Cerebral Blood Flow In Animals Research Articles

L‐arginine Supplementation and Thromboxane Synthase Inhibition Reverse Cerebral Ischemia in Murine Cerebral Malaria by Plasmodium berghei ANKA

Cerebral malaria (CM) is one of the most severe and lethal complications of Plasmodium falciparum infection. The mainstay treatment for CM is intravenous artesunate, nevertheless 15–20% of the patients receiving this drug still die. Vascular dysfunction, with vasoconstriction, leads to decreased cerebral blood flow, ischemia, tissue hypoxia and death in CM. Nitric oxide (NO) and arachidonic acid metabolites are important regulators of physiological cerebral blood flow through their vasodilator or vasoconstrictive properties. The objective of this study was to determine the effects of L‐arginine supplementation and pharmacological inhibition of thromboxane A2 (TXA2) synthesis on the reversal of ischemia in experimental cerebral malaria (ECM). C57BL/6 mice infected with Plasmodium berghei ANKA (PbA) and showing clinical signs of ECM were treated subcutaneously with the NO precursor L‐arginine (50mg/kg) and/or the thromboxane synthase inhibitor ozagrel (100mg/kg). Cerebral blood flow was measured by Laser Speckle Contrast Imaging (LSCI). The adjuvant effect of L‐arginine in combination with artesunate on survival of mice with late‐stage ECM was evaluated. Animals that developed ECM showed a significant decrease (25%) in cerebral blood flow compared to non‐infected control animals. L‐arginine induced a marked increase (22.5%) in cerebral blood flow in mice with ECM one hour after administration. The administration of ozagrel, which prevents the generation of the vasoconstrictor metabolite TXA2, also led to increased (16.5%) cerebral blood flow in animals with ECM, and this was consistent with decreased levels of brain TXA2 in ozagrel‐treated compared to saline‐treated animals. The combination of ozagrel and L‐arginine showed no synergistic effect on cerebral blood flow. Treatment of animals with late‐stage ECM with artesunate plus L‐arginine increased survival compared to artesunate plus saline. Conclusion: L‐arginine and ozagrel increase cerebral blood flow, and L‐arginine increase survival in mice with cerebral malaria and show potential as adjuvant therapy for this malaria complication.Support or Funding InformationCAPES, FAPERJ, IOC‐FiocruzThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effects of Kaempferol, an Antioxidant, on the Bioavailability and Pharmacokinetics of Nimodipine in Rats

The aim of this study was to investigate the effects of kaempferol on the pharmacokinetics of nimodipine in rats. Nimodipine and kaempferol interact with cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp), and the increase in the use of health supplements may result in kaempferol being taken concomitantly with nimodipine as a combination therapy to treat orprevent cardiovascular disease. The effect of kaempferol on P-gp and CYP3A4 activity was evaluated and Pharmacokinetic parameters of nimodipine were determined in rats after an oral (12 mg/kg) and intravenous (3 mg/kg) administration of nimodipine to rats in the presence and absence of kaempferol (0.5, 2.5, and 10 mg/kg). Kaempferol inhibited CYP3A4 enzyme activity in a concentration-dependent manner with 50% inhibition concentration (IC50) of 17.1 µM. In addition, kaempferol significantly enhanced the cellular accumulation of rhodamine-123 in MCF-7/ ADR cells overexpressing P-gp. Compared to the oral control group, the area under the plasma concentration-time curve (AUC0-∞) and the peak plasma concentration (Cmax) of nimodipine significantly increased, respectively. Consequently, the absolute bioavailability of nimodipine in the presence of kaempferol (2.5 and 10 mg/kg) was 29.1-33.3%, which was sig- nificantly enhanced compared to the oral control group (22.3%). Moreover, the relative bioavailability of nimodipine was 1.30- to 1.49-fold greater than that of the control group. The pharmacokinetics of intravenous nimodipine was not affected by kaempferol in contrast to those of oral nimodipine. Kaempferol significantly enhanced the oral bioavailability of nimo- dipine, which might be mainly due to inhibition of the CYP3A4-mediated metabolism of nimodipine in the small intestine and /or in the liver and to inhibition of the P-gp efflux transporter in the small intestine by kaempferol. The increase in oral bioavailability of nimodipine in the presence of kaempferol should be taken into consideration of potential drug interactions between nimodipine and kaempferol. Key wordsNimodipine, Kaempferol, Pharmacokinetics, Bioavailability, P-gp, CYP3A4, Rats Nimodipine is a dihydropyridine calcium channel blocker that has been shown to selectively dilate cerebral arteries and increase cerebral blood flow in animals and humans (Kazda et al., 1982). Its major therapeutic indication is for the prevention and treatment of delayed ischemic neurological disorders that often occur in patients with subarachnoid hemorrhages (Epstein and Loutzenhister, 1990; Scholz, 1997). Nimodipine is rapidly absorbed after oral administration and is widely dis- tributed throughout the body. Orally administered nimodipine is subject to an extensive first-pass hepatic metabolism from the portal circulation, resulting in a low systemic bioavail- ability (Maruhn et al., 1985; Suwelack et al., 1985). Usually only the parent compound is active and most of the metabolic steps involve reactions catalyzed by cytochrome P450 (CYP) enzymes. CYP enzymes have been shown to catalyze pyridine

