Effects of intravenous glucose loading on oxygen consumption, carbon dioxide production, and resting energy expenditure in infants with bronchopulmonary dysplasia

To determine the effects of intravenous glucose loading on basal oxygen consumption, resting energy expenditure, and basal carbon dioxide production in infants with bronchopulmonary dysplasia who were still oxygen dependent, we administered intravenous glucose loads of 4 and 12 mg/kg-1/min-1 on 2 consecutive days, under identical experimental conditions, to six infants with bronchopulmonary dysplasia and six healthy control subjects. Infants were not fed for 9 hours before and during the 4- to 6-hour study periods; the intravenous glucose infusion, along with an amino acid mixture (2 gm.kg-1.24 hr-1), was started at the beginning of the fasting period. Oxygen consumption and carbon dioxide production and resting energy expenditure were measured by a flow-through indirect calorimetry technique under basal conditions. Infants with oxygen-dependent bronchopulmonary dysplasia had significantly higher basal oxygen consumption and resting energy expenditure than did control infants and significantly higher basal carbon dioxide production during the high glucose infusion. With glucose loading, infants with bronchopulmonary dysplasia had a significant rise in basal oxygen consumption (7.91 +/- 0.91 ml.kg-1.min-1 to 9.65 +/- 1.35 ml.kg-1.min-1, p less than 0.05), basal carbon dioxide production (5.93 +/- 0.72 ml.kg-1.min-1 to 7.10 +/- 1.04 ml.kg-1.min-1), and resting energy expenditure (53.8 +/- 5.75 kcal.kg-1.24 hr-1 to 65.3 +/- 7.0 kcal.kg-1.24 hr-1, all p values less than 0.05). Control infants had no significant changes with intravenous glucose loading. We conclude that intravenous glucose loading in infants with bronchopulmonary dysplasia resulted in a net increase in resting energy expenditure, which should be taken into account in assessing their energy intake during nutritional management. The risk of pulmonary stress caused by an increase in basal oxygen consumption and carbon dioxide production resulting from glucose load should also be considered.

Functional hepatocyte heterogeneity. Vascular 2-oxoglutarate is almost exclusively taken up by perivenous, glutamine-synthetase-containing hepatocytes

1. In isolated perfused rat liver maximal rates of 2-[1-14C]oxoglutarate uptake were about 0.4 mumol.g-1 .min-1; half-maximal rates of 2-[14C]oxoglutarate uptake were observed with influent concentrations of about 100 microM. 2-[14C]Oxoglutarate uptake by the liver was not affected by the direction of perfusion, but was decreased by about 80-90% when Na+ in the perfusion fluid was substituted by choline+, suggesting a Na+-dependence of hepatic 2-oxoglutarate uptake. In the absence of added ammonia, [14C]oxoglutarate uptake by the liver was about twice the net oxoglutarate uptake, indicating a simultaneous release of unlabeled oxoglutarate from perfused rat liver. 2. 14C-Labeled metabolites derived from [1-14C]oxoglutarate and recovered in the effluent perfusate were 14CO2 and 14C-labeled glutamate and glutamine; they accounted for 85-100% of the radiolabel taken up by the liver. 14CO2 was the major product (more than 70%) from [1-14C]oxoglutarate taken up the liver, provided glutamine synthesis was either inhibited by methionine sulfoximine or the endogenous rate of glutamine production was below 40 nmol.g-1.min-1. 3. Stimulation of glutamine synthesis by ammonia did not affect [14C]oxoglutarate uptake by the liver, but considerably increased net hepatic oxoglutarate uptake, indicating a decreased release of unlabeled oxoglutarate from the liver. Stepwise stimulation of hepatic glutamine synthesis led to a gradual decrease of 14CO2 production and radiolabel was recovered increasingly as [14C]glutamine in the effluent. At high rates of glutamine formation (i.e. about 0.6 mumol.g-1.min-1), about 60% of the [1-14C]oxoglutarate taken up by the liver was recovered in the effluent as [14C]glutamine. 14CO2 and [14C]glutamine production from added [1-14C]oxoglutarate were dependent on the rate of hepatic glutamine synthesis but not on the direction of perfusion. Extrapolation of 14C incorporation into glutamine to maximal rates of hepatic glutamine synthesis yielded an about 100% utilization of the [14C]oxoglutarate taken up by the liver for glutamine synthesis. This was again true for both the antegrade and the retrograde perfusion directions. On the other hand, addition of ammonia did not affect 14CO2 production from labeled oxoglutarate, when glutamine synthetase was inhibited by methionine sulfoximine. 4. The data suggest that vascular oxoglutarate is almost exclusively taken up by the small perivenous hepatocyte population containing glutamine synthetase, i.e. a cell population comprising only 6-7% of all hepatocytes. Thus, the findings demonstrate the existence of a, to date, uniquely zonally distributed oxoglutarate transport system which is probably Na+-dependent in the plasma membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Whole body gas exchange: amino acid and lactate clearance as indicators of initial and early allograft viability in liver transplantation

