The effects of phosphoproteins on acid balance in normal subjects

Diet and Metabolism in CKD-Related Metabolic Acidosis

Metabolic acidosis is a common complication in patients with chronic kidney disease that occurs when the daily nonvolatile acid load produced in metabolism cannot be excreted fully by the kidney. A reduction in urine net acid excretion coupled with a high nonvolatile acid load may play a role in its pathogenesis. Diet is important in generation of the nonvolatile acid load. Acids are produced from metabolism of dietary protein and from the endogenous production of organic anions from neutral precursors. Acids can be balanced by alkali precursors ingested in the diet in the form of combustible organic anions. These typically are reflected indirectly by the excess of mineral cations to mineral anions in a food or diet. These principles underscore widely used methods to estimate the nonvolatile acid load from dietary intake using formulas such as the net endogenous acid production equation and the potential renal acid load equation. Empiric data largely validate these paradigms with high net endogenous acid production and potential renal acid load contributed by foods such as protein, grains, and dairy, and low net endogenous acid production and potential renal acid load contributed by fruits and vegetables along with corresponding dietary patterns. Although further studies are needed to understand the health benefits of altering nonvolatile acid load via diet, this review provides a detailed assessment on our current understanding of the role of diet in chronic kidney disease-related acidosis, providing an updated resource for researchers and clinicians.

Dietary Contributions to Metabolic Acidosis

Eating a net acid-producing diet can produce an "acid stress" of severity proportional to the diet net acid load, as indexed by the steady-state renal net acid excretion rate. Depending on how much acid or base is ingested or produced from endogenous metabolic processes and how well our homeostatic mechanisms can buffer or eliminate the additional acids or bases, we can alter our systemic acid-base balance. With increasing age, the kidney's ability to excrete daily net acid loads declines (a condition similar to that of mild CKD), invoking increased utilization of potential base stores (eg, bone, skeletal muscle) on a daily basis to mitigate the acid accumulation, thereby contributing to development of osteoporosis, loss of muscle mass, and age-related renal insufficiency. Patients suffering from more advanced CKD often present with more severe acid stress or metabolic acidosis, as the kidney can no longer excrete the entire acid load. Alkaline diets based on fruits and vegetables may have a positive effect on long-term preservation of renal function while maintaining nutritional status. This chapter discusses the biochemistry of dietary precursors that affect acid or base production.

Mechanisms for falling urine pH with age in stone formers

One of the main functions of the kidney is to excrete an acid load derived from both dietary and endogenous sources, thus maintaining the pH of other fluids in the body. Urine pH is also of particular interest in stone formers, since it determines the presence of either calcium phosphate or uric acid content in stones. Others have noted in epidemiological studies a rise in incidence of low pH-dependent uric acid stones with age, coinciding with a decrease in the incidence of high pH-dependent phosphate stones. Taken together, these trends are suggestive of a longitudinal decline in urine pH in stone-forming patients, and, if true, this could explain the observed trends in stone incidence. We studied 7,891 stone formers, all of whom collected a 24-h urine sample and matching serum. Multivariate modeling revealed that urine pH did indeed fall with age and particularly between the ages of 20 and 50 yr old in both men and women. We sought to explain this trend through the inclusion of traditionally understood determinants of urine pH such as urinary buffers, estimates of glomerular filtration, and dietary acid load, but these, taken together, accounted for but a small fraction of the pH fall. Gastrointestinal anion absorption was the strongest predictor of urine pH in all age groups, as we have previously reported in middle-aged normal men and women. However, we found that, despite a decreasing urine pH, gastrointestinal anion absorption increased monotonically with age. In fact, after adjustment for gastrointestinal anion absorption, urine pH declined more markedly, suggesting that bicarbonate-producing anion absorption is regulated in a manner that offsets the decline of urine pH.

