Neutralization of infused acid by nephrectomized dogs

Pathophysiology of Diet-Induced Acid Stress

Diets can influence the body's acid-base status because specific food components yield acids, bases, or neither when metabolized. Animal-sourced foods yield acids and plant-sourced food, particularly fruits and vegetables, generally yield bases when metabolized. Modern diets proportionately contain more animal-sourced than plant-sourced foods, are, thereby, generally net acid-producing, and so constitute an ongoing acid challenge. Acid accumulation severe enough to reduce serum bicarbonate concentration, i.e., manifesting as chronic metabolic acidosis, the most extreme end of the continuum of "acid stress", harms bones and muscles and appears to enhance the progression of chronic kidney disease (CKD). Progressive acid accumulation that does not achieve the threshold amount necessary to cause chronic metabolic acidosis also appears to have deleterious effects. Specifically, identifiable acid retention without reduced serum bicarbonate concentration, which, in this review, we will call "covert acidosis", appears to cause kidney injury and exacerbate CKD progression. Furthermore, the chronic engagement of mechanisms to mitigate the ongoing acid challenge of modern diets also appears to threaten health, including kidney health. This review describes the full continuum of "acid stress" to which modern diets contribute and the mechanisms by which acid stress challenges health. Ongoing research will develop clinically useful tools to identify stages of acid stress earlier than metabolic acidosis and determine if dietary acid reduction lowers or eliminates the threats to health that these diets appear to cause.

Physiochemical effects of acid exposure on bone composition and function

Bone is primarily composed of collagen and apatite, two materials which exhibit a high sensitivity to pH dysregulation. As a result, acid exposure of bone, both clinically and in the laboratory is expected to cause compositional and mechanical changes to the tissue. Clinically, Metabolic acidosis (MA), a condition characterized by a reduced physiological pH, has been shown to have negative implications on bone health, including a decrease in bone mineral density and volume as well as increased fracture risk. The addition of bone-like apatite to ionic solutions such as phosphate buffered saline (PBS) and media has been shown to acidify the solution leading to bone acid exposure. Therefore, is it essential to understand how reduced pH physiochemically affects bone composition and in turn its mechanical properties. This study investigates the specific changes in bone due to physiochemical dissolution in acid. Excised murine bones were placed in PBS solutions at different pHs: a homeostatic pH level (pH 7.4), an acidosis equivalent (pH 7.0), and an extreme acidic solution (pH 5.5). After 5 days, the bones were removed from the solutions and characterized to determine compositional and material changes. We found that bones, without cells, were able to regulate pH via buffering, leading to a decrease in bone mineral content and an increase in collagen denaturation. Both of these compositional changes contributed to an increase in bone toughness by creating a more ductile bone surface and preventing crack propagation. Therefore, we conclude that the skeletal systems' physiochemical response to acid exposure includes multifaceted and spatially variable compositional changes that affect bone mechanics.

The Importance of Recognizing and Addressing the Spectrum of Acid Stress

Acid accumulation sufficient to reduce plasma bicarbonate concentration, thereby recognized as chronic metabolic acidosis, harms bones and muscles and appears to enhance progression of CKD. Evolving evidence supports that progressive acid accumulation that is not enough to cause chronic metabolic acidosis nevertheless has deleterious effects. Measurable acid retention without reduced plasma bicarbonate concentration, called eubicarbonatemic acidosis, also appears to cause kidney injury and exacerbate CKD progression. Furthermore, chronic engagement of mechanisms to mitigate the ongoing acid challenge of net acid-producing diets of developed societies also appears to be deleterious, including for kidney health. This review challenges clinicians to consider the growing evidence for a spectrum of acid-accumulation disorders that include lesser degrees of acid accumulation than metabolic acidosis yet are harmful. Further research will develop clinically useful tools to identify individuals suffering from these earlier stages of acid stress and determine if the straightforward and comparatively inexpensive intervention of dietary acid reduction relieves or eliminates the harm they appear to cause.

The Continuum of Acid Stress

Acid-related injury from chronic metabolic acidosis is recognized through growing evidence of its deleterious effects, including kidney and other organ injury. Progressive acid accumulation precedes the signature manifestation of chronic metabolic acidosis, decreased plasma bicarbonate concentration. Acid accumulation that is not enough to manifest as metabolic acidosis, known as eubicarbonatemic acidosis, also appears to cause kidney injury, with exacerbated progression of CKD. Chronic engagement of mechanisms to mitigate the acid challenge from Western-type diets also appears to cause kidney injury. Rather than considering chronic metabolic acidosis as the only acid-related condition requiring intervention to reduce kidney injury, this review supports consideration of acid-related injury as a continuum. This "acid stress" continuum has chronic metabolic acidosis at its most extreme end, and high-acid-producing diets at its less extreme, yet detrimental, end.

Water Quality for Grazing Livestock I

Water is the most important nutrient for rangeland livestock. However, competition with municipalities, industry, and other water users often results in grazing livestock being forced to use water supplies that are less than perfect. Surface water in western rangleands are often contaminated by mineral extraction, irrigation runoff and other human activities. Mineral contaminants in drinking water are additive with similar contaminants in feedstuffs. The goal of this and the subsequent article is to provide producers and veterinarians with the basic background to make informed decisions about whether a given water supply is "safe" for livestock.