A method for the rapid assessment of liver allograft circulation and function after liver transplantation is described. In 12 patients undergoing liver transplantation continuous recording of whole body energy production was made on the basis of gas exchange measurements during the surgical procedure. Oxygen consumption decreased rapidly by 25% when the blood supply to the native liver was interrupted. After the anhepatic period, there was a sharp increase of oxygen consumption with successful reperfusion of the allograft. Carbon dioxide production fell by 14% and returned to preanhepatic values after successful declamping. In two cases with suboptimal reperfusion the return of gas exchange values was slow and incomplete. Results from the studies of whole body energy production were compared with biochemical measurements. No significant accumulation of amino acids occurred during the anhepatic period, but in the two patients with incomplete revascularization, clearance of amino acids, after the anhepatic phase, was impaired and plasma amino acids accumulated. The same pattern was found for plasma lactate levels. By the techniques described in this article, rapid and reliable assessment of initial and early graft function in hepatic transplantation is possible. This is of great value for the intraoperative and early postoperative assessment and planning of surgical and anesthesiologic strategies.

Metabolism of aspartate in Mycobacterium smegmatis

Mycobacterium smegmatis grows best on L-asparagine as a sole nitrogen source; this was confirmed. [14C]Aspartate was taken up rapidly (46 nmol.mg dry cells-1.h-1 from 1 mM L-asparagine) and metabolised to CO2 as well as to amino acids synthesised through the aspartate pathway. Proportionately more radioactivity appeared in the amino acids in bacteria grown in medium containing low nitrogen. Activities of aspartokinase and homoserine dehydrogenase, the initial enzymes of the aspartate pathway, were carried by separate proteins. Aspartokinase was purified as three isoenzymes and represented up to 8% of the soluble protein of M. smegmatis. All three isoenzymes contained molecular mass subunits of 50 kDa and 11 kDa which showed no activity individually; full enzyme activity was recovered on pooling the subunits. Km values for aspartate were: aspartokinases I and III, 2.4 mM; aspartokinase II, 6.4 mM. Aspartokinase I was inhibited by threonine and homoserine and aspartokinase III by lysine, but aspartokinase II was not inhibited by any amino acids. Aspartokinase activity was repressed by methionine and lysine with a small residue of activity attributable to unrepressed aspartokinase I. Homoserine dehydrogenase activity was 96% inhibited by 2 mM threonine; isoleucine, cysteine and valine had lesser effects and in combination gave additive inhibition. Homoserine dehydrogenase was repressed by threonine and leucine. Only amino acids synthesised through the aspartate pathway were tested for inhibition and repression. Of these, only one, meso-diaminopimilate, had no discernable effect on either enzyme activity.

Proton translocation coupled to the oxidation of carbon monoxide to CO2 and H2 in Methanosarcina barkeri

Cell suspensions of acetate-grown Methanosarcina barkeri mediate the conversion of CO and H2O to CO2 and H2. The reaction is coupled with the phosphorylation of ADP. Evidence is presented that CO oxidation by the cells is associated with the transient acidification of the suspension medium. Up to 2 mol vectorial protons were measured/mol CO oxidized when the transmembrane electrical gradient was kept low by the addition of valinomycin (20 nmol/mg protein) and KCl (200 mM) or of KSCN (50 mM). No transient acidification was observed in the presence of the protonophore tetrachlorosalicylanilide which stimulated rather than inhibited CO oxidation. Proton extrusion remained unaltered when the proton-translocating ATPase was specifically inhibited by dicyclohexylcarbodiimide. The latter finding indicates that proton translocation is associated with CO conversion to CO2 and H2 rather than with ATP hydrolysis in the cells. The data substantiate that the coupling of CO oxidation with ADP phosphorylation in M. barkeri occurs via a chemiosmotic mechanism.

Hyper and hypodynamic models of sepsis in guinea pigs

The acute metabolic response following experimentally induced sepsis can generally be classified as either hypodynamic ("low flow") or hyperdynamic ("high flow"). We have found that in conscious guinea pigs the bolus infusion of 10(10) live Escherichia coli bacteria can elicit either response, depending on the route of administration of the bacteria. Intravenous infusion results in the hypodynamic condition of septic shock in which oxygen consumption (VO2) is reduced to approximately 60% of the control level, plasma glucose is elevated 4 hr after infusion with a reversal to extreme hypoglycemia 12 hr after infusion, and body temperature is reduced by approximately 5 degrees C in 12 hr. In contrast, subcutaneous injection results in increased VO2, body temperature, and plasma glucose. In both models the concentration of cortisol, catecholamines and glucagon were elevated, but the responses were more pronounced in the hypodynamic model. In both cases, insulin concentration was decreased. These models of sepsis are useful because many aspects of response are comparable to man, they are simple to create, and they are consistent and reproducible.

Propionic acidemia--biochemical studies

The first documented case of propionic acidemia in Israel is described. Diagnosis was based on three independent methods: analysis of urinary organic acids by gas chromatography/mass spectrometry, assay of propionyl CoA carboxylase activity and oxidation of 1-14C-propionate by cultured skin fibroblasts. The use of more than one method for confirmation of the diagnosis is considered to be of importance in providing an additional margin of safety in cases where genetic counseling and prenatal diagnosis in future pregnancies are indicated.