Comparison of potential dietary and urinary risk factors for ammonium urate nephrolithiasis in two bottlenose dolphin ( Tursiops truncatus) populations

Dietary and urinary risk factors have been implicated in conditions favoring ammonium urate nephrolithiasis in managed dolphins compared with free-ranging dolphins. In this study, urine samples were collected from 16 dolphins (8 cases, 8 controls) from the U.S. Navy Marine Mammal Program for the purposes of assessing changes in urinary biomarkers after a large meal. Urinary biomarkers and nephrolithiasis presence were assessed opportunistically in 15 long-term resident free-ranging dolphins living in Sarasota Bay, Florida. Additionally, the total purine contents of fish commonly consumed by each dolphin population were measured to evaluate potential dietary risk factors. Populations were compared for total dietary purine composition, recently fed status, nephrolithiasis presence, and differences in urinary biochemical, acid-base, and physicochemical parameters via Wilcoxon rank sum analysis and least square means. Managed dolphins had higher urinary pH and ammonium ([Formula: see text]) in both pre- and postprandial conditions and higher urinary uric acid and saturation indices of NH₄U in the postprandial condition compared with free-ranging dolphins ( P < 0.05). The purine content was greater ( P < 0.0001) in the diet consumed by managed dolphins [7 mmol/Mcal metabolizable energy (ME)] than in the free-ranging dolphin diet (4 mmol/Mcal ME). Free-ranging dolphins did not show evidence of nephrolithiasis. Observed differences in urinary biomarkers and dietary purine content in these two dolphin populations suggest a pathophysiologic basis for the role of fish types on the risk of NH₄U stone formation. Future research should investigate fish type and feeding frequency, inhibitors and promoters, and alkalinizing therapy for reducing NH₄U nephrolithiasis in dolphins.

Acid Balance, Dietary Acid Load, and Bone Effects-A Controversial Subject

Modern Western diets, with higher contents of animal compared to fruits and vegetable products, have a greater content of acid precursors vs. base precursors, which results in a net acid load to the body. To prevent inexorable accumulation of acid in the body and progressively increasing degrees of metabolic acidosis, the body has multiple systems to buffer and titrate acid, including bone which contains large quantities of alkaline salts of calcium. Both in vitro and in vivo studies in animals and humans suggest that bone base helps neutralize part of the dietary net acid load. This raises the question of whether decades of eating a high acid diet might contribute to the loss of bone mass in osteoporosis. If this idea is true, then additional alkali ingestion in the form of net base-producing foods or alkalinizing salts could potentially prevent this acid-related loss of bone. Presently, data exists that support both the proponents as well as the opponents of this hypothesis. Recent literature reviews have tended to support either one side or the other. Assuming that the data cited by both sides is correct, we suggest a way to reconcile the discordant findings. This overview will first discuss dietary acids and bases and the idea of changes in acid balance with increasing age, then review the evidence for and against the usefulness of alkali therapy as a treatment for osteoporosis, and finally suggest a way of reconciling these two opposing points of view.

Three-Stream, Bicarbonate-Based Hemodialysis Solution Delivery System Revisited: With an Emphasis on Some Aspects of Acid-Base Principles

Hemodialysis patients can acquire buffer base (i.e., bicarbonate and buffer base equivalents of certain organic anions) from the acid and base concentrates of a three-stream, dual-concentrate, bicarbonate-based, dialysis solution delivery machine. The differences between dialysis fluid concentrate systems containing acetic acid versus sodium diacetate in the amount of potential buffering power were reviewed. Any organic anion such as acetate, citrate, or lactate (unless when combined with hydrogen) delivered to the body has the potential of being converted to bicarbonate. The prescribing physician aware of the role that organic anions in the concentrates can play in providing buffering power to the final dialysis fluid, will have a better knowledge of the amount of bicarbonate and bicarbonate precursors delivered to the patient.

Titratable acidity: a Pitts concept revisited

Titratable Acidity (TA) in urine can be measured directly or calculated from actual and reference pH, by using the pKa₂ 6,8 for phosphate. In urine, H₂PO₄(-) represents the excretion of filtered H₂PO₄(-), filtrated HPO₄(2-) being completely reabsorbed by the proximal tubule (the Van Slyke approach). Since excretion of H₂PO₄(-) frequently exceeds its glomerular filtration, this approach is considered inadequate by Pitts. He claimed that it is the tubular H(+) secretion which converts filtered HPO₄(2-) to H₂PO₄(-), thereafter excreted in urine. This is only true under conditions of inorganic acid or neutral phosphate loading, when the maximum tubular phosphate reabsorption (TmPi) is overcharged. In controls, H₂PO₄(-) excretion is lower than its glomerular filtration, provided that acid-base status is normal and tubular phosphate reabsorption is below the TmPi. The TmPi is lower than its glomerular filtration, provided that acid-base status is normal and tubular phosphate reabsorption is below the TmPi. When the TmPi is exceeded, a portion of HPO₄(2-) escapes proximal reabsorption, reaching the distal tubule where its absorption is precluded, while tubular H(+) secretion converts HPO₄(2-) to H₂PO₄(-). In man and dog, the attainment of TmPi is evidenced by a FE% of 20%, and only beyond this limit H₂PO₄(-) excretion exceeds glomerular filtration. When FE% is lower than 20%, H₂PO₄(-) filtration exceeds excretion, HPO4(2-) being completely reabsorbed at the proximal tubule by NaPi-2a and 2c cotransporters. While Van Slyke's approach is always valid, Pitts' approach is only valid under loading conditions, when the two processes of H₂PO₄(-) excretion overlap each other. NH (+4) increases inversely to TA excretion in conditions of acidosis and tP restriction, but is independent of TA in Pi-replete dogs, independently of acidosis.

