Prolonged total fasting: a feast for the integrative physiologist

Periodic Fasting and Acute Cardiac Events in Patients Evaluated for COVID-19: An Observational Prospective Cohort Study

BACKGROUND

Periodic fasting was previously associated with greater longevity and a lower incidence of heart failure (HF) in a pre-pandemic population. In patients with coronavirus disease 2019 (COVID-19), periodic fasting was associated with a lower risk of death or hospitalization. This study evaluated the association between periodic fasting and HF hospitalization and major adverse cardiovascular events (MACEs).

METHODS

Patients enrolled in the INSPIRE registry from February 2013 to March 2020 provided periodic fasting information and were followed into the pandemic (n = 5227). Between March 2020 and February 2023, N = 2373 patients were studied, with n = 601 COVID-positive patients being the primary study population (2836 had no COVID-19 test; 18 were excluded due to fasting <5 years). A Cox regression was used to evaluate HF admissions, MACEs, and other endpoints through March 2023, adjusting for covariables, including time-varying COVID-19 vaccination.

RESULTS

In patients positive for COVID-19, periodic fasting was reported by 180 (30.0% of 601), who periodically fasted over 43.1 ± 19.2 years (min: 7, max: 83). HF hospitalization (n = 117, 19.5%) occurred in 13.3% of fasters and 22.1% of non-fasters [adjusted hazard ratio (aHR) = 0.63, CI = 0.40, 0.99; p = 0.044]. Most HF admissions were exacerbations, with a prior HF diagnosis in 111 (94.9%) patients hospitalized for HF. Fasting was also associated with a lower MACE risk (aHR = 0.64, CI = 0.43, 0.96; p = 0.030). In n = 1772 COVID-negative patients (29.7% fasters), fasting was not associated with HF hospitalization (aHR = 0.82, CI = 0.64, 1.05; p = 0.12). In COVID-positive and negative patients combined, periodic fasting was associated with lower mortality (aHR = 0.60, CI = 0.39, 0.93; p = 0.021).

CONCLUSIONS

Routine periodic fasting was associated with less HF hospitalization in patients positive for COVID-19.

Association of periodic fasting with lower severity of COVID-19 outcomes in the SARS-CoV-2 prevaccine era: an observational cohort from the INSPIRE registry

Objectives

Intermittent fasting boosts some host defence mechanisms while modulating the inflammatory response. Lower-frequency fasting is associated with greater survival and lower risk from COVID-19-related comorbidities. This study evaluated associations of periodic fasting with COVID-19 severity and, secondarily, initial infection by SARS-CoV-2.

Design

Prospective longitudinal observational cohort study.

Setting

Single-centre secondary care facility in Salt Lake City, Utah, USA with follow-up across a 24-hospital integrated healthcare system.

Participants

Patients enrolled in the INSPIRE registry in 2013-2020 were studied for the primary outcome if they tested positive for SARS-CoV-2 during March 2020 to February 2021 (n=205) or, for the secondary outcome, if they had any SARS-CoV-2 test result (n=1524).

Interventions

No treatment assignments were made; individuals reported their personal history of routine periodic fasting across their life span.

Main outcome measures

A composite of mortality or hospitalisation was the primary outcome and evaluated by Cox regression through February 2021 with multivariable analyses considering 36 covariables. The secondary outcome was whether a patient tested positive for SARS-CoV-2.

Results

Subjects engaging in periodic fasting (n=73, 35.6%) did so for 40.4±20.6 years (max: 81.9 years) prior to COVID-19 diagnosis. The composite outcome occurred in 11.0% of periodic fasters and 28.8% of non-fasters (p=0.013), with HR=0.61 (95% CI 0.42 to 0.90) favouring fasting. Multivariable analyses confirmed this association. Other predictors of hospitalisation/mortality were age, Hispanic ethnicity, prior MI, prior TIA and renal failure, with trends for race, smoking, hyperlipidaemia, coronary disease, diabetes, heart failure and anxiety, but not alcohol use. In secondary analysis, COVID-19 was diagnosed in 14.3% of fasters and 13.0% of non-fasters (p=0.51).

Conclusions

Routine periodic fasting was associated with a lower risk of hospitalisation or mortality in patients with COVID-19. Fasting may be a complementary therapy to vaccination that could provide immune support and hyperinflammation control during and beyond the pandemic.