Iotrol, iodixanol, and 2-deoxy-D-glucose effects on neural tissue CO2 production

In vivo and in vitro experiments have demonstrated that the myelographic agent metrizamide decreases neural tissue glucose metabolism whereas iohexol and iopamidol do not. This study compares the changes in slices of rat hippocampus CO2 production caused by the nonionic dimers iotrol and iodixanol with the effects of metrizamide and 2-deoxy-D-glucose. After 6-hr incubations, 70-mmol/l concentrations of iotrol and iodixanol increased CO2 production by 11 +/- 20% and 31 +/- 35%, respectively, as compared with the artificial CSF control medium. Metrizamide at 70 mmol/l and 2-deoxy-D-glucose at 35 mmol/l decreased CO2 production by 32 +/- 13% and 96 +/- 1%, respectively. The increases in CO2 production with iotrol and iodixanol appear to indicate that these molecules have some effect on cell metabolism. The mechanism for the increase in CO2 production could involve an effect on the glucose metabolic pathway or could be indirect via a mechanism that increases cell energy utilization. These in vitro effects have not been verified with in vivo experiments.

Lipogenesis in liver and adipose tissue of the domestic cat (Felis domestica)

1. Production of fatty acids, CO2 and glycerol from glucose and acetate was determined in slices of liver and adipose tissue taken from mature cats. 2. Acetate was the predominant carbon source for de novo fatty acid synthesis in both liver and adipose tissue. 3. Fatty acid synthesis occurred at much greater rates in adipose tissue than in liver. 4. Relative lipogenic capacity (ratio of production of long-chain fatty acids and glycerol to oxidation of substrates) was 20 times greater in adipose tissue than in liver with both substrates.

Effect of dietary bulk on organ mass, fasting heat production and metabolism of the small and large intestines in sheep

Groups of 10 lambs were fed either a control diet or a diet consisting of 10% polyethylene at isoenergetic levels for 30 d to study the effect of dietary bulk on visceral organ mass and metabolism of mucosa from the jejunum and proximal colon. Fasting heat production was measured using an additional six lambs. Weights of the large intestine, stomach complex and lungs were greater in lambs fed the polyethylene diet than control lambs. Liver and small intestine weights were not affected by diet. Oxygen consumption rates of jejunal mucosa were not affected by diet while a trend existed for oxygen consumption rates of mucosa from the proximal colon to be increased due to feeding polyethylene. Na+,K+ ATPase activity of mucosa from both jejunum and colon was increased due to feeding polyethylene. Fasting heat production, oxygen consumption or carbon dioxide production did not differ with diet. Dietary bulk affects growth and metabolism of visceral organs but metabolic modifications appear different among tissues.

Effect of thiouracil in modifying folate function in severe vitamin B12 deficiency

The effects of thiouracil in correcting defects in folic acid function produced by B12 deficiency were studied. Addition of the thyroid inhibitor, thiouracil, to a low methionine diet containing B12, increased the oxidation of [2-14C]histidine to carbon dioxide, and increased liver folate levels. Addition of 10% pectin to the diet accentuated B12 deficiency as evidenced by a greatly decreased rate of histidine oxidation (0.19%) and an increased excretion of methylmalonic acid. Addition of thiouracil to the diet restored folate function as measured by increased histidine oxidation and increased liver folate levels similar to that produced by addition of methionine to a B12-deficient diet. Thiouracil decreased methylmalonate excretion, and increased hepatic levels of B12 in animals on both B12-deficient and -supplemented diets. Hepatic methionine synthase was increased by thiouracil, which may be the result of the elevated B12 levels. S-Adenosylmethionine and the enzyme methionine adenosyltransferase were also increased by thiouracil. Thus it is possible that the effect of thiouracil in increasing folate function consists both in the effect of thiouracil in decreasing levels of methylenetetrahydrofolate reductase, and also in its action in increasing S-adenosylmethionine which exerts a feedback inhibition of this enzyme.

Real importance of alanine in renal metabolism: in vitro studies in rat and dog

In vitro studies were performed on cortical renal tubules to clarify possible differences between dog and rat with regard to alanine production and to define more precisely the role of alanine on ammonia and glucose production by the kidney. It was established that glutamate-pyruvate transaminase has an activity that is seven times lower in the rat than in the dog kidney. At the same time, alanine production from lactate, pyruvate, and glutamate is three times lower in the rat than in the dog kidney. The enzymatic reaction could be completely inhibited in a competitive fashion with aminooxyacetate. O2 consumption and CO2 production by the renal tubules were lower than that observed with glutamine. CO2 production in the rat was lowest. Production of ammonia and glucose by the kidney from alanine during acidosis averaged less than 20% of that produced with L-glutamine. Furthermore, during metabolic acidosis the production of ammonia and glucose from alanine was not augmented and failed to be influenced by increasing the concentration of alanine in the incubation medium.