Net acid excretion capacity is related to blood hydrogen ion and serum carbon dioxide

Acid-base imbalance due to dietary food patterns has emerged as one of the hypotheses leading to modern-day diseases. This study examined if a new method to assess the renal ability to excrete an acid load, that is, the net acid excretion capacity (NAEC), constructed from net acid excretion (NAE) and urine pH, relates to blood hydrogen ion concentration ([H+]) and serum carbon dioxide concentration ([CO2]). In a second analysis, NAE to pH relationship was examined, and is de facto treated to be linear. This study used historical, cross-sectional data of 58 repeated measurements from 8 subjects for the primary measurements of NAEC, blood [H+], and serum [CO2]. Using fixed models, higher NAEC associated with lower [H+] and higher [CO2]. Using hierarchical models, the interindividual variations in [H+] and [CO2] explained the variations in NAEC. In the second analysis (n = 59), a quadratic NAE to pH relationship (NAE = -846.77 + 341.47 pH - 31.50 pH(2)) can be reported. Net acid excretion capacity, a noninvasive tool to assess the renal ability to excrete an acid load, has a physiologic base to it, in that it captures the inherent nonlinear relations of NAE to pH explaining endogenous [H+] retention/excretion. A higher vegetable and fruit consumption might relieve NAEC and allow excess [H+] loss via both renal and respiratory routes.

Amino Acid-Based Peritoneal Dialysis Solutions for Malnutrition: New Perspectives

Protein and energy malnutrition is frequently found in patients on maintenance dialysis and is associated with an increased risk of death. Among a variety of factors involved in the development of protein and energy malnutrition, such as acidosis, insulin resistance, inflammation, and dialysate protein losses, insufficient intake of proteins and energy as a result of anorexia plays a prominent role.

Amino acid (AA)-based peritoneal dialysis (PD) solutions can induce an anabolic response in malnourished patients on continuous ambulatory PD if enough calories are ingested simultaneously. Poor appetite, however, may impede the intake of sufficient calories. Peritoneal dialysis solutions containing a mixture of AAs and glucose in a proper ratio can serve as a source of proteins and calories. Such a dialysis solution can be used in fasting patients on nocturnal automated PD as part of a regular dialysis schedule. Using a sophisticated technique involving stable isotopes, this dialysis mixture has been found to induce acute anabolic changes in whole body protein metabolism. Such a metabolic response is similar to that induced by food. Intraperitoneal AAs, in common with ingested proteins, can induce generation of hydrogen ions and urea through oxidation of specific AAs. Supplying AAs together with calories could bring about utilization of AAs for the synthesis of proteins rather than the oxidation of AAs, thereby limiting production of acid and urea. Using dialysis solutions with a buffer concentration of 40 mmol/L further contributes to maintaining acid–base homeostasis.

We advocate consideration of usage of AA/glucose dialysate when PD patients cannot comply with dietary requirements. To evaluate the long-term effects of this approach on morbidity and mortality, clinical trials with large groups of patients are needed.

Dialysate as food as an option for automated peritoneal dialysis

Protein-energy malnutrition is frequently found in dialysis patients. Many factors play a role in its development including deficient nutrient intake as a result of anorexia. Peritoneal dialysis (PD) solutions containing a mixture of amino acids and glucose in an appropriate ratio could serve as a source of food. The authors of this article found that such a dialysis solution when administered to fasting patients who were on nightly automated peritoneal dialysis (APD), as part of a regular dialysis schedule, induced an acute anabolic effect. Also in PD patients in the fed state, dialysis solutions containing both amino acids and glucose were found to improve protein metabolism. It appears that the body responds similar to intraperitoneal and oral amino acid:dialysate as food. Like dietary proteins, intraperitoneal amino acids can bring about generation of hydrogen ions and urea as a result of oxidation. No rise of serum urea levels was found and serum bicarbonate remained within the normal range when a total buffer concentration of 40 mmol/L in the mixture was used. The use of this approach may be an option for PD patients who cannot fulfil dietary recommendations.