Trial registration

Clinicaltrials.gov, NCT02450006 (the INSPIRE registry).

The management of diabetic ketoacidosis in adults-An updated guideline from the Joint British Diabetes Society for Inpatient Care

This article summarises the Joint British Diabetes Societies for Inpatient Care guidelines on the management of ketoacidosis; available at https://abcd.care/resource/management-diabetic-ketoacidosis-dka-adults. The document explicitly states that when a person aged 16-18 is under the care of the paediatric team, then the paediatric guideline should be used, and if they are cared for by an adult team, then this guideline should be used. The guideline takes into account new evidence on the use of the previous version of this document, particularly the high prevalence of hypoglycaemia and hypokalaemia, and recommends that when the glucose concentration drops below 14 mmol/L, that de-escalating the insulin infusion rate from 0.1 to 0.05 units/kg/h should be considered. Furthermore, a section has been added to address the recognition that use of sodium glucose co-transporter 2 inhibitors is associated with an increased risk of euglycaemic ketoacidosis. The management of ketoacidosis in people with end-stage renal failure or on dialysis is also mentioned. Finally, the algorithms to illustrate the guideline have been updated.

Association of periodic fasting lifestyles with survival and incident major adverse cardiovascular events in patients undergoing cardiac catheterization

AIMS

Animal models repeatedly show fasting increases longevity. Human data, though, are limited to anecdotal claims. This study evaluated the association of routine fasting with survival and, secondarily, with incident major adverse cardiovascular events.

METHODS AND RESULTS

Cardiac catheterization patients enrolled in the Intermountain INSPIRE longitudinal cohort (n = 2785) during 2013-2015 were followed through March 2019. A fasting survey was completed in n = 2025 (73%) of this cohort and 1957 were included in the final data analysis after 68 participants were removed (24 for data issues and 44 for fasting less than 5 years). Self-reported routine fasting behaviour, years of participation in fasting, and other fasting characteristics were surveyed. Mortality was the primary outcome and incident myocardial infarction (MI), stroke, and heart failure (HF) were secondary. Routine fasters (n = 389, mean age 64 ± 14 years, 34% female) averaged 42 ± 18 years of routine fasting (minimum 5 years). Non-fasters (n = 1568, aged 63 ± 14 years, 36% female) included never fasters (n = 1120 with 0 years of fasting) and previous fasters (n = 448 who averaged 32 ± 21 years of prior fasting but had stopped prior to enrolment). Routine fasters had greater survival vs. non-fasters [adjusted hazard ratio (HR) = 0.54, 95% confidence interval (CI) = 0.36-0.80; P = 0.002] and lower incidence of HF (adjusted HR = 0.31, CI = 0.12-0.78; P = 0.013), but not MI or stroke after adjustment.

CONCLUSIONS

Routine fasting followed during two-thirds of the lifespan was associated with higher survival after cardiac catheterization. This may in part be explained by an association of routine fasting with a lower incidence of HF.

CLINICAL STUDY REGISTRATION

The Intermountain INSPIRE registry https://clinicaltrials.gov/, NCT02450006.

Starvation Ketosis and the Kidney

BACKGROUND

The remarkable ability of the body to adapt to long-term starvation has been critical for survival of primitive man. An appreciation of these processes can provide the clinician better insight into many clinical conditions characterized by ketoacidosis.

SUMMARY

The body adapts to long-term fasting by conserving nitrogen, as the brain increasingly utilizes keto acids, sparing the need for glucose. This shift in fuel utilization decreases the need for mobilization of amino acids from the muscle for purposes of gluconeogenesis. Loss of urinary nitrogen is initially in the form of urea when hepatic gluconeogenesis is dominant and later as ammonia reflecting increased glutamine uptake by the kidney. The carbon skeleton of glutamine is utilized for glucose production and regeneration of consumed HCO3-. The replacement of urea with NH4+ provides the osmoles needed for urine flow and waste product excretion. Over time, the urinary loss of nitrogen is minimized as kidney uptake of filtered ketone bodies becomes more complete. Adjustments in urine Na+ serve to minimize kidney K+ wasting and, along with changes in urine pH, minimize the likelihood of uric acid precipitation. There is a sexual dimorphism in response to starvation. Key Message: Ketoacidosis is a major feature of common clinical conditions to include diabetic ketoacidosis, alcoholic ketoacidosis, salicylate intoxication, SGLT2 inhibitor therapy, and calorie sufficient but carbohydrate-restricted diets. Familiarity with the pathophysiology and metabolic consequences of ketogenesis is critical, given the potential for the clinician to encounter one of these conditions.

