Polarographic determination of total oxygen content in small blood samples

Insufficient supply of reducing equivalents to the respiratory chain in cerebral cortex during severe insulin-induced hypoglycemia in cats

The ability of endogenous substrates in brain to substitute for glucose as sources for energy metabolism during insulin-induced hypoglycemia was studied. The ratio of the arteriovenous difference of glucose to the arteriovenous difference of oxygen in the cerebral cortex was measured during progressive hypoglycemia in paralyzed, artificially ventilated cats that were anesthetized with pentobarbital sodium and nitrous oxide. The ratio did not change when blood glucose fell from a mean of 7.68 to approximately 2 mumol/ml. Below 2 mumol/ml the ratio decreased, indicating that substrates other than the glucose supplied by the blood were being utilized. In another series of experiments, changes in the redox state of respiratory chain NAD were monitored from the cerebral cortex using microfluorometry during the onset of hypoglycemia and the recovery. Hypoglycemia severe enough to produce isoelectric EEG was accompanied by an oxidation of NADH, demonstrating that the supply of reducing equivalents to the respiratory chain was decreased. Recovery from hypoglycemia, produced by intravenous glucose injections, was accompanied by an increase in blood glucose concentrations, the return of EEG activity, and a decrease in the NAD/NADH ratio. When blood glucose concentration reached 2.23 during the recovery, further increases in blood glucose had no effect on the redox state of NAD. Although alternative substrates appear to be utilized for energy metabolism during severe hypoglycemia, they cannot fully replace glucose as the source of reducing equivalent to the respiratory chain.

A venous outflow method for measurement of rapid changes of the cerebral blood flow and oxygen consumption in the rat

A technique for continuous measurement of cerebral venous outflow in the rat is described. The method involves cannulation of one retroglenoid vein close to its exit from the skull, and diversion of cerebral venous blood through a closed extracorporal circuit with a drop recording device, the blood being returned to the central venous circulation via a catheter in the external jugular vein. Occlusion of the contralateral retroglenoid vein increases measured flow and minimizes extracerebral contamination of the diverted cerebral venous blood. The venous outflow system is not further isolated from cerebral or potential extracerebral collaterals. Thus, the mass of tissue drained cannot be exactly defined anatomically. However, the experiments involving changes of PP, arterial CO2 tension, and induction of epileptic seizure activity, and simultaneous indirect measurements with radioactive tracer technique, indicate that significant extracerebral contamination does not occur and that in short term measurements the venous outflow represents cerebral blood flow (CBF) in a constant mass of (dorsal and central, mainly forebrain) cerebral tissue. Measurement of arterial blood pressure and pressure in the cisterna magna allows calculation of cerebral perfusion pressure (PP). By simultaneous measurement of arterial and cerebral venous oxygen content changes in cerebral oxygen consumption (CMRO2) can be calculated. The method has been applied to document several situations of transient CBF and CMRO2 changes.

Reduction of the cerebral protective effect of hypothermia by oligemic hypotension during hypoxia in the rat

The effect of arterial hypotension on cerebral cortical tissue levels of adenosine triphosphate (ATP), phosphocreatine (PGr), lactate, and reduced nicotinamide adenine dinucleotide (NADH) was studied in male Wistar rats with unilateral carotid ligation exposed to arterial by hypoxia (PaO2 25 torr) for 20 min. while the body temperature was maintained at 32 degrees C and 27 degrees C. Brain metabolite levels were normal in normotensive hypothermic animals exposed to hypoxia, but reduction in arterial pressure to 75 torr caused a significant (p less than 0.05) decrease in ATP and PCr values and a significant increase in lactate and NADH levels. These changes were comparable to those of normothermic normotensive, hypoxic animals. Furthermore, there was no significant differences in the brain metabolite levels between the two hypotensive hypoxic groups. These results indicate that arterial hypotension severely alters the cerebral protective effect of hypothermia against injury caused by hypoxia, and that further reduction in body temperature (from 32 degrees C to 27 degrees C) will not prevent the harmful effect of hypoxia upon the brain in hypotensive rats.