CO2 production of the chick embryo during the first day of post-laying development

The carbon dioxide production of the chick embryo cultured in vitro has been determined during the first 24 h of post-laying development using a non-invasive conductometric microtechnique. The mean CO2 production of the whole blastoderm (1) increased from 16 nmol/h at laying to 231 nmol/h at early neurulation, (2) became dependent on exogenous glucose and (3) was closely linked to mechanical tension generated in the blastoderm (loosening from vitelline membrane resulted in a decrease of 56%). In our experimental conditions, no significant influence of carbonic anhydrase on the CO2 production has been detected. The value of the respiratory exchange ratio varied from about 3 at pregastrular stages to 1 at neurula stage and CO2 was produced transiently in presence of antimycin A. Such results indicate that the source of CO2 is not exclusively mitochondrial and that the relative proportions of mitochondrial and non-mitochondrial CO2 productions might vary significantly throughout the early development. Our findings confirm that the metabolism of the chick embryo becomes more and more oxidative from laying onwards and suggest that the modifications of metabolism observed during the studied period of development could be associated with functional differentiation.

Pyruvate decarboxylation in astrocytes and in neurons in primary cultures in the presence and the absence of ammonia

Oxidative decarboxylation of [1-14C]pyruvate was studied in primary cultures of neurons and of astrocytes. The rate of this process, which is a measure of carbon flow into the tricarboxylic acid (TCA) cycle and which is inhibited by its end product, acetyl CoA, was determined under conditions which would either elevate or reduce the components of the malate-aspartate shuttle (MAS). Addition of aspartate (1 mM) was found to stimulate pyruvate decarboxylation in astrocytes whereas addition of glutamate (or glutamine) had no effect. Since aspartate is a precursor for extramitochondrial malate, and thus intramitochondrial oxaloacetate, whereas glutamate and glutamine are not, this suggests that an increase in oxaloacetate level stimulates TCA cycle activity. Conversely, a reduction of the glutamate content by 3 mM ammonia, which might reduce exchange between glutamate and aspartate across the mitochondrial membrane, suppressed pyruvate decarboxylation. This effect was abolished by addition of glutamate or glutamine or exposure to methionine sulfoximine (MSO). These findings suggest that impairment of MAS activity by removal of MAS constituents decreases TCA cycle activity whereas replenishment of these compounds restores the activity of the TCA cycle. No corresponding effects were observed in neurons.

Energy expenditure and adipose tissue development in 2- to 8-day-old Zucker rats

We investigated a possible relationship between impaired energy expenditure and the development of obesity in Zucker fa/fa pups in the first week of life; 19 fa/fa and 16 Fa/fa pups from four litters were studied. Gas exchanges were measured at 30 degrees C, from 17.00 to 18.00 hours, at the ages of 2, 5 and 7 days. At days 3, 6 and 8, a partial biopsy of inguinal adipose tissue was performed in the morning and used for determination of cellularity and TG content. At all ages studied, the level of gas exchange was significantly higher in Fa/fa than in fa/fa pups. At 5 and 7 days, but not at 2 days, adipose cell volume and triglyceride content were significantly higher in fa/fa than in Fa/fa pups, and a significant negative correlation was found between the level of O2 consumption and the volume of adipocytes. These results confirm the importance of the energy expenditure defect, which is present in fa/fa pups before the overdevelopment of adipose tissue, in the onset and development of this genetic obesity.

An in vitro model of anoxic-induced damage in mouse brain

An in vitro model of anoxic-induced brain damage was developed to help elucidate the biochemical basis of cell damage due to reduced oxygen availability. Mouse forebrain slices were preincubated under various conditions (treatment incubation). The effects of this treatment incubation on [14C]acetylcholine (ACh) and 14CO2 production from [U-14C]glucose were subsequently assessed in an incubation under optimal conditions (test incubation). A variety of treatment incubation conditions decreased 14CO2 and 14C-ACh production in the test incubation in parallel (r = 0.932). For example, treatment incubations with no oxygen and high K+ reduced test incubation ACh (-63.2%) and CO2 (-67.3%) production. An anoxic-induced increase in calcium-45 uptake and the amelioration of anoxic induced changes by the calcium antagonist verapamil or by the omission of calcium from the treatment incubation suggest that altered calcium homeostasis was important in the production of the anoxic-induced deficits. These results provide in vitro evidence that anoxic induced increases in calcium may be pathophysiologically important and that reducing calcium entry postsynaptically may alleviate anoxic-induced changes. This model may prove useful in elucidating the molecular basis of these changes.

Micromeasurement of total and regional CO2 productions in the one-day-old chick embryo

A conductometric micromethod combined with image analysis system has been developed allowing to determine the CO2 production within 'two-dimensional' tissues, i.e., flat and thin cell layers or epithelial sheets. The preparation was mounted into an airtight chamber separated in two compartments by a thin silicone membrane permeable to gases. The lower compartment contained the nutritive medium and the preparation. The upper compartment and a conductivity measuring capillary connected in series were perfused with a solution of Ba(OH)2. The CO2 produced by the tissue precipitated as BaCO3 and the resulting decrease of electrical conductivity was linearly related to the total CO2 production. In addition, the pattern of CO2 production was directly observable as the BaCO3 crystals formed upon the silicone membrane over the regions which produced CO2. The spatial distribution of the crystals was quantified by video image processing and the regional CO2 production evaluated with a spatial resolution of 100 microns. This new microtechnique was originally developed to study the CO2 production in the early chick blastoderm which is a disc 1-5 cells thick. At the stage of young neurula the CO2 production was found to be 235 +/- 37 nmol.h-1 (mean +/- SD; n = 10) per blastoderm and large variations of local CO2 production were detected from one region to another (from 0.6 to 6.5 nmol.h-1.mm-2). These results indicate a high metabolic and functional differentiation of cells within the blastoderm. The possible applications and improvements of such a microtechnique are discussed.

