Contribution of dialysate acetate to energy metabolism: metabolic implications

Comparison Between Sodium Acetate and Sodium Chloride in Parenteral Nutrition for Very Preterm Infants on the Acid-Base Status and Neonatal Outcomes

PURPOSE

To compare between sodium acetate (SA) and sodium chloride (SC) in parenteral nutrition (PN) with associated metabolic acidosis and neonatal morbidities in preterm infants.

METHODS

Preterm infants below 33 weeks gestational age, and with a birth weight under 1,301 g were enrolled and further stratified into two groups: i) <1,000 g, or ii) ≥1,000 g in birth weight. The subjects were randomized to receive PN containing SA or SC within the first day of life. The results of routine blood investigations for the first 6 days of PN were collated, and the neonatal outcomes were recorded upon discharge or demise.

RESULTS

Fifty-two infants entered the study, with 26 in each group: 29 infants had extremely low birth weight (ELBW). There were no significant differences in birth weight, gestation, sex, exposure to chorioamnionitis and antenatal steroids, surfactant doses and duration of mechanical ventilation between groups. The SA group had significantly higher mean pH and base excess (BE) from days 4 to 6 than the SC (mean pH, 7.36 vs. 7.34; mean BE -1.6 vs. -3.5 [p<0.01]), with a two-fold increase in the mean BE among ELBW infants. Significantly fewer on SA required additional bicarbonate (n=4 vs. 13, p=0.01). The rate of bronchopulmonary dysplasia (BPD) was approximately four-fold lower in SA than SC (n=3 vs. 11, p<0.01). No significant differences were observed in necrotizing enterocolitis, patent ductus arteriosus, retinopathy of prematurity, cholestatic jaundice, and mortality between groups.

CONCLUSION

The use of SA in PN was associated with reduced metabolic acidosis and fewer BPD.

Current explorations of nutrition and the gut microbiome: a comprehensive evaluation of the review literature

Context

The ability to measure the gut microbiome led to a surge in understanding and knowledge of its role in health and disease. The diet is a source of fuel for and influencer of composition of the microbiome.

Objective

To assess the understanding of the interactions between nutrition and the gut microbiome in healthy adults.

Data Sources

PubMed and Google Scholar searches were conducted in March and August 2018 and were limited to the following: English, 2010–2018, healthy adults, and reviews.

Data Extraction

A total of 86 articles were independently screened for duplicates and relevance, based on preidentified inclusion criteria.

Data Analysis

Research has focused on dietary fiber – microbiota fuel. The benefits of fiber center on short-chain fatty acids, which are required by colonocytes, improve absorption, and reduce intestinal transit time. Contrastingly, protein promotes microbial protein metabolism and potentially harmful by-products that can stagnate in the gut. The microbiota utilize and produce micronutrients; the bidirectional relationship between micronutrition and the gut microbiome is emerging.

Conclusions

Nutrition has profound effects on microbial composition, in turn affecting wide-ranging metabolic, hormonal, and neurological processes. There is no consensus on what defines a “healthy” gut microbiome. Future research must consider individual responses to diet.

Management of Small Intestinal Bacterial Overgrowth in Adult Patients

The human gastrointestinal tract is a complex system of digestive pathways aided by mechanical processes, enzymes, transport molecules, and colonic bacteria. Occasionally, these bacterial components transplant to atypical locations due to various gastrointestinal imbalances or anatomical structural issues. This may lead to bacterial overgrowth of the small intestine, where minimal or no bacteria are normally found. Symptoms of small intestinal bacterial overgrowth may mimic those of various functional gastrointestinal diseases. Small intestinal bacterial overgrowth is typically diagnosed through hydrogen breath tests or jejunal aspirate culture. Current recommendations indicate antibiotics as the first-line treatment to eradicate or modify the bacterial overgrowth to a more favorable state. Nutritional support is also indicated to correct deficiencies and aid in symptom alleviation. As small intestinal bacterial overgrowth is common in other conditions, much of the research for this area is based on findings in codisease states rather than independent disease research. To provide accurate recommendations for small intestinal bacterial overgrowth, more targeted research is needed.