Experimental protocol for metabolic acidosis induction by intravenous administration of hydrochloric acid in sheep

ABSTRACT The aim of this study was to assess the magnitude and duration of blood and urine changes and the side effects of hyperchloremic acidosis induced by the intravenous administration of hydrochloric acid in sheep. Five healthy, crossbred adult ewes, with a mean body weight of 44±2.9kg were used. The hydrochloric acid solution was administered intravenously at a rate of 25mL/kg/h for 4 hours continuously. Venous blood and urine samples were collected and pH values, blood carbon dioxide partial pressure, bicarbonate, base excess, strong ion difference, anion gap, total concentration of nonvolatile buffers, creatinine, plasma L-lactate, plasma and urine sodium, potassium, and chloride were determined. The experimental protocol induced severe hyperchloremic acidosis at the end of the infusion, with a decreased plasma strong ion difference. The fractional excretion of sodium and chloride remained increased during 4 hours after the infusion. Aciduria was observed at approximately 24 hours. Twenty-four hours after the infusion, the animals showed mild and compensated metabolic acidosis. This protocol was effective in inducing severe and long-lasting hyperchloremic acidosis and did not cause serious side effects. Therefore, this protocol can be used safely in adult sheep for studies on the treatment of this condition.

Kidney Response to the Spectrum of Diet-Induced Acid Stress

Chronic ingestion of the acid (H⁺)-producing diets that are typical of developed societies appears to pose a long-term threat to kidney health. Mechanisms employed by kidneys to excrete this high dietary H⁺ load appear to cause long-term kidney injury when deployed over many years. In addition, cumulative urine H⁺ excretion is less than the cumulative increment in dietary H⁺, consistent with H⁺ retention. This H⁺ retention associated with the described high dietary H⁺ worsens as the glomerular filtration rate (GFR) declines which further exacerbates kidney injury. Modest H⁺ retention does not measurably change plasma acid–base parameters but, nevertheless, causes kidney injury and might contribute to progressive nephropathy. Current clinical methods do not detect H⁺ retention in its early stages but the condition manifests as metabolic acidosis as it worsens, with progressive decline of the glomerular filtration rate. We discuss this spectrum of H⁺ injury, which we characterize as “H⁺ stress”, and the emerging evidence that high dietary H⁺ constitutes a threat to long-term kidney health.

Water Treatment by Magnetic Field Increases Bone Mineral Density of Rats

Water treatment using a magnetic field is an attractive but controversial issue with regard to its effects on human health. This study aimed to investigate the effects of water treatment using a magnetic field on the bone mineral density (BMD), bone mineral content (BMC), bone area (BA), bone resistance (BR), blood gas analysis, blood viscosity, and blood biochemical profile of rats. Forty-eight Wistar rats were divided into 2 groups: control (n = 24) and magnetic water-treated (n = 24). Each of these groups was subdivided into 3 groups to evaluate 3 consumption periods (15, 30, and 45 d). The animals were kept in metabolic cages throughout the experiment. A completely randomized design distributed to a 2 × 3 factorial arrangement was used. No significant difference was found in the water intake, dry matter intake, BA, or femoral head resistance between the groups. However, higher anion gap and lower CHCO₃ were found in the arterial blood of the magnetic water-treated group. There was significant interaction between the water consumption period and the BR, BMD, and BMC. With 15 d of consumption, there was no difference in the BMC and BR. With 30 d of consumption, the BR (midshaft), BMD, and BMC showed increases; the increases were greater with 45 d of consumption. In adulthood, every month of the animal is approximately equivalent to 2.5 human years. The consumption of water treated by magnetic field for 45 d provided an effective way to improve BMD, BMC and BR in rats.

Transient dilutional acidosis but no lactic acidosis upon cardiopulmonary bypass in patients undergoing coronary artery bypass grafting

INTRODUCTION

Dilutional acidosis may result from the introduction of a large fluid volume into the patients' systemic circulation, resulting in a considerable dilution of endogenous bicarbonate in the presence of a constant carbon dioxide partial pressure. Its significance or even existence, however, has been strongly questioned. Blood gas samples of patients operated on with standard cardiopulmonary bypass (CPB) were analyzed in order to provide further evidence for the existence of dilutional acidosis.

MATERIAL AND METHODS

Between 07/2014 and 10/2014, a total of 25 consecutive patients scheduled for elective isolated coronary artery bypass grafting with CPB were enrolled in this prospective observational study. Blood gas samples taken regularly after CPB initiation were analyzed for dilutional effects and acid-base changes.

RESULTS

After CPB initiation, hemoglobin concentration dropped from an average initial value of 12.8 g/dl to 8.8 g/dl. Before the beginning of CPB, the mean value of the patients' pH and base excess (BE) value averaged 7.41 and 0.5 mEq/l, respectively. After the onset of CPB, pH and BE values significantly dropped to a mean value of 7.33 (p < 0.0001) and -3.3 mEq/l (p < 0.0001), respectively, within the first 20 min. In the following period during CPB they recovered to 7.38 and -0.5 mEq/l, respectively, on average. Patients did not show overt lactic acidosis.

CONCLUSIONS

The present data underline the general existence of dilutional acidosis, albeit very limited in its duration. In patients undergoing coronary artery bypass grafting it seems to be the only obvious disturbance in acid-base homeostasis during CPB.

