Potassium deficiency in chronic renal failure

Early reduction of skin potassium without sodium accumulation in the pathogenesis of salt sensitivity in primary aldosteronism

Introduction

Primary aldosteronism is the most common form of secondary hypertension and blood pressure salt sensitivity. In the setting of hyperaldosteronism and a high-salt diet, disturbances in tissue sodium and potassium levels may contribute to salt sensitivity. This study aimed to determine whether aldosterone-dependent changes in tissue and plasma sodium and potassium concentrations occur before or after the development of salt sensitivity and hypertension in a rat model of primary aldosteronism. Previous studies in this model show that aldosterone-dependent salt sensitivity develops after 7-10 days on a high-salt diet. A secondary objective was to investigate differences in skin gene expression between aldosterone-treated rats and vehicle-treated controls.

Methods

Unilaterally nephrectomized male Sprague-Dawley rats received continuous infusions of aldosterone or vehicle while being fed a high-salt diet. Electrolyte concentrations in plasma, carcass, and skin were measured after 2 and 14 days of high-salt feeding. Tissue sodium and potassium concentrations were determined by atomic absorption spectroscopy and expressed as mmol/g tissue dry weight, while plasma ions (mmol/L) were measured using ion-selective electrodes. RNA sequencing (RNAseq) was used to identify differentially expressed genes in the skin, and gene set enrichment analysis (GSEA) was performed to explore biological processes associated with aldosterone treatment.

Results

After 2 days on the high-salt diet, aldosterone-treated rats showed significantly lower skin and plasma potassium concentrations compared to vehicle-treated controls, while sodium concentrations in the carcass, skin, and plasma did not differ significantly. At 14 days, aldosterone-treated rats continued to exhibit lower plasma potassium levels, although skin potassium differences were no longer significant. Carcass sodium concentrations were significantly higher in aldosterone-treated rats at 14 days. GSEA revealed that, at 2 days, aldosterone treatment affected biological processes related to electrolyte homeostasis and hyperosmotic responses. At 14 days, biological processes related to muscle function and calcium ion transport were significantly altered.

Conclusion

Aldosterone-treated rats on a high-salt diet for 2 days had lower skin and plasma potassium levels compared to salt-loaded controls, suggesting early potassium depletion precedes significant sodium accumulation and blood pressure increases. These findings raise the possibility that early potassium depletion contributes to the development of aldosterone-induced salt sensitivity. Further studies with detailed time-course analysis will be of interest to elucidate the role of early potassium depletion in increasing vascular resistance and triggering aldosterone-dependent salt sensitivity and hypertension.

Seasonal variation of serum potassium in hemodialysis patients: myth or reality? A narrative review of literature

Research has shown that patients undergoing hemodialysis experience seasonal variations in their serum potassium levels. There was inconsistent seasonal fluctuation in serum potassium levels among the hemodialysis population across different locations. In the form of narrative review for the first time, the article discusses the seasonal changes of serum potassium in this population and its potential reasons, this article demonstrates that it is primarily attributable to seasonal dietary potassium intake. However, existing studies have not quantified seasonal dietary potassium intake, so the results are still speculative. Furthermore, future research ought to further expound upon the clinical implications of seasonal variations in serum potassium levels among dialysis patients, as well as other influencing mechanisms such as the pathophysiological causes of these seasonal changes, particularly those pertaining to dietary, geographical, and regional factors. These findings contribute to a more thorough interpretation of laboratory results in hemodialysis patients and provide important guidance for their individualized dietary management.

Muscle Sodium Accumulation in Kidney Failure: Physiological Impact and Mitigation Strategies

Skeletal muscle has recently been recognized as a nonosmotic sodium reservoir that buffers dietary sodium. The in-vivo quantification of muscle sodium is based on a novel technology, sodium magnetic resonance imaging. Studies using this technology have shown that muscle sodium accumulation may be a clinical complication of chronic kidney disease (CKD). This review aims to summarize existing evidence on muscle sodium accumulation in patients with CKD and to identify knowledge gaps and topics for further research. The literature examined in this review suggests that muscle sodium accumulation is associated with CKD progression and pathological conditions. However, the causalities between muscle sodium accumulation and its related pathological changes are still elusive mainly because it is still uncertain where and how sodium accumulates in the muscle. More research is needed to address these gaps and determine if muscle sodium is a new intervention target in CKD.