Diabetic ketoacidosis

Diabetic ketoacidosis (DKA) is the most common acute hyperglycaemic emergency in people with diabetes mellitus. A diagnosis of DKA is confirmed when all of the three criteria are present - 'D', either elevated blood glucose levels or a family history of diabetes mellitus; 'K', the presence of high urinary or blood ketoacids; and 'A', a high anion gap metabolic acidosis. Early diagnosis and management are paramount to improve patient outcomes. The mainstays of treatment include restoration of circulating volume, insulin therapy, electrolyte replacement and treatment of any underlying precipitating event. Without optimal treatment, DKA remains a condition with appreciable, although largely preventable, morbidity and mortality. In this Primer, we discuss the epidemiology, pathogenesis, risk factors and diagnosis of DKA and provide practical recommendations for the management of DKA in adults and children.

Approach to the Treatment of Diabetic Ketoacidosis

Diabetic ketoacidosis (DKA), a common cause of severe metabolic acidosis, remains a life-threatening condition due to complications of both the disease and its treatment. This Acid-Base and Electrolyte Teaching Case discusses DKA management, emphasizing complications of treatment. Because cerebral edema is the most common cause of mortality and morbidity, especially in children with DKA, we emphasize its pathophysiology and implications for therapy. The risk for cerebral edema may be minimized by avoiding a bolus of insulin, excessive saline resuscitation, and a decrease in effective plasma osmolality early in treatment. A goal of fluid therapy is to lower muscle venous Pco₂ to ensure effective removal of hydrogen ions by bicarbonate buffer in muscle and diminish the binding of hydrogen ions to intracellular proteins in vital organs (such as the brain). In patients with DKA and a relatively low plasma potassium level, insulin administration may cause hypokalemia and cardiac arrhythmias. It is suggested in these cases to temporarily delay insulin administration and first administer potassium chloride intravenously to bring the plasma potassium level close to 4mmol/L. Sodium bicarbonate administration in adult patients should be individualized. We suggest it be considered in a subset of patients with moderately severe acidemia (pH<7.20 and plasma bicarbonate level < 12mmol/L) who are at risk for worsening acidemia, particularly if hemodynamically unstable. Sodium bicarbonate should not be administered to children with DKA, except if acidemia is very severe and hemodynamic instability is refractory to saline administration.

Voluntary weight loss: systematic review of early phase body composition changes

Weight loss follows when adult humans enter a phase of negative energy balance brought about by reducing energy intake and/or increasing energy expenditure. The weight loss period is usually viewed as a continuous process, ending when energy equilibrium is achieved at a lower weight or with death following depletion of fuel stores. However, growing evidence supports the expanded view that induction of negative energy balance leads to well-defined physiological effects characterized by three discrete phases (I-III). At present there are no comprehensive reviews of the 'early' phase of weight loss, a gap highlighted by recent interest in rapidly testing new treatments with short-term protocols. Herein we show from earlier reports and with new data that weight loss during phase I is: mathematically quantifiable with a t(1/2) < 1-week and 4- to 6-week duration; includes well-defined rapidly evolving body composition and energy expenditure changes; and is moderated by multiple factors including subject sex and activity level, nutrients ingested at baseline and during the negative energy balance period, and hormone and pharmacologic treatments. Our in depth review collectively characterizes phase I as a distinct weight loss period while revealing important knowledge gaps that can be filled with appropriately designed future studies.

Physiology of acid-base balance: links with kidney stone prevention

Two processes permit the urine pH and the medullary interstitial pH to remain in an "ideal range" to minimize the risk of forming kidney stones. First, a medullary shunt for NH(3) maintains the urine pH near 6.0 to minimize uric acid precipitation when distal H(+) secretion is high. Second, excreting dietary alkali excreting alkali as a family of organic anions--including citrate--rather than as bicarbonate maintains the urine pH near 6.0 while urinary citrate chelates ionized calcium, which minimizes CaHPO(4) precipitation. In patients with idiopathic hypercalciuria and recurrent calcium oxalate stones, the initial nidus is a calcium phosphate precipitate on the basolateral membrane of the thin limb of the loop of Henle (Randall's plaque). Formation of this precipitate requires medullary alkalinization; K(+) -depletion and augmented medullary H(+)/K(+) -ATPase may be predisposing factors.