Effect of acute acid loading on acid-base and calcium metabolism

OBJECTIVE

To investigate the acid-base and calcium metabolic responses to acute non-carbonic acid loading in idiopathic calcium stone-formers and healthy males using a quantitative organ physiological approach.

MATERIAL AND METHODS

Five-h ammonium chloride loading studies were performed in 12 male recurrent idiopathic calcium stone-formers and 12 matched healthy men using a randomized, placebo-controlled, cross-over design. Arterialized capillary blood, serum and urine were collected hourly for measurement of electrolytes, ionized calcium, magnesium, phosphate, parathyroid hormone and acid-base status. Concentrations of non-metabolizable base (NB) and acid (NA) were calculated from measured concentrations of non-metabolizable ions.

RESULTS

The extracellular acid-base status in the stone-formers during basal conditions and acid loading was comparable to the levels in the healthy controls. The stone-formers tended to have lower renal excretion rates of NA during acid loading; however, for a given degree of non-carbonic acidosis, controls and stone-formers excreted approximately the same amount of NA in the urine, suggesting that the capacity of tubular regeneration of NB was comparable in the two groups. Acid loading resulted in significantly increased concentrations of ionized calcium in serum in both controls and stone-formers. The increase in serum ionized calcium in response to acid loading was, however, significantly higher in the calcium stone-formers than in the healthy individuals. Acid loading resulted in massive calciuria in both groups, with significantly higher urinary calcium excretion rates in the stone-formers compared to the healthy subjects. Renal excretion rates of NA correlated significantly with renal calcium excretion rates in both groups. However, the stone-formers excreted significantly more calcium in the urine at a given rate of renal NA excretion.

CONCLUSIONS

The hypercalciuric and hypercalcaemic responses to loading with non-carbonic acid are more pronounced in recurrent idiopathic calcium stone-formers than in healthy individuals. Acid loading (i.e. protein ingestion) may contribute to disturbed bone metabolism in idiopathic calcium nephrolithiasis as well as calcium stone formation.

Bone buffering of acid and base in humans

The sources and rates of metabolic acid production in relation to renal net acid excretion and thus acid balance in humans have remained controversial. The techniques and possible errors in these measurements are reviewed, as is the relationship of charge balance to acid balance. The results demonstrate that when acid production is experimentally increased among healthy subjects, renal net acid excretion does not increase as much as acid production so that acid balances become positive. These positive imbalances are accompanied by equivalently negative charge balances that are the result of bone buffering of retained H+ and loss of bone Ca2+ into the urine. The data also demonstrate that when acid production is experimentally reduced during the administration of KHCO3, renal net acid excretion does not decrease as much as the decrease in acid production so that acid balances become negative, or, in opposite terms, there are equivalently positive HCO3- balances. Equivalently positive K+ and Ca2+ balances, and thus positive charge balances, accompany these negative acid imbalances. Similarly, positive Na+ balances, and thus positive charge balances, accompany these negative acid balances during the administration of NaHCO3. These charge balances are likely the result of the adsorption of HCO3- onto the crystal surfaces of bone mineral. There do not appear to be significant errors in the measurements.

Acid and mineral balances and bone in familial proximal renal tubular acidosis

BACKGROUND

Metabolic acidosis caused by increased rates of fixed acid production is associated with increased urinary excretion of Ca and negative Ca balances. Metabolic acidosis caused by a reduced capacity of the kidneys to excrete acid contributes to the development of bone disease in the course of chronic renal failure and may be associated with bone disease among some patients with renal tubular acidosis.

METHODS

To assess the effects of life-long metabolic acidosis alone in the absence of other physiological disturbances, we measured the net balances of fixed acid and minerals in two brothers in a Costa Rican family with hereditary proximal renal tubular acidosis. Bone radiographs were assessed, and radial bone densities were measured. On a subsequent occasion, transiliac bone biopsies, following double-tetracycline labeling, were obtained from these two patients and an unaffected brother.