Chronic Hyperkaliemia in Chronic Kidney Disease: An Old Concern with New Answers

Increasing potassium intake ameliorates blood pressure (BP) and cardiovascular (CV) prognoses in the general population; therefore the World Health Organization recommends a high-potassium diet (90–120 mEq/day). Hyperkalaemia is a rare condition in healthy individuals due to the ability of the kidneys to effectively excrete dietary potassium load in urine, while an increase in serum K⁺ is prevalent in patients with chronic kidney disease (CKD). Hyperkalaemia prevalence increases in more advanced CKD stages, and is associated with a poor prognosis. This scenario generates controversy on the correct nutritional approach to hyperkalaemia in CKD patients, considering the unproven link between potassium intake and serum K⁺ levels. Another concern is that drug-induced hyperkalaemia leads to the down-titration or withdrawal of renin-angiotensin system inhibitors (RASI) and mineralocorticoids receptors antagonists (MRA) in patients with CKD, depriving these patients of central therapeutic interventions aimed at delaying CKD progression and decreasing CV mortality. The new K⁺-binder drugs (Patiromer and Sodium-Zirconium Cyclosilicate) have proven to be adequate and safe therapeutic options to control serum K⁺ in CKD patients, enabling RASI and MRA therapy, and possibly, a more liberal intake of fruit and vegetables.

Hyperkalemia in patients undergoing hemodialysis: its pathophysiology and management

Potassium is a major intracellular cation in the body, regulating membrane potential of excitable cells, such as cardiomyocytes and skeletal muscle cells. Because the kidney plays a critical role in controlling potassium balance, the elevation in serum potassium levels is one of the most common complications in patients with maintenance hemodialysis (MHD). In addition to reduced renal potassium excretion, the alteration in body potassium distribution owing to comorbid conditions may also contribute to dyskalemia. Besides potassium elimination through hemodialysis in MHD patients, accumulating data indicate the potential importance of extra‐renal elimination involving the gastrointestinal system, which can be affected by the inhibitors of the renin‐angiotensin‐aldosterone system. In this article, the literature on potassium physiology in MHD patients is reviewed with an emphasis on the changes from individuals with normal kidney function. This article also summarizes the findings of recent studies on dietary control, dialysate prescription, and pharmacological therapy.

Abnormalities of serum potassium concentration in dialysis-associated hyperglycemia and their correction with insulin: a unique clinical/physiologic exercise in internal potassium balance

The absence of significant losses of potassium in the urine makes dialysis-associated hyperglycemia (DH) a model for the study of the internal potassium balance. Studies of DH have revealed that hyperkalemia is frequent at presentation, insulin infusion is usually the only treatment required, and the magnitude of the decrease in serum potassium concentration (K(+)) during treatment of DH with insulin depends on the starting serum K(+) level, the decreases in serum glucose concentration and tonicity, and the increase in serum total carbon dioxide level. We present an analysis of these findings based on previously studied actions of insulin. Calculations of transcellular potassium shifts based on the combined effects of insulin-the increase in the electrical potential differences (hyperpolarization) of the cell membranes and the correction of the hyperglycemic intracellular dehydration through decrease in serum glucose concentration-produced quantitative predictions of the decrease in serum K(+) similar to the reported changes in serum K(+) during treatment of DH with insulin. The lessons from analyzing serum K(+) changes during treatment of DH with insulin are applicable to other conditions where internal potassium balance is called upon to protect serum K(+), such as the postprandial state. The main questions related to internal potassium balance in DH that await clarification include the structure and function of cell membrane potassium channels, the effect of insulin on these channels, and the mechanisms of feedforward potassium regulation.

