Measured O2 Consumption Research Articles

The H+/e- stoicheiometry of respiration-linked proton translocation in the cytochrome system of mitochondria.

1. The -->H(+)/e(-) quotients for proton release from mitochondria associated with electron flow from succinate and duroquinol to O(2), ferricyanide or ferricytochrome c, and from NNN'N'-tetramethyl-p-phenylenediamine+ascorbate to O(2), were determined from rate measurements of electron flow and proton translocation. 2. Care was taken to avoid, or to take into account, unrelated electron flow and proton translocation, which might take place in addition to the oxido-reductions that were the subject of our analysis. Spectrophotometric techniques were chosen to provide accurate measurement of the rate of consumption of oxidants and reductants. The rate of proton translocation was measured with fast pH meters with a precision of 10(-3) pH unit. 3. The -->H(+)/O quotient for succinate or duroquinol oxidation was, at neutral pH, 4, when computed on the basis of spectrophotometric determinations of the rate of O(2) consumption or duroquinol oxidation. Higher -->H(+)/O quotients for succinate oxidation, obtained from polarographic measurements of O(2) consumption, resulted from underestimation of the respiratory rate. 4. The -->H(+)/2e(-) quotient for electron flow from succinate and duroquinol to ferricyanide or ferricytochrome c ranged from 3.9 to 3.6. 5. Respiration elicited by NNN'N'-tetramethyl-p-phenylenediamine+ascorbate by antimycin-inhibited mitochondria resulted in extra proton release in addition to that produced for oxidation of ascorbate to dehydroascorbate. Accurate spectrophotometric measurement of respiration showed that the -->H(+)/e(-) ratio was only 0.25 and not 0.7-1.0 as obtained with the inadequate polarographic assay of respiration. Proton release was practically suppressed when mitochondria were preincubated aerobically in the absence of antimycin. Furthermore, the rate of scalar proton consumption for water production was lower than that expected from the stoicheiometry. Thus the extra proton release observed during respiration elicited by NNN'N'-tetramethyl-p-phenylenediamine+ascorbate is caused by oxidation of endogenous hydrogenated reductants. 6. It is concluded that (i) the -->H(+)/O quotient for the cytochrome system is, at neutral pH, 4 and not 6 or 8 as reported by others; (ii) all the four protons are released during electron flow from quinol to cytochrome c; (iii) the oxidase transfers electrons from cytochrome c to protons from the matrix aqueous phase and does not pump protons from the matrix to the outer aqueous phase.

Energy balance in man measured by direct and indirect calorimetry

In six 24-hr measurements of energy balance, direct and indirect calorimetry agreed within +/-3%, which is probably the range of experimental error. But in seven other 24-hr periods there was disagreement in the range of 8 to 23%, and these were usually days when the subjects ate much less than they spent metabolically. Our direct calorimeter is an insulated, water cooled suit. Continous measurements of O2 consumption and CO2 production provided data on metabolic expenditure (M) by indirect calorimetry. The 24-hr values for M matched the energy losses within +/-60 kcal (+/-3% of M) in four men who rested all day and lay down to sleep at night. Similar agreement was seen in one of the four who worked on a treadmill for 4 hr and stayed busy all day. but in another energy losses were 342 kcal greater than M (10% of M). When the experiments gave values for M minus the losses greater than +/-60 kcal, this is called "unmeasured energy". In further experiments, two subjects stayed awake for 24 hr, and their unmeasured energies were 279 and 393 kcal. The same two men, eating sparingly, also worked for 24 hr so as to double their resting metabolic expenditures; the unmeasured energies were even larger, 380 and 958 kcal. When they repeated the 24 hr of mild work, but ate nearly as much as they spent metabolically, one man was near energy balance, while the other showed an unmeasured energy of -363 kcal. Little heat storage was evident in these experiments; therefore, heat balance was present and energy balance should have been present. In the group of 13 experiments, it appeared that the greater the food deficit, the larger was the unmeasured energy (excess of metabolic expenditure over loss of energy).