Chronic consumption of ethanol increases glucose oxidation in isolated cerebral tissue of rat

Tolerance to ethanol was induced in male Wistar rats by adding 15% ethanol to the drinking water for 3 and 9 months. The oxidation of [U-14C]glucose was measured in cerebral cortex prisms. 14CO2 production in prisms for ethanol-treated animals was markedly increased when compared to controls. Neither a single injection of a low dose of ethanol nor a comparable concentration of ethanol in vitro had this stimulatory effect.

Diet-induced thermogenesis in cafeteria-fed rats: a myth?

Oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory quotient were measured in rats given a high-fat cafeteria diet of the type that is said to promote diet-induced thermogenesis. No significant difference in the measurements as compared with controls was found at room temperature, at 5 degrees C, or in animals exposed to cold for several weeks. The result was the same whether open- or closed-circuit methods were used. The stimulatory effect of norepinephrine on the VO2 was identical in each dietary group. These results cast doubt on the alleged identity of diet-induced and nonshivering thermogenesis and may reflect the change in body composition of the animals rather than a primary response to dietary variation.

Ventilation and breathing patterns during hemodialysis-induced carbon dioxide unloading

Important CO2 unloading occurs during hemodialysis (HD) when acetate-buffered dialysate is used. This is accompanied by alveolar hypoventilation. To gain more insight into the mechanisms of this alveolar hypoventilation, breathing patterns were studied in 5 patients with end-stage renal failure during HD using acetate-buffered dialysate, which induces CO2 unloading, or bicarbonate without CO2 loss. Ventilation was continuously measured with calibrated respiratory inductance plethysmography using techniques of multiple linear regression analysis. At regular intervals, arterial blood gas was sampled and expired air was analyzed. Breathing patterns were analyzed for VE, VT, TI, TE, and VT/TI. All data were compared with the respective starting value and with the respective value in the other setup. A greater decrease in ventilation was seen during HD with an acetate-containing dialysate because of irregular breathing patterns that resulted in a prolongation of expiratory time. Important variations in tidal volumes, striking apnea periods, and occasional periodic breathing were observed. We suggest that these irregularities are due to CO2 unloading leading to the point where ventilation is totally mediated through the output of the peripheral chemoreceptors.

Interactions of propionate and carnitine metabolism in isolated rat hepatocytes

Accumulation of propionate and its metabolic products propionyl-CoA and methylmalonyl CoA results in disruption of normal hepatic metabolism. Carnitine can partially restore normal cellular function in the presence of propionate. This beneficial effect of carnitine has been hypothesized to result from removal of propionyl groups in the form of propionylcarnitine. The present study was designed to elucidate the kinetics of propionylcarnitine formation in isolated rat hepatocytes, and the consequences of propionylcarnitine formation on propionate and carnitine metabolism. 14C-Propionate was converted to CO2, glucose, and propionylcarnitine in the hepatocyte system. Rates of CO2 production plateaued at propionate concentrations above 0.5 to 1.0 mmol/L, while in contrast, rates of glucose production declined as the propionate concentration was increased from 1.0 to 10.0 mmol/L. Increasing concentrations of carnitine up to 10.0 mmol/L resulted in increased production of propionylcarnitine. Despite formation of propionylcarnitine, propionate conversion to CO2 and glucose was unaffected by addition of carnitine. Thus, 10 mmol/L carnitine was able to increase total propionate metabolism (conversion to CO2, glucose and propionylcarnitine) by 40%. Hepatocyte metabolism of propionate was associated with a decrease in carnitine concentration and an increase in short chain acylcarnitines. This decrease in carnitine concentration was also seen in the presence of 150 mumol/L added carnitine, and was greater with propionate as a substrate as compared to butyrate. High performance liquid chromatography was used to permit specific quantification of propionylcarnitine. This technique confirmed that in the presence of propionate, propionylcarnitine was the major acylcarnitine generated and was responsible for the depletion of free carnitine from the system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of induced leucocyte migration on mammary cell morphology and milk component biosynthesis

Effects of increasing milk somatic cell count on milk composition, milk component biosynthesis, and quantitative mammary histology were studied following intramammary infusion of sterile oyster glycogen in lactating ewes. Oyster glycogen had no direct effect on mammary tissue utilization of radiolabeled acetate. Intramammary infusion of oyster glycogen following each of six consecutive milkings in six lactating ewes increased mean milk somatic cell count (6-fold) and increased percent fat and protein but decreased milk lactose concentration. Quantity of damaged or nonsecretory epithelial cells was increased. Infused glands had increased concentrations of neutrophils (3-fold) and plasma cells (1.3-fold) in the subepithelial stroma and of neutrophils (2.7-fold) within the epithelial lining of alveoli. Infusion of oyster glycogen every 3 d for 30 d in four ewes elicited similar changes in milk somatic cell count and mammary histology. Loss of functional mammary cells associated with leucocytosis may explain lost milk production associated with increased milk somatic cell count.

