HYPERKALEMIA AND HYPERCHLOREMIC ACIDOSIS IN CHRONIC PYELONEPHRITIS

Lipopolysaccharide directly inhibits bicarbonate absorption by the renal outer medullary collecting duct

Acidosis is associated with E. coli induced pyelonephritis but whether bacterial cell wall constituents inhibit HCO₃ transport in the outer medullary collecting duct from the inner stripe (OMCDi) is not known. We examined the effect of lipopolysaccharide (LPS), on HCO₃ absorption in isolated perfused rabbit OMCDi. LPS caused a ~ 40% decrease in HCO₃ absorption, providing a mechanism for E. coli pyelonephritis-induced acidosis. Monophosphoryl lipid A (MPLA), a detoxified TLR4 agonist, and Wortmannin, a phosphoinositide 3-kinase inhibitor, prevented the LPS-mediated decrease, demonstrating the role of TLR4-PI3-kinase signaling and providing proof-of-concept for therapeutic interventions aimed at ameliorating OMCDi dysfunction and pyelonephritis-induced acidosis.

Serum electrolyte patterns in end-stage renal disease

The charts of 70 successive patients presenting for dialysis therapy for end-stage renal disease (ESRD) were evaluated for their serum electrolyte values. The "classical" pattern of low total CO2 (tCO2), elevated anion gap ("delta"), and normal chloride was found in a minority of patients (14 of 70, or 20%). Hyperchloremia was noted in 46%; in 21 patients (30%), this was associated with a normal delta and in 11 (16%), hyperchloremia was accompanied by an elevated delta. Fourteen patients (20%), most with diabetic nephropathy, had normal serum electrolytes. Patients with chronic glomerulonephritis had a hyperchloremic pattern as often as not, and two of four patients with interstitial nephritis demonstrated hyperchloremia without an elevated delta. We conclude that the previously held thesis that hyperchloremia is a rare or absent finding by the time renal failure progresses to ESRD is no longer tenable. Furthermore, a significant minority of ESRD patients may require the initiation of dialysis at a time when their serum electrolytes are still normal.

Effect of acute potassium load on reabsorption in Henle's loop in chronic renal failure in the rat

To determine the effect of an acute load of potassium on potassium reabsorption by the loop of Henle in chronic renal failure, the right kidney was removed and branches of the left renal artery were ligated in 17 rats. One week later and after 2 days of a potassium-free diet, rats were studied before (period 1) and after (period 2) acute loads of potassium chloride (KCl group), equimolar sodium chloride (NaCl group) or no solute (time control). The KCl load increased urinary potassium excretion to a greater extent (from 5 to 50%, P less than 0.005) than in NaCl (14 to 27%) or time control (9 to 14%), and caused as great a diuresis and natriuresis as did NaCl. Fractional delivery of water, sodium, and potassium to the end-proximal tubule increased similarly in the NaCl and KCl groups and slightly less so in the time control group in period 2. The major finding was a striking increase in potassium delivery to the beginning of the distal tubule (from 17 to 37%) in period 2 which was substantially greater than in the combined control groups (13 to 19%, P less than 0.025) and was equivalent to three-quarters of urinary potassium excretion. This was the consequence of an increase in the filtered load of potassium, an increase in absolute delivery of potassium from the proximal tubule (P less than 0.005), and a decrease in fractional potassium reabsorption by the loop of Henle from 64 to 48%, versus 72 to 69% in the control groups (P less than 0.01). These results suggest that the proximal tubule and, in particular, Henle's loop play a role in excreting an acute potassium load in chronic renal failure.

Control of plasma aldosterone in diabetic patients with hyporeninemic hypoaldosteronism

In three patients with diabetes and hyporeninemic hypoaldosteronism changes in renin activity, plasma aldosterone and cortisol were examined under various conditions: orthostasis and intravenous furosemide, infusion of synthetic beta1-24 ACTH on two consecutive days and diurnal variations in basal hormone fluctuations. Each patient showed unmeasurably low renin activity unresponsive to orthostasis and intravenous furosemide while plasma aldosterone was below normal range. Under ACTH-infusion only marked increases in aldosterone were observed in one patient whereas cortisol responded normally in all diabetics tested. Analysis of diurnal night day fluctuations (20.00-8.00) in plasma aldosterone and cortisol revealed a close and statistically significant relationship between both hormones in each of the three patients (p less then 0.05-less than 0.001). Variations in plasma aldosterone thus were mediated through changes in endogenous pituitary ACTH. Compared with normal controls however, diurnal aldosterone curves were set at a lower level. Our results demonstrate that a reduced sensitivity of the adrenal gland to ACTH is not responsible for the observed subnormal plasma aldosterone levels in these patients. Therefore, the lack of circulating angiotensin II seems to be the causative reason of hypoaldosteronism. The exact mechanism of undetectable renin activity in these patients remains unknown.