Effects of respiratory apparatus on breathing pattern.

The effects of ventilatory apparatus on breathing pattern and gas exchange were studied in normal supine subjects. Using a canopy system, measurements of O2 consumption, CO2 production, tidal volume (VT), frequency (f), minute ventilation, mean inspiratory flow, and inspiratory, and expiratory time (TI and TE) were made and compared to data obtained with the use of a mask (m) and mouthpiece plus noseclip (mp + nc). Use of the m or mp + nc caused a 32.5 and 15.5% increase in VT, respectively, whereas f, TI, and TE remained unchanged. As TI did not change the increase in VT was caused entirely by increased inspiratory flow.

Insulin resistance in soleus muscle from obese Zucker rats. Involvement of several defective sites

1. The effect of insulin upon glucose transport and metabolism in soleus muscles of genetically obese (fa/fa) and heterozygote lean Zucker rats was investigated at 5-6 weeks and 10-11 weeks of age. Weight-standardized strips of soleus muscles were used rather than the intact muscle in order to circumvent problems of diffusion of substrates. 2. In younger obese rats (5-6 weeks), plasma concentrations of immunoreactive insulin were twice those of controls, whereas their circulating triacylglycerol concentrations were normal. Insulin effects upon 2-deoxyglucose uptake and glucose metabolism by soleus muscles of these rats were characterized by both a decreased sensitivity and a decrease in the maximal response of this tissue to the hormone. 3. In older obese rats (10-11 weeks), circulating concentrations of insulin and triacylglycerols were both abnormally elevated. A decrease of 25-35% in insulin-binding capacity to muscles of obese rats was observed. The soleus muscles from the older obese animals also displayed decreased sensitivity and maximal response to insulin. However, at a low insulin concentration (0.1m-i.u./ml), 2-deoxyglucose uptake by muscles of older obese rats was stimulated, but such a concentration was ineffective in stimulating glucose incorporation into glycogen, and glucose metabolism by glycolysis. 4. Endogenous lipid utilization by muscle was calculated from the measurements of O(2) consumption, and glucose oxidation to CO(2). The rate of utilization of fatty acids was normal in muscles of younger obese animals, but increased in those of the older obese rats. Increased basal concentrations of citrate, glucose 6-phosphate and glycogen were found in muscles of older obese rats and may reflect intracellular inhibition of glucose metabolism as a result of increased lipid utilization. 5. Thus several abnormalities are responsible for insulin resistance of muscles from obese Zucker rats among which we have observed decreased insulin binding, decreased glucose transport and increased utilization of endogenous fatty acid which could inhibit glucose utilization.

Instrument for Continuous Measurement of O2 Consumption and CO2 Production of Men in Hyperbaric Chambers

We describe an open circuit method for measuring O2 consumption and CO2 production suitable for use in hyperbaric atmospheres and designed to yield continuous data while allowing the critical instrumentation to remain outside the hyperbaric chamber. The subject wears a light, loosely fitting, full face mask of clear plastic, through which ambient chamber gas is drawn at either 100 l/min for rest or sleep, or 200 l/min during exercise. Samples of the chamber gases and of the mixed expired gases are bled out of the chamber, then compared in differential analyzers. The analog signals from the analyzers are conditioned, proportioned to the mask ventilation rate, totalized and integrated to yield gas volumes, then printed every 10 min. A method of calibrating the system using inflows of pure CO2 was devised for use at 1 atm absolute and also at hyperbaric pressures. Data taken by this method during a 17-day saturation dive compared well to the data obtained using conventional Douglas bag techniques.

Simultaneous measurement of glucose and O2 consumption in cell suspensions with minielectrodes.