The effect of indomethacin on cerebral blood flow and oxygen consumption in the rat at normal and increased carbon dioxide tensions

The effect of the fatty acid cyclo-oxygenase inhibitor indomethacin on cerebral blood flow (CBF) and the metabolic rate for oxygen (CMRO2) was studied in paralyzed and artificially ventilated rats. In normocapnic animals, the drug (10 mg.kg-1i.v.) reduced CBF to 50% of control without a measurable effect on CMRO2. During hypercapnia (PaCO2 70-80 mmHg) the increase in CBF was reduced by about 80% but CMRO2 remained unchanged. Autoradiographic evaluation of local CBF in 20 brain structures indicated that the reduction in CBF was relatively uniform throughout the brain. Dose response curves showed that an effect on CBF was evident already at an indomethacin dose of 1 mg.kg-1 and maximal effects were obtained with 3-5 mg.kg-1. Following i.v. injection of the drug reduction in CBF was observed already after 10 s and the full response occurred after 1-2 min. It is concluded that metabolites of arachidonic acid, possibly mainly prostacyclin, are powerful modulators of normal cerebrovascular tone, and help to mediate the CBF response to increased CO2 tensions. However, since indomethacin does not modify the circulatory response in other conditions with increased CBF these substances do not qualify as general coupling factors controlling CBF in physiological or pathological states.

Insulin increases glucose transfer across the blood-brain barrier in man

The influence of insulin on unidirectional flux of glucose across the blood-brain barrier and on net uptake of glucose by the brain was investigated in seven fasting patients. The unidirectional extraction, E, of [14C]D-glucose was determined using 36Cl- as an intravascular reference, by the indicator dilution method. 0.4 U insulin/kg body wt was infused intravenously over 30 min while blood glucose was maintained constant by glucose infusion. Six determinations were made in each patient, two before, two during insulin infusion, and two after. In connection with each blood-brain barrier study, arterial and cerebral venous samples were taken for measurement of glucose, oxygen, insulin, K+, and phosphate. Cerebral blood flow (CBF) was measured in each patient. The main finding was an increased extraction of glucose from 14 to 21% and a highly significant increase in unidirectional flux (CBF X unidirectional extraction X arterial glucose concentration) from 0.46 to 0.66 mumol/g X min during insulin infusion (plasma insulin approximately 1,500 microU/ml). The net brain uptake of glucose (CBF X arterio-venous difference for glucose) as unaltered during the investigation period of 45 min, which is too short a time for insulin to penetrate the barrier. It follows that the backflux of glucose from the brain was increased during insulin application. The effect of insulin might be a speeding up of the glucose carrier in analogy to heart muscle.

Effects of indomethacin on cerebral blood flow and oxygen consumption in barbiturate-anesthetized Normocapnic and hypercapnic rats

Although results obtained in baboons and rats have demonstrated that the fatty acid cyclo-oxygenase inhibitor indomethacin reduces cerebral blood flow (CBF) under control conditions and markedly attenuates the CBF response to hypercapnia, nonconfirmatory results have been obtained in rabbits and cats. Since these latter studies were carried out under barbiturate anesthesia, we tested the effect of indomethacin (10 mg kg-1) on CBF and cerebral oxygen consumption in rats anesthetized with 150 mg kg-1 of phenobarbital. At normocapnia the barbiturate reduced CBF, measured with a 133Xe modification of the Kety-Schmidt technique, to about 50% of nitrous oxide control values as previously determined with a similar technique. At this CBF level, indomethacin induced a small, albeit highly significant decrease in CBF. We suggest that a reduction of this magnitude will escape detection with some CBF techniques in current use. Indomethacin induced a highly significant decrease in CBF during hypercapnia, demonstrating that the barbiturate does not eliminate the effect of indomethacin on CO2 responsiveness. The magnitude of the reduction in CO2 response was so large that is should be detected with most methods for measuring CBF. A comparison with previous data on animals under 70% N2O demonstrated that phenobarbital reduced the CO2 responsiveness. defined as the ratio deltaCBF/deltaPCO2, to 39% of that observed under nitrous oxide analgesia. With both types of anesthesia, indomethacin curtailed the CO2 responsiveness 4- to 5-fold.

A gas chromatographic technique for determination of blood flow and metabolism in individual organs (with special reference to the heart)

A method for determining blood flow, oxygen uptake and carbon dioxide release in individual organs is presented. For blood flow measurement an inert gas (N2O) technique was used. Blood contents of O2, CO2 and N2O were measured by a gas chromatographic method with use of a special vacuum chamber for extracting the gases from blood. There was a strong correlation between the contents of O2 determined by the gas chromatographic and a spectophotometric method (correlation coefficient 0.953). Good agreement was found between CO2 in gas samples analysed by the Scholander technique and by the gas chromatographic method. A correlation coefficient of 0.998 was obtained between the N2O content calculated theoretically and that determined by the gas chromatographic technique. The new technique presented makes it possible to calculate blood flow in ml/100 g tissue/min, O2 uptake and CO2 production in an individual organ, whereby the predominant type of metabolism in the organ can be ascertained.