Amelioration of metabolic acidosis with fludrocortisone therapy in hyporeninemic hypoaldosteronism

In four patients with renal hyperchloremic acidosis and hyperkalemia, hyporeninemic hypoaldosteronism and chronic renal insufficiency (glomerular filtration rates of 13, 31, 35 and 44 ml per minute per 1.73 m2), prolonged administration of fludrocortisone increased urinary potassium and net acid excretion, corrected hyperkalemia and substantially ameliorated acidosis. Except in the patient with the lowest glomerular filtration rate, the increased net acid excretion was due mostly to increased ammonium excretion. Urine pH decreased initially in each patient, but in the three patients with the highest filtration rates, it increased subsequently as ammonium excretion increased, indicating that renal ammonia production increased. Urinary ammonium excretion correlated inversely with serum potassium concentration and did not decrease on discontinuation of therapy if hyperkalemia was prevented from recurring. In patients with renal acidosis and hyporeninemic hypoaldosteronism, administration of mineralocorticoid hormone can augment both renal hydrogen-ion secretion and, by correction of hyperkalemia, renal ammonia production, and thereby ameliorate metabolic acidosis.

Big renin and biosynthetic defect of aldosterone in diabetes mellitus

To determine the cause of selective aldosterone deficiency in two patients with diabetes mellitus, studies of renin and of aldosterone-precursor metabolites were performed under conditions of sodium depletion and ACTH stimulation. Plasma renin concentration was elevated in both patients, and stimulated plasma renin activity was low in one and normal in the other. Fractionation of plasma extracts demonstrated the presence of "big renin," a relatively inactive precursor of renin. Metabolites of aldosterone precursors were increased, suggesting deficient 18-hydroxylase in one patient and dehydrogenase in the other. The results suggest that hypoaldosteronism in diabetic patients may result from combined defects in both renin and aldosterone biosynthesis.

Isohydric regulation of plasma potassium by bicarbonate in the rat

pH and bicarbonate affect many metabolic reactions but each may change independently. To study bicarbonate's effect onplasma potassium, blood bicarbonate in normal, hypokalemic or hyperkalemic rats was either maintained constant, lowered by hydrochloric acid or raised by sodium bicarbonate administraion. Blood pH was maintained constant by changing PCO2. In normokalemia lowering bicarbonate increased plasma potassium 2.0mEq above values obtained in the other groups. To eliminate urinary potassium losses, experiments were also performed in rats with bilateral ureteral ligation. Again, plasma potassium concentration rose significantly more in the lowered bicarbonate group. Similarly, in hypokalemia, plasma potassium rose 1.2 and 0.4mEq in the lowered and unchanged groups, but fell 0.2mEq/liter in the elevated group. Differences could not be ascribed to renal potassium losses as potassium excretion was essentially zero in each group. In hyperkalemia, plasma potassium concentration remained elevated for 150 min in the lowered bicarbonate group but fell 1.3 and 2.0mEq in the unchanged and elevated groups, respectively. Urinary potassium losses in the three groups were statistically identical. In all experiments blood pH was maintained unchanged during the experiment. The data show that bicarbonate, independent of blood pH, alters transcellular potassium distribution suggesting the usefulness of bicarbonate therapy in hyperkalemia even at a compensated blood pH.

Pathologic hypofunction of the renin-angiotensin-aldosterone system

The literature now contains reports of many cases of aldosterone deficiency. Usually, the presenting features are persistent hyperkalemia and tendencies to serious urinary sodium loss and hypotension. A classification of defects leading to pathologic hypofunction of the renin-angiotensin-aldosterone system (RAAS hypofunction) is presented, with emphasis on idiopathic hyporeninemia (probably the most common). Criteria for diagnosis are (1) normal adrenal glucocorticoid function, (2) low aldosterone excretion under basal and stimulated conditions, and (3) renal tubular responsiveness to exogenous mineralocorticoid. The condition is effectively managed with mineralocorticoid replacement therapy and should be considered in the presence of unexplained persistent hyperkalemia, hyponatremia, or postural hypotension.