Hexose monophosphate shunt in rat lens: stimulation by vitamin C

The metabolism of glucose through the hexose monophosphate (HMP) shunt has been studied in rat lens in vitro, in the absence and presence of ascorbic and dehydroascorbic acids. Both forms of the vitamin stimulated the utilization of glucose through the HMP shunt, the stimulatory effect of dehydroascorbate being substantially greater than that of ascorbate. The stimulatory effect of ascorbate, as well as of dehydroascorbate, was antagonized by sodium iodide, and N,N-bis (dichloroethyl)-N-nitrosourea, compounds known to inhibit glutathione reductase. N-ethylmaleimide also antagonized the stimulation. These findings, therefore, suggest that the DHA/AA redox couple acts in concert with the GSSG/GSH couple in stimulating the tissue shunt activity.

Gluconate metabolism in germinated spores of Bacillus megaterium QM B1551: primary roles of gluconokinase and the pentose cycle

The metabolic pathway of gluconate, a major product of glucose metabolism during spore germination, was investigated in Bacillus megaterium QM B1551. Compared to the parent, mutant spores lacking gluconokinase could not metabolize gluconate, whereas the revertant simultaneously restored the enzyme activity and the ability to metabolize it, indicating that gluconokinase was solely responsible for the onset of gluconate metabolism. To identify a further metabolic route for gluconate, we determined 14C yields in acetate and CO2 formed from [14C]gluconate, and found that experimental ratios of 14CO2/[14C]acetate obtained from [2-14C]gluconate and [3,4-14C]gluconate were not compatible with the ratios predicted from the Entner-Doudoroff pathway. In contrast, when CO2 release caused by recycling (approx. 30%) was corrected, the ratios almost agreed with those from the pentose cycle. Comparison of specific radioactivities in acetate also supported the conclusion that gluconate was metabolized via the pentose cycle, subsequently metabolized via the Embden-Meyerhof pathway, and finally degraded to acetate and CO2 without a contribution by the Krebs cycle.

Effect of amiodarone on rat heart myosin isoenzymes

The effects of amiodarone on heart weight, production of 14C-CO2 from labelled glucose, myosin ATPase activity, and myosin isoenzyme patterns were determined by comparing control and amiodarone-treated male Wistar rats. Since it has been suggested that amiodarone may interfere with thyroid hormone action on the heart, similar experiments were also carried out in hypothyroid and amiodarone-plus-triiodothyronine(T3)-treated rats, and the data were compared to those obtained in amiodarone-treated rats. Amiodarone treatment for 6 weeks resulted in lower heart weight, decreased atrial production of 14C-CO2 from labelled glucose, decreased myosin Ca-ATPase activity, and preferential synthesis of V3 isomyosin. These effects were similar to those observed in hypothyroid rats but were lesser in magnitude. T3 treatment of amiodarone-treated rats reversed all the changes induced by amiodarone. Serum thyroxine (T4) was higher in amiodarone-treated than in control rats, while serum T3 was similar. Serum T3 was higher in the amiodarone-plus-T3 than in the amiodarone-treated group. These results show that 1) amiodarone-induced changes resemble hypothyroidism with respect to cardiac myosin expression and atrial CO2 production, 2) amiodarone causes hypothyroid-like changes despite normal serum T3 and increased serum T4, and 3) T3 reverses the effects of amiodarone. These data support the hypothesis that amiodarone inhibits the action of thyroid hormone on the heart.

Validation of doubly labeled water for assessing energy expenditure in infants

Previous studies show that the doubly labeled water method is accurate for measuring energy expenditure in the adult human. To validate this method in infants, carbon dioxide production rate and energy expenditure were measured for 5 to 6 days by doubly labeled water (DLW) and periodic open circuit respiratory gas exchange (RGE) in 10 blinded studies in nine infants following abdominal surgery. Infants were maintained on consistent oral or parenteral nutrition prior to and during study. This avoided diet-related changes in baseline isotopic enrichment of body water which could theoretically contribute to significant errors in calculation of carbon dioxide production rate. For DLW, insensible water loss was assumed to be proportional to respiratory volume and body surface area, where the former was predicted from carbon dioxide production rate. Insensible water loss thus calculated averaged 18% of water turnover. Rates of carbon dioxide production measured by DLW were not significantly different from that of RGE (10.4 +/- 1.1 and 10.5 +/- 0.9 l/kg/day, mean +/- SD, respectively). Energy expenditure was calculated using respiratory quotients from dietary intake (DLW:DIET) and RGE (DLW:RGE) data. There was no significant difference between energy expenditure determined by DLW (DLW:DIET and DLW:RGE) and that measured by RGE (58.5 +/- 6.1, 56.8 +/- 6.1, and 57.3 +/- 5.1 kcal/kg/day, mean +/- SD, respectively). Rate of carbon dioxide production, DLW:diet, and DLW:RGE calculated by DLW differed from corresponding RGE values by -0.9 +/- 6.2, -1.1 +/- 6.1, and 1.6 +/- 6.2%, mean +/- SD, respectively. These findings demonstrate the validity of the doubly labeled water method for determining energy expenditure in infants without concurrent water balance studies.