Cerebral metabolic and circulatory changes in the rat during sustained seizures induced by DL-homocysteine

Sustained, generalized seizure activity was induced in anaesthetized (70% N2O), paralyzed and artifically ventilated rats by i.p. DL-homocysteine thiolactone in a dose of 11 mmol/kg. Epileptic discharges in the EEG were accompanied by marked perturbation of tissue metabolites. There was a fall in phosphocreatine concentration to 40% of control but only moderate changes in adenine nucleotides, a marked rise in lactate concentration, and a pronounced increase in the lactate/pyruvate ratio. Excessive amounts of dihydroxyacetone phosphate (and glyceraldehyde phosphate) accumulated, indicating that depletion of NAD+ occurred. There was marked accumulation of ammonia, glutamine and alanine, and reduction in glutamate and aspartate concentrations. Administration of a subconvulsive dose of homocysteine (7.5 mmol/kg) gave rise to changes in ammonia and amino acids, qualitatively similar to those occurring during seizures. It is concluded that although changes in the metabolites of the energy reserve were mainly caused by the induced seizures, those affecting amino acid concentrations were significantly influenced by accumulation of ammonia, secondary to metabolism of injected homocysteine. Cerebral blood flow (CBF) and oxygen utilization (CMRO2) were measured during sustained seizures. CMRO2 rose to 150% of control, with a corresponding increase in CBF.

Cerebral blood flow and oxygen consumption during ethanol withdrawal in the rat

The ethanol withdrawal syndrome in man and animals is characterized by signs of CNS hyperactivity although a direct measurement of a physiological variable reflecting this CNS hyperactivity has never been performed in untreated man or in animals. We induced ethanol dependence in the rat by means of intragastric intubation with a 20% w/v ethanol solution, thus keeping the animals in a state of continuous severe intoxication for 3--4 days; during the subsequent state of withdrawal characterized by tremor, rigidity, stereotyped movements and general seizures a 25% increase in cerebral oxygen consumption (CMRO2) could be measured; this increase was not due to catecholamines originating from adrenal medulla as adrenomedullectomized animals showed a similar increase in CMRO2 (28%); the withdrawing animals showed a corresponding cerebral blood flow (CBF) increase. The elevated CMRO2 and CBF could be reduced to normal by administration of a beta-adrenergic receptor blocker (propranolol 2 mg/kg i.v.), and hence the increased CMRO2 during ethanol withdrawal could be related to catecholaminergic systems in the brain, e.g. the noradrenergic locus coeruleus system which is anatomically well suited as a general activating system. This interpretation is supported by the earlier neurochemical finding of an increased cerebral noradrenaline turnover during ethanol withdrawal. The exact mechanism underlying the increased cerebral oxygen consumption during ethanol withdrawal and the effect of propranolol on cerebral function during this condition remains to be clarified.

Adaptive changes in cerebral blood flow and oxygen consumption during ethanol intoxication in the rat

Cerebral blood flow (CBF) and oxygen consumption (CMRO2) were measured during acute and long-term ethanol intoxication in the rat. The purpose was to investigate whether the adaptive changes (development of tolerance) occurring in the CNS during ethanol intoxication were associated with changes in CBF and/or CMRO2. Consistent with other studies we found that acute severe ethanol intoxication (median blood alcohol concentration (BAC = 5.4 mg/ml)) caused a significant decrease in CBF and CMRO2. After 3-4 days of severe intoxication (BAC of 6.6 mg/ml) these physiological variables were less affected indicating that functional tolerance had developed: CMRO2 and CBF during acute ethanol intoxication were 9.3 ml/100 g/min and 60 ml/100 g/min respectively; after the long term intoxication period these variables reached 11.2 ml/100 g/min and 78 ml/100 g/min respectively, i.e. values not significantly lower than those of the control group. After induction of hypercapnia (PaCO2 about 80 mmHg) CBF increased by 360% in the control group; in the acutely intoxicated group CBF increased by only 127% and in the long term intoxicated group by 203% indicating that the cerebrovascular CO2-reactivity had also adapted to the ethanol intoxication. It is concluded that adaptive changes of the CNS to chronic ethanol intoxication comprise alterations in CMRO2, CBF and cerebrovascular reactivity.