Compensation for Acid-Base Disorders

Hydrogen concentration is a critical determinant of many physiologic functions and is tightly regulated. Any alteration in acid-base equilibrium sets into motion a compensatory response by either the lungs or the kidneys. The compensatory response attempts to return the ratio between Pco₂ and [HCO₃^-] to normal and thereby minimize the pH change. A primary increase or decrease in one component is associated with a predictable compensatory change in the same direction in the other component, and the expected compensation can be estimated clinically in dogs and cats.

Analytic Reviews : Acid-Base Abnormalities in Cardiopulmonary Arrest: Varying Patterns in Different Locations Within the Hospital

Arterial blood gas analysis performed in 67 episodes who suffered cardiopulmonary arrest revealed that the degree of acidemia correlated with the location of the patient within the hospital: emergency department (ED), general hospital bed (HB), or intensive care unit (ICU). Acidemia was most severe in patients who pre sented either in the ED (pH = 7.15) or in a HB (pH = 7.10) as a result of combined metabolic (bicarbonate ion [HCO 3-] = 20 ± 16 and 15 ± 10 mEq/L) and respiratory acidosis (arterial carbon dioxide tension [PaCO2] = 59 ± 30 and 50 ± 24 mm Hg). In contrast, patients in the ICU had only mild acidemia or even alkalemia (pH = 7.28); respiratory acidosis was un common in this setting (PaCO2 = 36 ± 18 mm Hg), and patients exhibited a degree of metabolic acidosis ([HCO3 - ] = 18 ± 8 mEq/L) similar to that seen in patients in EDS or HBS. This relative hypocarbia seen in patients in the ICU was attributed to the fact that most (14 of 22, 64% ) were already receiving mechanical ven tilation at the time of the cardiopulmonary arrest. Pa tients who were successfully resuscitated (20, 30% ) did not differ from those in whom resuscitation failed (47, 70% ) in degree of acidemia or location of arrest. Serum potassium levels obtained in 29 patients at the time of arrest revealed that serum potassium levels were greater than 5.2 mEq/L only 8 times; there was only one mea surement greater than 6.0 mEq/L, which did not corre late with the degree of acidemia.

Intravenous administration of a polyionic solution containing 84 mEq/l of lactate resolves experimentally induced hyperchloraemic acidosis in horses

REASONS FOR PERFORMING STUDY

Treatment of metabolic acidosis using sodium bicarbonate solutions is safe when blood gas analysis is available. The evidence that solutions containing metabolisable buffers can be used as an alternative for treatment of metabolic acidosis in horses is of practical interest.

OBJECTIVES

To investigate the safety and efficacy of a polyionic solution containing 84 mEq/l of lactate (L84) for the correction of induced hyperchloraemic metabolic acidosis.

STUDY DESIGN

Non-randomised crossover design.

METHODS

Five healthy, adult, crossbred horses were used. A solution containing 100 mmol/l of HCl was infused intravenously (100 ml/kg bwt) for 5 h to induce metabolic acidosis. Metabolic acidosis was induced in each horse twice, with a minimum 15-day interval after recovery from the first induction: the first time no treatment was administered (control group) and the second time horses were treated with an intravenous infusion of L84 solution, 100 ml/kg bwt for 5 h, beginning 3 h after the end of HCl infusion. Venous blood samples were taken at 0, 2.5, 5, 8, 10.5, 13, 24 and 48 h; and urine at 0, 5, 8 and 13 h. Laboratory data included pH (blood and urine), PCO₂ , HCO₃^- , base excess, total plasma protein concentration, l-lactate, Na⁺ , K⁺ , Cl^- , strong ion difference (SID₄ ), anion gap, change in plasma volume and fractional excretions of Na⁺ , K⁺ and Cl^- . Effects of time and treatment were tested by 2-way repeated measures ANOVA.

RESULTS

Severe hyperchloraemic metabolic acidosis was induced. In the untreated horses, correction of the imbalance occurred gradually, and mild acidosis was still present at 48 h. In horses treated with the L84 solution, acidosis was corrected by the end of the infusion. There were no adverse effects with the administration of the L84 solution.

CONCLUSIONS

A polyionic solution containing 84 mEq/l of lactate effectively corrected induced metabolic acidosis in horses within 5 h.

A Long Affair with Renal Tubules

This essay provides a summary of my professional activities. My interest in renal physiology started as a medical student in Vienna, when I became acquainted with Homer Smith's essays on kidney function. After moving to the United States in 1951, I was fortunate to be mentored by Robert Pitts, in whose Department of Physiology at Cornell Medical College in New York I was given early independence, intellectual stimulation, and the opportunity to pursue experiments on single renal tubules. The problem of how the nephron manages its myriad of transport functions has never lost its fascination for me, and I am profoundly grateful to the many colleagues at Cornell Medical College and at Yale University School of Medicine who shared my passion for the kidney.

