The role of pH gradient in the distribution of ammonia between blood and cerebrospinal fluid, brain and muscle

Alkalemia and Hepatic Encephalopathy in a Chronic Dialysis Patient

Hepatic encephalopathy (HE) includes cognitive, psychiatric and neuromotor abnormalities observed from brain dysfunction secondary to liver disease and/or porto-systemic shunting. HE can have a wide range of clinical manifestations ranging from trivial lack of awareness, decreased attention span, personality changes to confusion, seizures, coma, and death. The onset of HE in cirrhosis is a poor prognostic factor. While HE has a complex pathogenesis which is not completely understood, hyperammonemia plays an important role in neurotoxicity and brain dysfunction. Alkalemia facilitates the conversion of NH₄⁺ to NH₃, which is free to cross the blood-brain barrier exacerbating HE. Prompt recognition and correction of underlying risk factors is central to the management of HE.

Exploring the hidden potential of a benzothiazole-based Schiff-base exhibiting AIE and ESIPT and its activity in pH sensing, intracellular imaging and ultrasensitive & selective detection of aluminium (Al3+)

The hidden potential of an AIE-ESIPT active, simple substituted benzothiazole compound has been explored.

The resting membrane potential of white muscle from brown trout (Salmo trutta) exposed to copper in soft, acidic water

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=−52.2+/−4.9 mV) and compared with that of unexposed, control animals (E(M)=−86.5+/−2.9 mV) (means +/− s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

Portal systemic encephalopathy

The goal of this article is to update the status of Portal systemic encephalopathy (PSE) in the light of new data. First, PSE is the context of other types of hepatic encephalopathy. Subsequently, current views of the pathogenesis of the disorder are discussed, followed by an analysis of therapeutic options. Diagnosis will not be considered, as no major new developments have recently been documented in this area.

Effect of a low-carbohydrate diet on plasma and sweat ammonia concentrations during prolonged nonexhausting exercise

The purpose of this investigation was to examine the effect of low body glycogen stores on plasma ammonia concentration and sweat ammonia excretion during prolonged, nonexhausting exercise of moderate intensity. On two occasions seven healthy untrained men pedalled on a cycle ergometer for 60 min at 50% of their predetermined maximal O2 uptakes (VO2max) firstly, following 3 days on a normal mixed diet (N-diet) (60% carbohydrates, 25% fat and 15% protein) and secondly, following 3 days on a low-carbohydrate diet (LC-diet) (less than 5% carbohydrates, 50% fat and 45% protein) of equal energy content. Blood was collected from the antecubital vein immediately before, at 30th and at 60th min of exercise. Sweat was collected from the hypogastric region using gauze pads. It was shown that plasma ammonia concentrations after the LC-diet were higher than after the N-diet at both the 30th and 60th min of exercise. Sweat ammonia concentration and total ammonia loss through the sweat were also higher after the LC-diet. The higher ammonia concentrations in plasma and sweat after the LC-diet would seem to indicate an increased ammonia production, which may be related to reduced initial carbohydrate stores.

Changes in blood ammonia induced by a maximum effort in trained and untrained subjects

Twelve healthy male volunteers, either trained or untrained, performed a maximal exercise on a cycloergometer. Venous blood samples were taken for analysis during the effort and the following recovery. Blood concentrations of lactate and ammonia, and plasmatic concentrations of alanine, glutamate and glutamine were measured. At the beginning on the effort, ammonia decreased by 32% (P < 0.01) in comparison with its mean level at rest; at 77% and 78% of maximum load there was a steeper ascent of blood ammonia and lactate vs load curve. There was a high correlation (P < 0.001) between ammonia and lactate during exercise. At the end of the effort, these two variables had significantly increased in comparison with their values at rest (P < 0.01 for ammonia and P < 0.001 for lactate), but they did not correlate with VO2max. The negative correlation existing between ammonia and VO2max at the beginning of the recovery period may imply that muscle NH3 release is inversely proportional to the subject's sports training level, this relation being less evident when blood lactate vs VO2max correlation was considered. Increase in blood glutamate level was greater in trained subjects (P < 0.05). This finding suggests that ammonia elimination is favoured by physical training. In conclusion, ammonia measurements during exercise provide a valuable information about muscle cell oxidative capacity.

Plasma ammonia is the principal source of ammonia in sweat

Sweat contains ammonia. However, neither its source nor factors affecting its concentration in the sweat are known. The aim of this study was to examine the effect of plasma concentrations of ammonia and urea on the concentration of ammonia in the sweat. Four groups of male volunteers were examined: one control, two after ingestion of ammonium chloride, three cirrhotic, hyperammonaemic, four uraemic. Sweat was collected from each subject from the palmar side of the forearm using gauze pads, after previous iontophoresis of pilocarpine. Ammonia and urea concentrations were determined in the sweat and in the plasma. It was found that elevated plasma ammonia concentration in healthy subjects after ingestion of ammonium chloride as well in the cirrhotic patients resulted in an increase of ammonia concentration in the sweat. High plasma and sweat urea concentration in the uraemic subjects did not affect the concentration of ammonia in the sweat. It was concluded that plasma ammonia was the principal source of ammonia in the sweat.