Muscle water and electrolytes in patients undergoing continuous ambulatory peritoneal dialysis

Muscle water and electrolytes were determined in percutaneous muscle biopsy material from m. quadriceps femoris in 33 uremic patients undergoing continuous ambulatory peritoneal dialysis (CAPD) for 1-38 months, and in 34 normal subjects. The patients showed increased muscle contents of water, sodium, and chloride relative to fat-free solids (FFS); both intra- and extracellular water contents were increased. The total water content was inversely correlated with the duration of CAPD. The muscle potassium content was increased, both relative to FFS and to magnesium, whereas the intracellular potassium concentration was normal. Despite hypermagnesemia, the muscle content of magnesium was normal and the intracellular concentration was even slightly decreased due to the increase in intracellular water. We conclude that muscle water and electrolyte status is abnormal in CAPD patients, but the alterations appear to be less marked than in uremic patients undergoing other forms of therapy.

Comparison of different measurements of lean body mass in normal individuals and in chronic peritoneal dialysis patients

To evaluate different methods of measuring lean body mass (LBM) in chronic peritoneal dialysis (CPD) patients, we first made comparisons in seven normal subjects. Seven methods (total body potassium [TBK] counting, bioelectrical impedance with calculations according to Segal and Deurenberg, near-infrared interactance with and without exercise level included as a variable, anthropometric measurements, and creatinine kinetics) were compared with the standard method of underwater weighing (UW) for measuring LBM. Significant correlations with LBM measured by UW (r > 0.938) were found with LBM measured by all other methods. Compared with UW, the best result in normals was found with TBK as it had high r values, small y-intercepts, and slopes of regression lines close to unity in both measurements of LBM and %LBM; in addition, fat-free mass index by TBK best approximated that by UW and TBK had the lowest mean prediction error with UW. In 11 patients on CPD, LBM was measured by all the above methods except UW. Significant correlations of all methods with LBM measured by TBK used as the reference standard were noted (all r > 0.76) in the CPD population. The LBM measured by creatinine kinetics correlated best (by kilograms or percentage of body weight [%BW]) with LBM from TBK compared with the other methods in which values tended to be higher. The fat-free mass index by creatinine output was nearest to the fat-free mass index by TBK. The root mean square prediction error was lowest between LBM by creatinine output and that by TBK. The findings support the concept of measuring creatinine outputs in CPD patients for estimates of LBM as an index of nutritional status as well as for creatinine clearances as an index of adequacy. Total body potassium and creatinine output measurements of LBM reflect the LBM at normal body fluid volumes ("dry weight") and may be better indices of nutrition in dialysis patients than the other techniques, which include excess fluid in the LBM.

A patient with hyperkalemia and metabolic acidosis

Uptake of potassium by extrarenal tissues, primarily muscle and liver, represents a major defense mechanism in the maintenance of normokalemia following an acute elevation in the serum potassium concentration. Insulin, epinephrine, and aldosterone all play major roles in maintaining the normal distribution of potassium between the intracellular and extracellular environment. In addition to hormonal regulation, changes in blood pH and tonicity also exert a strong influence on extrarenal potassium metabolism. Last, the serum potassium concentration per se directly influences its own cellular uptake and this transport mechanism appears to be inhibited by uremia.

Potassium tolerance

The maintenance of potassium homeostasis with an increased potassium intake or decreased renal function is dependent in part on the renal adaptation observed in 'potassium tolerance'. However other factors, including control of ingestion, and increased distal delivery of fluid, also play a role.