Separation procedures which yield cell suspensions with homogeneous cell populations greatly facilitate the study of cell metabolism, but yield a limited amount of material. Multiple recording of metabolic parameters from minimum volumes is therefore useful. We have developed a method for the simultaneous recording of glucose and O2 concentrations with Polarographic electrodes in 0.26 ml suspensions of rabbit epididymal spermatozoa (RES). These cells are found “pre-separated” as a homogeneous population in the cauda epididymidis. They consume glucose and O2 and produce lactate (Murdoch and White, 1967) and so provide a useful system to test the method as well as a system in which to study the effect of perturbations on aerobic glycolysis.

Microbial metabolic activity in soil as measured by dehydrogenase determinations

The dehydrogenase technique for measuring the metabolic activity of microorganisms in soil was modified to use a 6-h, 37 degrees C incubation with either glucose of yeast extract as the electron-donating substrate. The rate of formazan production remained constant during this time interval, and cellular multiplication apparently did not occur. The technique was used to follow changes in the overall metabolic activities of microorganisms in soil undergoing incubation with a limiting concentration of added nutrient. The sequence of events was similar to that obtained by using the Warburg respirometer to measure O2 consumption. However, the major peaks of activity occurred earlier with the respirometer. This possibly is due to the lack of atmospheric CO2 during the O2 consumption measurements.

Metabolic Gas Exchange Measurement in the Premature

Accurate measurement of total body production and O2 consumption in premature infants would make possible estimates of total caloric production to guide nutritional replacement and assess adequacy of food substrate utilization. A practical method for making these measurements in extubated, premature infants following patent ductus (PDA) ligation was developed: the infant is placed in a clear plastic bag sealed except for a gas inlet opposite the face and gas and lead/tubing exit at the foot; using a computerized mass spectrometer already in use for automated respiratory monitoring in the surgical unit, O2 and CO2 concentrations are sampled at the inlet and outlet; gas flow (0.5 - 1.0 1/min/Kg) is measured by a timed Wright spirometer or Douglas Bag collection and corrected to STPD. , , RE and caloric estimates are calculated. Daily serial measurements in a 1.15 and a 1.41 Kg. infant were made for I week after FDA ligation. , averaged 2.6 = 0.8 cc/min and caloric production 17 ± 4 ana 22 ± 5 KCAL/day, both independent of actual caloric intake (range 24-100 KCAL/day) and below predicted levels. Insulin levels were normal. These low values suggest a depressed overall metabolic rate.

PO2 in the carotid body perfused and/or superfused with cell-free media

We measured with a micro-O2 electrode the tissue PO2 (PtO2) in the cat carotid body (CB) to see whether it was adequately oxygenated when perfused or superfused with artificial, cell-free (c-f) solutions (pH = 7.4; temp = 35-38 degrees C). To obtain a relative measure of O2 consumption (VO2), we also measured the rate of disappearance of O2 following stoppage of the blood flow, and compared these disappearance curves with those during stoppage of the c-f perfusion solutions. In 14 cats normal (blood perfusion) PtO2 values ranged from 10 to 104 mmHG; chi = 72 +/- 4 (SE--as used throughout). During 3 h of c-f perfusion with air-equilibrated Locke's solution, PtO2 ranged from 62 to about 160 mmHg; chi = 133 +/- 4. When perfused with Fay's equilibrated with 98% O2-2% CO2 no PtO2 values in the CB were below 300 mmHg (4 cats). In eight additional cats the CB was cleared of blood then superfused with saline equilibrated with 50% O2 underneath and air-equilibrated saline over. Less than 5% of the PtO2 values found were below 5 mmHg. We conclude that most studies on the artificially perfused or superfused CB cannot be invalidated on the basis that the preparations were hypoxic. O2 disappearance curves taken during blood perfusion were significantly faster than during c-f perfusion indicating a marked reduction in VO2 with c-f perfusion.