Acid retention accompanies reduced GFR in humans and increases plasma levels of endothelin and aldosterone

Dietary alkali slows GFR decline in humans with a moderately reduced glomerular filtration rate (GFR) despite the absence of metabolic acidosis. Similarly, dietary alkali slows GFR decline in animals with 2/3 nephrectomy (Nx), a chronic kidney disease (CKD) model without metabolic acidosis in which GFR decline is mediated by acid (H(+)) retention through endothelin (ET) and mineralocorticoid receptors. To gain insight as to whether this mechanism might mediate GFR decline in humans, we explored whether macroalbuminuric subjects with moderately reduced (CKD stage 2 = 60-90 ml/min; CKD 2) compared with normal estimated GFR (> 90 ml/min; CKD 1), each without metabolic acidosis, have H(+) retention that increases plasma levels of ET-1 and aldosterone. Baseline plasma ET and aldosterone concentrations were each higher in CKD 2 than CKD 1. Baseline dietary H(+) and urine net acid excretion (NAE) were not different between groups, but an acute oral NaHCO₃ bolus reduced urine NAE less (i.e., postbolus urine NAE was higher) in CKD 2 than CKD 1, consistent with greater H(+) retention in CKD 2 subjects. Thirty days of oral NaHCO₃ reduced H(+) retention in CKD 2 but not CKD 1 subjects and reduced plasma ET and aldosterone in both groups but to levels that remained higher in CKD 2 for each. Subjects with CKD stage 2 eGFR and no metabolic acidosis nevertheless have H(+) retention that increases plasma ET and aldosterone levels, factors that might mediate subsequent GFR decline and other untoward vascular effects.

Effects of acute dilutional hyponatremia on acid-base changes and electrolyte concentrations in rats with bilateral renal pedicle ligation

OBJECTIVE

To describe the effects of increasing the extracellular fluid (ECF) volume by approximately 20% on acid-base changes and electrolyte concentrations in anesthetized rats.

ANIMALS

18 adult male Sprague-Dawley rats.

PROCEDURES

Rats were assigned to a control group (n = 6 rats) and a treatment group (12). All rats were anesthetized, and instrumentation and bilateral renal pedicle ligation were performed. The treatment group was infused IV with sterile water throughout a 30-minute period. Acid-base variables and concentrations of electrolytes, lactate, albumin, phosphorus, and hemoglobin were measured before (baseline) and 30 and 60 minutes after onset of infusion. Anion gap, strong ion difference, strong ion gap, and contributions of sodium, chloride, albumin, phosphorus, and lactate concentrations to base excess were calculated at each time point.

RESULTS

Infusion of sterile water led to an increase in ECF volume of approximately 18%. This had no effect on acid-base balance, compared with that in control rats. Infusion of sterile water caused a significant decrease in sodium, chloride, ionized calcium, lactate, and albumin concentrations, compared with concentrations in the control group. Anion gap and calculated effects of sodium, chloride, albumin, and lactate concentrations on base excess at 60 minutes differed significantly between infused and control rats.

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of sterile water did not cause clinically relevant dilutional acidosis. The acidotic impact of water administration was offset by generation of new bicarbonate via carbonic acid equilibration and intracellular buffering in combination with the alkalotic effects of decreases in albumin, phosphorus, and lactate concentrations.

Chronic acidosis-induced alteration in bone bicarbonate and phosphate

Chronic metabolic acidosis increases urinary calcium excretion without altering intestinal calcium absorption, suggesting that bone mineral is the source of the additional urinary calcium. In vivo and in vitro studies have shown that metabolic acidosis causes a loss of mineral calcium while buffering the additional hydrogen ions. Previously, we studied changes in femoral, midcortical ion concentrations after 7 days of in vivo metabolic acidosis induced by oral ammonium chloride. We found that, compared with mice drinking only distilled water, ammonium chloride induced a loss of bone sodium and potassium and a depletion of mineral HCO3(-) and phosphate. There is more phosphate than carbonate in neonatal mouse bone. In the present in vitro study, we utilized a high-resolution scanning ion microprobe with secondary ion mass spectroscopy to test the hypothesis that chronic acidosis would decrease bulk (cross-sectional) bone phosphate to a greater extent than HCO3(-) by localizing and comparing changes in bone HCO3(-) and phosphate after chronic incubation of neonatal mouse calvariae in acidic medium. Calvariae were cultured for a total of 51 h in medium acidified by a reduction in HCO3(-) concentration ([HCO(-)]; pH approximately 7.14, [HCO3(-)] approximately 13) or in control medium (pH approximately 7.45, HCO3(-) approximately 26). Compared with incubation in control medium, incubation in acidic medium caused no change in surface total phosphate but a significant fall in cross-sectional phosphate, with respect to the carbon-carbon bond (C2) and the carbon-nitrogen bond (CN). Compared with incubation in control medium, incubation in acidic medium caused no change in surface HCO3(-) but a significant fall in cross-sectional HCO3(-) with respect to C2 and CN. The fall in cross-sectional phosphate was significantly greater than the fall in cross-sectional HCO3(-). The fall in phosphate indicates release of mineral phosphates, and the fall in HCO3(-) indicates release of mineral HCO3(-), both of which would be expected to buffer the additional protons and help restore the pH toward normal. Thus a model of chronic acidosis depletes bulk bone proton buffers, with phosphate depletion exceeding that of HCO3(-).