Quantitative evaluation of 11C-ABP688 as PET ligand for the measurement of the metabotropic glutamate receptor subtype 5 using autoradiographic studies and a beta-scintillator

In this study we assessed the new glutamatergic ligand 11C-ABP688 with regard to the following characteristics: (A) brain distribution, (B) first pass extraction fraction, (C) suitable model to describe tracer kinetics and (D) specificity for the mGlu5 receptor. These parameters were assessed using autoradiography and a beta-scintillator positioned in the striatum. The study included 13 male rats. In 2 animals cerebral blood flow was measured using H215O. The 11C-ABP688 data were analyzed using compartmental modeling. A two-tissue compartment model turned out to fit the data more adequately (parameters: K1, k2′, k3′, k4, total distribution volume DVtot=K1/k2′ (1+k3′/k4) than a one-tissue compartment model. The autoradiographic studies revealed high uptake in hippocampus, striatum and cortex and low accumulation in thalamus and cerebellum. The uptake was markedly reduced following blockade with the mGlu5 antagonist M-MPEP. The first pass extraction fraction exceeded 85%. Baseline DVtot was 15.16±2.67 ml plasma/ml tissue and decreased by 56, 67 and 72% following blockade with 1, 2 and 6 mg/kg M-MPEP, respectively. These results show that 11C-ABP688 is a promising PET ligand for the quantification of mGlu5 receptors in humans and animals. It readily crosses the blood–brain barrier and binds with high specificity to the mGlu5 receptor. The study furthermore demonstrates the usefulness of a beta-scintillator, if necessary in connection with autoradiography, to evaluate new receptor tracers.

Abstracts of literature

Abstracts of literature

The effect of lumbar epidural anesthesia on maternal middle cerebral artery blood flow in normal pregnancy: A prospective, randomized, double-blind comparison study