Experimental Model for Studying the Effects of 2-Ethylhexyl-Phthalate and Dialysate on Connective Tissue

In order to have a model for studying the possible implications of 2-ethylhexyl-phthalate and dialysate on connective tissue, we evaluated their direct effects on the air pouch lining tissue and on fibroblast cultures. Air pouches were formed on the backs of 60 ten-week-old Wistar rats by subcutaneous injections of 10 ml sterile air. On the tenth day 2 ml sterile air, or 2 ml 5μg/L or 2 ml 10 μg/L 2-ethylhexyl-phthalate in olive oil, or 2 ml olive oil alone, or 2 ml 5 mg/ml or 12 mg/ml lyophilized dialysate were injected into the air pouches. After sampling at seven or twenty-one days, the rats were killed. The biochemical data showed an increase in sulphated glycosaminoglycans with 2-ethylhexyl-phthalate and dialysate. Electron microscopy findings revealed cellular alterations such as vacuolation and cell remnants with 2-ethylhexyl-phthalate, while the cells of the air pouches treated with dialysate showed regular organelles with increased and dilated cisternae of rough endoplasmic reticulum. Moreover, an increase in collagen fibres surrounding the damaged zones was noticed in 2-ethylhexyl-phthalate and dialysate treated rats. The glycosaminoglycan modifications and collagen fibre increase seem to suggest that the morfological changes, with the features of fibrosis, could be the result of 2-ethylhexyl-phthalate and dialysate action on connective tissue. Moreover, the air pouch technique can be considered a good model for studying the direct effects of 2-ethylhexyl-phthalate and other substances, such as uremic toxins, on connective tissue.

Enhanced Extracorporeal CO2 Removal by Regional Blood Acidification: Effect of Infusion of Three Metabolizable Acids

Acidification of blood entering a membrane lung (ML) with lactic acid enhances CO2 removal (VCO2ML). We compared the effects of infusion of acetic, citric, and lactic acids on VCO2ML. Three sheep were connected to a custom-made circuit, consisting of a Hemolung device (Alung Technologies, Pittsburgh, PA), a hemofilter (NxStage, NxStage Medical, Lawrence, MA), and a peristaltic pump recirculating ultrafiltrate before the ML. Blood flow was set at 250 ml/min, gas flow (GF) at 10 L/min, and recirculating ultrafiltrate flow at 100 ml/min. Acetic (4.4 M), citric (0.4 M), or lactic (4.4 M) acids were infused in the ultrafiltrate at 1.5 mEq/min, for 2 hours each, in randomized fashion. VCO2ML was measured by the Hemolung built-in capnometer. Circuit and arterial blood gas samples were collected at baseline and during acid infusion. Hemodynamics and ventilation were monitored. Acetic, citric, or lactic acids similarly enhanced VCO2ML (+35%), from 37.4 ± 3.6 to 50.6 ± 7.4, 49.8 ± 5.6, and 52.0 ± 8.2 ml/min, respectively. Acids similarly decreased pH, increased pCO2, and reduced HCO3 of the post-acid extracorporeal blood sample. No significant effects on arterial gas values, ventilation, or hemodynamics were observed. In conclusion, it is possible to increase VCO2ML by more than one-third using any one of the three metabolizable acids.

Metabolomics – the complementary field in systems biology: a review on obesity and type 2 diabetes

This paper highlights the metabolomic roles in systems biology towards the elucidation of metabolic mechanisms in obesity and type 2 diabetes.