Electrophysiology of rat distal colon after partial nephrectomy. Implications for K transport

Previous in vivo studies in rat and man indicate that chronic renal insufficiency leads to an increase in the capacity of the large intestine for K secretion. The present studies were performed in isolated rat distal colon with conventional and K-sensitive microelectrodes to determine the cellular basis for enhanced colonic K secretion after 70% nephrectomy. The data revealed that in animals fed a regular diet, nephrectomy had no effect on the Na or K conductance of the apical membrane, or the kinetics of the basolateral membrane Na-K pump, but intracellular K activity decreased from 70 +/- 4 mmol/l to 58 +/- 4 mmol/l (P less than 0.005). In control (non-nephrectomised) animals, feeding a diet modestly (4-fold) enriched with K resulted in small but significant increases in the Na and K conductance of the apical membrane, no change in the kinetics of the basolateral membrane Na-K pump, and a rise in intracellular K activity from 70 +/- 4 mmol/l to 94 +/- 7 mmol/l (P less than 0.005). In contrast, in animals fed the K enriched diet, nephrectomy resulted in (i) large, amiloride-sensitive increases in transepithelial voltage and total tissue conductance (consistent with an appreciable degree of secondary hyperaldosteronism), (ii) marked increases in the Na and K conductance of the apical membrane, (iii) significant hyperpolarization of the basolateral membrane, (iv) a 100% increase (P less than 0.02) in the maximum activity of the basolateral membrane Na-K pump, and (v) a rise in intracellular K activity from 94 +/- 7 mmol/l to 129 +/- 7 mmol/l (P less than 0.0025). These data suggest that the combination of modest dietary K enrichment and 70% nephrectomy stimulated an active K secretory process which reflected an increase in the K excretory load applied to the colonic mucosa, and the effects of aldosterone. In this model of renal insufficiency, enhanced K secretion by the transcellular and paracellular (potential-dependent) pathways results in a marked rise in the K excretory capacity of the colon.

Impairment of beta 2-adrenoceptor-stimulated potassium uptake in end-stage renal disease

An abnormality of extrarenal mechanisms is believed to contribute importantly to the impaired potassium homeostasis in chronic renal failure. We evaluated the plasma potassium response to inhalation of albuterol, a beta 2 agonist, in eight patients who had end-stage renal disease and who were undergoing chronic hemodialysis and in eight control subjects. The purpose was to assess if an abnormality of the beta 2 adrenoceptor mechanism is present in uremia. The maximal decrement in plasma potassium concentration in the patients (0.12 +/- 0.04 mEq/L) was significantly less than that of the control subjects (0.30 +/- 0.05). Furthermore, the final plasma potassium concentration slightly exceeded baseline in the patients but was significantly reduced in controls, leading to the conclusion that an abnormal responsiveness of the beta 2 adrenoceptor may contribute to the impaired potassium tolerance found in patients who have end-stage renal disease.

Correction of uremic cellular injury with a protein-restricted amino acid-supplemented diet

Untreated patients with uremia show an abnormally low resting transmembrane potential (Em) of skeletal muscle cells. This finding corresponds to impaired sodium transport. Adequate hemodialysis corrects this abnormality. Toxins derived from protein precursors have been implicated as the hypothetical cause of impaired transport and membrane depolarization in untreated uremia. To inferentially examine this hypothesis in further detail, we deliberately reduced dialysis time until Em fell in six uremic patients in whom it had been previously corrected. When Em fell, we examined the effect of reducing crude protein in their diet in conjunction with adding an essential amino acid supplement. Five of six patients who complied with the diet showed correction of their abnormally low Em despite continued reduction of dialysis time. These findings support the notion that in patients with uremia, a product of crude dietary protein may be responsible for membrane depolarization and, in addition, direct measurement of resting muscle transmembrane potential may be a useful index to determine adequacy of dialysis therapy.

Tubular handling of bicarbonate in dogs with experimental renal failure

In this study, micropuncture experiments were performed to examine the segmental reabsorption of bicarbonate and chloride in the normal dog kidney (stage 1) and in the remnant kidney (stage 3) of dogs with experimental renal failure. The protocol consisted of three phases: (1) 3% extracellular fluid volume expansion, (2) infusion of Ringer's solution containing 90 mM of sodium bicarbonate, and (3) infusion of 150 mM of sodium bicarbonate in Ringer's solution. In the animals with remnant stage 3 kidneys, the ratio of absolute bicarbonate reabsorption/absolute sodium reabsorption was increased compared to dogs with stage 1 kidneys at both the proximal and distal sampling sites. These data suggest that bicarbonate reabsorption was elevated in both the distal and the proximal tubules in experimental chronic renal failure. In contrast to the reabsorption of bicarbonate, chloride reabsorption was depressed in stage 3 kidneys at the late proximal puncture site. This resulted in greater delivery to the distal nephron. The distal segments reabsorbed a constant fraction of delivered chloride, resulting in an increase in fractional chloride excretion in chronic renal failure compared to that in normal animals.

