma norepinephrine correlated directly with fractional proximal sodium reabsorption (r = 0.893; P less than 0.01). These findings suggest that ineffective circulatory volume is detected in nonascitic cirrhotic patients only under conditions of sodium restriction, but it is always present in cirrhotic patients with ascites, irrespectively of the amount of sodium in the diet. These results are compatible with the existence of fixed arterial vasodilation in cirrhosis.

Antidiuretic hormone and renal function after water loading in patients with cirrhosis of the liver

Renal function and plasma antidiuretic hormone (ADH) levels were studied basally and after oral water load in four groups of subjects: 15 healthy controls (group I), 15 cirrhotics without ascites (group II), 15 cirrhotics with ascites (group III), and 10 decompensated cirrhotics with hyponatremia (group IV). Renal function and ADH levels were normal in group II. In groups III and IV water diuresis and fractional proximal sodium excretion were significantly decreased, whereas fractional distal sodium resorption and fractional excretion of potassium did not differ from those of controls. Basal ADH was significantly increased only in patients of group IV. In these patients ADH remained abnormally high after water loading. ADH did not correlate with water diuresis, plasma osmolality, mean arterial pressure, and plasma renin activity. We conclude that impaired water excretion in decompensated cirrhotics without hyponatremia cannot be ascribed to high serum levels of ADH. On the contrary, it seems to be related mainly to a reduced delivery of filtrate to the diluting segment of the nephron. In cirrhotic patients with hyponatremia high levels of ADH may play an additional role.

Tubular sodium handling in cirrhotic patients with ascites as analysed by the renal lithium clearance method

The proximal and distal sodium reabsorption were calculated from lithium clearance in 21 healthy controls and 24 cirrhotic patients with ascites after 4 days under a sodium-restricted diet. The values of fractional lithium clearance were lower in patients than in controls (7.37 +/- 0.87 vs. 18.13 +/- 1.76%, P less than 0.001). Fractional proximal sodium reabsorption was increased in patients compared with controls (92.8 +/- 1.1 vs. 81.8 +/- 1.7%, P less than 0.001). No differences were found in fractional distal sodium reabsorption between controls and patients (96.9 +/- 0.8 vs. 98.6 +/- 0.1%). When patients were separated into two subgroups according to their sodium balance, it was found that fractional distal sodium reabsorption was increased in patients whose balance remained positive, compared with patients on a negative sodium balance (98.99 +/- 0.26 vs. 94.11 +/- 1.50%, P less than 0.05). In addition, the natriuretic response to a specific dose of spironolactone was higher in patients on positive sodium balance compared with patients on negative sodium balance (per cent increase in natriuresis after spironolactone 300 mg day-1: 355.24 +/- 73.98 vs. 84.21 +/- 15.8%, P less than 0.01). We conclude that proximal sodium reabsorption is increased in cirrhotics with ascites. In addition, distal sodium reabsorption is enhanced only in those patients which exhibit avid sodium retention.

Tubular site of renal sodium retention in ascitic liver cirrhosis evaluated by lithium clearance

Renal tubular sodium handling was evaluated in 27 non-azotemic cirrhotic patients with ascites and positive sodium balance and in 17 controls after at least 5 days of a constant sodium intake using the lithium clearance as an index of fluid delivery to the distal tubule. Plasma renin activity and plasma aldosterone were also evaluated. Sodium fractional excretion, filtered sodium load, absolute sodium distal delivery, lithium fractional excretion and absolute distal sodium reabsorption were significantly lower in cirrhotics than in controls (0.58 +/- 0.11 vs. 1.29 +/- 0.12%, P less than 0.001; 12529 +/- 677 vs. 15707 +/- 796 microEq min-1 1.73 m-2 BSA, P less than 0.005; 2384 +/- 135.2 vs. 3685 +/- 219.3 microEq min-1 1.73 m-2 BSA, P less than 0.001; 19.5 +/- 1.0 vs. 24.2 +/- 1.3%, P less than 0.01; 2299 +/- 127 vs. 3485 +/- 214 microEq min-1 1.73 m-2 BSA, P less than 0.001, respectively). A correlation was found between lithium clearance and sodium clearance only in cirrhotic patients (r = 0.62; P less than 0.01). Distal sodium reabsorption evaluated as a per cent of filtered sodium load was lower in cirrhotics than in controls (19.1 +/- 1.0 vs. 22.4 +/- 1.2%, P less than 0.05) while distal sodium reabsorption evaluated as a per cent of sodium distal delivery was higher in cirrhotics than in controls (96.7 +/- 0.4 vs. 94.4 +/- 0.5%, P less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