Isotonic is better than hypotonic saline for intravenous rehydration of children with gastroenteritis: a prospective randomised study

AIMS

To determine whether the risk of hyponatraemia in children with gastroenteritis receiving intravenous (IV) fluids is decreased by the use of 0.9% saline.

METHODS

A prospective randomised study was carried out in a tertiary paediatric hospital. A total of 102 children with gastroenteritis were randomised to receive either 0.9% saline + 2.5% dextrose (NS) or 0.45% saline + 2.5% dextrose (N/2) at a rate determined by their treating physician according to hospital guidelines and clinical judgement. Plasma electrolytes, osmolality, and plasma glucose were measured before (T(0)) and 4 hours after (T(4)) starting IV fluids, and subsequently if clinically indicated. Electrolytes and osmolality were measured in urine samples. Results were analysed according to whether children were hyponatraemic (plasma sodium <135 mmol/l) or normonatraemic at T(0).

RESULTS

At T(0), mean (SD) plasma sodium was 135 (3.3) mmol/l (range 124-142), with 37/102 (36%) hyponatraemic. At T(4), mean plasma sodium in children receiving N/2 remained unchanged in those initially hyponatraemic (n = 16), but fell 2.3 (2.2) mmol/l in the normonatraemic group. In contrast, among children receiving NS, mean plasma sodium was 2.4 (2.0) mmol/l higher in those hyponatraemic at baseline (n = 21) and unchanged in the initially normonatraemic children. In 16 children who were still receiving IV fluids at 24 hours, 3/8 receiving N/2 were hyponatraemic compared with 0/8 receiving NS. No child became hypernatraemic.

CONCLUSIONS

In gastroenteritis treated with intravenous fluids, normal saline is preferable to hypotonic saline because it protects against hyponatraemia without causing hypernatraemia.

High antidiuretic hormone levels and hyponatremia in children with gastroenteritis

OBJECTIVES

Nonosmotic antidiuretic hormone (ADH) activity can cause severe hyponatremia during involuntary fluid administration. We looked for evidence of this before and during intravenous (IV) fluid administration in children treated for gastroenteritis.

METHODOLOGY

In this prospective observational study, plasma ADH, electrolytes, osmolality, and glucose were measured in 52 subjects before (T0) and 4 hours after (T4) starting 0.45% saline + 2.5% dextrose and subsequently when indicated. Hormonal markers of stress were measured at T0. Urine samples were collected to measure electrolytes and osmolality.

RESULTS

The nonosmotic stimuli of ADH secretion that we identified were vomiting (50 of 52), dehydration (median: 5%; range: 3-8%), hypoglycemia (2 of 52), and raised hormonal markers of stress (mean +/- SD: cortisol, 1094 +/- 589 nmol/L; reverse triiodothyronine, 792 +/- 293 pmol/L). At T0, half the children were hyponatremic (plasma sodium concentration of < 135 mmol/L; n = 27). The median plasma ADH concentration at T0 was significantly elevated (median: 7.4 pg/mL; range: < 1.9-85.6 pg/mL). ADH was high in both hyponatremic and normonatremic children and remained high at T4 in 33 of the 52 children, 22 of whom were concurrently hyponatremic. At T4, mean plasma sodium concentration was unchanged in the hyponatremic children but was 2.6 mmol/L (+/-2.0) lower in those who were initially normonatremic. Urine tonicity was high compared with 0.45% saline in 16 of 19 children at baseline and in 20 of 37 children after 3 to 12 hours of IV fluids.

CONCLUSIONS

Nonosmotic stimuli of ADH secretion are frequent in children with gastroenteritis. Their persistence during IV-fluid administration predisposes to dilutional hyponatremia. The use of hypotonic saline for deficit replacement needs to be reassessed.