Metabolic balance studies and dietary protein requirements in patients undergoing continuous ambulatory peritoneal dialysis

Balance studies for nitrogen, potassium, magnesium, phosphorus, and calcium were carried out in eight men undergoing continuous ambulatory peritoneal dialysis (CAPD) to determine dietary protein requirements and mineral balances. Patients were fed high energy diets for 14 to 33 days which provided either 0.98 (seven studies) or 1.44 g (six studies) of primarily high biological value protein/kg body wt/day. Mean nitrogen balance was neutral with the lower protein diet (+0.35 +/- 0.83 SEM g/day) and strongly positive with the higher protein diet (+2.94 +/- 0.54 g/day). With the higher protein diet the balances for potassium, magnesium, and phosphorus were strikingly positive, there was an increase in body weight in all patients, and a rise in mid-arm muscle circumference in five of the six patients. The relation between protein intake and nitrogen balance suggests that the daily protein requirement for clinically stable CAPD patients should be at least 1.1 g/kg/day; to account for variability among subjects 1.2 to 1.3 g protein/kg/day is probably preferable. Potassium balance correlated directly with nitrogen balance (r = 0.81). High fecal potassium losses (19 +/- 1.2 mEq/day) in all patients probably helped maintain normal serum potassium concentrations. Mean serum magnesium was increased (3.1 +/- 0.1 mg/dl), and magnesium balances were positive suggesting that the dialysate magnesium of 1.85 mg/dl is excessive. The net gain of calcium from dialysate was 84 +/- 18 mg/day; this correlated inversely with serum calcium levels (r = -0.90).

Disorders of body fluids, sodium and potassium in chronic renal failure

A stable volume and composition of extracellular fluid are essential for normal functioning of the body. Since the kidney is primarily responsible for regulating extracellular fluid, loss of kidney function should have catastrophic consequences. Fortunately, even with loss of more than 90 percent of renal function, a remarkable capacity to regulate body fluid volumes and sodium and potassium persists. Nevertheless, this capacity is limited to chronic renal disease and this has important consequences for clinical management of these patients. How can sodium and potassium homeostasis be assessed? Methods for evaluating the steady-state regulation of sodium include measurement of body fluids and their distribution in different compartments and measurement of exchangeable and intracellular sodium. Short-term regulation of body sodium can be assessed from measurement of sodium balance during changes in dietary salt. Potassium is predominantly contained within cells and thus the assessment of its regulation requires special emphasis on measurement of steady-state body stores and potassium distribution across cell membranes. However, the methods used to make all of these measurements require assumptions that may not hold in the altered state of uremia. This raises problems in interpretation requiring critical analysis before conclusions can be made regarding sodium and potassium homeostasis in patients with chronic renal failure. This review focuses on abnormalities of body fluids, sodium and potassium in patients with creatinine clearances of less than 20 ml/min due to chronic renal failure and the impact of conservative therapy, dialysis and renal transplantation on these patients.

Effect of digoxin upon intracellular potassium in man

The effect of digoxin upon intramuscular potassium was studied by use of whole body counting and biopsy technique. Twelve healthy subjects and twelve outpatients with mild cardiac insufficiency or atrial arrhythmia were digitalised. Before and after digitalization total body potassium (TBK) was measured. Potassium concentration in muscle specimens (MK) was analysed by the neutron activation technique. Digoxin was measured in serum and in skeletal muscle tissue by radioimmunoassay, and QS2-index as a measure of the electromechanical systole. In both groups a significant decrease in TBK (P less than 0.05) and MK (P less than 0.01) was demonstrated in connection to digitalization. There was no correlation between the decrease in TBK and MK, or between the concentrations of digoxin in serum or muscle and the decrease in potassium concentration. The digoxin in serum in healthy subjects was 0.9 +/- 0.33 nmol/l and in patients 1.2 +/- 0.41 nmol/l. The digoxin in muscle was 39 +/- 10.9 nmol/kg dry weight in seven of the healthy individuals and 37 +/- 9.5 nmol/kg dry weight in nine patients. After digitalization a decrease of QS2-index was found in both groups (P less than 0.01).