Diet-microbiota interactions and their implications for healthy living

It is well established that diet influences the health of an individual and that a diet rich in plant-based foods has many advantages in relation to the health and well-being of an individual. What has been unclear until recently is the large contribution of the gut microbiota to this effect. As well as providing basic nutritional requirements, the long-term diet of an animal modifies its gut microbiota. In adults, diets that have a high proportion of fruit and vegetables and a low consumption of meat are associated with a highly diverse microbiota and are defined by a greater abundance of Prevotella compared to Bacteroides, while the reverse is associated with a diet that contains a low proportion of plant-based foods. Furthermore, it is becoming increasingly clear that the effect of the microbial ecology of the gut goes beyond the local gut immune system and is implicated in immune-related disorders, such as IBS, diabetes and inflamm-ageing. In this review, we investigate the evidence that a balanced diet leads to a balanced, diverse microbiota with significant consequences for healthy ageing by focusing on conditions of interest.

Absorption and metabolism of [U-14C] acetic acid in growing pigs

By tracing 14C after an injection of [U-14C] sodium acetate into the caecum of pigs, it was found that proportionately 0·93 of the acetate injected was absorbed. About 0·25 of the administered acetate was recovered in the body 96 h later. It is assumed that the remainder was oxidized during this period and exhaled as carbon dioxide.

The 14C initially predominated in plasma lipids, but it progressively shifted over the 96 h to plasma proteins. In the lipid fraction of blood plasma there was a continuous shift of 14C from triglycerides and free cholesterol to cholesterol esters over the 96-h period of measurement.

In the body most of the 14C was recovered in the fat, liver and intestinal wall. The highest concentration of 14C was in the bile, especially in glycine-conjugated bile acids.

It was shown that the absorbed acetate was a source of energy to the pigs and it was recycled and metabolized into more complex components in the body during 96 h.

Sodium acetate induces a metabolic alkalosis but not the increase in fatty acid oxidation observed following bicarbonate ingestion in humans

We conducted this study to quantify the oxidation of exogenous acetate and to determine the effect of increased acetate availability upon fat and carbohydrate utilization in humans at rest. Eight healthy volunteers (6 males and 2 females) completed 2 separate trials, 7 d apart in a single-blind, randomized, crossover design. On each occasion, respiratory gas and arterialized venous blood samples were taken before and during 180 min following consumption of a drink containing either sodium acetate (NaAc) or NaHCO3 at a dose of 2 mmol/kg body mass. Labeled [1,2 -13C] NaAc was added to the NaAc drink to quantify acetate oxidation. Both sodium salts induced a mild metabolic alkalosis and increased energy expenditure (P < 0.05) to a similar magnitude. NaHCO3 ingestion increased fat utilization from 587 +/- 83 kJ/180 min to 693 +/- 101 kJ/180 min (P = 0.01) with no change in carbohydrate utilization. Following ingestion of NaAc, the amount of fat and carbohydrate utilized did not differ from the preingestion values. However, oxidation of the exogenous acetate almost entirely (90%) replaced the additional fat that had been oxidized during the bicarbonate trial. We determined that 80.1 +/- 2.3% of an exogenous source of acetate is oxidized in humans at rest. Whereas NaHCO3 ingestion increased fat oxidation, a similar response did not occur following NaAc ingestion despite the fact both sodium salts induced a similar increase in energy expenditure and shift in acid-base balance.

Acetate generation in rat liver mitochondria; acetyl-CoA hydrolase activity is demonstrated by 3-ketoacyl-CoA thiolase

Acetate has been found as an endogenous metabolite of beta-oxidation of fatty acids in liver. In order to investigate the regulation of acetate generation in liver mitochondria, we attempted to purify a mitochondrial acetyl-CoA hydrolase in rat liver. This acetyl-CoA-hydrolyzing activity in isolated mitochondria was induced by the treatment of rats with di(2-ehtylhexyl)phthalate (DEHP), a peroxisome proliferator which induces expression of several peroxisomal and mitochondrial enzymes involved in beta-oxidation of fatty acids. The purified enzyme was 43-kDa in molecular mass by SDS/PAGE. Internal amino acid sequencing of this enzyme revealed that it was identical with mitochondrial 3-ketoacyl-CoA thiolase, suggesting that this enzyme has two kinds of activities, 3-ketoacyl-CoA thiolase and acetyl-CoA hydrolase activities. Kinetic studies clearly indicated that this enzyme had the both activities and each activity was inhibited by the substrates of the other activity, that is, 3-ketoacyl-CoA thiolase activity was inhibited by acetyl-CoA, on the other hand, acetyl-CoA hydrolase activity was inhibited by acetoacetyl-CoA in a competitive manner. These findings suggested that acetate generation in liver mitochondria is a side reaction of this known enzyme, 3-ketoacyl-CoA thiolase, and this enzyme may regulate its activities depending on each substrate level.