Influence of chlormethiazole on cerebral blood flow and oxygen consumption in the rat, and its effect on the recovery of cortical energy metabolism after pronounced, incomplete ischaemia

The influence of an anaesthetic dose of chlormethiazole (Hemineurin) on blood flow (CBF) and oxygen consumption (CMRO2) in the rat brain was investigated. In spontaneously breathing animals a dose of 160 mg . kg-1 of chlormethiazole, infused i.v., induced a state close to surgical anaesthesia. In paralyzed animals, the same dose decreased CBF and CMRO2 to about 60% of control, an effect similar to that observed after an anaesthetic dose of phenobarbitone. Neither a protective nor a detrimental effect of chlormethiazole could be demonstrated when the drug was given during reversible and pronounced, incomplete ischaemia, as evaluated from the postischaemic tissue concentrations of labile phosphates (PCr, ATP, ADP, AMP) and of lactate and pyruvate. It is concluded that protection in this situation (as earlier shown with phenobarbitone) must, at least partly, be related to other mechanisms than a depression of metabolism.

The effect of propranolol on cerebral oxygen consumption and blood flow in the rat: measurements during normocapnia and hypercapnia

The cerebral blood flow (CBF) and cerebral oxygen consumption (CMRO2) in the rat during normocapnia and hypercapnia were investigated by means of the intraarterial 133Xenon injection technique; measurements were performed during normocapnia and hypercapnia and the effect of propranolol upon CBF and CMRO2 was studied. The CBF technique applied to rat yield reliable results even in high flow situations. A steady state period of only 10--15 s is all that is necessary to obtain the initial slope of the 133Xenon clearance curve from which CBF is calculated and measurements may be repeated within minutes. Hypercapnia caused an increase in CMRO2 of 35% which confirms the findings of other investigators. The beta-adrenergic receptor blocker propranolol (2 mg per kg i.v.) prevented this increase and could eliminate an increase in CMRO2 already induced; this indicates that CO2 affects adrenergic mechanisms. Although propranolol eliminated the CMRO2 response to hypercapnia, it only reduced the CBF response; this dissociation of CBF and CMRO2 response occurred probably because the beta-receptor blockage only eliminated a CBF increase mediated through an increased CMRO2 (cellular response) whereas a direct CO2 effect upon the arterioles (vascular response) persisted.

Effects of bicuculline-induced seizures on cerebral metabolism and circulation of rats rendered hypoglycemic by starvation

To evaluate the effects of substrate deficiency on cerebral function, metabolism, and blood flow during seizures, rats were injected intravenously with bicuculline (1.2 mg.kg-1) following a 24-hour period of starvation. During the course of seizures, blood glucose concentrations fell, and when they were reduced to below about 3 mumol.gm-1, cerebral function, metabolism, and blood flow altered. Changes in function involved the transition of an electroencephalographic pattern of bursts and suppression into one of frequent or sparse single spikes. Oxygen consumption, which initially increased at least twofold, fell toward normal or subnormal values in the single-spike period. Cortical blood flow was markedly reduced, and there was an attenuated response to carbon dioxide administration. Simultaneously, a small but clear fall was detected in the cerebral phosphorylation potential, and concentrations of glycolytic metabolites (including lactate) and citric acid cycle intermediates were reduced. Changes in amino acids and ammonia were somewhat similar to those observed in insulin-induced hypoglycemia, but since the amino acid pool did not fall, the experiments failed to give evidence that amino acids serve as oxidative substrates. The perturbation of cerebral energy state (and of levels of carbohydrate substrates and amino acids) was reversed by glucose administration; but since neither this procedure nor additional bicuculline injections could cause resumption of continuous seizure activity, the results suggest that cellular substrate depletion may have given rise to a sustained disturbance of synaptic transmission.

Additive effects of hypothermia and phenobarbitol upon cerebral oxygen consumption in the rat

The quantitative effects of a combination of hypothermia and phenobarbital on cerebral oxygen uptake (CMRo2) was studied in rats, curarized and artificially ventilated with 70% nitrous oxide in oxygen. Cerebral blood flow (CBF) was measured with a modification of the KETY & SCHMIDT (1948) technique, using 133xenon as a tracer. Arteriovenous difference in oxygen content over the brain was measured and CMRo2 was calculated. Four groups were studied. Group 1 was a control group. The three experimental groups were injected with phenobarbital intraperitoneally: Group 2 with 50 mg/kg body weight; Group 3 with 150 mg/kg; and Group 4 with 50 mg/kg of phenobarbital, and, in addition, body temperature was lowered to 32 degrees C in this group. CMRo2 in groups 2, 3 and 4 was reduced by 22, 37 and 43%, respectively, compared to Group 1. The changes in CBF were of the same magnitude. In a previous study we have found that CMRo2 decreases by 5% per 1 degree C decrease in body temperature. The value for CMRo2 in Group 4 is close to the value obtained if the effect of 50 mg/kg body weight of phenobarbital on CMRo2 is added to the effect of a temperature reduction of 5 degrees C. It is concluded that the effects of barbiturates and hypothermia on CMRo2 are additive.