COMPARATIVE EFFECTS OF PROPRANOLOL AND PRACTOLOL IN THE EARLY STAGES OF EXPERIMENTAL CANINE MYOCARDIAL INFARCTION

1 The effects of propranolol and practolol, at equivalent myocardial beta-adrenoceptor blocking doses, (as assessed by the degree of shift of isoprenaline dose-response curves) were investigated in anaesthetized greyhounds before and after acute coronary artery ligation. 2 When administered intravenously to the intact close-chest dog, propranolol (0.1 mg/kg) and practolol (0.5 mg/kg) caused similar decreases in heart rate, left ventricular dP/dt max, myocardial blood flow and cardiac output. Only propranolol increased peripheral vascular resistance. 3 When administered 2-3h after acute coronary artery ligation, propranolol (0.1 mg/kg) significantly decreased blood flow in both normally perfused and ischaemic regions of the heart. There was also electrocardiographic evidence of further deterioration after propranolol; two out of seven animals died following this treatment. 4 Practolol (0.5 mg/kg) when administered after coronary artery ligation also decreased normal myocardial blood flow but flow in the ischaemic area remained unchanged. Evidence was obtained from electrocardiographic, myocardial temperature, myocardial O2 consumption and lactate measurements that the administration of practolol, in contrast to propranolol, benefited the ischaemic myocardium. 5 Analysis of the results suggests that this beneficial action of practolol may be related to at least two mechanisms. Firstly the ability of practolol to increase the period during diastole when perfusion of the subendocardium is possible, without decreasing the transventricular pressure during this period. Secondly that practolol does not unmask alpha-adrenoceptor vasoconstriction in the ischaemic region.

Adaptive cardiovascular modifications in the western chipmunks genusEutamias

Metabolic and cardiovascular parameters were studied in four western chipmunks, genusEutamias, to elucidate the mechanisms underlying the maintenance of normal aerobic metabolism while the heart rate were profoundly depressed (Jones and Wang, 1976). It was postulated that cardiovascular adaptations involving either an increase of stroke volume and/or an increase of arterial-venous oxygen difference (A-V O2) must have evolved to account for such alterations (Jones and Wang, 1976). Simultaneous measurements of O2 consumption, heart rate and A-V O2 were made in anesthetized animals at thermal neutral temperature of 25°C. The mean cardiac output ranged between 16.2–23.5 ml/min, and the calculated stroke volume was between 0.032–0.057 ml/beat, not atypical for similar sized mammals (Table 1). Measurements of heart weight as an indirect indicator for stroke volume also indicated normal stroke volume in the chipmunks (Table 2). The mean A-V O2, on the other hand, was between 5.6–10.4 vol % (Table 1), comparatively greater than the 4–6 vol % typical of resting mammals. The measured hematocrit, hemoglobin concentration, red blood cell counts, and blood volume, were within the range of values for similar sized mammals (Table 3), suggesting normal O2 capacity as well as O2 content carried in blood. Taken together, it was concluded that the major cardiovascular modification in the chipmunks while accomplishing normal aerobic metabolism under profoundly depressed heart rates is by the increased ability to extract O2 across the capillary beds. Possible mechanisms relating to this adaptation are discussed.

Life History and Energy Relations of the Giant Fairy Shrimp Branchinecta gigas Lynch 1937 (Crustacea: Anostraca)

The life cycle and energy relations of the giant fairy shrimp, Branchinecta gigas Lynch, in a turbid, aestival lake in western Canada are described for 1972. Hatching of overwintered eggs began when lake sediments thawed in April, at which time salinity was low as a result of snow runoff; hatching ceased after a few days as salt deposits redissolved and salinity of the water incresed. The population, being of almost uniform age, was treated as a single cohort. Larval and post—larval growth in length followed a sigmoid pattern that could be well described by a logistic curve. Maximum growth rates occurring at 3—4 wk of age were 2.54 mm/day for ♂ ♂ and 2.95 mm/day for ♀ ♀, representing daily length increments of 11.3% and 10.3%, respectively. Corresponding max dry weight increases were 33% of body weight per day in each case. Average max lengths of 47.7 mm for ♂ ♂ and 60.6 mm for ♀ ♀ were attained at ages of 40—45 days; max longevity was 60 days. The species is exclusively predaceous for most of its life cycle, feeding primarily upon Branchinecta mackini and Diaptomus nevadensis. Females were estimated to produce three clutches of eggs, with clutch size being proportional to total body length of the ♂, and average fecundity in 1972 was calculated at 630 eggs. Measurements of feeding rate and O2 consumption were made over 24—h periods in the lake and an energy budget was cosntructed for most of the life cycle (46 days) on the basis of logistic growth curves fitted to field data. Males assimilated 67% and ♂ ♂ 94% of ingested food, investing 23% and 22% of assimilated energy, respectively, in somatic growth. Molting losses were estimated at 5%—6%, and an extreme estimate of 14% was calcualted to represent nitrogen excretion, on the assumption of strictly carbohydrate and lipid—based metabolism. Maintenance costs were estimated at 58% in ♂ ♂ and 47% ♀ ♀. The difference (11.3%) corresponded precisely to the costs of egg production.