The efficiency of potassium removal during bicarbonate hemodialysis

Patients on chronic hemodialysis often portray high serum [K+]. Although dietary excesses are evident in many cases, in others, the cause of hyperkalemia cannot be identified. In such cases, hyperkalemia could result from decreased potassium removal during dialysis. This situation could occur if alkalinization of body fluids during dialysis would drive potassium into the cell, thus decreasing the potassium gradient across the dialysis membrane. In 35 chronic hemodialysis patients, we compared two dialysis sessions performed 7 days apart. Bicarbonate or acetate as dialysate buffers were randomly assigned for the first dialysis. The buffer was switched for the second dialysis. Serum [K+], [HCO3-], and pH were measured in samples drawn before dialysis; 60, 120, 180, and 240 min into dialysis; and 60 and 90 min after dialysis. The potassium removed was measured in the dialysate. During the first 2 hr, serum [K+] decreased equally with both types of dialysates but declined more during the last 2 hr with bicarbonate dialysis. After dialysis, the serum [K+] rebounded higher with bicarbonate bringing the serum [K+] up to par with acetate. The lower serum [K+] through the second half of bicarbonate dialysis did not impair potassium removal (295.9 +/- 9.6 mmol with bicarbonate and 299.0 +/- 14.4 mmol with acetate). The measured serum K+ concentrations correlated with serum [HCO3-] and blood pH during bicarbonate dialysis but not during acetate dialysis. Alkalinization induced by bicarbonate administration may cause redistribution of K during bicarbonate dialysis but this does not impair its removal. The more marked lowering of potassium during bicarbonate dialysis occurs late in dialysis, when exchange is negligible because of a low gradient.

Production of acetate in the liver and its utilization in peripheral tissues

In experimental rat liver perfusion we observed net production of free acetate accompanied by accelerated ketogenesis with long-chain fatty acids. Mitochondrial acetyl-CoA hydrolase, responsible for the production of free acetate, was found to be inhibited by the free form of CoA in a competitive manner and activated by reduced nicotinamide adenine dinucleotide (NADH). The conditions under which the ketogenesis was accelerated favored activation of the hydrolase by dropping free CoA and elevating NADH levels. Free acetate was barely metabolized in the liver because of low affinity, high K(m), of acetyl coenzyme A (acetyl-CoA) synthetase for acetate. Therefore, infused ethanol was oxidized only to acetate, which was entirely excreted into the perfusate. The acetyl-CoA synthetase in the heart mitochondria was much lower in K(m) than it was in the liver, thus the heart mitochondria was capable of oxidizing free acetate as fast as other respiratory substrates, such as succinate. These results indicate that rat liver produces free acetate as a byproduct of ketogenesis and may supply free acetate, as in the case of ketone bodies, to extrahepatic tissues as fuel.