Influence of "lytic cocktail" on blood flow and oxygen consumption in the rat brain

The influence of a sedative dose of "lytic cocktail" (chlorpromazine, promethazine and pethidine) on cerebral blood flow (CBF) and oxygen consumjtion (CMRO2) was tested in artificially ventilated rats, maintained on either 70% N2 or 70% N2O. When given alone, the lytic cocktail had no significant effect on CBF or CMRO2. However, in the presence of nitrous oxide there was a 25% reduction in blood flow and oxygen consumption.

Influence of intravenously administered catecholamines on cerebral oxygen consumption and blood flow in the rat

In order to study effects of catecholamines on cerebral oxygen consumption (CMRo2) and blood flow (CBF), rats maintained on 75% N2O and 25% O2 were infused i.v. with noradrenaline (2, 5, or 8 microgram.kg-1.min-1) or adrenaline (2 or 8 microgram.kg-1.min-1) for 10 min before CBF and CMRo2 were measured. In about 50% of animals infused with 2--8 microgram.kg-1.min-1 of noradrenaline, CMRo2 (and CBF) rose. However, there was no dose-dependent response, and CMRo2 did not exceed 150% of control. The effects of noradrenaline in a dose of 5 microgram.kg-1.min-1 on CMRo2 and CBF were blocked by propranolol (2.5 mg.kg-1). In animals infused with adrenaline (8 microgram.kg-1.min-1) CMRo2 was doubled and, in many, CBF rose 4- to 6-fold. It is concluded that, when given in sufficient amounts, catecholamines have pronounced effects on cerebral metabolism and blood flow, the effects of adrenaline on CMRo2 and CBF resembling those observed in status epilepticus.

Circulatory and metabolic effects in the brain induced by amphetamine sulphate

Cerebral circulatory and metabolic effects of amphetamine sulphate (0.25-25 mg.kg-1 i.v. or 5-10 mg.kg-1 i.p.) were studied in anesthetized, paralyzed and artifically ventilated rats. Cerebral blood flow (CBF) was measured with a modification of the Kety and Schmidt (1948) technique, and oxygen consumption (CMRO2) was calculated from CBF and arteriovenous differences in oxygen content. Regional CBF was evaluated from the uptake of 14C-ethanol. Cortical metabolites were analysed following freezing of tissue in situ. Amphetamine administration gave rise to a marked increase in CBF that was doubled following 0.25 mg.kg-1 and increased 4-fold following 15 mg.kg-1. However, such excessive increases in flow were confined to frontoparietal cortical regions, while other cortical or subcortical areas showed more moderate hyperemia. The increase in CBF was unrelated to changes in arterial PCO2, blood pressure, or tissue lactate content. CMRO2 increased by 30% to 95% depending on dose and rat strain used. At all doses employed, amphetamine gave rise to glycogenolysis in cerebral cortex but, in animals studied within the first 30 min after 5 mg.kg-1, or less, the only other changes were increases in glucose-6-phosphate and alpha-ketoglutarate concentrations. When the dose was increased to 15 mg.kg-1, there were moderate increased in lactate concentration and lactate/pyruvate ratio. Sixty min after 5 mg.kg-1 there were increases in tissue concentrations of pyruvate, citric acid cycle intermediates and alanine, as well.

Reduction of cerebral blood flow and oxygen consumption with a combination of barbiturate anaesthesia and induced hypothermia in the rat

The influence of phenobarbitone anaesthesia on cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) during hypothermia (23 degrees C & 27 degrees C) was studied in the rat, using a modification of the Kety & Schmidt (1948) technique and arterio-venous differences for oxygen. Phenobarbitone (150 mg/kg) was found to decrease CMRo2 by 40-60% during hypothermia, when compared to N2O anaesthesia. At a body temperature of 23 degrees C, and during phenobarbitone anaesthesia, CMRo2 was reduced to about 15% of normal control value (about 10.3 ml.100g-1). CBF was reduced to about 50% of the phenobarbitone control value but was similar to the value obtained with N2O anaesthesia at 22 degrees C. It is concluded that the combination of phenobarbitone anaesthesia and hypothermia results in a more pronounced reduction in cerebral metablic rate for oxygen than can be achieved by administration of barbiturates to normothermic animals, or by reducing body temperature by 15 degrees C during superficial anaesthesia.