RESULTS

During the balance studies, serum [HCO3-] concentrations of the two affected patients were stable at 12.5 +/- 0.9 and 19.2 +/- 0.7 mmol/L, respectively. Their rates of net fixed acid production were normal and appropriate for their body weights, averaging 0.90 and 1.02 mEq/kg/day. Because their distal renal tubular function was normal, they were capable of acidifying their urine maximally, allowing sufficient urinary excretion of titratable acid and ammonium to maintain net acid excretion at a level that matched acid production. Thus, their acid balances were near zero, as observed among healthy subjects, at -1.9 +/- 2.3 and -2.2 +/- 2.2 mEq/day, respectively. Their rates of urinary Ca excretion were normal at 1.6 +/- 0.3 and 2.7 +/- 2.4 mmol/day, and the their balances of Ca and other minerals were close to zero so that ongoing bone loss was not occurring despite the acidosis. Nevertheless, their heights, relative to their ages, were shorter than the heights of their unaffected relatives. Their radial bone densities were lower than normal for their age and sex, and their iliac cortices were thinner than that of their unaffected brother. However, they had no histomorphometric evidence of osteomalacia or osteitis fibrosa, and their rates of bone mineralization were normal.

CONCLUSIONS

The results indicate that this chronic metabolic acidosis reduces growth, including that of bone. We speculate, without direct supporting evidence, that bone stores of HCO3-/CO3= are reduced, as has been observed in patients with the metabolic acidosis of chronic renal failure and in experimental metabolic acidosis in animals.

New perspectives on acid-base balance

This review will cover two main areas of acid-base balance, both of which are attended with much misconception and misunderstanding. One is the external balance of acids and alkali; the other is the contribution of bone buffering in acute and chronic metabolic acidosis.

Effects of a high protein intake on renal acid excretion in bodybuilders

Bodybuilders often prefer a high protein diet to achieve maximum skeletal muscle hypertrophy. In this study the effect of a high protein diet on renal acid load and renal handling of proton excretion was studied comparing dietary intake and urinary ionograms in 37 male bodybuilders and 20 young male adults. Energy intake (+ 7%), protein intake (128 vs 88 g/d/1.73 m2), and renal net acid excretion (95 vs 64 mmol/d/1.73 m2) were higher in the bodybuilders than in the controls, however, urine-pH was only slightly lower (5.83 vs 6.12). In the bodybuilders renal ammonium excretion was higher at any given value of urine pH than in the controls. In a regression analysis protein intake proved to be an independent factor modulating the ratio between urine-pH and renal ammonium excretion. The concomitant increase of renal net acid excretion and maximum renal acid excretion capacity in periods of high protein intake appears to be a highly effective response of the kidney to a specific food intake leaving a large renal surplus capacity for an additional renal acid load.

[The effect of long-term increased protein administration on mineral metabolism and kidney function in the rat. I. Renal and enteral excretion of calcium, magnesium, phosphorus, sulfate and acid]

The influence of continuous imbalanced high protein intake on the metabolism of minerals (calcium, magnesium, phosphorus) and renal function was the subject of a long-term experiment with rats. In the first part of the study particular attention was directed to the contribution of protein-induced endogenous acid production and renal excretion of hydrogen ions and sulphate to the development of hypercalciuria. For 61 weeks 200 male Wistar rats in eight groups were fed isocaloric diets, whose protein contents were increased from 13 to 26 and 40 J% at the expense of carbohydrate intake. The fat content of the diets was 40 J%. In two groups with 13 and 26 J% protein the effect of different kinds of animal protein was also studied, replacing casein by beef. Mineral contents were kept constant in these diets. To examine the excretion mechanisms of calcium and phosphorus especially under conditions of excessive protein intake, the ratio of calcium to phosphorus was varied in three diets with 40 J% protein by increasing both minerals alternatively or together from 0.6 to 1.2%. An increase in dietary protein content from 13 to 26 or 40 J% produced a sustained hypercalciuria and also hypermagnesiuria over a period of more than 400 days (after 58 weeks: 3.3, 5.9, and 6.8 mg calcium/day; 2.2, 3.3, and 3.4 mg magnesium/day; p less than or equal to 0.05). No adaptation to high protein intake occurred. Hypermagnesiuria, which equally hasn't been described before as a result of high protein intake, was accompanied by a reduced fecal excretion of magnesium. With increased protein intake (casein and beef) hypercalciuria and also hypermagnesiuria were positively correlated with an increased formation and renal excretion of hydrogen ions and sulphate, which resulted from protein catabolism. The dietary protein source influenced the extent of hypercalciuria, irrespective of a constant phosphorus intake. Although leading to equal increases in renal total acid and sulphate excretion, beef as the main protein source caused a lower calciuria than casein. High phosphorus intake caused the highest total acid excretion of all groups, but resulted in a reduced hypercalciuria and hypermagnesiuria and counteracted the influence of an increased protein intake.