Acidosis in a patient with cholera: a need to redefine concepts

A patient presented with cholera and a severe degree of ECF volume contraction. Despite large losses of bicarbonate (HCO3-)-containing diarrhoeal fluid, laboratory acid-base values were remarkably close to normal. A detailed analysis emphasizing principles of physiology and a quantitative approach provided new insights and eventually better definitions of metabolic and respiratory acidosis. A shift in focus from HCO3- concentration to HCO3- content in the extracellular fluid (ECF) compartment revealed the presence of metabolic acidosis. Central to this analysis was an emphasis on the haematocrit to enable a more accurate estimate of the degree of ECF volume contraction. The latter also revealed 'contraction' metabolic alkalosis, which masked the underlying metabolic acidosis. The presence of a respiratory acidosis of the tissue type was evident from the raised venous PCO2, which was not surprising once the magnitude of the ECF contraction had been appreciated. 'Bad buffering', as defined by Professor McCance, was the immediate danger and prompted swift action to restore an effective circulation. The haematocrit and the venous PCO2 also contribute valuable information to monitor the response to therapy. Nevertheless, there were still dangers to be discovered when an in-depth analysis suggested that the administration of isotonic saline would introduce an unanticipated danger for the patient.

An unusual cause for ketoacidosis

A 22-year-old male developed a severe degree of metabolic acidosis (plasma pH 7.20, bicarbonate 8 mmol/l), with a large increase in the plasma anion gap (26 mEq/l). Ketoacidosis was suspected because of the odour of acetone on his breath and a positive qualitative test for acetone in plasma (to a 1:4 dilution). Later, his plasma beta-hydroxybutyrate concentration was found to be 4.5 mmol/l. After receiving an infusion of 1 l of half-isotonic saline and 1 l of 5% dextrose in water over 24 h, as well as curtailing his large oral intake of sweetened beverages, all blood tests became normal. Diabetic ketoacidosis, alcoholic ketoacidosis, starvation ketosis and hypoglycaemic ketoacidosis were all ruled out, and his toxin screen was negative for salicylates. Finding another possible cause for ketoacidosis became the focus of this case.

Dogmas and controversies in the handling of nitrogenous wastes: Excretion of nitrogenous wastes in human subjects

Two major nitrogenous waste products, urea and ammonium(NH4+), are produced in humans when proteins are oxidized, and in this manuscript their excretions are examined from two perspectives. First, the specific physiology of each nitrogenous waste is reviewed and the current dogmas summarized. Second, their excretions are considered in the context of integrative physiology, i.e. the need to ensure that the urine composition is appropriate to minimize the risk of kidney stone formation. After the latter analysis, weak links in our understanding of the overall physiology become apparent and a conundrum is defined. The conundrum for the excretion of urea focuses on the fact that urea is not an effective osmole in the medullary-collecting duct when vasopressin acts. As a result, it appears that urinary urea cannot prevent a large decline in the urine flow rate and thereby minimize the risk of forming kidney stones in electrolyte-poor urine. The conundrum for the excretion of NH4+ is: high rates of NH4+excretion require a low urine pH, yet a pH ∼6.0 must be maintained in order to reduce the risk of precipitating uric acid in the urine. Possible ways of resolving these conundrums require novel physiological interpretations.

A conceptual approach to the patient with metabolic acidosis. Application to a patient with diabetic ketoacidosis

We shall illustrate that management of patients with an acid-base disorder could be improved if the acid-base analysis was based on a better understanding of basic concepts of physiology. Three concepts of acid-base physiology and their clinical implications are emphasized in a patient with diabetic ketoacidosis. First, when an acid is produced from neutral precursors in the body, there is a net increase in the number of hydrogen ions (H(+)) and new anions. The corollary is that H(+) will be removed when the accompanying anion is metabolized to a neutral end-product or is excreted in the urine with H(+) or ammonium (NH(4)(+)). Second, buffering of H(+) is beneficial if H(+) are removed by bicarbonate rather than being able to bind to proteins. This latter function depends on having a low tissue PCO(2), due to a combination of hyperventilation plus an adequate blood flow rate to vital organs. Third, the kidneys add new bicarbonate to the body when NH(4)(+) is excreted with chloride ions.

The role of falling leptin levels in the neuroendocrine and metabolic adaptation to short-term starvation in healthy men

To elucidate the role of leptin in regulating neuroendocrine and metabolic function during an acute fast, six to eight healthy, lean men were studied under four separate conditions: a baseline fed state and three 72-hour fasting studies with administration of either placebo, low-dose recombinant-methionyl human leptin (r-metHuLeptin), or replacement-dose r-metHuLeptin designed to maintain serum leptin at levels similar to those in the fed state. Replacement-dose r-metHuLeptin administered during fasting prevents the starvation-induced changes in the hypothalamic-pituitary-gonadal axis and, in part, the hypothalamic-pituitary-thyroid axis and IGF-1 binding capacity in serum. Thus, in normal men, the fall in leptin with fasting may be both necessary and sufficient for the physiologic adaptations of these axes, which require leptin levels above a certain threshold for activation. In contrast to findings in mice, fasting-induced changes in the hypothalamic-pituitary-adrenal, renin-aldosterone, and growth hormone-IGF-1 axes as well as fuel utilization may be independent of leptin in humans. The role of leptin in normalizing several starvation-induced neuroendocrine changes may have important implications for the pathophysiology and treatment of eating disorders and obesity.