Changes in activities of some ammonia-metabolizing enzymes in the rat liver and the brain after chronic ethanol administration

The changes in the activities of ammonia-metabolizing enzymes in liver and brain after ethanol intoxication has been investigated in rats. After administration of ethanol 30% (w/v) 6g kg-1 for 4 weeks we found an increase in liver glutamate dehydrogenase and glutaminase activity. In brain tissue the glutaminase activity was significantly higher and glutamate dehydrogenase was significantly lower. Glutamine synthetase activity in liver and brain was practically unchanged. The reasons for these changes in the activities of some ammonia-metabolizing enzymes in liver and brain after ethanol ingestion have been discussed.

Syndrome of idiopathic hyperammonemia after high-dose chemotherapy: review of nine cases

PURPOSE

The syndrome of idiopathic hyperammonemia occurs in patients who have received high-dose cytoreductive therapy for the treatment of hematologic malignancy. It is characterized by abrupt alteration in mental status and respiratory alkalosis associated with markedly elevated plasma ammonium levels in the absence of any identifiable cause, and frequently results in intractable coma and death. Our goal was to survey clinical and pathologic manifestations of the disorder and discuss treatment options.

PATIENTS AND METHODS

Plasma ammonium levels were measured in patients on the acute leukemia service or on the bone marrow transplant service at The Johns Hopkins Hospital, and a level more than twice normal was considered diagnostic of hyperammonemia. The syndrome was identified in nine patients; in eight, hyperammonemia occurred after administration of intensive cytoreductive therapy that resulted in profound leukopenia. The disorder occurred in the ninth patient two months after allogeneic bone marrow transplantation.

RESULTS

Three of the nine patients survived an episode of idiopathic hyperammonemia; one patient subsequently died of leukemia and one of recurrent idiopathic hyperammonemia. The one long-term survivor is currently alive and well without neurologic sequelae 250 days after autologous bone marrow transplantation.

CONCLUSION

Because neurologic function can deteriorate rapidly, early recognition of this disorder and close monitoring of the patient's neurologic status are critical.

The pathogenesis of vascular headaches in patients with hypertension; the role of the ammonia-potassium axis

Headaches may occur in as many as 25% of hypertensive patients and generally bears little relationship to level of diastolic blood pressure. Previous observations, in normotensive patients, suggested that abnormalities in both potassium and ammonia metabolism might be related to the pathogenesis of these headaches. The present study was undertaken to see whether these factors also occurred in hypertensive patients with headaches. The present observations were made in thirteen hypertensive patients with vascular headaches. The major findings include potassium levels of 3.45 +/- 0.25 mEq/L; CO2, 29.85 +/- 1.21 mEq/L; blood ammonia, 41 +/- 8.40 U mol/L and an alkaline pH of the urine. The blood ammonia levels, when factored by the BUN, yielded elevated ammonia to BUN ratios (3.81 +/- 1.82). These findings are similar to those previously observed in normotensive patients with vascular headaches. The profile of hypokalemia and/or alkalosis, increased blood ammonia to BUN ratios and a relatively alkaline urine appears to be a commonly observed pattern in patients with vascular headaches. These data suggest that a biochemical basis exists for the genesis of vascular headaches in patients with hypertension.

Arterial ammonemia changes of renal origin induced in the rat by acid and alkaline diets

The aim of this study was to investigate the influence of acid and alkali food supplementation on systemic ammonemia to explain the hyperammonemia previously observed in rats fed a high protein diet. In normal rats, arterial ammonia concentration significantly increases after 4 days of HCl-supplemented diet. Following a NaHCO3-enriched food, there is only a slight but not significant decrease in arterial ammonia level. These changes occur before any variation in arterial acid-base status and are of renal origin. Indeed, there is a positive linear correlation (r = 0.946; P less than 0.001) between arterial ammonia level and the ammonia concentration difference between the renal vein and artery (which varies proportionally to the urinary ammonium excretion). Hindquarter uptake and intestinal release of ammonia do not significantly participate in the arterial ammonia changes observed. Following HCl-enriched diets, increased renal glutamine uptake, enhanced hindquarter glutamine release, and perhaps decreased intestinal glutamine uptake occur simultaneously. In conclusion, acid and alkali food supplementation intervenes on the renal ammonia release into the circulation with concomitant arterial ammonemia changes.