Effect of human insulin administration on urinary acidification in patients with insulin-dependent diabetes

A previous study has shown that oral glucose administration results in a transient fall in urinary acid excretion in humans. The present study was undertaken to determine the effect of physiologic doses of insulin on urinary acidification while maintaining serum glucose concentration constant. This was accomplished by using a euglycemic insulin clamp method. Eight patients with insulin-dependent diabetes and no clinical or laboratory evidence of detectable renal disease were studied. Data obtained during two 2-hour periods of steady state insulin infusion rates of 0.2 and 0.5 mU/kg/min were compared. This resulted in steady state serum free insulin levels of 15 +/- 0.1 and 39 +/- 0.6 uU/ml respectively. Urinary pH and bicarbonate excretion rate rose while the excretion rates of titratable acid, ammonium and net acid fell significantly with increased insulin administration. These changes occurred in the absence of any significant changes in serum glucose, potassium, Ca2+ or phosphorus concentrations or urinary excretion rates of Na+, K+, phosphorus or Ca2+. These data suggest that increased insulin levels within the physiological range can result in a transient fall in the rate of urinary acid excretion. These findings confirm previous observations in animals and suggest that insulin may be the cause of post prandial urinary "alkaline tide".

Chronic effects of dietary protein in the rat with intact and reduced renal mass

The chronic effects of dietary protein on renal structure and function were studied in rats with normal and reduced renal mass. Control rats with two kidneys were compared with unilaterally nephrectomized rats, and with one and one-third nephrectomized rats obtained by unilateral nephrectomy and infarction of one-third of the remaining kidney. Rats at each level of renal mass were maintained on chow containing either 6% or 40% protein content. Separate cohorts of rats were studied four and eight months after ablation and institution of these dietary regimens. At both time intervals and at all levels of renal mass, rats fed the high protein diet had higher average values for GFR than comparable animals fed the low protein chow. Within each of the dietary regimens the animals with loss of renal mass developed greater prevalences of sclerotic glomeruli by eight months. Furthermore, at each level of initial renal mass, rats eating the high protein diet had a greater prevalence of sclerotic glomeruli than those on the low protein diet. Similarly, rats on the high protein diet had greater rates of protein excretion than those on the low protein diet at each degree of ablation. The prevalence of sclerosed glomeruli increased between four and eight months in each group. Thus, the extent of renal injury as manifested by proteinuria and glomerular sclerosis was directly related to the degree of initial loss of renal mass, and dietary protein restriction retarded these manifestations of injury across a wide range of initial renal mass.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypophosphaturia impairs the renal defense against metabolic acidosis

It is known that Pi normally provides the major source of non-NH3 urinary buffer and that Pi-buffered renal H+ excretion (titratable acidity, TA) accounts for a large fraction of daily renal net acid excretion (NAE). Whether the presence of luminal non-NH3 buffers is a prerequisite to normal renal regulation of systemic acid-base equilibrium under any conditions has not been investigated. Accordingly, I investigated whether chronic renal regulation of plasma (p) [HCO3] might be impaired under conditions of normophosphatemic hypophosphaturia (NHP) produced by short-term dietary Pi restriction. During a steady-state of HCl-induced acidosis in NaCl-replete NHP dogs (group 1A, N = 6), [HCO3-]p averaged 14.1 +/- 0.6 mEq/liter and arterial (a) [H+] averaged 54 +/- 2 nEq/liter. Substitution K+ 2.5 mEq/kg as neutral Pi for equivalent dietary KCl for 7 to 8 days resulted in significant amelioration of acidosis (delta [HCO3-]p + 2.2 +/- 0.5 mEq/liter, P less than 0.01; delta [H+]a -6 +/- 2 nEq/liter, P less than 0.01) in association with a cumulative increment (sigma delta) in TA excretion (+ 103 mEq, P less than 0.001) and NAE (+ 22 mEq). To investigate whether Pi-induced amelioration of acidosis was related to enhanced urinary buffer capacity, an additional group (group 1B, N = 5) with NHP and chronic HCl acidosis was administered the non-Pi buffer, neutral creatinine (5.0 mmoles/kg daily). As with Pi, acidosis was ameliorated by creatinine administration and sigma delta NAE increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrogen ion balance in dialysis therapy