Postischemic cerebral blood flow and oxygen utilization rate in rats anesthetized with nitrous oxide or phenobarbital

The present experiments were undertaken to measure postischemic regional cerebral blood flow (rCBF) and oxygen utilization rate (CMRo2) in rats anesthetized with either 70% N2O or phenobarbital (150 mg x kg-1). In previous studies we have found that extensive restitution of cerbral energy metabolites occurs after 30 min of complete cerebral ischemia irrespective of the type of anesthesia used. Following 30 min of pronounced, incomplete ischemia, however, a comparable restitution of cerebral energy state was obtained in deeply anesthetized (phenobarbital 150 mg x kg-1) but not in superfically anesthetized (70% N2O) rats. The objectives of the present investigation were (1) to study whether postischemic cerebral blood flow was higher in barbiturate-anesthetized animals during the initial recirculation period, and (2) to investigate if the protective effects of phenobarbital previously observed could be attributed to a decrease in CMRo2. In both groups of animals a considerable variability in postischemic rCBF was observed between different animals. However, no signs of gross inhomogeneity in blood flow were found and no consistent differences in flow values between the two groups of animals were observed. Since the measured postischemic CMRo2 were identical in both groups of animals and since cerebral venous oxygen contents were above normal the results leave little support to the assumption that, in the present model of transient, incomplete cerebral ischemia, failure of recovery of cerebral metabolism (N2O group) is primarily due to impaired recirculation, nor do they indicate that the protective effects of barbiturates is due to their ability to reduce rate of cerebral energy utilization.

Experimental head injury in the rat. Part 3: Cerebral blood flow and oxygen consumption after concussive impact acceleration

Cerebral blood flow (CBF) and oxygen consumption (CMRO2) were determined during timmediate posttraumatic period in rats subjected to concussive impact acceleration. According to previous studies an impact of 9 m/sec velocity elicited typical and marked symptoms of experimental concussion and often a prolonged comatose state, accompanied by cerebral metabolic signs of energy failure. During the immediate concussive response there was an increase of the CBF, followed within the next few minutes by a decrease to about one-third of normal flow, and then by a tendency toward normalization of flow 20 to 40 minutes posttrauma. Simultaneous measurements of cerebral oxygen extraction indicated an increase of the CMRO2 during the first minute. During the ischemic phase oxygen extraction increased but the lowest CBF values were only partially compensated for, and normal oxygen availability could not be maintained. The combined data, including cerebrospinal fluid pressure measurements, indicated primary cerebrovascular effects of the concussive trauma. These vasomotor effects may induce critical cerebral ischemia and thus profoundly influence posttraumatic cerebral function, and cause irreversible damage.

Purification of human granulocyte catalase in chronic myeloid leukemia

Human granulocyte catalase (hydrogen peroxide:hydrogen peroxide oxidoreductase, EC 1.11.1.6) was purified from chronic myeloid leukemia cells. The purification procedure included heat precipitation, ammonium sulphate fractionation, DEAE-Sephadex chromatography, gel chromatography on Sephadex G-200 and isoelectric focusing with an approximate yield of 30% and a 1000-fold purification. The molecular weight of the subunit obtained by sodium dodecyl sulphate electrophoresis was 65 800. So20,w was 11.6 +/- 0.24. The pH-optimum was 6.6-6.7 and the spectrum showed a major peak at 405 nm and shoulders at 500, 540 and 625 nm typical for catalase. The electrophoretic mobility was towards the anode at pH 8.6 and identical to normal granulocyte and erythrocyte catalase. These three species of catalase gave the reaction of identity on immunodiffusion and crossed immunoelectrophoresis. The content of catalase and its activity of isolated granulocytes were approximately identical in normal and chronic myeloid leukemia granulocytes while the specific activity of leukemic catalase was higher than normal. No difference in catalase content was found between mature and immature leukemic granulocytes.

