Cerebral cytochrome a,a3 inhibition by cyanide in bloodless rats

Inhalation Injury, Respiratory Failure, and Ventilator Support in Acute Burn Care

Sustaining an inhalation injury increases the risk of severe complications and mortality. Current evidential support to guide treatment of the injury or subsequent complications is lacking, as studies either exclude inhalation injury or design limit inferences that can be made. Conventional ventilator modes are most commonly used, but there is no consensus on optimal strategies. Settings should be customized to patient tolerance and response. Data for pharmacotherapy adjunctive treatments are limited.

Noninvasive optical cytochrome c oxidase redox state measurements using diffuse optical spectroscopy

A major need exists for methods to assess organ oxidative metabolic states in vivo. By contrasting the responses to cyanide (CN) poisoning versus hemorrhage in animal models, we demonstrate that diffuse optical spectroscopy (DOS) can detect cytochrome c oxidase (CcO) redox states. Intermittent decreases in inspired O2 from 100% to 21% were applied before, during, and after CN poisoning, hemorrhage, and resuscitation in rabbits. Continuous DOS measurements of total hemoglobin, oxyhemoglobin, deoxyhemoglobin, and oxidized and reduced CcO from muscle were obtained. Rabbit hemorrhage was accomplished with stepwise removal of blood, followed by blood resuscitation. CN treated rabbits received 0.166  mg/min NaCN infusion. During hemorrhage, CcO redox state became reduced concurrently with decreases in oxyhemoglobin, resulting from reduced tissue oxygen delivery and hypoxia. In contrast, during CN infusion, CcO redox state decreased while oxyhemoglobin concentration increased due to CN binding and reduction of CcO with resultant inhibition of the electron transport chain. Spectral absorption similarities between hemoglobin and CcO make noninvasive spectroscopic distinction of CcO redox states difficult. By contrasting physiological perturbations of CN poisoning versus hemorrhage, we demonstrate that DOS measured CcO redox state changes are decoupled from hemoglobin concentration measurement changes.

Cyanide intoxication as part of smoke inhalation--a review on diagnosis and treatment from the emergency perspective

This paper reviews the current literature on smoke inhalation injuries with special attention to the effects of hydrogen cyanide. It is assumed that cyanide poisoning is still an overlooked diagnosis in fire victims. Treatment against cyanide poisoning in the emergency setting should be given based on the clinical diagnosis only. Oxygen in combination with a recommended antidote should be given immediately, the first to reduce cellular hypoxia and the second to eliminate cyanide. A specific antidote is hydroxycobalamin, which can be given iv. and has few side effects.

Noninvasive in vivo monitoring of cyanide toxicity and treatment using diffuse optical spectroscopy in a rabbit model

Currently, no reliable noninvasive methods exist for monitoring the severity of in vivo cyanide (CN) toxicity, treatment, and resulting physiological changes. We developed a broadband diffuse optical spectroscopy (DOS) system to measure bulk tissue absorption and scattering. DOS was used to optically monitor CN toxicity and treatment with sodium nitrite (NaNO2). To perform experiments, the DOS probe was placed on the hind leg of rabbits. A sodium CN solution was infused intravenously. DOS and concurrent physiologic measurements were obtained. After completion of CN infusion, NaNO2 was infused to induce methemoglobinemia (MetHb). During infusion of CN, blood gas measurements showed an increase in venous partial pressure of oxygen (pO2), and following reversal, venous pO2 values decreased. DOS measurements demonstrated corresponding changes in hemoglobin oxygenation states and redox states of cytochrome-c oxidase (CcO) during CN infusion and NaNO2 treatment. Therefore, DOS enables detection and monitoring of CN toxicity and treatment with NaNO2.

Induced mitochondrial failure in the feline brain: implications for understanding acute post-traumatic metabolic events

OBJECTIVE

Recently, evidence has become available implicating mitochondrial failure as a crucial factor in the pathogenesis of acute brain damage following severe traumatic brain injury (TBI). However, it remains unclear how mitochondrial dysfunction affects cerebral metabolism. Therefore the aim of the study was to evaluate the impact of 'isolated' mitochondrial failure on local cerebral metabolism.