Incorporation and utilization of [3-13C]lactate and [1,2-13C]acetate by rat skeletal muscle

Skeletal muscle can utilize many different substrates, and traditional methodologies allow only indirect discrimination between oxidative and nonoxidative uptake of substrate, possibly with contamination by metabolism of other internal organs. Our goal was to apply 1H- and 13C-nuclear magnetic resonance spectroscopy to monitor the patterns of [3-13C]lactate and [1,2-13C]acetate (model of simple carbohydrates and fats, respectively) utilization in resting vs. contracting muscle extracts of the isolated perfused rat hindquarter. Total metabolite concentrations were measured by using NADH-linked fluorometric assays. Fractional oxidation of [3-13C]lactate was unchanged by contraction despite vascular endogenous lactate accumulation. Although label accumulated in several citric acid cycle (CAC) intermediates, contraction did not increase the concentration of CAC intermediates in any muscle extracts. We conclude that 1) the isolated rat hindquarter is a viable, well-controlled model for measuring skeletal muscle 13C-labeled substrate utilization; 2) lactate is readily oxidized even during contractile activity; 3) entry and exit from the CAC, via oxidative and nonoxidative pathways, is a component of normal muscle metabolism and function; and 4) there are possible differences between gastrocnemius and soleus muscles in utilization of nonoxidative pathways.

Lipid turnover in alcoholics before and after an ethanol load

Alcohol ingestion decreases plasma free fatty acids (FFAs) and lipid oxidation. This study was conducted to determine palmitate turnover in alcoholics during a short abstinence period and after an ethanol load and in a group of nonalcoholic control subjects, looking for correlations between palmitate turnover, FFA, acetate, and acetoacetate/beta hydroxybutyrate ratio (AKBR). Palmitate C14 turnover was studied in five alcoholics during early abstinence and after a 0.8 g/kg ethanol load, and in five nonalcoholic normal controls. Plasma levels of FFA, acetate, acetoacetate, and beta hydroxybutyrate were measured before and during the ethanol load. A needle hepatic biopsy was performed in alcoholics. FFA levels, palmitate flux, oxidation, and nonoxidative disposal were similar in alcoholics compared with control subjects, decreasing significantly after the ethanol load in both groups. AKBR and ketone bodies were similar in both groups in the basal period. After the alcohol infusion, AKBR decreased significantly. Acetoacetate levels did not change, and beta hydroxybutyrate and total ketone bodies increased significantly in alcoholics and control subjects. A positive correlation was found between FFA levels and palmitate flux. Liver biopsies showed mild changes in the patients studied. The similar inhibition of lipid turnover, FFA release, and the drop in AKBR observed after an alcohol load in alcoholics and control subjects suggest that this effect is mediated by alcohol metabolism and not by metabolic alterations present in alcoholics.

Direct inhibitory effect of uremic toxins and polyamines on proliferation of VERO culture cells

The dialysate fluid of uremic patients exhibits, in vitro, an inhibitory effect on cell growth, owing to urea, guanidino compounds, and substances named middle molecules. The polyamines are compounds which exhibit high levels in biological fluids during either normal development or disease such as psoriasis, uremia, and tumors. Dialysate and middle molecules show toxicity and degeneration of the organotype cultures, whereas the free polyamines and nonrecirculated dialysate do not have any toxic effect. The aim of this study is to analyze the effects of polyamines, nonrecirculated dialysate, and middle molecules of uremic patients in periodic hemodialysis on cultured VERO (fibroblast-like cells) growth. These cells show an inhibition of growth in middle molecules or 2 x 10(-4) M putrescine and a stimulation with nonrecirculated dialysate and 2 x 10(-8) M putrescine. The effect is different because the cultures with middle molecules begin growth again after 24 hr, whereas in the presence of 2 x 10(-4) M putrescine no further growth is observed. Cells maintained in middle molecules + 2 x 10(-8) M putrescine show an irreversible degeneration, attesting a toxic effect due to the low molarities of putrescine. The electron microscopy shows alteration of cytoplasmic, mitochondrial, and nuclear membranes, but no chromatin fragmentation with either middle molecules or 2 x 10(-4) M putrescine: this suggests that the cells do not die of apoptosis. In conclusion, during uremia the polyamines could cause toxic effects, even at low concentrations, on cells stressed by other toxic stimuli.

Effects of alcohol on energy metabolism and body weight regulation: is alcohol a risk factor for obesity?