Periodic cell cycle changes in the rate of CO2 production in the fission yeast Schizosaccharomyces pombe persist after a block to protein synthesis

CO2 production has been followed by manometry in synchronous and asynchronous control cultures of Schizosaccharomyces pombe prepared by elutriation from the same initial culture. Earlier results showed a periodic change in the rate of production, which took place once per cell cycle. These changes were most clearly shown as oscillations in the difference between values of the second differential (acceleration) for the synchronous and asynchronous cultures. This paper shows that the oscillations continue for at least three cycles in the presence of cycloheximide (with and without chloramphenicol). Protein synthesis is virtually absent and there is no cell division. The control of this metabolic oscillation is therefore not directly dependent on translation. The period of the oscillation under these conditions is about 60% of the normal cycle time.

Respiratory phase detection and delay determination for breath-by-breath analysis

The delay between air flow and gas concentration signals is generally assumed to be constant within a breath as well as from breath to breath, but it was not possible to examine the constancy of the delay with the delay determination techniques so far available. Thus we developed new methods for respiratory phase detection and delay determination. The presented algorithm for the detection of the start of inspiration and expiration (phase detection) replaces the generally used valve assembly with two pneumotachographs. Now, the pneumotachograph is used in a bidirectional mode, but with a volume criterion for phase detection replacing the less reliable threshold criterion. To measure the delay between flow and gas concentration signals, a test gas is periodically injected as a marker. This test gas contains less N2 than ambient air. Therefore, the delay is determined as time between the moment of injection and the drop of N2. These two methods rendered it possible to examine delay variations and their consequences. The investigation of various breathing patterns demonstrated that the usually assumed errors caused by delay uncertainty are underestimated. We suggest reliance on a breath-by-breath delay determination to account for delay variations.

Metabolism of glucose by human embryos

Glucose turnover, as measured by CO2 production, lactate accumulation and carbon incorporation from [U-14C]glucose as sole energy substrate, was low on the 2nd day of culture of human embryos resulting from in-vitro fertilization but above that of unfertilized oocytes. In general, all parameters of metabolism increased substantially during the following 2 days of development but the rate of increase in lactate production was greater than that of CO2, especially between Days 3 and 4. Within developing embryos, no correlation was evident between the metabolic turnover of glucose and the method of patient stimulation, the morphological quality of embryos or the apparent rate of cleavage in culture. The results indicate that, before Day 3 of development, glucose is not effective as an energy source for the human embryo because of a blockade to glycolysis similar to that in mouse embryos.

The accuracy and precision of an open-circuit system to measure oxygen consumption and carbon dioxide production in neonates

We measured the oxygen consumption, carbon dioxide production, and respiratory quotient during the combustion of a known mass of anhydrous ethanol and methanol to assess the accuracy of an open-circuit flow-through system. Continuous measurements were made of the mass of alcohol burned, the velocity of gas flow through the apparatus, and simultaneous measurements of the fractional concentration of oxygen, carbon dioxide and nitrogen of the inlet and outlet gas using paramagnetic oxygen analyzer, infrared carbon dioxide meter, and mass spectrometer. Standard respiratory and stoichiometric equations were used to calculate the oxygen consumption, carbon dioxide production and RQ for the mass of absolute alcohol combustion per unit time. In a series of 12 consecutive laboratory experiments (on 7 days), the measured values of gas exchange (similar to the rate of respiratory gas exchange by an infant of 1-4 kg) were in agreement within 5% of the true values for ethanol and methanol combustion, confirming the validity of the open-circuit method. The paramagnetic oxygen analyzer and the mass spectrometer gave similar oxygen consumption results and differed very little when the rate of absolute alcohol combustion was used to quantify the accuracy of the complete measurement system. A positive measurement error was observed for the carbon dioxide production results from both the IR meter and mass spectrometer, with the result that the respiratory quotient measurements were 3.4-4.7% higher than the true value. The mass spectrometer gave more precise oxygen consumption results, whereas smaller variance of carbon dioxide production measurements was observed using the infrared CO2 meter.(ABSTRACT TRUNCATED AT 250 WORDS)

Day-to-day energy expenditure variability in low birth weight neonates

We estimated the metabolic rate of 13 low birth weight infants over a 9-day period, using indirect calorimetry in conjunction with serial measurements of oxygen consumption, carbon dioxide production, and total urinary nitrogen excretion. The mean percent error for oxygen consumption and carbon dioxide production measurements (determined by alcohol combustion experiments) assignable to the open-circuit system was 0.4 and 3.8%, respectively. Error in the total urinary nitrogen excretion measurement was less than 1% by the Kjeldahl technique. In the clinical setting, however, the range of deviation of measured oxygen consumption, carbon dioxide production and total urinary nitrogen excretion was +/- 12, 12, and 15% of the mean value respectively for an individual patient under standardized controlled conditions. The variability of metabolic rate between infants may be as much as 76%. Factors that had a small effect on metabolic rate were difficult to detect because of the variability inherent in the short-term measurement of metabolic rate. It was virtually impossible to control the sources of variation in the resting metabolism of low birth weight neonates over extended experimental periods. Day-to-day variations in resting energy expenditure may explain, in part, the widely different growth rates of premature infants receiving similar caloric intakes.