METHODS

Cerebral mitochondrial metabolism was blocked by local microdialysis perfusion with cyanide in seven cats. Local brain tissue oxygen tension (p(tiO(2))), carbon dioxide tension (p(tiCO(2))) and pH, as well as extracellular cerebral fluid, glucose, lactate, pyruvate and glutamate were monitored, using a Neurotrend sensor and microdialysis, respectively. Tissue oxygen consumption was measured in a microrespirometric system, and ultrastructural changes evaluated via electron microscopy.

RESULTS

Brain tissue oxygen tension increased from a baseline of 31+/-9 mmHg to 84+/-30 mmHg after 60 min of cyanide perfusion (P<0.05), concomitant a decrease in oxygen consumption from 14.45+/-3.91 microl/h/mg to 10.83+/-1.74 microl/h/mg (P<0.05). Brain tissue pH was decreased after 60 min of cyanide perfusion (6.83+/-0.16) compared to baseline (7.07+/-0.39) (P<0.05), whereas p(tiCO(2)) did not show significant changes. Lactate massively increased from a baseline of 599+/-270 micromol/l to 2609+/-1188 micromol/l immediately after cyanide perfusion (P<0.05). The lactate:glucose ratio increased from 0.79+/-0.15 before cyanide perfusion to 6.40+/-1.44 at 40 min after cyanide perfusion (P<0.05), while no significant changes in the lactate:pyruvate ratio could be observed. Glutamate increased from a baseline of 11.6+/-7.2 micromol/l to 61.4+/-44.7 micromol/l after cyanide perfusion (P<0.05).

CONCLUSION

The results of this study show that 'isolated' cerebral mitochondrial failure initiates changes in cerebral substrates and biochemistry, which are very similar to most of the changes seen after severe human head injury, except for the early fall in p(tiO(2)), further indicating a crucial involvement of mitochondrial impairment in the development of brain damage after TBI.

Use of mitochondrial inhibitors to demonstrate that cytochrome oxidase near-infrared spectroscopy can measure mitochondrial dysfunction noninvasively in the brain

The use of near-infrared spectroscopy to measure noninvasively changes in the redox state of cerebral cytochrome oxidase in vivo is controversial. We therefore tested these measurements using a multiwavelength detector in the neonatal pig brain. Exchange transfusion with perfluorocarbons revealed that the spectrum of cytochrome oxidase in the near-infrared was identical in the neonatal pig, the adult rat, and in the purified enzyme. Under normoxic conditions, the neonatal pig brain contained 15 micromol/L deoxyhemoglobin, 29 micromol/L oxyhemoglobin, and 1.2 micromol/L oxidized cytochrome oxidase. The mitochondrial inhibitor cyanide was used to determine whether redox changes in cytochrome oxidase could be detected in the presence of the larger cerebral hemoglobin concentration. Addition of cyanide induced full reduction of cytochrome oxidase in both blooded and bloodless animals. In the blooded animals, subsequent anoxia caused large changes in hemoglobin oxygenation and concentration but did not affect the cytochrome oxidase near-infrared signal. Simultaneous blood oxygenation level-dependent magnetic resonance imaging measurements showed a good correlation with near-infrared measurements of deoxyhemoglobin concentration. Possible interference in the near-infrared measurements from light scattering changes was discounted by simultaneous measurements of the optical pathlength using the cerebral water absorbance as a standard chromophore. We conclude that, under these conditions, near-infrared spectroscopy can accurately measure changes in the cerebral cytochrome oxidase redox state.