Objective: Lumbar epidural anesthesia is associated with a transient elevation in intracranial pressure in both animals and humans and decreased cerebral blood flow in animals. We sought to determine the effect of medium-onset and slow-onset local anesthetic lumbar epidural anesthesia on maternal cerebral blood flow in normal human pregnancy. Study Design: In an Institutional Review Board–approved, double-blind study, 24 healthy, normotensive, nonlaboring, term gravida women undergoing elective cesarean section were prospectively placed into random groups to receive either 2% lidocaine with 8.4% sodium bicarbonate (1:10) or 0.5% bupivacaine lumbar epidural anesthesia. After prehydration with 20 mL/kg crystalloid and 15-degree left-wedged supine positioning with 15-degree head tilt, transcranial Doppler ultrasound (Nicolet Pioneer EME) and simultaneous electrocardiogram, automatic blood pressure (Dinamap), and end-tidal CO 2 (SAR-Trans) monitoring were performed. Pulse, blood pressure, respiratory rate, end-tidal CO 2 , middle cerebral artery blood flow velocity, and pulsatility index were measured at (1) baseline (once supine positioning was assumed); (2) immediately after administration of 20 mL local anesthetic; and (3) every 5 minutes for 25 minutes. Timing of the attainment of a T4 dermatome anesthetic level was noted. Comparisons were made by t test, rank sum tests, χ 2 , and repeated measures analysis of variance. P < .05 was considered significant. Results: Maternal heart rate, blood pressure, respiratory rate, and end-tidal CO 2 were not significantly different within or between groups. No significant difference was found in baseline middle cerebral artery blood flow velocity or pulsatility index values between groups. Neither middle cerebral artery blood flow velocity nor pulsatility index changed significantly within or between groups up to 25 minutes after institution of epidural anesthesia. Conclusions: Maternal middle cerebral artery blood flow velocity, as measured by transcranial Doppler ultrasonography, is maintained in normotensive, nonlaboring term gravida women receiving either lidocaine or bupivacaine lumbar epidural anesthesia, which supports intact cerebrovascular autoregulation in normal pregnancy. (Am J Obstet Gynecol 1998;179:1237-40.)

Cerebral Protection Against Ischemia by Locomotor Activity in Gerbils

A previous communication of this laboratory demonstrated reduced mortality and neuronal damage by spontaneous locomotor activity preceding forebrain ischemia in Mongolian gerbils. The present experiments seek to elucidate potential mechanisms of protection by measurement of cerebral blood flow, cerebral tissue conductance as an indicator of ischemic cell swelling, and the cerebral release of eicosanoids. Gerbils were maintained either in conventional cages (nonrunners) or with free access to running wheels (runners) for 2 weeks preceding 15 minutes of forebrain ischemia. During ischemia and 2.5 hours of reperfusion, cerebral tissue conductance was determined with a two-electrode system. Simultaneously, prostaglandin D2, prostaglandin F2 alpha, and thromboxane B2 were measured in ventriculocisternal perfusate. In additional animals cerebral blood flow was assessed by hydrogen clearance. Decreases in tissue conductance during ischemia were similar in nonrunners (56 +/- 3%) and runners (62 +/- 3%) but normalized more rapidly in runners during reperfusion. In both groups reperfusion was accompanied by marked increases of perfusate prostaglandin D2, prostaglandin F2 alpha, and thromboxane B2. In nonrunners, however, thromboxane B2 was already elevated during ischemia (147 +/- 9%, P < .01) and remained elevated longer during recirculation (P < .05). Postischemic perfusion maxima were higher in runners (70.8 +/- 7.4 versus 47.0 +/- 5.0 mL/100 g per minute, P < .05) and were observed sooner (27.4 +/- 6.9 versus 62.2 +/- 12.3 minutes, P < .05). Both groups displayed delayed hypoperfusion of a similar magnitude (runners, 29.0 +/- 2.4 mL/100 g per minute; nonrunners, 30.1 +/- 2.4 mL/100 g per minute). Protection by preischemic locomotor activity may involve enhanced postischemic reperfusion, leading to more rapid normalization of conductance and thus of cell volume. Enhanced reperfusion may be the consequence of attenuated thromboxane liberation during and after ischemia.