Continuous measurement of O2 consumption and CO2 elimination during a wakeful hypometabolic state.

A previous investigation has demonstrated that the practice of a meditational technique elicits a wakeful, hypometabolic state. Measurement of O2 consumption and CO2 elimination was made by sampling techniques; mean values of these parameters were calculated from 6-10 minute samples. The present study extends this investigation, using a recently developed method of continuous measurement of O2 consumption and CO2 elimination. Continuous measurement of these parameters permitted the determination of mean values for the entire experimental periods as well as for selected intervals and permitted the examination of the sequence of respiratory changes. The present study reports statistically significant decreases in O2 consumption of 5 per cent and CO2 elimination of 6 percent for the entire 20 minutes of the mediation period. These are lower than the sample values of 16 percent and 15 percent reported in the previous study. However, when selected intervals of the mediation period are examined, decreases in O2 consumption and CO2 elimination are comparable to those previously reported. The results are consistent with the difference between the discontinuous sampling measurement method originally employed and the continuous measurement method of the present investigation.

Zum Energieumsatz phytophager insekten im Buchenwald. I

Die Bestimmung des Energieumsatzes der Curculioniden-Populationen vonRhynchaenus fagi L.,Strophosomus (Schonherr) undOtiorrhynchus singularis L. wurde in folgenden Schritten vorgenommen:

Effects of Hypothyroidism, Hyperthyroidism, and Thyroxine on Net Synthesis of Plasma Proteins by the Isolated Perfused Rat Liver: MODULATION OF THE RESPONSE TO INSULIN PLUS CORTISOL IN THE NET SYNTHESIS OF ALBUMIN, FIBRINOGEN, α1-ACID GLYCOPROTEIN, α2-(ACUTE PHASE) GLOBULIN, AND HAPTOGLOBIN

Abstract The isolated rat liver perfused for 12 hours has been used to study effects of added thyroxine and effects of hyperthyroidism and hypothyroidism in the liver donor on net biosynthesis of five specific plasma proteins, namely, rat serum albumin, fibrinogen, α1-acid glycoprotein, α2-(acute phase) globulin, and haptoglobin. Hypothyroidism was produced either by surgical thyroidectomy or by feeding methimazole (0.5 g per kg) in the powdered diet; hyperthyroidism was induced by injecting normal rats with thyroxine (10µg/100g body weight subcutaneously per day). The metabolic status of each animal was confirmed by O2 consumption measurements. The basic perfusate consisted of washed bovine red cells suspended in Krebs-Ringer-bicarbonate solution containing bovine serum albumin (3.0 g/100 ml) to which was added nutritional (glucose, amino acids) and hormonal (cortisol, insulin) constituents. When used, thyroxine was added along with the other hormones at the start of perfusion as well as by constant infusion throughout the experiment. Livers from hyperthyroid liver donors synthesized significantly more albumin than those from hypothyroid rats; however, addition of thyroxine to the perfusion of livers from euthyroid and hyperthyroid rats decreased albumin synthesis. Fibrinogen synthesis was not altered significantly among the experimental groups studied here, nor was there any change in the phenomenon of induction, shown previously to be dependent upon the presence of cortisol. Synthesis of α1-acid glycoprotein and α2-(acute phase) globulin was somewhat higher by livers from hypothyroid rats than by those from euthyroid controls, and maximum rates occurred in hyperthyroid livers given a total of 4.0 µg of thyroxine. Haptoglobin synthesis was greater by livers from hyperthyroid rats than by those from normal and hypothyroid donors; the addition of 4.0 µg of thyroxine to the perfusate of normal and hyperthyroid livers increased haptoglobin synthesis while 22.0 µg caused a decrease. Nitrogen balance was estimated for the perfusion system in terms of net cumulative changes in amino acid nitrogen and urea nitrogen in the perfusate and bile. Hyperthyroidism in the liver donor and 4.0 µg of thyroxine in the perfusate resulted in negative nitrogen balance, simultaneously with maximum uptake of glucose and increased oxidation of l-[1-14C]lysine to 14CO2. Positive nitrogen balance was not a requirement for normal or enhanced net synthesis of specific plasma proteins; however, under conditions of extremely negative nitrogen balance, synthesis of acute phase proteins was impaired. Limited data on the dose-response relationship between thyroxine added to the perfusate and the metabolic response of the liver revealed that the addition of 2.0 µg of thyroxine at zero time plus the continuous infusion of an additional 2.0 µg over a 12-hour period elicited optimal anabolic responses.