The relationship of oxygen delivery to absolute haemoglobin oxygenation and mitochondrial cytochrome oxidase redox state in the adult brain: a near-infrared spectroscopy study

Near-infrared spectroscopy was used to determine the effect of changes in the rate of oxygen delivery to the adult rat brain on the absolute concentrations of oxyhaemoglobin, deoxyhaemoglobin and the redox state of the CuA centre in mitochondrial cytochrome oxidase. The cytochrome oxidase detection algorithm was determined to be robust to large changes in haemoglobin oxygenation and concentration. By assuming complete haemoglobin deoxygenation and CuA reduction following mechanical ventilation on 100% N2O, the absolute concentration of oxyhaemoglobin (35 microM), deoxyhaemoglobin (27 microM) and the redox state of CuA (82% oxidized) were calculated in the normal adult brain. The mean arterial blood pressure was decreased by exsanguination. When the pressure reached 100 mmHg, haemoglobin oxygenation started to fall, but the total haemoglobin concentration and oxidized CuA levels only fell when cerebral blood volume autoregulation mechanisms failed at 50 mmHg. Haemoglobin oxygenation fell linearly with decreases in the rate of oxygen delivery to the brain, but the oxidized CuA concentration did not start to fall until this rate was 50% of normal. The results suggest that the brain maintains more than adequate oxygen delivery to mitochondria and that near-infrared spectroscopy may be a good measure of oxygen insufficiency in vivo.

A portable diffuse reflectance spectrophotometer for the rapid and automatic measurement of meat pigments

A portable reflectance spectrophotometry system, which can measure a wide range of absorbance and has an adhesive pad type fibre optic probe, was developed to improve the availability of non-invasive reflectance spectrophotometry. A Czerny-Turner type spectrometer, which can be connected to an optical fibre probe, was developed, and a linear charge coupled device (CCD) was used as its light detector to increase data acquisition speed. The scanning time of the linear CCD is automatically controlled in accordance with the reflectance of meat to increase the dynamic range of absorption. We tried to apply this instrument to samples of meat pigments in order to demonstrate whether reflectance spectrophotometry is suitable for evaluating the freshness of meat. We examined the myoglobin solution in the form of the met-derivative in order to detect the concentration of myoglobin. The absorbance spectrum of myoglobin in the range of 0-4 mg dl(-1) was successfully distinguished with this instrument.

Electrocardiographic responses to carbon monoxide and cyanide in the conscious rat

Carbon monoxide (CO) and cyanide (CN), commonly found in exhaust fumes and smoke, act as hypoxic agents in eliciting morbid and lethal effects. This study explored the effects of these two toxicants on the ECG in a controlled and well-characterized animal model. Levine-prepared awake female rats were treated with 1500 and 2400 ppm CO for 90 min, CN at 4 mg/kg, or 1500 ppm CO plus 4 mg/kg CN. As in past studies, CO initially induced hyperglycemia and many-fold increases in blood lactate concentration, and rebound increases in blood glucose during recovery. CN produced hyperglycemia, however, there was no glucose rebound, nor was there a significant increase in lactate. CN plus 1500 ppm CO produced glucose changes similar to that of CO alone. CO exposure also induced hypothermia and hypotension, while CN produced little change in these parameters. CO increased heart rate, while CN tended to decrease heart rate. PR interval was increased significantly 4.5-17.0 ms by exposure to CO, with or without combination with CN, while CN alone produced minimal change in the PR interval. QT interval was increased up to 20 ms by exposure to CO, with or without combination with CN. CN alone produced no change in the QT interval. T wave duration was increased up to 22.5 ms by exposure to 1500 ppm CO, with or without combination with CN. CN alone produced minimal changes in T wave duration. There were no changes in duration of the (Q)RS complex or of the R wave. QT interval lengthening was positively correlated with the decrease in systolic blood pressure (0-30 min, r = 0.657, P < 0.05; 0-60 min, r = 0.704, P < 0.05). Hypothermia was correlated with increase in lactate concentration (r = 0.73, P < 0.05) and with decrease in blood pressure (r = 0.69, P < 0.05). No correlation between body temperature and QT interval was observed. The results indicate that CO at the concentrations used in the Levine-prepared rat has major effects on the ECG in slowing AV conduction and ventricular repolarization. In contrast, CN at 4 mg/dl has little or no effect on either conduction or repolarization in this animal model. These findings are discussed in light of past animal and human studies.