[Concentration of water, sodium, and potassium in the tissues of rats with circulatory insufficiency caused by constriction of the thoracic portion of the inferior vena cava]

In edematous rats with circulatory insufficiency, the content of water and sodium in the muscle and liver rises while that of potassium declines per 1 g wet weight. The increased sodium and decreased potassium content in the tissues cannot be accounted for only by enlargement of the extracellular volume. In contrast to normal rats, the edematous ones show a negative linear correlation between the content of sodium and potassium in the muscle and liver. The total content of sodium and potassium in the tissues increases. It is assumed that part of intracellular potassium in the test tissues of rats with circulatory insufficiency is replaced by sodium. The proportion of sodium bound to structural components of the cell increases.

Resting skeletal muscle membrane potential as an index of uremic toxicity. A proposed new method to assess adequacy of hemodialysis

Electrochemical disturbances of skeletal muscle cells in untreated uremia are characterized by an increase in the intracellular sodium and chloride content, a decrease in intracellular potassium, and a low resting membrane potential. In this study, we have reexamined the foregoing and, in addition, have examined the effects of hemodialysis. Three groups of patients were studied. In the first group of 22 uncomplicated uremic patients, whose creatinine clearance (Ccr) ranged from 2 to 12 cm(3)/min per 1.73 m(2), resting transmembrane potential difference (Em) of skeletal muscle cells was measured. In each of the nine patients whose Ccr ranged between 6.3 and 12 cm(3)/min, the Em was normal (i.e., -90.8+/-0.9 mV, mean+/-SEM). However, as Ccr dropped below 6.3 cm/min, the Em became progressively reduced and assumed a linear relationship with the Ccr. In the second study, nine individuals with end-stage renal disease, whose mean Ccr was 4.3 cm(3)/min, underwent measurement of Em and intracellular electrolyte concentration before and after 7 wk of hemodialysis. Before dialysis, the Em was -78.5+/-2.1 mV, intracellular sodium and chloride were elevated, and the intracellular potassium was reduced. After 7 wk of hemodialysis the Em rose to -87.8+/-1.3 mV, and the intracellular sodium, chloride, and potassium became normal. In the third study, seven patients who were stable on 6-h thrice-weekly dialysis were studied before and after reduction of dialysis to 6 h twice weekly. In those individuals whose Em remained normal after 6 wk, dialysis time was reduced further. On thrice-weekly dialysis the Em was -91.2+/-1.0 mV. With reduced dialysis, the Em fell to -80.1+/-0.8 mV (P < 0.001). In each case, the Em became abnormal before significant signs or symptoms of uremia were noted. These findings demonstrate that end-stage renal disease is associated with serious electrochemical changes in the muscle cell which are reversed by hemodialysis and recur when dialysis time is reduced. Thus, serial observations of muscle Em may be a potentially powerful tool to assess adequacy of dialysis therapy.