Cerebral salt wasting: truths, fallacies, theories, and challenges

BACKGROUND

The reported prevalence of cerebral salt wasting has increased in the past three decades. A cerebral lesion and a large natriuresis without a known stimulus to excrete so much sodium (Na ) constitute its essential two elements.

OBJECTIVES

To review the topic of cerebral salt wasting. There is a diagnostic problem because it is difficult to confirm that a stimulus for the renal excretion of Na is absent.

DESIGN

Review article.

INTERVENTION

None.

MAIN RESULTS

Three fallacies concerning cerebral salt wasting are stressed: first, cerebral salt wasting is a common disorder; second, hyponatremia should be one of its diagnostic features; and third, most patients have a negative balance for Na when the diagnosis of cerebral salt wasting is made. Three causes for the large natriuresis were considered: first, a severe degree of extracellular fluid volume expansion could down-regulate transporters involved in renal Na resorption; second, an adrenergic surge could cause a pressure natriuresis; and third, natriuretic agents might become more potent when the effective extracellular fluid volume is high.

CONCLUSIONS

Cerebral salt wasting is probably much less common than the literature suggests. With optimal treatment in the intensive care unit, hyponatremia should not develop.

Facilitating an understanding of integrative physiology: emphasis on the composition of body fluid compartments

As a teaching exercise, we used deductive reasoning and a quantitative analysis to convert a number of facts into a series of concepts to facilitate an understanding of integrative physiology and shed light on the composition of the different body fluid compartments. The starting point was the central need to regenerate ATP to perform biologic work. Because a large quantity of O2 must be delivered to cells at a sufficiently high concentration to aid its diffusion into mitochondria, approximately one third of the O2 in inspired air was extracted; this led to a P(CO2) in arterial blood of 40 mmHg (1 mmHg = 133.322 Pa). Blood flow to individual organs must be adjusted precisely to avoid having too low or too high a P(O2) in mitochondria--the latter augments the formation of reactive O2 species. The extracellular fluid (ECF) bicarbonate concentration (E(HCO3)) must be high to minimize H+ buffering by proteins. This high E(HCO3) sets the ECF concentrations of ionized calcium (Ca2+) and inorganic phosphate (HPO4(2-)) because of solubility issues. Three features defined the intracellular fluid (ICF) volume and composition. First, expelling monovalent anions minimized its mass (volume). Second, controlling the tissue P(CO2) ensured a relatively constant net valence on intracellular proteins. Third, the range of ICF Ca2+ concentrations must both induce regulatory signals and avoid Ca3(PO4)2 formation. All the above were incorporated into the integrated response that optimized the capacity for vigorous exercise.

Effect of fasting for two days on the excretion of ammonium in dogs with chronic metabolic acidosis

BACKGROUND

The source of glutamine for renal ammonium production is ultimately dietary protein in the fed state and body proteins in fasting.

OBJECTIVE

Our objective was to determine if less NH(+)(4) would be excreted by fasted dogs with chronic metabolic acidosis resulting in conservation of lean body mass.

METHODS

Acid-loaded fed and fasted dogs were given 10 mmol NH(4)Cl/kg for 5 days; the fasted group had food withheld on days 4 and 5.

RESULTS

The renal production of NH(+)(4) was not significantly different in both acid-loaded groups, yet the rate of NH(+)(4) excretion was significantly lower in the fasted dogs (8 vs. 21 mmol NH(+)(4)/mmol creatinine). The urine pH was significantly higher (6.0 versus 5.5) while titratable acid and the urine flow rate were significantly lower in these fasted dogs. Despite nearly equal urine flow rates and Na(+) excretion rates after an infusion of saline, the fasted dogs failed to increase the rate of excretion of NH(+)(4) to rates seen in the fed group.

CONCLUSIONS

The lower rate of excretion of NH(+)(4) in fasted, acidotic dogs appeared to be due to a lower distal H(+) secretion. This may help preserve lean body mass during fasting.