The effects of cyanide on brain mitochondrial cytochrome oxidase and respiratory activities

Brain mitochondrial cytochrome oxidase and respiratory activities were compared after in vivo and in vitro exposure to cyanide. For the in vivo studies, mice were exposed to a non-lethal (4 mg kg-1) or lethal (20 mg kg-1) dose of KCN. From these mice, purified brain mitochondria were prepared and cytochrome oxidase and respiratory activities measured. Results of these experiments revealed greater inhibition of cytochrome oxidase activity following a lethal (20 mg kg-1) than a non-lethal (4 mg kg-1) KCN dose (57 and 45% inhibition, respectively). Respiration states 3 and 4 of brain mitochondria prepared from mice that received 4 mg kg-1 KCN were inhibited by 15 and 20%, respectively. In mice that received a lethal 20 mg kg-1 KCN dose, respiration states 3 and 4 were each inhibited by ca. 30% (P < 0.05). In vitro, mitochondrial cytochrome oxidase activity was inhibited in a concentration-dependent fashion at cyanide concentrations of 10(-6)-10(-2) M. A biphasic inhibition of ADP-stimulated (state 3) respiration was observed. Cyanide concentrations of 10(-6)-10(-4) M produced only a 25% inhibition of respiration state 3, whereas 10(-3) M produced 80% inhibition. Because this dramatic inhibition only occurred at cyanide concentrations that caused > 50% inhibition of mitochondrial cytochrome oxidase activity, these findings suggest that a large proportion of cytochrome oxidase activity may be functional reserve and that cyanide poisoning likely involves other mechanisms in addition to inhibition of cytochrome oxidase.

Cardiovascular, metabolic and neurologic effects of carbon monoxide and cyanide in the rat

Levine-prepared, female Sprague-Dawley rats were used to investigate the effects of carbon monoxide (CO) and cyanide (CN) on heart rate, blood pressure, hematocrit, body temperature, blood glucose, lactate, and neurologic function. Rats were exposed to either 2400 ppm CO, 1500 ppm CO, 4 mg/kg NaCN, or both 1500 ppm CO and 4 mg/kg NaCN for 90 min, followed by 4 h of room air recovery. Following exposure to 2400 ppm CO, rats exhibited a significant bradycardia which normalized by 2 h of recovery. All groups exhibited an initial hypotension which was either maintained or exaggerated during exposure in all but the rats exposed to CN, and which returned to pre-exposure values by 90 min. All groups experienced a significant hypothermia during the exposure period, with those in the 1500 ppm CO or the CN returning to initial values over the recovery period. The only significant change in hematocrit was due to 2400 ppm CO (4.1% increase). During exposure, all groups experienced an initial surge in glucose concentration which was maintained in all but rats exposed to 2400 ppm CO. The greatest hyperglycemic response resulted from the combination of CO and CN, whereas 2400 ppm CO produced the smallest. CN alone produced no significant rise in lactate concentration. However, lactate concentration in all other groups was significantly elevated during the exposure period, returning to initial values by 4 h of recovery. Lactate concentrations and neurologic deficit in rats exposed to 1500 ppm CO, when added to those rats treated with CN, closely approximated the lactate and neurologic deficit of the combination treatment. Neurologic deficit was greatest in rats exposed to 2400 ppm CO. While in most cases the responses of the rats to CO and CN differed whether the substances were administered alone or in combination, a synergistic relationship is not suggested. An additive or less than additive relationship is more likely.