The Diffusion and Consumption of Oxygen in Submerged Soils

AbstractSix O2 diffusion models, which included several oxygen consumption processes, were evaluated by measuring O2 consumption rates under conditions which approached the steady state and under transient‐state conditions. Consumption rates under approximately steady‐state conditions were determined by placing undisturbed lake‐bottom cores in water and measuring the decrease in O2 concentration of the water. Transient‐state consumption rates were determined from the amount of O2 gas that had to be injected above an initially reduced soil to maintain a constant O2 concentration at the soil surface. The distribution of extractable Fe in the cores was obtained by sectioning frozen soil cores and extracting the sections with NaOAc at pH 2.8 and with dithionite in EDTA.Considerable amounts of Fe2+ were found to diffuse from the reduced zone to the oxidized zone where it accumulated as precipitated Fe3+. The oxygen consumption was best described by models which included consumption by microbial respiration in the aerobic zone and oxidation of mobile and nonmobile reductants such as Fe2+. The latter components of oxygen consumption accounted for about 50% of the consumption by cores after 11 days when the cores were initially uniformly reduced.

Activity patterns and energetics of the moth, Hyalophora cecropia.

ABSTRACT The time of activity and the duration of active periods (flight) of moths of the species Hyalophora cecropia has been determined by monitoring thoracic temperature. The metabolic cost of flight per day and per adult life has been determined directly by measuring O2 consumption and indirectly by analysis of cooling curves of individual moths. An energy balance sheet has been derived which gives the metabolic cost of flight and maintenance (during torpor) over the insect’ s adult life. The metabolic stores mobilized for daily activity appear to be fixed and independent of air temperature. This mobilization of fat stores may be under hormonal control. It is metabolically more expensive for moths to be active at low air temperatures. The number and duration of active periods at low air temperatures is reduced, but, the metabolic expenditure for activity is equal to that of animals held at higher air temperatures. Females have a smaller total energy reserve than males. The number of active periods per day is not significantly different between the sexes at any given temperature, but in females the active periods are significantly shorter in duration. The flight speed has been determined, and estimates of the flight range per day and per adult life have been calculated. The ecology of H. cecropia has been discussed with respect to the timing and duration of active periods, the range and speed of flight, and the energetic cost of flight and maintenance metabolism.

Estimating oxygen consumption from body length for some chironomid larvae

The relationship between oxygen consumption and body length was determined for eight larval chironomid species in Bear Lake, Utah-Idaho. Respiration was measured by the micro-Winkler method in 1-cc tuberculin syringes filled with lake water and lowered to lake bottom. A total of 144 measurements of O2 consumption was made.