Some studies have suggested that drinking in moderation may be beneficial for health, but many of these studies do not address body weight. Evidence suggests that consuming moderate amounts of alcohol is a risk factor for obesity, which is a risk factor for several adverse health outcomes. Recommendations regarding alcohol intake thus should take into account a variety of factors, including baseline body weight, location of body fat, and overall diet.

Fecal short chain fatty acids in South African urban Africans and whites

Diminished levels for fecal short chain fatty acids (SCFAs) have been linked to occurrence of ulcerative colitis, colorectal polyps, and colon cancer, diseases that are rare or uncommon in African populations.

PURPOSE

The aim of this study was to determine fecal SCFA concentrations and fecal pH values in groups of black South Africans (African) and white South Africans (white) subjects.

METHODS

Twenty healthy Africans (all women; mean age, 35 years) and 17 healthy whites (7 women; 10 men; mean age, 32 years) were tested.

RESULTS

Mean total concentrations of SCFAs in the two groups were 142.1 (+/- 53.9) and 69.2 (+/- 26.0) mmol/kg wet feces, respectively (P = 0.0001). Mean values for Africans were significantly higher in all subfractions except butyrate. There was a significant inverse correlation between fecal pH value and total fecal SCFA concentration (r = 0.704; P = 0.001).

CONCLUSION

High concentrations of fecal SCFAs in the African group could protect against chronic bowel diseases.

Skeletal muscle pyruvate dehydrogenase activity during acetate infusion in humans

Pyruvate dehydrogenase activity (PDHa), acetyl group, and citrate accumulation were examined in human skeletal muscle at rest and during cycling exercise while acetate was infused. Eight subjects received 400 mmol of sodium acetate (Ace) at a constant rate during 20 min of rest, 5 min of cycling at 40% maximal O2 uptake (VO2max) and 15 min of cycling at 80% VO2max. Two weeks later experiments were repeated while 400 mmol of sodium bicarbonate was infused in the control condition (CON). Ace infusion increased muscle acetyl-coenzyme A (acetyl-CoA), citrate, and acetylcarnitine. A decline in resting PDHa during 20 min of Ace infusion (0.37 +/- 0.08 vs. 0.16 +/- 0.03 mmol.min-1.kg wet wt-1) coincided with an elevation in the acetyl-CoA-to-free CoA ratio (acetyl-CoA/CoASH; 0.28 +/- 0.04 to 0.73 +/- 0.14). After 20 min of CON infusion, resting PDHa (0.32 +/- 0.06 mmol.min-1.kg wet wt-1) was similar to PDHa before Ace infusion. During exercise, acetyl-CoA, citrate, and acetyl-CoA/CoASH were further elevated, and the differences that existed at rest were resolved. PDHa increased to the same extent in Ace and CON, in which it was 44-47% transformed after 5 min at 40% VO2max and completely transformed after 15 min at 80% VO2max. At rest PDHa was regulated by variations in acetyl-CoA/CoASH secondary to enhanced acetate metabolism. Conversely, during exercise PDHa regulation appeared independent of variations in acetyl-CoA/CoASH. The resting data are consistent with a central role for PDHa and citrate in the regulation of the glucose-fatty acid cycle in skeletal muscle, as classically proposed. However, in the present study Ace infusion was not effective in perturbing the glucose-fatty acid cycle during exercise.

The effect of ethanol on fat storage in healthy subjects

BACKGROUND

Ethanol can account for up to 10 percent of the energy intake of persons who consume moderate amounts of ethanol. Its effect on energy metabolism, however, is not known.

METHODS

We studied the effect of ethanol on 24-hour substrate-oxidation rates in eight normal men during two 48-hour sessions in an indirect-calorimetry chamber. In each session, the first 24 hours served as the control period. On the second day of one session, an additional 25 percent of the total energy requirement was added as ethanol (mean [+/- SD], 96 +/- 4 g per day); during the other session, 25 percent of the total energy requirement was replaced by ethanol, which was isocalorically substituted for lipids and carbohydrates.