Immunohistochemical localization of rhodanese

The role of rhodanese in the detoxication of acute cyanide exposure is controversial. The debate involves questions of the availability of rhodanese to cyanide in the peripheral circulation. Blood-borne cyanide will distribute to the brain and may induce lesions or even death. The present study addresses the dispute by determining the distribution of rhodanese in tissues considered to have the highest rhodanese activity and thought to serve as major detoxication sites. The results indicate that rhodanese levels are highest in (1) hepatocytes that are in close proximity to the blood supply of the liver (2) epithelial cells surrounding the bronchioles (a major entry route for gaseous cyanide) and (3) proximal tubule cells of the kidney (serving to facilitate cyanide detoxication and elimination as thiocyanate). Rhodanese activity in the brain is low compared with liver and kidney (Mimori et al., 1984; Drawbaugh & Marrs, 1987); the brain is not considered to be a major site of cyanide detoxication. The brain, however, is the target for cyanide toxicity. In this study our goal was also to differentiate the distribution of rhodanese in an area of the brain. We found that the enzyme level is highest in fibrous astrocytes of the white matter. Cyanide-induced brain lesions may thus occur in areas of the brain lacking sufficient sites for detoxication.

The Erlangen micro-lightguide spectrophotometer EMPHO I

The Erlangen micro-lightguide spectrophotometer EMPHO 1 was designed for fast diffuse reflection (remission) spectrophotometry in small tissue volumes. The aim was to construct a compact, modular instrument with a high repetition rate which can be adapted to moving organs, e.g. the beating heart in situ, by the use of highly flexible micro-lightguides. Focusing problems, which cannot be solved when conventional optical devices such as microscopes are used in moving tissues, become negligible. A bandpass interference filter disk, which is rotated by a motor serves as a monochromating unit. One diffuse reflection spectrum in a selected wavelength domain is recorded during each revolution of the motor. Special filter disks, with spectral ranges of 400-520, 500-630, 600-1200 nm can be used for different tasks. The monochromated light is transmitted by means of a flexible fluid-lightguide to a photomultiplier tube. The electrical signal, which is proportional to the light intensity is recorded by an IBM-compatible AT. An analogue to digital converter has been developed for the AD conversion. Sampling of the spectra occurs in steps of 2 nm triggered by a decoding unit, containing an EPROM where the function between the wavelength-angular position characteristic of the filter disk is stored. A decoder wheel mounted on the same axle as the driving motor is used to program the decoder unit and to recall the wavelength position function. The decoding procedure enables a high wavelength reproducibility to be attained. The monochromating device allows a sampling velocity of 100 spectra per second. The EMPHO I has been successfully applied to experiments in the beating heart, the brain, the eye, the liver, the small intestine and the skeletal muscle of mammals. First investigations have also been performed in the heart during open heart surgery and in human skin. The apparatus has a high sampling rate and the small catchment volume allows measurements of remission spectra in tissue volumes supplied by only a few capillaries. The absolute oxygenation and the relative haemoglobin concentration can be determined by on-line computer evaluation of the recorded spectra and displayed on a screen.

Cyanide metabolism in the isolated, perfused, bloodless hindlimbs or liver of the rat

Female CD1 rats weighing 250-300 g were anesthetized with ip pentobarbital, 50 mg/kg, and either the liver or the hindlimbs were surgically isolated and perfused in situ with a Krebs-Henseleit buffer, pH 7.4, at 38 degrees C, containing 40 g/liter dextran and 30 mg/liter papaverine. Perfusion pressure was continuously monitored, and in most experiments, flow was maintained at the physiological rate of 8.5 ml/min. In-line Clark-type electrodes allowed the continuous measurement of oxygen extraction. Potassium cyanide to 0.15 mM was usually added to the perfusate just prior to the start of a run. After a period of equilibration, samples of the perfusate were taken periodically for cyanide (CN) and thiocyanate (SCN) analyses. The results were used to determine CN extraction ratios or clearance and rates of SCN formation. When it was apparent that a steady state had been reached with respect to the above, sodium thiosulfate (TS) was added to the perfusate (to 0.1, 1.0, or 2.0 mM), and periodic samples were again collected after an equilibration period. In the absence of albumin, TS rapidly and significantly increased the rate of conversion of CN to SCN in both the liver and the hindlimbs. The rate of CN clearance in milliliters per minute per kilogram perfused tissue was 20-fold greater in the liver than in the hindlimbs. However, when the results from hindlimbs were extrapolated to the total body skeletal muscle mass, the rate of CN clearance by the total liver mass was only 1.5-fold greater than in total muscle mass. In the absence of TS, total muscle mass cleared CN at a rate that was 2.6-fold greater than the total liver mass, but the rates in both tissues were very much less than in the presence of TS. The extraction ratio for CN in the liver was 0.8 and the clearance was dependent on the flow rate. The extraction ratio for CN in the hindlimbs was 0.2, and the clearance was independent of the flow rate. Thus, CN clearance by the liver probably increases (within limits) with increasing portal blood flow. Evidence was obtained for the existence of a significant CN "sink," particularly in the liver, which presumably represents reversible binding to unknown tissue constituents.