A model to describe hydrogen ion balance (H+B) in acetate and bicarbonate dialysis therapy was developed based on measurement of metabolic addition of hydrogen ion (H+) to the body between and during dialyses and measurement of net buffer repletion during dialysis. Metabolic H+ generation was shown to be equal to 0.77 times the protein catabolic rate plus the total net removal of lactate and beta-hydroxybutyrate ions during dialysis. Buffer repletion was calculated from total net flux of acetate and bicarbonate during dialysis. The model was used for eight paired studies of H+B on one week each of acetate and bicarbonate dialysis and showed that cumulative H+B with acetate was -7 +/- 28 (M +/- SEM) mmol/week compared to -175 +/- 45 mmol/week with bicarbonate (P less than 0.001). It is concluded that there is an initial, strongly negative H+B when patients on acetate dialysis are converted to bicarbonate. The possible physiologic significance of this is discussed.

Metabolism and acid-base physiology

The purpose of this paper is to review the pathways of hydrogen ion production and removal due to intermediary metabolism. The principal method of analysis employed was one based on a theoretical approach because it is the most accurate and has the broadest application. In the absence of hypoxia and insulin deficiency, carbohydrates and neutral lipids will not make significant contributions to acid-base balance. During normal metabolism, the oxidation of proteins leads to an acid load. The majority of protons are produced from the oxidation of cationic plus sulfur-containing amino acids, whereas they are removed when anionic amino acids are oxidized. Organic anions, if they can be metabolized in vivo, lead to an equivalent degree of proton removal. Small contributions to acid-base metabolism are made by phospholipid and purine oxidations. Special reactions involving calcium contribute to the acid load in that the precipitation of calcium carbonate or phosphate in bone or in the gastrointestinal tract will result in proton liberation. When all of the above are considered, the clinician can make a reasonably accurate estimate of the rate of acid production.

The calciuria of increased fixed acid production in humans: evidence against a role for parathyroid hormone and 1,25(OH)2-vitamin D

We measured mineral and acid balances, serum iPTH, urinary cAMP/creatinine, and plasma concentrations of 25OHD and 1,25(OH)2D in 7 healthy adults during control conditions and during increased fixed acid production achieved either by the administration of NH4Cl (N = 3) or by increased dietary protein intake (N = 4). When acid production was increased, the subjects were in positive acid balance and negative Ca balance because of increased urinary Ca excretion. Serum iPTH fell slightly but urinary cAMP and the plasma levels of vitamin D metabolites did not change. W conclude that the accelerated skeletal and urinary losses of Ca that occur when fixed acid production is increased are not contributed to nor compensated for by the parathyroid-vitamin D endocrine systems.

Renal glutamine metabolism in rats fed high-protein diets

The influence of protein intake on acid excretion and renal glutamine metabolism was investigated and compared to the effects of NH4Cl-induced metabolic acidosis. Rats fed a diet containing 55% casein excreted more ammonia, phosphate, sulphate, and chloride than did rats fed a 13% casein diet, but, when they were given an 0.1 M NaHCO3 solution to drink, ammonia excretion was no longer elevated. Renal phosphate-dependent glutaminase and phosphoenolpyruvate carboxykinase activities, ammoniagenesis by isolated mitochondria, and the rate of renal gluconeogenesis were all elevated in the rats fed the high-protein diet but not if these rats also drank the sodium bicarbonate solution. Increased glutaminase and phosphoenolpyruvate carboxykinase activities, mitochondrial ammoniagenesis, and gluconeogenesis were all evident in rats made acidotic with NH4Cl. It is concluded that these metabolic adaptations evident in the kidneys of rats fed the high-protein diet are due to the acidogenic effects of increased protein intake.

The nature of the renal response to chronic disorders of acid-base equilibrium

The rate of acid excretion by the kidney appears to be determined by factors regulating the site and the rate of sodium reabsorption, rather than by a homeostatic mechanism that responds to systemic pH. This hypothesis, although unconventional, is supported by much experimental evidence, and it accounts for a wide variety of clinical and physiologic findings that heretofore have been difficult or impossible to explain.