A catecholamine-mediated increase in cerebral oxygen uptake during immobilisation stress in rats

Anxiety and grave apprehension have been supposed to increase cerebral metabolism, and it has earlier been suggested that intravenous infusion of adrenaline may increase cerebral blood flow (CBF) and cerebral oxygen consumption (CMR02). In an experimental model on rats, it could be shown that immobilisation stress increased CBF and CMR02 after 5 min (about 150% of control values) and 30 min (about 190% of control values). By previous adrenalectomy or by administration of a beta-receptor blocker (propranolol, 1.4 mg/kg) the changes in CBF and CMR02 could be prevented. It is concluded that the excessive increase in CBF and CMR02 was mediated via release of catecholamines from the adrenal glands.

Restoration of oxygen uptake and blood flow in the rat cerebral cortex after halothane anaesthesia

Halothane decreases both the cerebral blood flow (CBF) and the cerebral metabolic rate for oxygen (CMRO2) when given in anaesthetic doses. A recent report (GJEDDE & HINDFELT 1975) suggests that when halothane is administered to rats for 1 hour, CBF and CMRO2 are depressed by about 30 and 40%, respectively, for as long as 4 hours after discontinuation of the halothane anaesthesia. In the present study rats were anaesthetized with 1% halothane for 1 hour, and CBF and CMRO2 were measured at the end of a 30 min recovery period, during which 70% N2O was administered. Comparison with animals maintained on 70% N2O throughout the entire 90 min period showed that previous halothane anaesthesia had no effects on CBF or CMRO2.

The effect of halothane anaesthesia upon cerebral oxygen consumption in the rat

The influence of halothane (0.6 and 2%) upon cerebral (cortical) blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) was studied in artificially ventilated rats, using a modified technique of Kety & Schmidt (1948). The values obtained in halothane anaesthesia were compared to those recorded in nitrous oxide anaesthesia, or to those measured in unanesthetized animals given an analgesic drug (fentanyl citrate). Although it could be confirmed that halothane induces vasodilatation in the brain, there were relatively small differences in CBF between the groups. The results demonstrate that, in the rat, halothane depresses CMRo2 in a dose-dependent way. With 0.6% halothane, CMRo2 was reduced by 20-30% and, with 2% halothane, CMRo2 was reduced by about 50%. Thus, in the rat the effect of 2% halothane upon metabolic rate is comparable to that observed in barbiturate anaesthesia.

The effect of nitrous oxide on oxygen consumption and blood flow in the cerebral cortex of the rat

The effect of 70% nitrous oxide upon cerebral oxygen consumption (CMRo2) and cerebral blood flow (CBF) was studied in artificially ventilated rats. The control groups consisted of unanaesthetized animals in which a stress-induced increase in CMRo2 and CBF was prevented by previous adrenalectomy, or by administration of a beta blocker (propranolol). There were no significant differences in CMRo2 between animals ventilated with either N2O or N2. It is concluded that if nitrous oxide depresses cerebral metabolism the depression cannot exceed 10%.

A method for determining blood flow and oxygen consumption in the rat brain

Cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) were measured in rats under nitrous oxide anaesthesia, using a 133Xenon modification of the Kety and Schmidt inert gas technique with sampling of cerebral venous blood from the retroglenoid vein. Extracerebral contamination of the venous blood sampled was studied by comparing the rates at which the activity of 133Xenon decreased in blood and tissues. Contamination was avoided by gentle compression of the contralateral retroglenoid vein during sampling. CBF and CMRo2 of the rat brain were 80+/-2 and 7.6+/-0.2 ml-(100g)-1-min-1, respectively. These values are about 25% lower than those previously obtained for cerebral cortical tissue under similar conditions. Induced hypercapnia (Paco2 about 70 mm Hg) or hypocapnia (Paco2 15-20 mm Hg) gave rise to expected changes in CBF but did not alter CMRo2. The CMRo2 of the rat brain is at least twice that of the human brain. This species difference, which is similar to that previously reported for the oxygen uptake of cerebral tissue in vitro, probably reflects on inverse relationship between brain weight and neuronal packing density.