Histochemical localization of rhodanese activity in rat liver and skeletal muscle

A previously described histochemical technique was applied to the localization of rhodanese (thiosulfate sulfurtransferase, EC 2.8.1.1) activity in rat skeletal muscle and liver. The physiological function of rhodanese is controversial, but it and other sulfurtransferases can catalyze the conversion of cyanide to the much less toxic thiocyanate. The volume of distribution of cyanide in human and dog is said to correspond roughly to the blood volume. Because of this and other observations, it was hypothesized that sulfurtransferase activity associated with the vascular endothelium on smooth muscle layers of blood vessels might play a role in cyanide detoxification. However, little enzyme activity as identified histochemically was associated with those sites in comparison with others examined. As expected, high activity was found in the liver and moderately high levels were present in skeletal muscle. In muscles sectioned longitudinally, points of rhodanese staining occurred in linear arrays along the lengths of the muscle fiber corresponding to the location of mitochondria within the fiber. The original technique called for incubation of tissue sections with both thiosulfate and cyanide. When thiosulfate was omitted, staining for rhodanese activity was still clearly identifiable in both liver and muscle sections with cyanide alone. In muscle sections the inclusion of both thiosulfate and cyanide resulted in a preferential staining of type I fibers presumably because of their higher content of mitochondria. Thus, this technique is a potential alternative to the NADH dehydrogenase stain for distinguishing between type I and type II muscle fibers. Incubation of tissue sections with only thiosulfate produced results that did not appear to differ from those obtained when both substrates were omitted. From these observations it may be inferred that the endogenous pool of sulfane-sulfur available to sulfurtransferases is larger than any alleged endogenous pool of cyanide. Although sulfurtransferase activity in muscle appeared to be lower than that in liver, the total body muscle mass is greater than the liver mass. Thus, these results support other evidence that skeletal muscle may make a significant contribution to total cyanide biotransformation in the absence of exogenously added thiosulfate.

Cyanide-related changes in cerebral O2 delivery and metabolism in fluorocarbon-circulated rats

Cyanide-induced cytotoxicity is primarily a result of inhibition of O2 uptake by the terminal enzyme of the mitochondrial respiratory chain, cytochrome-c oxidase (cytochrome aa3). The oxidase in the brain is highly vulnerable to cyanide cytotoxicity, but few studies have evaluated the effects of cyanide on cerebral oxygen metabolism. In the present study, we measured oxidation-reduction responses of cerebrocortical cytochrome aa3 to cyanide and related changes in cerebral blood flow (CBF) and O2 metabolism (CMRO2). Accurate measurement of cytochrome aa3 redox state in vivo by reflectance spectrophotometry was accomplished by using fluorocarbon-circulated rats to eliminate spectral interference from hemoglobin. The data indicate that constant intravenous infusions of cyanide caused rapid, progressive reduction responses by cerebrocortical cytochrome aa3 concomitant with increases in CBF of up to 200%. However, CMRO2 was maintained near normal until cerebral O2 delivery began to fall. These cerebral oxidative responses to cyanide may be explained either by redistribution of intracellular O2 supply to mitochondria respiring in an O2-dependent manner or by branching effects within brain mitochondria in vivo.