Mechanisms used to dispose of progressively increasing alkali load in rats

Our objective was to describe the process of alkali disposal in rats. Balance studies were performed while incremental loads of alkali were given to rats fed a low-alkali diet or their usual alkaline ash diet. Control groups received equimolar NaCl or KCl. Virtually all of the alkali was eliminated within 24 h when the dose exceeded 750 micromol. The most sensitive response to alkali input was a decline in the excretion of NH(4)(+). The next level of response was to increase the excretion of unmeasured anions; this rise was quantitatively the most important process in eliminating alkali. The maximum excretion of citrate was approximately 70% of its filtered load. An even higher alkali load augmented the excretion of 2-oxoglutarate to >400% of its filtered load. Only with the largest alkali load did bicarbonaturia become quantitatively important. We conclude that renal mechanisms eliminate alkali while minimizing bicarbonaturia. This provides a way of limiting changes in urine pH without sacrificing acid-base balance, a process that might lessen the risk of kidney stone formation.

Studies on the pathophysiology of the low urine pH in patients with uric acid stones

BACKGROUND

A very low urine pH is the major risk factor for uric acid stone formation.

METHODS

A subgroup of patients with a history of uric acid stones and a persistently low urine pH (<5.5 for at least 12 h/day) were selected for detailed study. Based on their relative ammonium (NH(+)(4)) and sulfate (SO(2-)(4)) excretions, patients were divided into two groups.

RESULTS

The first group (N = 2) excreted 173 and 139% more NH(+)(4) than SO(2-)(4). Their daily urinary unmeasured anion excretion was higher than their calculated net diet alkali input (38 and 61 vs. 24 and 49 mEq, respectively). In the second group (N = 12), NH(+)(4) excretion was 69 +/- 5% that of SO(2-)(4). In 2 of 12, decreased renal ammoniagenesis was suspected due to a plasma potassium of 5.3 mmol/L and/or a lower GFR (65 and 59 L/day); these patients had an extremely low citrate excretion (3 and 1 mEq/day). In contrast, citrate excretion was not low in the remaining 10 patients (10.4 +/- 1.3 mEq/day).

CONCLUSIONS

Patients in group 1 needed a higher NH(+)(4) excretion possibly because of a H+ load from excessive renal excretion of organic anions. We speculate that an alkaline proximal tubular cell pH could be the basis for the low NH(+)(4) and high citrate excretions in 10 of 12 patients in group 2. Dietary factors and/or a molecular lesion may contribute to their pathophysiology.

A method to estimate urinary electrolyte excretion in patients at risk for developing cerebral salt wasting

OBJECT

Two major criteria are necessary to diagnose cerebral salt wasting (CSW): a cerebral lesion and a large urinary excretion of Na+ and Cl- at a time when the extracellular fluid (ECF) volume is contracted. Nevertheless, it is difficult for the physician to confirm from bedside observation that a patient has a contracted ECF volume. Hyponatremia, although frequently present, should not be a criterion for a diagnosis of salt wasting. A contracted ECF volume is unlikely if there are positive balances of Na+ and Cl-. The goal of this study was to assess the accuracy of calculating balances for Na+ plus K+ and of Cl- over 1 to 10 days in an intensive care unit (ICU) setting.

METHODS

A prospective comparison of measured and estimated quantities of Na+ plus K+ and of Cl- excreted over 1 to 10 days in 10 children and 12 adults who had recently received a traumatic brain injury or undergone recent neurosurgery. Plasma concentrations of electrolytes were recorded at the beginning and end of the study period. The total volumes infused and excreted and the concentrations of Na+, K+, and Cl- in the infusate were obtained from each patient's ICU chart. The electrolytes in the patients' urine were measured and calculated. Correlations between measured and calculated values for excretions of Cl- and of Na+ plus K+ were excellent.

CONCLUSIONS

Mass balances for Na+ plus K+ and for Cl- can be accurately estimated. These data provide information to support or refute a clinical diagnosis of CSW. The danger of relying on balances for these electrolytes measured within a single day to diagnose CSW is illustrated.