A lithium clearance study of sodium reabsorption at the proximal tubule in liver cirrhosis with ascites

Since the reabsorption of lithium occurs almost exclusively in the proximal tubule and is associated with that of sodium, the fractional excretion of lithium (FELit) ws examined in 18 patients with cirrhosis in order to examine the reabsorption rate of sodium at the proximal tubule. As expected, the fractional excretion of sodium (FENa) was significantly lower in cirrhotic patients with ascites (0.43 +/- 0.10%, mean +/- SEM) than in cirrhotic patients without ascites (0.75 +/- 0.14%, P less than 0.05) and healthy controls (0.82 +/- 0.17%, P less than 0.05). By contrast, there was no significant difference in FELit among cirrhotic patients with ascites (16.7 +/- 2.0%), cirrhotic patients without ascites (15.4 +/- 2.0%) and controls (17.4 +/- 1.5%). It is unlikely, therefore, that in cirrhotic patients with ascites, the impaired sodium excretion is solely caused by the abnormal sodium reabsorption capacity of the proximal tubule.

Disorders of the serum electrolytes, acid-base balance, and renal function in alcoholism

This chapter reviews the disturbances of the serum sodium and potassium concentrations, acid-base imbalances, and acute renal dysfunction that are seen frequently in alcoholic patients. The hyponatremia common in decompensated cirrhotics is caused by an impairment of renal free water clearance and concomitant water ingestion. Excessive proximal renal tubular sodium reabsorption and nonosmotic vasopressin release underlie the defect in renal water excretion in cirrhosis. Restriction of water intake is the principal therapeutic measure for hyponatremia. Hypokalemia is common in alcoholics but when observed does not always represent true potassium depletion. Although most cirrhotics have a diminished total body potassium content, intracellular potassium concentration is usually normal. In some patients gastrointestinal and renal potassium losses and nutritional potassium deficiency may cause true potassium depletion. Respiratory and metabolic alkalosis are the acid-base disturbances seen most frequently in alcoholics. Acidosis is relatively uncommon and is usually due to renal insufficiency, lactic acid or keto-acid accumulation. Toxin ingestion (methanol, ethylene glycol, or isopropanol) may also cause severe acidosis. Rhabdomyolysis, common in severe alcoholism, may produce various electrolyte disturbances and acute renal failure. The prognosis for recovery is good although temporary dialysis may be necessary.

The pathogenesis of renal sodium retention and ascites formation in Laennec's cirrhosis

This chapter critically reviews our current understanding of the pathogenesis, clinical syndrome, and therapy of the disturbances of renal sodium handling, renal perfusion, and glomerular filtration rate that occur in patients with Laennec's cirrhosis. Avid renal sodium reabsorption, a characteristic feature of cirrhosis, occurs independent of moderate changes in renal function and precedes the onset of ascites. The initiation of sodium retention may be a direct consequence of the hepatic disease process and may also result from defective intravascular filling. In the presence of ascites the most important sodium retaining signal is a defective intravascular volume. The principal effectors of renal sodium retention and vasoconstriction are stimulation of the renin-angiotensin-aldosterone axis and augmentation of renal sympathetic nerve activity. Deficient production of natriuretic hormone(s) and endogenous renal vasodilators, such as prostaglandins and kinins, also contributes to the sodium retention and renal hypoperfusion seen in cirrhosis. The hepatorenal syndrome is an extreme imbalance in these renal vasoconstrictor and vasodilator forces. In the therapy of ascites in Laennec's cirrhosis, abstention from alcohol, sodium restriction, and cautious diuresis are the principal therapeutic measures. A grave prognosis accompanies the diagnosis of the hepatorenal syndrome although recoveries have been reported.