Importance of timing of risk factors for cerebral oedema during therapy for diabetic ketoacidosis

Cerebral oedema is the most common cause of mortality and morbidity during the first day of conventional treatment for diabetic ketoacidosis in paediatric patients. It is possible that therapy contributes to its development. Risk factors that predispose to cerebral oedema should lead to an expansion of the intracellular and/or the extracellular fluid compartment(s) of the brain because water normally accounts for close to 80% of brain weight. With respect to the intracellular fluid compartment, the driving force to cause cell swelling is a gain of effective osmoles in brain cells and/or a significant decline in the effective osmolality of the extracellular fluid compartment. Factors leading to an expansion of the intracerebral extracellular fluid volume can be predicted from Starling forces acting at the blood-brain barrier. Some of these risk factors have an early impact, while others have their major effects later during therapy for diabetic ketoacidosis. Based on a theoretical analysis, suggestions to modify current therapy for diabetic ketoacidosis in children are provided.

Chronic metabolic acid load induced by changes in dietary electrolyte balance increased chloride retention but did not compromise bone in growing swine

The effects of chronic dietary acid loads on shifts in bone mineral reserves and physiological concentrations of cations and anions in extracellular fluids were assessed in growing swine. Four trials were conducted with a total of 38 (8.16 +/- 0.30 kg, mean +/- SEM) Large White x Landrace x Duroc pigs randomly assigned to one of three dietary treatments. Semipurified diets, fed for 13 to 17 d, provided an analyzed dietary electrolyte balance (dEB, meq/kg diet = Na+ + K+ - Cl-) of -35, 112, and 212 for the acidogenic, control, and alkalinogenic diets, respectively. Growth performance, arterial blood gas, serum chemistry, urine pH, mineral balance, bone mineral content gain, bone-breaking strength, bone ash, and percentage of bone ash were determined. Dietary treatments created a range of metabolic acid loads without affecting (P > 0.10) growth or feed intake. Urine pH was 5.71, 6.02, and 7.65 +/- 0.48 (mean +/- SEM) and arterial blood pH was 7.478, 7.485, and 7.526 +/- 0.006 for pigs fed acidogenic, control, and alkalinogenic treatments, respectively. A lower dEB resulted in an increased (P < 0.001) apparent Cl- retention (106.6, 55.4, and 41.2 +/- 6.3 meq/d), of which only 1.6% was accounted for by expansion of the extracellular fluid Cl- pool as calculated from serum Cl- (105.5, 103.4, 101.6 +/- 0.94 meq/L (mean +/- SEM) for pigs fed acidogenic, control, and alkalinogenic treatments, respectively. A lower dEB did not decrease (P > 0.10) bone mineral content gain, bone-breaking strength, bone ash, percentage of bone ash, or calcium and phosphate balance. In conclusion, bone mineral (phosphate) was not depleted to buffer the dietary acid load in growing pigs over a 3-wk period.

Acute acidosis-induced alteration in bone bicarbonate and phosphate

During an acute fall in systemic pH due to a decrease in the concentration of serum bicarbonate ([HCO(3)(-)]), metabolic acidosis, there is an influx of hydrogen ions into the mineral phase of bone, buffering the decrement in pH. When bone is cultured in medium modeling acute metabolic acidosis, the influx of hydrogen ions is coupled to an efflux of sodium and potassium and a depletion of mineral carbonate. These ionic fluxes would be expected to neutralize some of the excess hydrogen ions and restore the pH toward normal. Approximately one-third of bone carbonate is located on the hydration shell of apatite, where it is readily accessible to the systemic circulation, whereas the remainder is located in less accessible areas. We hypothesize that the surface of bone would respond to acidosis in a different manner than the interior of bone, with depletion of carbonate preferentially occurring on the bone surface. We utilized a high-resolution scanning ion microprobe with secondary ion mass spectroscopy to localize the changes in bone carbonate, as measured by HCO(3)(-), and phosphate and determine their relative contribution to the buffering of hydrogen ions during acute metabolic acidosis. Neonatal mouse calvariae were incubated in control medium (pH approximately 7.44, [HCO(3)(-)] approximately 27 mM) or in medium acidified by a reduction in [HCO(3)(-)] (pH approximately 7.14, [HCO(3)(-)] approximately 13). Compared with control, after a 3-h incubation in acidic medium there is a fivefold decrease in surface HCO(3)(-) with respect to the carbon-carbon bond (C(2)) and a threefold decrease in surface HCO(3)(-) with respect to the carbon-nitrogen bond (CN) with no change in cross-sectional HCO(3)(-). Compared with control, after a 3-h incubation in acidic medium there is a 10-fold decrease in cross-sectional phosphate with respect to C(2) and a 10-fold decrease in cross-sectional phosphate with respect to CN, with no change in surface phosphate. On the bone surface, there is a fourfold depletion of HCO(3)(-) in relation to phosphate, and, in cross section, a sevenfold depletion of phosphate in relation to HCO(3)(-). Thus acute hydrogen ion buffering by bone involves preferential dissolution of surface HCO(3)(-) and of cross-sectional phosphate.

Renal excretion of calcium and phosphorus in premature infants with incipient late metabolic acidosis

BACKGROUND

Premature infants receiving alimentation with cow milk-based formulas run a considerably high risk of incipient late metabolic acidosis, an early stage developing of manifest late metabolic acidosis. Is bone metabolism involved in pathophysiologic mechanisms characterizing this early stage of retention acidosis?

METHODS

Urinary ionography was performed in 10 premature infants with spontaneous development of incipient late metabolic acidosis (indicated by urine pH < 5.4 on 2 consecutive days) and 10 pair-matched premature infants with normal values of urine pH; both groups were receiving full oral nutrition with the same standard formula. Moreover, in 37 premature infants with incipient late metabolic acidosis who were randomly allocated to oral therapy with 2 mmol. kg(-1). d(-1) of either NaHCO 3 or NaCl over a period of 7 days, urinary excretion of calcium and phosphorus was assessed on day 1 and day 7.