PH strategies and cerebral energetics before and after circulatory arrest

The pH-stat strategy compared with the alpha-stat strategy provides more rapid recovery of brain high-energy phosphate stores and intracellular pH after 1 hour of hypothermic circulatory arrest in pigs. Possible mechanisms for this difference are (1) improved oxygen delivery and homogeneity of brain cooling before deep hypothermic circulatory arrest and (2) greater cerebral blood flow and reduced reperfusion injury owing to extracellular acidosis during the rewarming phase. To identify which of these mechanisms is predominant, we studied 49 4-week-old piglets undergoing 1 hour of deep hypothermic circulatory arrest. Four groups were defined according to cooling/rewarming strategy: alpha/alpha, alpha/pH, pH/alpha, and pH/pH. In 24 animals cerebral high-energy phosphate levels and intracellular pH were measured by magnetic resonance spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 5). In 25 animals cerebral blood flow was measured by labeled microspheres, cerebral metabolic rate by oxygen and glucose extraction, and the redox state of cytochrome aa 3 and hemoglobin oxygenation by near infrared spectroscopy (alpha/alpha group 7, alpha/pH group 5, pH/alpha group 7, pH/pH group 6). Cerebral blood flow was greater with pH-stat than alpha-stat during cooling (56.3% ± 3.7% versus 32.9% ± 2.1% of normothermic baseline values, p < 0.001). Cytochrome aa 3 values became more reduced during cooling with alpha-stat than with pH-stat ( p = 0.049). Recovery of adenosine triphosphate levels in the initial 45 minutes of reperfusion was more rapid in group pH/pH compared with that in the other groups ( p = 0.029). Recovery of cerebral intracellular pH in the initial 30 minutes was faster in group pH/pH compared with that in group alpha/alpha ( p = 0.026). Intracellular pH became more acidic during early reperfusion only in group alpha/alpha, whereas it showed continuous recovery in the other groups. This study suggests that there are mechanisms in effect during both the cooling and rewarming phases before and after deep hypothermic circulatory arrest that could contribute to an improved cerebral outcome with pH-stat relative to more alkaline strategies. (J T HORAC C ARDIOVASC S URG 1995; 109: 948-58)

Nimodipine. A review of its pharmacological properties, and therapeutic efficacy in cerebral disorders.

Nimodipine is a dihydropyridine calcium antagonist which dilates cerebral blood vessels and increases cerebral blood flow in animals and humans. Preliminary findings reveal its potential benefit for the treatment of a wide range of cerebrovascular disorders, particularly for prophylaxis and treatment of delayed ischaemic neurological deficits resulting from cerebral vasospasm in patients with subarachnoid haemorrhage. Studies involving patients aged up to 79 years have confirmed these preliminary findings by showing that nimodipine reduces the incidence of severe ischaemic deficit after subarachnoid haemorrhage. Initial results from studies of patients with acute ischaemic stroke indicate that nimodipine, started within 72 hours of onset, improved recovery, particularly in patients over 65 years. However, other investigators have found no marked difference in 6-month mortality or morbidity rates of stroke patients aged up to 97 years. Findings from other studies suggest that nimodipine may improve symptoms of cognitive dysfunction in elderly patients. Nimodipine is well tolerated by both younger and older patients. The most frequently reported adverse event has been hypotension. Thus, nimodipine therapy offers important benefits as part of the approach to management of patients with subarachnoid haemorrhage and has potential in other cerebral disorders, including stroke and impaired cognitive function, although confirmation of initial results in patients with cerebral impairment are required.

Nimodipine

Nimodipine is a dihydropyridine calcium antagonist which has been shown to dilate cerebral arterioles and increase cerebral blood flow in animals and humans. It has potential in the treatment of a range of cerebrovascular disorders. Major interest to date, however, has focused on its use in the prevention and treatment of the delayed ischaemic neurological deficits that frequently occur in patients with subarachnoid haemorrhages as a result of sustained cerebral vasospasm. Initial studies in which patients were treated with an intravenous infusion of nimodipine for up to 2 weeks, followed by oral treatment for 7 days, indicated that a higher proportion of patients than would normally be expected recovered with little or no permanent neurological damage. In a number of controlled studies oral nimodipine treatment for 3 weeks significantly decreased mortality rates and increased the number of patients who had a 'good' neurological outcome as compared with placebo treatment. In some of these trials fewer of the nimodipine-treated patients developed neurological deficits during the treatment period, but in none was there a significant effect on the incidence of angiographic vasospasm. It would seem that other pharmacological actions, such as increasing collateral blood flow to underperfused regions or a direct anti-ischaemic effect at the cellular level, may contribute to the clinical benefits obtained with nimodipine treatment. Preliminary results suggest that nimodipine is potentially useful in other cerebrovascular disorders, particularly ischaemic stroke. To date, nimodipine has been well-tolerated, the only adverse effects of any significance being reductions in the blood pressure of some patients and reversible increases in liver enzymes during intravenous therapy. Thus, nimodipine has significant potential in the treatment of patients with subarachnoid haemorrhage. Wider clinical use should confirm its value as a significant addition to the very limited range of therapeutic choices currently available for patients with this disorder.