Derangements of renal water handling in liver disease

It is apparent that renal water retention in patients with advanced liver disease constitutes a fascinating clinical constellation with numerous and diverse causes and an elusive pathophysiology. The dissociation between elevated AVP levels and the attendant changes in renal water handling under diverse experimental conditions, and the demonstration of an impairment in renal water excretion in response to prostaglandin synthetase inhibition, underscore the multifactorial nature of the derangement. It is likely that the development of impaired renal water handling is attributable to a panoply of several hormonal or neural mediators, or both, acting in concert. Additional insight into this fascinating problem must await further characterization of some of the mediators and a delineation of their pathophysiologic role.

Renal water and sodium handling in compensated liver cirrhosis: mechanism of the impaired natriuresis after saline loading

The present study was attempted to evaluate sodium and water balance in compensated liver cirrhosis. Renal sodium and water handling was studied in six cirrhotic patients without ascites and/or oedema and in six controls before and after saline loading. Fractional sodium reabsorption at the various nephron sites (proximal, diluting and distal) was evaluated by means of clearance techniques during maximal water diuresis and hypotonic saline infusion. Compensated cirrhotic patients showed a normal baseline sodium and water balance but a blunted natriuretic response when saline loaded (urinary sodium excretion after saline load = 338 +/- 290 compared to 933 +/- 504 mumol min-1 of controls; P less than 0.05). The impaired natriuresis was found to be related to an increased reabsorption of sodium in the proximal tubule (proximal fractional sodium reabsorption = 88.4 +/- 3.8 compared to 81.7 +/- 4.3% of controls; P less than 0.05). These findings confirm the hypothesis that renal sodium handling abnormalities might precede ascites formation. Additional studies, however, are necessary to further define renal factors mediating the increased reabsorption of sodium in compensated liver cirrhosis.

The role of prostaglandins in Na retention of porta-cava shunted rats

The importance of prostaglandins (PG) in Na and water retention of liver cirrhosis was studied in rats with porta-cava shunt (PCS) compared to control, non-shunted animals. Balance studies were performed in metabolic cages with diets of high, normal and low Na. An experimental phase, during which the animals received either 5 mg X kg-1 of indomethacin daily or placebo, was preceded by a control period and followed by a post-indomethacin period identical to the control phase. In each diet, indomethacin, but non placebo, caused a positive Na balance, correlated with Na intake, which in overall pooled data amounted to -1453 +/- 255 muEq in PCS rats, significantly larger than that measured in controls, of -295 +/- 320 muEq (P less than 0.01). This was attended by a reverse change in K balance of -35.6 +/- 349 muEq versus -1566 +/- 582 muEq (P less than 0.01); glomerular filtration rate (GRF) was unchanged. These data demonstrate that PGs contribute to the control of Na homeostasis in the presence of PCS.

[Kidney involvement in liver diseases. Pathophysiology and clinical course]

Renal disorders complicating liver disease are a frequent finding. Extrahepatic causes like intoxications and circulatory dysfunction or diseases that simultaneously affect both the liver and the kidney, like multisystem or viral diseases (hepatitis B) have to be differentiated from clinical entities in which, like in liver cirrhosis or in fulminant hepatitis, the manifestation of renal disease has to be understood as a consequence of the hepatic disorders. Functional disturbances like the increases in tubular sodium reabsorption or the hepatorenal syndrome have been thoroughly investigate because of their clinical importance. Substantial research dealing with the consequences of the increased intrahepatic vascular resistance on systemic and renal hemodynamics and with vasoactive substances, either arising from the liver or accumulating due to poor inactivation by the liver, have led - in the last years - to a better understanding of the pathophysiology of renal involvement in liver disease. However, the exact pathophysiologic role of factors like the effective blood volume, the sympathoadrenergic tonus, the activation of the renin-angiotensin-aldosterone system, changes of kinin activity or in prostaglandin release and the accumulation of "false" neurotransmitters and endotoxins still remains to be established.