RESULTS

Incipient late metabolic acidosis was accompanied by increased phosphaturia in premature infants receiving full oral nutrition. Seventeen premature infants receiving NaCl therapy (19 treatment periods) showed increased calciuria from day 1 to day 7, whereas, in 20 premature infants receiving NaHCO 3 therapy (23 treatment periods), calcium or phosphorus excretion in urine did not increase.

CONCLUSIONS

The data of urinary calcium and phosphorus excretion in premature infants support the hypothesis that bone mineralization may already be impaired in the early stage of incipient late metabolic acidosis.

Citric acid ingestion: a life-threatening cause of metabolic acidosis

We present a case that illustrates the acute (<6 hours) metabolic and hemodynamic effects of the ingestion of a massive oral citric acid load. The principal findings included metabolic acidosis accompanied by an increase in the plasma anion gap that was not caused by L -lactic acidosis, hyperkalemia, and the abrupt onset of hypotension. A unique feature was a dramatic clinical improvement when ionized calcium was infused. The case illustrates the importance of considering the properties of the conjugate base (anion) of the added acid because, in this instance, the citrate anion had a unique and life-threatening consequence (lower ionized calcium level) that was rapidly reversible.

Contribution of organic material to the ion composition of bone

Studies of bone mineral ranging from cadaveric analysis to the use of high-resolution ion microprobe with secondary ion mass spectroscopy (SIMS) have concluded that bone is rich in sodium and potassium relative to calcium. Exposure of bone to acid conditions either in vitro or in vivo leads to an exchange of hydrogen ions for sodium and potassium buffering the acidity of the medium or blood, respectively. Whether these monovalent ions reside within the mineral or organic phases of bone has never been determined. To determine the contribution of organic material to bone ion composition, we dissected calvariae from 4- to 6-day-old mice, removed organic material of some with hydrazine (Hydr), and prepared all bones for analysis using a high-resolution scanning ion microprobe coupled to a secondary ion mass spectrometer. We found that in non-Hydr-treated calvariae (Ctl) there was far more surface sodium and potassium than calcium (23Na/ 40Ca = 15.7 + 1.9, ratio of counts of detected secondary ions, mean + 95% CI, 39K/40Ca = 44.0 + 1.5). Removal of organic material with hydrazine (Hydr) led to a marked fall in the ratio of sodium to calcium and potassium to calcium (23Na/40Ca = 5.9 + 1.4, p < 0.025 vs. respective Ctl and 39K/40Ca = 1.1 + 1.5, p < 0.001 vs. respective Ctl). Similarly, when examining the cross-section of the calvariae there was more sodium and potassium than calcium (23Na/40Ca = 8.6 + 1.6, 39K/40Ca = 26.7 + 1.8). Treatment with Hydr again caused a marked fall in both ratios (23Na/40Ca = 0.3 + 1.6, p < 0.001 vs. respective Ctl and 39K/40Ca = 0.02 + 1.9, p < 0.001 vs. respective Ctl). Thus, within bone the organic material contains the majority of the sodium and potassium. This suggests that the organic material in bone and not the mineral itself is responsible for the acute buffering of the additional hydrogen ions during metabolic acidosis.

The effects of acid on bone

Metabolic acidosis induces calcium efflux from bone and in the process buffers the additional hydrogen ions. Initially metabolic acidosis stimulates physicochemical mineral dissolution and then cell-mediated bone resorption. Acidosis increases activity of the bone resorbing cells, the osteoclasts, and decreases activity of the bone forming cells, the osteoblasts. Osteoblastic immediate early response genes are inhibited as are genes controlling matrix formation.

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 in vivo metabolic acidosis on midcortical bone ion composition

Chronic metabolic acidosis increases urine calcium excretion without altering intestinal calcium absorption, suggesting that bone mineral is the source of the additional urinary calcium. During metabolic acidosis there appears to be an influx of protons into bone mineral, lessening the magnitude of the decrement in pH. Although in vitro studies strongly support a marked effect of metabolic acidosis on the ion composition of bone, there are few in vivo observations. We utilized a high-resolution scanning ion microprobe with secondary ion mass spectroscopy to determine whether in vivo metabolic acidosis would alter bone mineral in a manner consistent with its purported role in buffering the increased proton concentration. Postweanling mice were provided distilled drinking water with or without 1.5% NH(4)Cl for 7 days; arterial blood gas was then determined. The addition of NH(4)Cl led to a fall in blood pH and HCO(-)(3) concentration. The animals were killed on day 7, and the femurs were dissected and split longitudinally. The bulk cortical ratios Na/Ca, K/Ca, total phosphate/carbon-nitrogen bonds [(PO(2) + PO(3))/CN], and HCO(-)(3)/CN each fell after 1 wk of metabolic acidosis. Because metabolic acidosis induces bone Ca loss, the fall in Na/Ca and K/Ca indicates a greater efflux of bone Na and K than Ca, suggesting H substitution for Na and K on the mineral. The fall in (PO(2) + PO(3))/CN indicates release of mineral phosphates, and the fall in HCO(-)(3)/CN indicates release of mineral HCO(-)(3). Each of these mechanisms would result in buffering of the excess protons and returning the systemic pH toward normal.