Sodium 5-(3'-pyridinylmethyl)benzofuran-2-carboxylate (U-63557A) potentiates protective effect of intravenous eicosapentaenoic acid on impaired CBF in ischemic gerbils.

Eicosapentaenoic acid (EPA) has been reported to improve postischemic cerebral blood flow (CBF). The present study was designed to determine whether sodium 5-(3'-pyridinylmethyl)benzofuran-2-carboxylate (U-63557A), a selective thromboxane synthetase inhibitor, could potentiate the effects of EPA on CBF in ischemic gerbils. Ischemia was produced by bilateral carotid artery occlusion for 15 minutes followed by reperfusion for 2 hours. Immediately after ischemia, gerbils were given either an intravenous bolus of 0.167 mg of EPA followed by a continuous infusion of EPA at 1 mg/hr, or U-63557A (10 mg/kg intraperitoneally), or U-63557A and EPA, or a saline infusion. Regional CBF was measured by the hydrogen clearance method, and brain water by the specific gravity technique. Brain prostaglandins were measured by radioimmunoassay. Preischemic CBF's ranged from 27.4 to 29.5 ml/100 gm/min for the four animal groups. After ischemia and 2 hours of reperfusion, CBF in the saline-infused gerbils was significantly decreased to 19.2 ml/100 gm/min. Gerbils treated with either EPA or U-63557A alone had a CBF of 23.7 and 21.6 ml/100 gm/min, respectively. Postischemic CBF in animals treated with both U-63557A and EPA was 30.0 ml/100 gm/min, significantly higher than in saline-infused gerbils. Brain levels of 6-keto prostaglandin (PG)F1 alpha (the metabolite of PGI2) were significantly higher in gerbils treated with U-63557A and EPA compared to gerbils given EPA alone. This study indicates that U-63557A potentiates the effects of EPA on postischemic CBF. This is probably due to the ability of U-63557A to increase prostacyclin formation in the vessel wall.

Acute cardiovascular effects of indomethacin in anesthetized newborn dogs.

Cardiac output and regional blood flow distribution were measured in 14 newborn dogs before and 90 min following 0.3 mg/kg of indomethacin and in 4 control animals who received buffer alone using the Radioactive Microsphere Reference Organ Technique. Indomethacin produced no significant change in cardiac output or blood flow to the gastrointestinal tract or kidney. There were no changes in cerebral blood flow in animals over 4 days of age. However, in 3 of 8 puppies less than 3 days of age, indomethacin resulted in a 47% fall in cerebral blood flow. In newborn dogs, indomethacin in the dose employed had no deleterious effects on cardiac output and, with the possible exception of the cerebral circulation, on blood flow distribution.

Preservation of cerebral autoregulation in the unanesthetized hypoxemic newborn dog

Studies were conducted to determine the effects of hypoxemia on cerebral blood flow and the influence of hyperoxia and hypoxemia on autoregulation of cerebral blood flow in the unanesthetized newborn dog.Twenty-one newborn dogs less than 2 weeks of age were studied. Cerebral blood flow was measured using radioactive microspheres during successive periods of normotension, hypotension (produced by blood withdrawal) and normotension (produced by infusion of previously withdrawn blood). In the hyperoxic animals, arterial pO 2 was maintained above 250 torr by having the animal breathe 100% oxygen, while in the hypoxemic animals arterial pO 2 was maintained between 30 and 35 torr by having the animal breathe 12% O 2. Cerebral blood flow increased significantly with hypoxemia. In both hypoxemic and hyperoxic animals cerebral blood flow was maintained constant in spite of a large fall in arterial blood pressure and cardiac output, demonstrating the presence of autoregulation. Calculated oxygen transport to the brain was constant during hypoxemia and hypotension in all animals. Thus autoregulation of cerebral blood flow is present in newborn animals and is preserved under conditions of moderate hypoxemia.