RESULTS

Both the addition of ethanol and the isocaloric substitution of ethanol for other foods reduced 24-hour lipid oxidation. The respective mean (+/- SE) decreases were 49.4 +/- 6.7 and 44.1 +/- 9.3 g per day (i.e., reductions of 36 +/- 3 percent and 31 +/- 7 percent from the oxidation rate during the control day; P less than 0.001 and P less than 0.0025). This effect occurred only during the daytime period (8:30 a.m. to 11:30 p.m.), when ethanol was consumed and metabolized. Neither the addition of ethanol to the diet nor the isocaloric substitution of ethanol for other foods significantly altered the oxidation of carbohydrate or protein. Both regimens including ethanol produced an increase in 24-hour energy expenditure (7 +/- 1 percent with the addition of ethanol, P less than 0.001; 4 +/- 1 percent with the substitution of ethanol for other energy sources, P less than 0.025).

CONCLUSIONS

Ethanol, either added to the diet or substituted for other foods, increases 24-hour energy expenditure and decreases lipid oxidation. Habitual consumption of ethanol in excess of energy needs probably favors lipid storage and weight gain.

Measurement of plasma acetate kinetics using high-performance liquid chromatography

Previous studies suggest that plasma acetate may be an important fuel in man, accounting for approximately 10% of energy expenditure. Available methods for the determination of plasma acetate kinetics are difficult and time consuming. We describe here a procedure for the determination of plasma acetate concentration and specific activity using automated high-performance liquid chromatography that is precise and sensitive and accommodates large numbers of samples. The procedure involves extraction from plasma with diethyl ether, derivatization with bromoacetophenone, and separation on a C-18 reversed-phase column. The specific activities of D-beta-hydroxybutyrate and lactate can also be determined. Acetate turnover was measured in four dogs and was similar to that previously reported in sheep and humans. Transport of [14C]acetate into red blood cells was negligible.

Plasma acetate levels in response to intravenous fat or glucose/insulin infusions in diabetic and non-diabetic subjects

We measured plasma levels of acetate, glucose, insulin, fatty acids and 'ketone bodies' (KB), during fat infusion and continuous simultaneous infusion of insulin and glucose according to a computerized algorithm to maintain fasting euglycaemia and derive indices of tissue insulin sensitivity (hyperinsulinaemic euglycaemic clamping HEC). (i) Plasma acetate levels (mmol/l) approximately doubled (0.14 +/- (SEM) 0.02 to 0.25 +/- 0.02, p less than 0.01) during INTRALIPID infusion in 7 non-diabetic individuals while total 'ketone bodies' and non-esterified fatty acids (NEFAs) increased 10-fold. (ii) Early in the HEC, plasma acetate levels decreased as did NEFAs in 13 non-diabetic (0.17 +/- 0.01 to 0.12 +/- 0.01, p less than 0.001) and 9 diabetic (0.22 +/- 0.02 to 0.15 +/- 0.01, p less than 0.005) individuals. However while acetate levels later rose to fasting values in the non-diabetics, they remained low in the diabetics. NEFA levels were low throughout the clamp but glucose flux was increased as judged from the glucose infusion even with maintained euglycaemia. The change in acetate values during the second hour of the clamp correlated with neither BMI nor two indices of insulin sensitivity (glucose metabolic clearance rate and steady state glucose infusion rate). These results accord with acetate production from glucose and fat oxidation, via acetyl CoA. The differing metabolism of acetate in the second hour of clamping between diabetics and non-diabetics may reflect altered post-receptor glucose metabolism with the onset of diabetes.