A quantitative bioassay to measure the rate of respiration of isolated rat tooth pulp tissue

The formation of carbon dioxide, expressed as milligrammes of carbon dioxide per gramme wet weight, was used to determine the rate of succinate-induced respiration in rat incisal dental pulp, after incubation in a phosphate buffer. Seven experimental parameters: (a) physical nature of the tissue; (b) mass of the rat; (c) pre-incubation time; (d) incubation time; (e) substrate concentration; (f) effect of pH; and (g) effects of technique on pH, were analysed; pH was a critical determinant for success with this assay.

A theoretical approach to excessive CO2 expiration due to lactate production in exercise

Cerretelli et al. (1982) proposed a model to estimate pH changes due to lactate production in exercise. This model was modified in the present study so as to express the relationship between CO2 excess and lactate production. The modified model fitted to the data reported on endurance-trained men.

Effects of hypoxia and hyperoxia on ventilatory kinetics during recovery from exercise

The purpose of this investigation was to determine the effects of breathing hyperoxic and hypoxic gas mixtures on ventilatory kinetics in the transition from submaximal exercise to rest. Eight male subjects performed three separate single blind exercise tests at 80% of their ventilatory threshold. Inspired oxygen concentration was varied in each experimental condition: test one (55% O2 -45% N2), test two (14% O2 -76% N2), and test three (21% O2 -79% N2). Ventilation, heart rate, and gas exchange were measured every 15 s for 6 min of exercise and during 9 min of recovery from exercise. Data analysis revealed no significant (p less than 0.05) differences in the kinetics of heart rate, oxygen uptake, expired volume of carbon dioxide, or ventilation among treatments during the transition from exercise to rest. Given the belief that hyperoxia attentuates the carotid bodies and hypoxia augments carotid body chemosensitivity, these findings suggest that the carotid bodies are not important regulators of VE kinetics during recovery from exercise.

Effects of a low carbohydrate isoenergetic diet on sleep behavior and pulmonary functions in healthy female adult humans

To study the effects of a low carbohydrate, isoenergetic diet on pulmonary physiology and sleep behavior, we measured pulmonary functions and respiratory gas exchange and carried out ambulatory electroencephalographic studies after a week's intake of isoenergetic diet containing only 50 g carbohydrate per day in 6 healthy female adult humans in a free-living condition. Compared with their normal intake, during the week of low carbohydrate intake there was a rise in the level of fasting plasma 3-hydroxybutyrate from 0.12 +/- 0.07 (mean +/- SD) to 1.01 +/- 0.40 mmol/L(P less than 0.01, paired t-test); a fall in serum bicarbonate from 26.2 +/- 0.75 to 25.0 +/- 1.41 mmol/L (P less than 0.05) and in serum chloride from 107 +/- 1.3 to 105 +/- 1.8 mmol/L (P less than 0.05). Serum urea rose from 4.3 +/- 0.71 to 5.7 +/- 0.70 mmol/L (P less than 0.01), and serum uric acid from 0.34 +/- 0.08 to 0.39 +/- 0.10 mmol/L (P less than 0.05). Functional residual capacity was increased from 2.07 +/- 0.35 to 2.26 +/- 0.34 L (P less than 0.01). Respiratory gas exchange ratio fell from 0.81 +/- 0.05 to 0.75 +/- 0.04 (P less than 0.05) and partial pressure of expired carbon dioxide reduced from 22 +/- 3.3 to 21 +/- 3.1 mmHg (P less than 0.05). There was a reduction in endogenous carbon dioxide production and arterial carbon dioxide tension. An analysis of ambulatory electroencephalogram showed that REM latency increased from 66 +/- 8 to 111 +/- 38 min (P less than 0.05), with no significant changes in sleep time and stages. These studies show that a low carbohydrate isoenergetic diet is tolerable, influences sleep behavior, reduces carbon dioxide production and respiratory gas exchange ratio, and may be therapeutically useful in patients with hypercapnic respiratory failure.

Change in the rate of CO2 production in synchronous cultures of the fission yeast Schizosaccharomyces pombe: a periodic cell cycle event that persists after the DNA-division cycle has been blocked

CO2 production has been followed by manometry in synchronous and asynchronous cultures of Schizosaccharomyces pombe prepared by elutriation from the same initial culture. The rate of production follows a linear pattern in synchronous cultures with a rate change once per cycle at the time of cell division. This pattern is most clearly shown in oscillations of the difference between values of the second differential (acceleration) for the synchronous and asynchronous cultures. The association between the rate change and the time of division is maintained during growth speeded up in rich medium and slowed down in poor medium and at lower temperature. It is also maintained after a shift-up in temperature. Results with wee mutants suggest that the association is with the S period rather than division itself. The rate and acceleration of CO2 production are approximately proportional to cell size (protein content) in asynchronous cultures. When synchronous cultures of the temperature-sensitive mutants cdc2.33 and cdc2.33 wee1.6 are shifted up to the restrictive temperature, the DNA-division cycle is blocked. The oscillatory pattern of CO2 production, however, continues for one to two cycles until the acceleration reaches a constant value, after which the oscillations are undetectable. This point is reached later in the double mutant and there is a phase difference in the oscillations compared to those in the single mutant. With both blocked mutants the ‘free-running’ oscillations are about 15% shorter than the normal cycle time. There are well-known examples of such oscillations in eggs but they are rare in growing systems.