ChemInform Abstract: CEREBROVASODILATATION THROUGH SELECTIVE INHIBITION OF THE ENZYME CARBONIC ANHYDRASE. 3. 5‐(ARYLTHIO)‐, 5‐(ARYLSULFINYL)‐, AND 5‐(ARYLSULFONYL)THIOPHENE‐2‐SULFONAMIDES

AbstractDie Thiophene (I) werden in die Sulfonamide (II) umgewandelt, die mit den Thiophenolen (III) die Thioether (IV) bilden.

Cerebrovasodilatation through selective inhibition of the enzyme carbonic anhydrase. 3. 5-(Arylthio)-, 5-(arylsulfinyl)-, and 5-(arylsulfonyl)thiophene-2-sulfonamides.

A series of 5-(arylthio)-, 5-(arylsulfinyl)-, and 5-(arylsulfonyl)thiophene-2-sulfonamides is described and anticonvulsant activities are listed for the compounds. In most cases, the sulfones had the highest activity and the sulfides the least. Sulfones with 3- or 4-halo substituents generally had the highest activity, and one analogue, 5-[(4-fluorophenyl)sulfonyl]thiophene-2-sulfonamide (51, UK-17022), had an anticonvulsant ED50 fo 2 mg/kg when administered orally to mice. Compound 51 selectively increased cerebral blood flow in animals without an unacceptable level of diuresis.

Cerebrovasodilatation through selective inhibition of the enzyme carbonic anhydrase. 2. Imidazo[2,1-b]thiadiazole and imidazo[2,1-b]thiazolesulfonamides

A series of imidazo[2,1-b]thiadiazole and imidazo[2,1-b]thiazolesulfonamide carbonic anhydrase inhibitors is described and their anticonvulsant activities are listed. Many of the compounds have the same degree of ionization as acetazolamide and methazolamide, but their higher lipophilicity means that they are more able to penetrate into the central nervous system. One compound, 6-tert-butyl-2-sulfamoylimidazo[2,1-b]-1,3,4-thiadiazole (8, UK-15,454) had an anticonvulsant ED50 of 2.6 mg/kg when administered orally to mice. 8 selectively increased cerebral blood flow in animals without producing a high level of metabolic acidosis.

Cerebrovasodilatation through selective inhibition of the enzyme carbonic anhydrase. 1. Substituted benzenedisulfonamides.

A series of substituted benzenedisulfonamide carbonic anhydrase inhibitors is described and their anticonvulsant activities are listed. One compound, 4-(4-methoxypiperidinosulfonyl)-2-chlorobenzenesulfonamide (19, UK-12130), was found to have anticonvulsant activity in animals at a dose level that gave only a minimal diuretic effect. 19 selectively increased cerebral blood flow in animals and man without producing an unacceptable level of metabolic acidosis.

Cerebral Circulation

THE MODERN era of cerebrovascular disease began in 1946 with a landmark paper by Kubik and Adams.¹A description of antecedent symptoms and those of onset as well as of neurological abnormalities of the final illness was provided for each of the 18 patients. The authors did not discuss the possible importance of antecedent symptoms, ie, attacks, in six patients and probable warning symptoms in four others. These episodes are now called transient ischemic (focal cerebral) attacks (TIA). <h3>Review of the Literature</h3> The report of the nitrous oxide method for the quantitative determination of cerebral blood flow in man in 1948 by Kety and Schmidt²opened an era that has seen the publication of thousands of papers about cerebral blood flow in animals and man. The Kety and Schmidt method, ie, Fick principle, has been modified in a number of ways, particularly with technical improvements, including computer analysis.