Dynamic interactions between integrative physiology and molecular medicine: The key to understand the mechanism of action of aldo sterone in the kidney

Our objective is to illustrate how an approach that integrates new insights from molecular biology and traditional physiology can lead to the development of new concepts. This dynamic interaction is illustrated by examining the steps taken to improve our understanding of the renal actions of aldosterone. We began by defining the big picture of what aldosterone does in the kidney. This led to the conclusion that aldosterone must at times become a sodium chloride-retaining hormone, while at other times it must function primarily or exclusively as a kaliuretic hormone. The second step was to define the major molecular actions of this hormone. Acting on the principal cells in the cortical collecting duct (CCD), aldosterone leads to the insertion of active epithelial sodium ion channels (ENaC) in their luminal membranes. This active ENaC, however, does not distinguish between the two major renal actions of aldosterone. Accordingly, we returned to integrative physiology and examined a possible role of renal and non-renal events. We implicated the potential importance of the delivery of bicarbonate ions to the CCD to determine which effect of aldosterone will become manifest. This, however, required that we reconsider some of the traditional views in interpretation of acid-base balance. At the clinical level, this global view can help us understand why, for example, a low dietary intake of potassium salts might predispose a person to an elevated blood pressure. Using a similar approach, it is possible to understand how the risk of the formation of kidney stones can be minimized.Key words: acid-base, hypertension, integrative physiology, kidney stones, potassium, sodium.

Distal renal tubular acidosis and high urine carbon dioxide tension in a patient with southeast Asian ovalocytosis

Southeast Asian ovalocytosis (SAO) is the best-documented disease in which mutation in the anion exchanger-1 (AE1) causes decreased anion (chloride [Cl-]/bicarbonate [HCO3-]) transport. Because AE1 is also found in the basolateral membrane of type A intercalated cells of the kidney, distal renal tubular acidosis (dRTA) might develop if the function of AE1 is critical for the net excretion of acid. Studies were performed in a 33-year-old woman with SAO who presented with proximal muscle weakness, hypokalemia (potassium, 2.7 mmol/L), a normal anion gap type of metabolic acidosis (venous plasma pH, 7. 32; bicarbonate, 17 mmol/L; anion gap, 11 mEq/L), and a low rate of ammonium (NH4+) excretion in the face of metabolic acidosis (26 micromol/min). However, the capacity to produce NH4+ did not appear to be low because during a furosemide-induced diuresis, NH4+ excretion increased almost threefold to a near-normal value (75 micromol/L/min). Nevertheless, her minimum urine pH (6.3) did not decrease appreciably with this diuresis. The basis of the renal acidification defect was most likely a low distal H+ secretion rate, the result of an alkalinized type A intercalated cell in the distal nephron. Unexpectedly, when her urine pH increased to 7.7 after sodium bicarbonate administration, her urine minus blood carbon dioxide tension difference (U-B Pco2) was 27 mm Hg. We speculate that the increase in U-B Pco2 might arise from a misdirection of AE1 to the apical membrane of type A intercalated cells.

Physiological disposal of the potential alkali load in diet of the rat: steps to achieve acid-base balance

The purpose of this study was to provide a better understanding of the physiological role of endogenous net organic acid production in rats consuming their usual diet. Balance studies were performed over 24 h, and urine was collected in the day and night portions of the diurnal cycle. A supplemented low-electrolyte diet(LED) was fed to determine whether urinary organic anions were identical to those in the diet. A titration procedure was developed to determine the pK of titratable groups in the urine of rats studied with and without an acid load. Although normal rats excreted net acid (NAE), the latter was inversely related to the amount of food consumed. The rates of excretion of bicarbonate (HCO3), citrate, unmeasured organic anions, and NH+4 were higher in the night portion of the diurnal cycle. NAE rose dramatically when alkali intake was decreased by consuming the LED. Dietary and urinary organic anions were not identical because rats fed the LED supplemented with potassium citrate excreted <10% of this alkali load as citrate and <25% as HCO3. In the 24 h after 3,000 ¿mol NH4Cl was given intraperitoneally, H+ did not appear to be retained, yet NAE rose by only close to 2,000 ¿eq. The rate of excretion of titratable groups with a pK in the 3 to 5 pH range fell by close to 1,000 ¿eq; most of these changes occurred in the first 7 h after NH4Cl was given. We conclude that rat chow provides a large net alkali load. There appear to be two types of endogenous acid production, a form associated with a rise in NAE (e.g., sulfuric acid) and dietary alkali-driven endogenous net acid production, which titrates this alkali. Renal excretion of organic anions makes these acids end products of metabolism.