Potassium

In a logical, stepwise approach to patients presenting with hypokalaemia or hyperkalaemia the clinician must first recognise circumstances in which the dyskalaemia represents a clinical emergency because therapy then takes precedence over diagnosis. If a dyskalaemia has been present for a long time, there is an abnormal renal handling of K+. The next step to analyse is the rate of excretion of K+ and, if necessary, its two components (urine flow rate and K+ concentration in the cortical collecting duct [CCD]) analysed independently. If the K+ concentration in the CCD is not in the expected range, its basis should be defined at the ion-channel level in the CCD from clinical information that can be used to deduce the relative rates of reabsorption of Na+ and Cl- in the CCD. This analysis provides the basis for diagnosis and may indicate where non-emergency therapy should then be directed.

Acid-base disorders in medicine

The practice of internal medicine involves daily exposure to abnormalities of acid-base balance. A wide variety of disease states either predispose patients to develop these conditions or lead to the use of medications that alter renal, gastrointestinal, or pulmonary function and secondarily alter acid-base balance. In addition, primary acid-base disease follows specific forms of renal tubular dysfunction (renal tubular acidosis). We review the acid-base physiologic functions of the kidney and gastrointestinal tract and the current understanding of acid-base pathophysiologic conditions. This includes a review of whole animal and renal tubular physiologic characteristics and a discussion of the current knowledge of the molecular biology of acid-base transport. We stress an approach to diagnosis that relies on knowledge of acid-base physiologic function, and we include discussion of the appropriate treatment of each disorder considered. Finally, we include a discussion of the effects of acidosis and alkalosis on human physiologic functions.

Long-term metabolic effects of urinary diversion on skeletal bone: histomorphometric and mineralogic analysis

OBJECTIVES

To evaluate the long-term influence of different types of intestinal urinary diversion on skeletal bone and its mineral content.

METHODS

Densitometry was used to estimate bone mineral content, and bone biopsies were analyzed with histomorphometric technique. The study comprised 20 patients with conduit urinary diversion and 19 with cecal continent reservoir, all followed up for more than 5 years, with normal or near-normal renal function.

RESULTS

Bone mineral content did not differ significantly between the patients with cecal continent urinary reservoir and those with conduit diversion or between these groups and a reference group. At the cellular level, the histomorphometric analysis revealed no defective bone mineralization or increased bone resorption in either group of patients. The trabecular bone volume was greater than normal in the reservoir group, but not in the conduit group. The appositional rate was significantly below normal in both groups of patients, but did not differ between conduit and reservoir patients.

CONCLUSIONS

Subtle changes in electrolytes and acid-base homeostasis identified in adults with intestinal segments incorporated in the urinary tract and with largely normal renal function do not seem to influence bone mineralization in the long term. At the cellular level, a lower than normal appositional rate was found in the patients with conduit or continent urinary diversion. In the latter group, this finding, together with increased trabecular bone volume, may indicate a decrease of bone turnover.

A model of the hyperkalemia produced by metabolic acidosis

In both humans and animals, mineral acids predictably result in hyperkalemia, whereas plasma K+ remains normal or may even decrease during organic acidosis. The purpose of these studies was to define the mechanism for these effects in the opossum kidney cell, an established epithelial cell line derived from the renal cortex of the opossum. This cell was chosen because the acid/base transport pathways in this cell type are well defined and because it is one of the few cells known to express K/H antiport, the transport pathway that has been proposed to mediate the hyperkalemia of acidosis. Cell K+ at pH 7.4 averaged 988 +/- 48 nmol/mg protein. Relative to this value (100%), cell K+ increased when buffer pH was increased to pH 8.4 with NaOH (108% +/- 3%) and decreased when buffer pH was acidified with HCl to pH 6.4 (93% +/- 4%), producing a highly significant correlation of cell K+ with buffer pH: cell K+ (% of baseline at pH 7.4) = 6.9 (cell pH) + 49 (r = 0.5, P < 0.004). In contrast, acidification of the buffer to pH 6.4 with either butyric or lactic acid increased cell K+ (115% +/- 4% and 110% +/- 2%, respectively, both P < 0.05 v 7.4 or HCl value). Cell pH acidified in response to HCl at a rate of 0.0053 +/- 0.0007 pH U/s, a significantly slower rate than in response to lactic acid or butyric acid (0.0071 +/- 0.0007 and 0.0091 +/- 0.0007 pH U/s, respectively). Unidirectional ouabain-sensitive 42K+ influx was significantly inhibited by HCl acidosis and less so by the organic acids.(ABSTRACT TRUNCATED AT 250 WORDS)

Can insulin administration cause an acute metabolic acidosis in vivo? An experimental study in dogs

Insulin is the cornerstone of therapy for diabetic ketoacidosis because it causes the rate of ketoacid production to fall; this action takes several hours to occur. Insulin also causes H+ to be transported from the intracellular fluid to the extracellular fluid in vitro. The purpose of this study was to determine if insulin led to the acute export of H+ from the intracellular fluid in vivo. If so, we wished to determine if this also occurred during chronic metabolic acidosis, to quantitate the magnitude of the H+ shift, and to evaluate the mechanisms involved. The administration of low- or high-dose insulin to normal dogs and high-dose insulin to dogs with chronic metabolic acidosis caused the concentration of bicarbonate in plasma to decline by close to 3 mmol/l. The PCO2 fell by close to 15% in all three groups of dogs, so one component of the fall was due to hyperventilation. As the pH of blood did not change, a primary metabolic acidosis also occurred. The fall in bicarbonataemia was not due to net accumulation of organic acids or to a loss of bicarbonate or organic anions in the urine. Taken together, insulin, when given at doses used to treat diabetic ketoacidosis, might induce a significantly greater degree of acidaemia in the extracellular fluid acutely after it is given.