Hypophosphatemia and rhabdomyolysis

Clinical observations suggest that overt rhabdomyolysis may occur if severe hypophosphatemia is superimposed upon a pre-existing subclinical myopathy. To examine this possibility, a subclinical muscle cell injury was induced in 23 dogs by feeding them a phosphorus- and calorie-deficient diet until they lost 30% of their original weight. To induce acute, severe hypophosphatemia in the animals after partial starvation, 17 of the dogs were given large quantities of the same phosphorus-deficient diet in conjunction with an oral carbohydrate supplement, which together provided 140 kcal/kg per day. After phosphorus and caloric deprivation, serum phosphorus and creatine phosphokinase (CPK) activity were normal. Total muscle phosphorus content fell from 28.0+/-1.3 to 26.1+/-2.5 mmol/dg fat-free dry solids. Sodium, chloride, and water contents rose. These changes resembled those observed in patients with subclinical alcoholic myopathy. When studied after 3 days of hyperalimentation, the animals not receiving phosphorus showed weakness, tremulousness, and in some cases, seizures. Serum phosphorus fell, the average lowest value was 0.8 mg/dl (P <0.001). CPK activity rose from 66+/-357 to 695+/-1,288 IU/liter (P <0.001). Muscle phosphorus content fell further to 21.1+/-7.7 mmol/dg fat-free dry solids (P <0.001). Muscle Na and Cl contents became higher (P <0.01). Sections of gracilis muscle showed frank rhabdomyolysis.6 of the 23 phosphorus- and calorie-deprived dogs were also given 140 kal/kg per day but in addition, each received 147 mmol of elemental phosphorus. These dogs consumed their diet avidly and displayed no symptoms. They did not become hypophosphatemic, their CPK remained normal, and derangements of cellular Na, Cl, and H(2)O were rapidly corrected. The gracilis muscle appeared normal histologically in these animals. These data suggest that a subclinical myopathy may set the stage for rhabdomyolysis if acute, severe hypophosphatemia is superimposed. Neither acute hypophosphatemia nor rhabdomyolysis occur if abundant phosphorus is provided during hyperalimentation.

Bicarbonate reabsorption in chronic renal failure

Bicarbonate reabsorption was studied in dogs before and after induction of renal failure, produced by infarction of one kidney and removal of the contralateral kidney. Glomerular filtration rate and renal plasma flow decreased to 21 and 37% of control values, respectively. Fractional potassium excretion and fractional phosphate excretion increased significantly. Volume expansion resulted in a significant decrease of bicarbonate reabsorption in both control and uremic groups. At comparable levels of fractional chloride excretion, bicarbonate reabsorption was significantly higher in renal failure than in control animals. In the second group of dogs, following induction of renal failure, sodium bicarbonate was given orally in an amount sufficient to neutralize endogenous acid production. Bicarbonate reabsorption was again significantly higher than in control animals. Thyroparathyroidectomy had no effect on bicarbonate reabsorption. Absolute bicarbonate reabsorption and sodium reabsorption were lineraly related in control animals and in those in renal failure; the ratio of absolute bicarbonate reabsorption/abolute sodium reabsorption was significantly higher in renal failure than in control. These data demonstrate that renal failure is associated with enhanced bicarbonate reabsorption which is not related to the state of extracellular volume, the need to increase acid excretion or the concentrations of parathyroid hormone. These findings suggest that there are additional unknown factors controlling bicarbonate reabsorption in renal failure.

Hyperglucagonemia of renal failure

Elevation of plasma glucagon concentration has been observed in starvation and illnesses associated with increased catabolism such as diabetes mellitus and severe infections. Thus, we examined plasma glucose, immunoreactive insulin (IRI, microunits per milliliter) and glucagon (IRG, picograms per milliliter) responses to a beef meal (1 g/kg body wt) and intravenous glucose (1.5 g/min for 45 min) in patients with chronic renal failure (CRF). After the beef meal (n = 6), plasma glucose did not change, IRI rose from 10.1+/-1.2 to 16.3+/-1.1 (P < 0.01), and IRG rose from a fasting value of 225+/-26 to 321+/-40 (P < 0.01) by 90 min (mean+/-SEM). Intravenous infusion of glucose in CRF patients resulted in significant elevations and prolonged disappearance of plasma glucose and insulin when compared to control subjects (P < 0.01). Glucose infusion failed to suppress elevated plasma glucagon concentrations to normal levels.6 wk of chronic hemodialysis in five patients resulted in normal plasma glucose and insulin responses to the same intravenous glucose load. In contrast, plasma glucagon concentration remained unchanged after hemodialysis and there was no correlation of plasma glucagon levels with carbohydrate intolerance.