The hypokalemic, bowel, bladder, headache relationship; a new syndrome. The role of the potassium ammonia axis

A conceptual approach that relates vascular headaches, bowel and bladder dysfunction to abnormalities of the "ammonia potassium axis" is presented. Hypokalemia alters smooth muscle function of both the bowel and bladder and results in the elaboration of an alkaline urine. The occurrence of an alkaline urine, along with bladder dysfunction and urinary stasis, predisposes to recurrent urinary tract infections. Hypokalemia and/or alkalosis increases the renal return of ammonia, exposes the brain to chronically higher concentration of ammonia and facilitates its passage into the central nervous system. Increased levels of blood ammonia predispose to hyperventilation which results in a superimposed respiratory alkalosis on a pre-existing hypokalemia and/or alkalosis therefore causing intense cerebral vasoconstriction. Varying degrees of cerebral ischemia and hypoxia occur and give rise to higher brain concentrations of ammonia. Vasodilatation occurs during the headache phase and may be a consequence of the sudden increase of brain ammonia and/or due to the release of other vasoactive mediators. As a consequence of increased blood ammonia, a reduction of protein intake may result in the alterations of amino acid precursors for brain uptake and therefore further interferes with the modulation of cerebral blood flow and brain function.

The metabolic basis for the genesis of seizures: the role of the potassium-ammonia axis

A conceptual approach to the understanding of the pathogenesis of idiopathic seizures is presented. Hypokalemia and/or alkalosis promotes the elaboration of an alkaline urine, which increases the renal return of ammonia and exposes the brain to chronically higher concentrations of ammonia. In the brain, ammonia is preferentially detoxified to glutamine and therefore depletes the available glutamic acid, which is also a precursor of GABA, the major mediator of central inhibition. Mild chronic elevations of ammonia may also result in long-term nutritional alterations of amino-acid precursors of other brain neurotransmitters. A linkage thus exists for the metabolic basis of seizures: the role of the potassium-ammonia axis may be important in the selective depletion of GABA, the major mediator of central inhibition.

The metabolic basis for the genesis of seizures: the role of the potassium-ammonia axis

A conceptual approach to the understanding of the pathogenesis of idiopathic seizures is presented. Hypokalemia and/or alkalosis promotes the elaboration of an alkaline urine, which increases the renal return of ammonia and exposes the brain to chronically higher concentrations of ammonia. In the brain, ammonia is preferentially detoxified to glutamine and therefore depletes the available glutamic acid, which is also a precursor of GABA, the major mediator of central inhibition. Mild chronic elevations of ammonia may also result in long-term nutritional alterations of amino-acid precursors of other brain neurotransmitters. A linkage thus exists for the metabolic basis of seizures: the role of the potassium-ammonia axis may be important in the selective depletion of GABA, the major mediator of central inhibition.

Plasma levels of false neurotransmitters across the brain in portal-systemic encephalopathy

Arterial and internal jugular venous levels of false neurotransmitters (FNTs: octopamine, OCT, and phenylethanolamine, PEA), aromatic and branched-chain amino acids, glutamine, ammonia, and pH were measured in patients with portal-systemic encephalopathy (PSE) and in appropriate controls to define the role of these parameters in the pathogenesis of hepatic coma. The typical plasma patterns reported in the literature were observed: hyperammonaemia (59 +/- 8 mumol/l v. controls 30 +/- 4, P less than 0.005), elevated OCT (19 +/- 3 nmol/l v. 6 +/- 1, P less than 0.001) and PEA (64 +/- 8 nmol/l v. 27 +/-3, P less than 0.001), high ratio of aromatic to branched-chain amino acids (0.92 +/- 0.12 v. 0.32 +/- 0.04, P less than 0.005), and variable glutamine levels 216-734 mumol/l). No consistent net flux into or out of the brain could be demonstrated for any of these substances. The degree of encephalopathy correlated with the level of respiratory alkalosis (r=0.325, P less than 0.05) which, in turn, correlated with the degree of elevation of plasma OCT (r=0.439, P less than 0.05) and PEA (r=0.489, P less than 0.05) as well as with the excess of glutamine efflux from the brain (r=0.927, P less than 0.05). These findings support current views that hyperammonaemia, plasma amino acid imbalance, and elevated production of FNTs are interrelated disturbances which contribute to the pathogenesis of PSE. In addition, the data suggest that alkalosis accentuates the altered metabolism of these substances within the brain.

Factors that affect the uptake of ammonia by the brain: the blood-brain pH gradient

The brain uptake index (BUI) for [13N]ammonia was measured in 7 areas of the rat brain at 8 different pH values ranging from 6.58 to 7.73. When the regional BUI was plotted as a function of the pH of the test bolus, a significant linear correlation was found for each region (P less than 0.001). The highest slope was observed in the thalamus-basal ganglia complex (0.392 +/- 0.018) (S.D.), and the lowest in the ventral pons (0.143 +/- 0.011). These studies indicate that the brain-blood pH gradient plays a major role in determining the forward flux of ammonia from the blood into the brain in the physiological pH range. Regional differences in the slope may be due to metabolic factors. This pH effect may be important in clinical conditions characterized by hyperammonemia such as hepatic encephalopathy, and in the interpretation of [13N]ammonia emission tomographic images of the brain.

Observations upon ammonia absorption from the human ileum

Experiments have been performed upon the absorption of ammonia and hydrazine from different solutions instilled into a human ileal sac with an exteriorized stoma. Ammonia and hydrazine absorption was greater from solutions of higher pH. It is concluded that non-ionic diffusion plays an important role in ammonia absorption from the human ileum.

Observations on the effect of exercise on blood ammonia concentration in man

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