Physicochemical effects of acidosis on bone calcium flux and surface ion composition

Net calcium flux (JCa) from bone in vitro is pH dependent. When pH falls below 7.40, through a reduction in [HCO3-], there is both physicochemical and cell-mediated JCa. To characterize the physicochemical effect of acidosis on bone we inhibited the bone-resorbing cells (osteoclasts) with the specific inhibitor calcitonin and studied the effect of acidosis on JCa and bone ion composition using an analytic high-resolution scanning ion microprobe. Neonatal mouse calvariae were cultured for 48 h in physiologically neutral pH medium (Ntl, pH = 7.41, [HCO3-] = 25 nM) or in medium that modeled metabolic acidosis (Met, pH = 7.10, [HCO3-] = 12), each with or without calcitonin (CT, 3 x 10(-9) M). There was net calcium efflux in Ntl (JCa = 631 +/- 36 nmol per bone per 48 h), which increased in Met (1019 +/- 53, p < 0.01); CT inhibited JCa in Ntl (-54 +/- 11, p < 0.01 versus Ntl), which increased in Met (197 +/- 15, p < 0.01 versus Ntl + CT). In the presence of CT the increase in JCa in Met versus Ntl represents physiochemical bone dissolution. The Ntl bone surface (approximately 2 nm in depth) was rich in Na compared to Ca (Na/Ca = 11.9, count/s of detected secondary ions), which fell in Met (Na/Ca = 6.0, p < 0.05); CT caused a further reduction of Na/Ca (3.1, p < 0.01 versus Ntl and versus Met), which was not altered in Met (2.6, p < 0.05 versus Ntl + CT).(ABSTRACT TRUNCATED AT 250 WORDS)

Extrarenal potassium tolerance in chronic renal failure: implications for the treatment of acute hyperkalemia

The role of extrarenal potassium homeostasis is well recognized as a major mechanism for the acute defense against the development of hyperkalemia. The purpose of this report is to examine whether or not the various mechanisms of extrarenal potassium regulation are intact in patients with end-stage renal disease (ESRD). The available data suggest that with the development of ESRD and the uremic syndrome there is impaired extrarenal potassium metabolism that is related to a defect in the Na,K-adenosine triphosphatase (ATPase). The responsiveness of uremic patients to the various effector systems that regulate extrarenal potassium handling is discussed. Insulin is well positioned to play an important role in the regulation of plasma potassium concentration in patients with impaired renal function. The role of basal insulin may be even more important than previously appreciated, since somatostatin infusion causes a much greater increase in the fasting plasma potassium in rats with renal failure than in controls. Furthermore, stimulation of endogenous insulin by oral glucose results in a greater intracellular translocation of potassium in uremic rats than in controls. Under at least two common physiologic circumstances, feeding and vigorous exercise, endogenous catecholamines might also act to defend against acute increments in extracellular potassium concentration. However, it is important to appreciate that the response to beta 2-adrenoreceptor-mediated internal potassium disposal is heterogeneous as judged by the variable responses to epinephrine infusion. Based on the evidence presented in this report, a regimen for the treatment of life-threatening hyperkalemia is outlined. Interpretation of the available data demonstrate that bicarbonate should not be relied on as the sole initial treatment for severe hyperkalemia, since the magnitude of the effect of bicarbonate on potassium is variable and may be delayed. The initial treatment for life-threatening hyperkalemia should always include insulin plus glucose, as the hypokalemic response to insulin is both prompt and predictable. Combined treatment with beta 2-agonists and insulin is also effective and may help prevent insulin-induced hypoglycemia.

Chloride-depletion metabolic alkalosis induces ECF volume depletion via internal fluid shifts in nephrectomized dogs

We recently reported that chloride-depletion metabolic alkalosis (CDMA) results in renal losses of Na, K, and water. In these studies we investigated whether CDMA (induced using a new model that avoids external changes in Na and water balance) was also associated with internal Na and water shifts out of the ECF. CDMA was induced using haemofiltration in functionally nephrectomized dogs. Plasma ultrafiltrate was substituted quantitatively with a solution duplicating each dog's plasma electrolyte composition in control animals, and with a solution containing HCO3 as the sole anion in CDMA animals. ECF volume was estimated as the space of distribution of [3H]-mannitol. Plasma composition and [3H]-mannitol distribution space were unchanged in control dogs. In CDMA dogs metabolic alkalosis developed; despite the absence of external changes in Na and water balance, the space of distribution of [3H]-mannitol decreased by 335 +/- 46 ml (equivalent to 8% of baseline ECF volume), calculated chloride space fell by 304 +/- 50 ml, and haematocrit increased from 45.6 to 48.5 vol%. We conclude that CDMA causes an internal shift of fluid out of the ECF. The resulting ECF volume contraction appears to be an inherent feature of CDMA.