Detection of an oxidizable fraction of cytochrome oxidase in intact rat brain

Rapid-scanning reflectance spectrophotometry was used to evaluate the reduction-oxidation state of cytochrome oxidase in normoxic rat brain. Reflectance spectra were recorded from intact blood-perfused cerebral cortices after increased oxidative metabolic activity induced by direct cortical stimulation. Reflectance spectra taken from blood-free rat brain and from the rat ear vascular bed were used to identify cytochrome and hemoglobin components of spectra taken from intact brain. Cortical stimulation provoked shifts toward increased oxidation of cytochrome oxidase that were detectable in reflectance spectra. Observations of an oxidizable fraction of cytochrome oxidase demonstrate that a fraction of the cytochrome oxidase pool exists in a reduced state in normoxic brain. The presence of reduced cytochrome oxidase suggests that oxygen delivery to the brain is restricted by microvascular control mechanisms either as a function of brain metabolic physiology or as protection against oxygen toxicity.

Liver damage does not increase the sensitivity of mice to cyanide given acutely

The major detoxification pathway for cyanide (CN) in many species is a biotransformation to the less toxic thiocyanate (SCN). Hepatic thiosulfate: cyanide sulfurtransferase (rhodanese) is the principal enzyme demonstrating in vitro catalytic activity. Despite the assumed importance of the hepatic enzyme for CN detoxification in vivo, the effects of liver damage (surgical or chemical) on cyanide lethality in animals have not been examined previously. Male CD-1 mice were pretreated with carbon tetrachloride (CCl4, 1 ml/kg, i.p.) 24 h prior to the administration of sodium cyanide (NaCN). In other experiments CCl4 was given in the same doses at both 48 h and 24 h prior to NaCN. Hepatotoxicity was documented by elevated serum glutamicpyruvic transaminase (SGPT) activity, by histologic evaluation of the extent of cellular necrosis, by electron microscopy of the mitochondrial fraction, and by the increased duration of zoxazolamine-induced paralysis. Lethality was not changed by CCl4 pretreatments when NaCN was given alone in doses of 4 or 6 mg/kg or at a dose of 10.7 mg/kg following sodium thiosulfate (Na2S203, 1 g/kg, i.p.). A small but statistically significant protective effect was exhibited by CCl4 when NaCN was given at a dose of 16 mg/kg following the administration of Na2S203. Rhodanese activity as measured in mitochondrial preparations fractionated from the livers of mice pretreated with CCl4 was not different from that in animals given the corn oil vehicle even though electron micrographs showed extensive mitochondrial damage. No difference in CN lethality was evident between sham-operated mice and partially (2/3) hepatectomized mice at 24 h post-surgery. An intact healthy liver does not appear to be essential for cyanide detoxification in mice whether or not thiosulfate is also given. Because rhodanese activity was slightly but significantly higher in mitochondria lysed by Triton X-100 than in intact mitochondria, the mitochondrial membrane may constitute a barrier to Na2S203.

Regional cerebral blood flow in normal blood circulated and perfluorocarbon transfused rats

Perfluorocarbon blood substitutes have been shown to exert a protective effect in animal models of cerebral ischemia. The mechanisms by which PFCs improve cerebral hemodynamics are uncertain, however decreased viscosity, small particle size and high oxygen solubility relative to plasma are important factors. Extensive perfluorocarbon exchange transfusion (FC-43) in the rat to a hematocrit of 1%, produces a 100% increase in total cerebral blood flow (FIO2 = 1.0, CaO2 = 6 vol%). Similar increases were seen in normal blood circulated animals breathing 12% O2 (CaO2 = 12 vol%). Therefore, immediately following PFC exchange and the resulting decrease in CaO2, oxygen delivery to the brain is maintained by increasing total blood flow in a manner similar to hypoxic hypoxia.