Oxygen consumption and body temperature of the Chuditch (Dasyurus geoffroii)

The average relation between O2 consumption rate and ambient temperature in the range 9–39°C for five adult litter‐mates was found to be y= 36.237–3.6821 x+ 0.26685 x2—0.0094468 x3+ 0.00011974 x4 where y is the O2 consumption rate in ml./kg min and x is the ambient temperature in °C. The O2 consumption rates of females showed a much greater variation about this regression than did the rates of males.This regression estimates the minimum O2 consumption to occur at an ambient temperature of 31.5°C but scatter diagrams show the thermal neutral range to extend from about 28 to 33°C.Twenty‐six oxygen consumption rates measured at 30°C (in the thermal neutral range) had a mean value of 67% of those predicted for eutherians of similar body weights but the range extended from 40 to 105%. Prolonged (13 to 28 hours) O2 consumption measurements at the same temperature show that, in the absence of activity, comparatively low O2 consumption rates are maintained for long periods.The linear regression equation relating simultaneous O2 consumption rates and colonic temperatures measured at an ambient temperature of 30°C estimates that O2 consumption will increase from 40 to 105% of that predicted when body temperature is raised from 34.5 to 38.7°C; and furthermore that an O2 consumption rate of 67% of the predicted should occur at a body temperature of 36.2°C.Animals kept in small cages at an ambient temperature of 30°C were found to have mean colonic temperatures of about 34.9°C during the day when they were resting and 37.4°C in the early evening when they were active. When kept at ambient temperatures lower than the thermal neutral a similar daily cycle in colonic temperature was found but the females showed a much larger variation about the daily trend than did males.The low O2 consumption rates maintained during inactivity and a lack of strict thermoregulation result in a relatively low body temperature and a considerable saving in metabolic energy is thereby effected. The higher colonic temperatures reached in the evening result mainly from the higher energy usage during acitvity.

Lebersauerstoffverbrauch kalt- und warmakklimatisierter Ratten und Faktoren, welche den oxydativen Leberstoffwechsel regulieren

1. Liver thermogenesis was determined by measuring the oxidative metabolism of isolated perfused rat liver. 2. Metabolism of isolated liver decreases during the perfusion experiment even when perfusion conditions are maintained constant. This decrease of metabolism is caused by changed blood composition occuring in the course of its recirculation. It can be concluded that only the highest level of oxygen consumption of isolated liver measured at the beginning of the perfusion experiment or after blood exchange during the experiment corresponds to the level of resting liver metabolism in vivo. On the basis of this finding it is necessary to assume that resting liver metabolism is much higher (about 6 to 8 ml O2/g of liver/hour) than was previously thought as a result of the measurement of O2 consumption of liver slices. 3. Livers and blood of rats (Sprague-Dawley strain) acclimated to warm (30°) or cold (6° C) were used. The average resting O2 consumption of liver isolated from cold-acclimated rats (7.8 ml O2/g/hour) differs significantly from the liver O2 consumption of warm-acclimated rats (6.2 ml O2/g/hour). Therefore, liver metabolism amounts to 19.3% of the basal metabolism in warm-acclimated and to 26.5% in cold-acclimated rats. Under basal conditions livers of rats acclimated to 6° C produce about 35% more heat than livers of rats acclimated to 30° C. 4. The utilization of liver thermogenesis for thermoregulatory purposes on exposure of the organism to cold can be estimated only roughly on the basis of changes of factors affecting the liver oxidative metabolism. Oxygen consumption of isolated perfused liver depends on perfusion factors connected with supplying the liver with oxygen, the rate of liver blood flow, temperature of environment and on metabolic factors connected with the content of metabolic substrates and hormones in the perfusion medium. These factors can increase the resting oxygen consumption of the liver. 5. We assume the existence of a thermogenetic mechanism, consisting of the hormone influence on the liver metabolism via changes in substrates concentration in the blood and by blood flow changes. However, there is some evidence that the quantiative significance of this thermogenetic mechanism is restricted.