EFFECTS OF HYPOTENSION INDUCED BY HALOTHANE, ON THE CEREBRAL CIRCULATION IN BABOONS WITH EXPERIMENTAL RENOVASCULAR HYPERTENSION

The effect of graded, progressive hypotension on the autoregulation of cerebral blood flow was studied in anaesthetized baboons with experimental renovascular hypertension. Graded hypotension was induced over a period of 5-6 h by the administration of increasing concentrations of halothane. In these chronically hypertensive animals cerebral blood flow remained constant until the mean arterial pressure had decreased to approximately 90 mm Hg. At mean arterial pressures of less than this value cerebral blood flow was pressure passive. At the completion of the investigation the brains were fixed by perfusion and submitted to neuropathological examination. Evidence of chronic hypertension and of ischaemic brain damage was found in every animal.

Oxidative metabolism of the cerebral cortex of the rat in severe insulin-induced hypoglycaemia.

Abstract—Measurements were made of organic phosphates, carbohydrate substrates, amino acids and ammonia in the cerebral cortex, as well as of cerebral blood flow and of cerebral metabolic rate for oxygen and glucose in rats that developed an isoelectric EEG pattern (‘coma’) during insulin‐induced hypoglycaemia. The results were compared to those obtained in control animals, as well as in hypoglycaemic animals with an EEG pattern of slow waves and polyspikes. In animals with slow waves and polyspikes, there was a decrease in all citric acid cycle intermediates except succinate and oxaloacetate, and a decrease in the pool size of intermediates. In animals that had an isoelectric EEG for 5–15 min, there were further decreases in citrate, isocitrate, α‐ketoglutarate, malate and fumarate, but since the concentration of succinate (and oxaloacetate) increased, the pool size remained the same. In isoelectric animals, the results revealed extensive utilization of amino acids by both transamination and deamination reactions. However, since glycogen had disappeared and the amino acid pattern was constant after the first 5 min of isoelectric EEG, further oxidation must have occurred at the expense of non‐carbohydrate, non‐amino acid substrates.There were two‐ to three‐fold increases in cerebral blood flow in animals with slow waves and polyspikes and in animals with isoelectric EEG, and no decrease in the cerebral metabolic rate for oxygen. Since less than half of the oxygen consumption could be accounted for in terms of glucose extraction, the data indicate that severe hypoglycaemia is associated with extensive oxidation of endogenous substrates other than carbohydrates and free acids.

THE DETERMINATION OF CEREBRAL BLOOD FLOW IN MAN BY THE USE OF NITROUS OXIDE IN LOW CONCENTRATIONS

Quantitative measurements of the total blood flow to the brain of man have not previously been reported and the few procedures which have been used for the purpose of obtaining relative or qualitative values have recently been subjected to considerable criticism (1). The method to be described is based on the principle that the rate at which the cerebral venous blood content of an inert gas approaches the arterial blood content depends upon the volume of blood flowing through the brain. Certain aspects of this principle were recognized by Haggard (2) who postulated that the rate at which an anesthetic gas is taken up by the brain depends in part on the rate of blood flow to that organ, and similarly by Ferris, Molle a,nd Ryder (3) who stated that the clearance of nitrogen from the brain during the inhalation of 100 per cent oxygen may be markedly influenced by the magnitude of cerebral blood flow. As far as we are aware, however, the principle has not previously been subjected to mathematical analysis and applied to actual measurements of cerebral blood flow in animals or man. The experiments described in the preceding report (4) a,fforded an opportunity for calibrating this procedure against direct measurements of cerebral blood flow and thus for refining the technical and theoretical fact,ors to a degree that would not otherwise have been possible. METHODS. The specific substance which is employed is not of consequence provided that it is physiologically inert in the concentrations employed, capable of diffusing rapidly across the blood-brain barrier, and susceptible of accurate analysis in the blood. It need not$ even be a gas if it meets all these requirements. In the present experimentIs nitrous oxide has been employed although ot#her gases may be found to be more suittable. Radioact,ive gases offer certain unique advantages and their use is being considered. In the animal experiments t,he inhaled gas consisted of 40 per cent! nitrous oxide in oxygen which was inhaled through the inspiratory valve attached to the tracheal cannula. In the early experiments on man 15 per cent nitrous oxide and 85 per cent oxygen was employed and was inhaled tlhrough the inlet, t,ube of an anesthesia mask. Because the presence of nit,rogen in t/he blood imroduces cer-