Influence of changes in arterial PCO2 on cerebral blood flow and cerebral energy state during hypothermia in the rat

In order to study the relationship between arterial PCO2 and cerebral blood flow (CBF) in hypothermia, the body temperature of artifically ventilated rats was decreased to 22 degreesC, and changes in CBF were evaluated from arteriovenous differences in oxygen content (AVDO2) at PaCO2 values of 15, 30, 40 and 60 mm Hg. The results were compared to those obtained at normal body temperature (37 degrees C) over the PaCO2 range 15-60 mm Hg. Separate experiments were performed to evaluate CBF and CMRO2 at 22 degrees C and a PaCO2 of 15 mm Hg, using an inert gas technique for CBF. The tissue contents of phosphocreatine, ATP, ADP, AMP and lactate were measured in hypothermic animals at PaCO2 values of 15, 30 and 60 mm Hg. The results showed that changes in CBF were of the same relative magnitude in hypothermia and normothermia when PaCO2 was increased from about 35 to about 60 mm Hg. However, with a decrease in PaCO2 the reduction in CBF was much more pronounced in hypothermia, and at PaCO2 15 Mm Hg CBF was less then 20% of the value measured in normothermic and normocapnic animals. The results of the metabolite measurements gave no evidence of tissue hypoxia in spite of the pronounced reduction in CBF. Although the results demonstrate that the brain of a hypothermic animal is protected against the harmful effects of a lowered CBF, it may not warrant recommending hyperventilation in clinical cases of hypothermia, especially not in patients with arteriosclerosis or cerebrovascular diseases.

The influence of acute normovolemic anemia on cerebral blood flow and oxygen consumption of anesthetized rats

The influence of acute normovolemic anemia on cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) was studied in normocapnic rats under nitrous oxide anaesthesia. The arterial hemoglobin content was reduced to values of about 12, 9, 6 and 3 g.(100 ml)(-1) by arterial bleeding and substitution with equal volumes of homolgous plasma. The CBF increased in proportion to the reduction in hemoglobin content to reach values of 500-600 per cent of normal at extreme degrees of anemia, but CMR02 remained unchanged. Cerebral venous PO2 and oxygen saturation did not decrease below normal values, indicating that tissue hypoxia did not develop. However, since the increase in CBF at hemoglobin concentrations of below 9 g(100 ml)(-1) was far in excess of that expected from the decrease in viscosity the results indicate thatdilatation of cerebral resistance vessels occurred. This dilatation, which was obviously related to the fall in arterial oxygen content, cannot be explained by any of the current theories proposed to explain cerebral hyperemia in hypoxia.

The relationship between arterial po2 and cerebral blood flow in hypoxic hypoxia

The relationship between arterial oxygen tension (PaO2) and cerebral blood flow (CBF) in hypoxic hypoxia was studied in artificially ventilated and normocapnic rats. Changes in CBF were evaluated from arteriovenous differences in oxygen content after 2, 5, 15 and 30 min exposure to PaO2 85, 75, 55, 45, 35, and 25 mm Hg. In separate experiments the PaO2 was decreased to 25 mm Hg for 1, 2, 5, 15 and 30 min in animals in which PaCO2 was allowed to fall by 5-10 mm Hg. There was a small, gradual increase in CBF when PaO2 was lowered in steps from 130 to 55 mm Hg, and a more pronounced increase at PO2 values below 50 mm Hg. At PaO2 25 mm Hg CBF increased to values of 500% of normal. Significant increased in CBF were recorded at PaO2 values of 85 and 75 mm Hg in spite of the fact that previous studies have failed to record an elevated tissue lactate content at these po2 levels, and in spite of an unchanged cerebral venous PO2. When the PaO2 was reduced to 25 mm Hg CBF increased markedly already at 1 and 2 min, and this increase in CBF occurred even if PaCO2 was allowed to fall by 5-10 mm Hg. Previous results have shown that in such short periods enough lactic acid is not formed to induce a net tissue acidosis. The results thus give no support to the hypothesis that cerebral hyperemia in hypoxia is coupled to accumulation of lactic acid in the tissue.

Cerebral blood flow and oxygen consumption in the rat in hypoxic hypoxia

In order to measure cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo(2)) at pronounced degrees of hypoxic hypoxia the Pao(2) of artificially ventilated and normocapnic rats was reduced to between 47 and 22 mm Hg for 15-25 min with subsequent measurements of CBF, using a -133Xenon modification of the Kety and Schmidt technique, and of the arteriovenous difference in oxygen content, the venous blood being obtained from the superior sagittal sinus. When the Pao(2) was reduced to minimal values of 22 mm Hg CBF increased 4- to 6-fold, the increase in CBF being unrelated to changes in blood pressure or Paco(2). The CMRo(2) remained unchanged at all levels of hypoxia. It is concluded that the maintenance of a normal, or near-normal, cerebral energy state even at extreme degrees of hypoxic hypoxia depends solely on a homeostatic increase in CBF.