Ethanol causes acute inhibition of carbohydrate, fat, and protein oxidation and insulin resistance

To study the mechanism of the diabetogenic action of ethanol, ethanol (0.75 g/kg over 30 min) and then glucose (0.5 g/kg over 5 min) were infused intravenously into six normal males. During the 4-h study, 21.8 +/- 2.1 g of ethanol was metabolized and oxidized to CO2 and H2O. Ethanol decreased total body fat oxidation by 79% and protein oxidation by 39%, and almost completely abolished the 249% rise in carbohydrate (CHO) oxidation seen in controls after glucose infusion. Ethanol decreased the basal rate of glucose appearance (GRa) by 30% and the basal rate of glucose disappearance (GRd) by 38%, potentiated glucose-stimulated insulin release by 54%, and had no effect on glucose tolerance. In hyperinsulinemic-euglycemic clamp studies, ethanol caused a 36% decrease in glucose disposal. We conclude that ethanol was a preferred fuel preventing fat, and to lesser degrees, CHO and protein, from being oxidized. It also caused acute insulin resistance which was compensated for by hypersecretion of insulin.

Acetate metabolism and bicarbonate generation during hemodialysis: 10 years of observation

The capacity of chronically hemodialyzed patients to metabolize acetate during conventional hemodialysis was evaluated using a retrospective study in 219 patients dialyzed for up to ten years under similar dialysis conditions. For each patient, and using all available data, a regression line relating the changes of plasma total CO2 during dialysis as a function of the pre-dialysis value was calculated. The intercept of this function indicates the plasma concentration where the losses of bicarbonate in the dialysate is matched by the generation of bicarbonate arising from the metabolism of acetate. This value therefore represents an individual index of the capacity of each patient to metabolize acetate. A value for this index smaller than 18.0 mM was considered abnormal. It was shown that around 10% of chronically hemodialyzed patients are clearly unable to metabolize acetate optimally. This defect is not related to the duration of dialysis, body weight or quality of hemodialysis treatments but is strongly related to sex, 19 of the 22 "acetate intolerant" patients being women. In a prospective study, all the 60 patients of the same population undergoing active dialysis were studied, and this index identified 12 abnormal (11 women, 1 man) patients and 48 normal patients. Plasma acetate measured at the end their dialysis treatments were significantly higher in abnormal than in normal patients. It is concluded: that this index is useful to identify the patients unable to metabolize acetate optimally; that only around 10% of hemodialyzed patients present a severe problem when dialyzed against acetate and should be dialyzed against bicarbonate; that dialysis against acetate does not fully correct the metabolic acidosis even in "normal" patients.

Pulmonary gas exchange during hemodialysis

Pulmonary gas exchange was continuously measured in 13 mechanically ventilated patients during 24 hemodialyses for acute renal failure. Minute-ventilation was maintained constant by controlled ventilation and gas exchange was continuously measured by a mass-spectrometer system. Three groups were compared: a cuprophan membrane with an acetate dialysate; a polyacrilonitrile membrane (PAN) with an acetate dialysate; and PAN with a bicarbonate dialysate. Arterial PO2 and the O2 alveolar-arterial gradient were the same regardless of the membrane used. [H+] mildly decreased with all dialysates used. Arterial PCO2 decreased only with the acetate dialysate. O2 consumption increased, up to 20 +/- 5% of the initial values during hemodialysis, and remained increased during the two hours following the hemodialysis. Respiratory exchange ratio was lower after than before the hemodialysis.

IN CONCLUSION

the maintenance of a constant minute ventilation prevented hemodialysis induced hypoxemia. VO2 increased during hemodialysis.

Pulmonary gas exchange during hemodialysis and peritoneal dialysis: interaction between respiration and metabolism

This review concerns the alterations in pulmonary gas exchange during hemodialysis and peritoneal dialysis. The occurrence of hypoxemia during hemodialysis has led to numerous studies that now provide sufficient data to explain this complex phenomenon. The role of substrate metabolism during hemodialysis and peritoneal dialysis are explored as it relates to alterations in ventilation. Comparison to similar types of ventilatory changes occurring during total parenteral nutrition are discussed. The effect of peritoneal dialysis on pulmonary function is also described.