INFLUENCE OF ANAESTHETICS ON THE BALANCE BETWEEN PRODUCTION AND UTILIZATION OF ENERGY IN THE BRAIN

Abstract— The influence of general anaesthesia upon the metabolic state of the brain was evaluated from the tissue concentrations of ATP, ADP and AMP, and from the concentrations of glycolytic and citric acid cycle intermediates, in immobilized and artificially ventilated rats anaesthetized either with 70% N₂O, 1% halothane or 60 mg/kg of pentobarbitone. The results were compared to the results obtained on awake animals in fentanyl-analgesia. The adenylate energy charge was identical in all groups studied and there were no H⁺-independent changes in the phosphocreatine/creatine ratios. In pentobarbitone anaesthesia there was an accumulation of glucose 6-phosphate and a fall in fructose 1,6-diphosphate, indicating inhibition of phosphofructokinase. No significant changes in these metabolites were observed with halothane or nitrous oxide anaesthesia and the substrate patterns differed from that obtained with pentobarbitone.
The blood glucose concentrations were higher in the unanaesthetized, immobilized rats given fentanyl than in those anaesthetized. There was a direct relationship between the glucose concentrations in blood and in tissue. The glucose concentration ratios intracellular water to blood were higher in the anaesthetized than in the unanaesthetized animals, increasing with increasing depth of anaesthesia. The intracellular lactate concentrations were lowest in the groups given pentobarbitone and fentanyl citrate, and there was thus no direct relationship between lactate concentration and depth of anaesthesia.     

The effects of althesin on luteinizing hormone release cannot be explained by actions of the GABAA receptor alone

Althesin and pentobarbitone are anaesthetics which act by prolonging the open time of the chloride channels of the GABA(A) receptor. To explain why luteinizing hormone (LH) release is less depressed by Althesin anaesthesia than by pentobarbitone anaesthesia we suggest that either Althesin is a less potent anaesthetic in the preoptic area or that Althesin as well as stimulating GABA(A) receptors has some other action, perhaps stimulation of GABA(B) receptors, which may facilitate LH release. To investigate the relative potency of the anaesthetics in the preoptic area nine cats were anaesthetised, six with Althesin and three with pentobarbitone, mounted in a stereotaxic frame and prepared for extracellular recording and stimulation of spontaneously active units in the preoptic region. When cats anaesthetised with Althesin were compared with cats anaesthetised with pentobarbitone there were significantly fewer of these units for the number of tracks made. These units also had a significantly lower frequency and a distribution significantly skewed toward lower frequencies. Electrical stimulation of the fornix and of sites in the medial basal hypothalamus and medial forebrain bundle inhibited about 50% of the units and the median duration of the inhibitory pause was significantly longer following stimulation at all three sites in cats anaesthetised with Althesin. We conclude that Althesin is a more potent anaesthetic than pentobarbitone in the preoptic region and that its effects on LH release cannot be explained by its effects on the GABA(A) receptor alone.     

Effect of change in particle number on pulmonary clearance of aerosolized 99mTc-DTPA

Pulmonary clearance (PCl) of inhaled aerosolized 99mTc-diethylenetriamine pentaacetic acid (DTPA) across the alveolocapillary membrane is diffusion limited. Therefore, if the mixing of the 99mTc-DTPA in the aqueous hypophase underlying surfactant is slow or incomplete or if there were no hypophase, an increase in the alveolar surface area occupied by 99mTc-DTPA particles would increase the absorption rate. The aim of this study was to examine whether there is an effect on PCl of changing the number of inhaled particles. The change in particle number was accomplished by a setup of four parallel jet nebulizers feeding a central delivery chamber of 400 cm3. We performed two kinds of experiments in eight healthy nonsmokers between 28 and 52 yr of age. In the first experiment, 99mTc-DTPA in saline was nebulized in one nebulizer, while saline was nebulized in the other three. In the second experiment the number of inhaled particles containing 99mTc-DTPA was increased by a factor of four by nebulizing 99mTc-DTPA in saline in all four nebulizers simultaneously. Increasing the number of inhaled 99mTc-DTPA particles caused an increase in PCl of 24.2% (P less than 0.01). We conclude that there is a slight but significant effect of changing the number of DTPA particles on PCl and that this is probably due to an uneven mixing of the 99mTc-DTPA in the aqueous hypophase underlying the surfactant lining and the alveoli.     

Nociception after intraperitoneal injection of a sodium pentobarbitone formulation with and without lidocaine in rats quantified by expression of neuronal c-fos in the spinal cord--a preliminary study

After a search on Medline, it appears that intraperitoneal injection of sodium pentobarbitone is often used for anaesthesia and euthanasia of rodents. In the present pilot study in rats, spinal nociception after intraperitoneal injection of sodium pentobarbitone, with and without lidocaine, was examined by estimation of the number of c-fos-expressing neurones in the spinal dorsal horn. One group of rats received an intraperitoneal injection of 0.4 mL/kg sodium pentobarbitone (100 mg/mL; n=4). Another group of rats received a similar intraperitoneal injection of sodium pentobarbitone formulated with lidocaine 10 mg/mL (n=4); a control group received a similar intraperitoneal injection of 0.9% saline (n=4). After 3 h, the animals were re-anaesthetized and perfused with 4% formaldehyde, and the spinal cord was collected and processed by immunohistochemistry for stereological quantification of the number of neurones with c-fos-like immunoreactivity (FLI). Intraperitoneal injection of the sodium pentobarbitone formulation caused a significantly increased number of neurones with FLI in the spinal cord (3930+/-247; mean+/-SEM; P<0.001) compared with the saline control group (765+/-131). The lidocaine added to the sodium pentobarbitone formulation significantly reduced the number to 2716+/-393 (P<0.05). In conclusion, intraperitoneal injection of sodium pentobarbitone caused a significant increase in nociception which was lowered by adding lidocaine to the formulation, although it was still significantly higher than the control level. Further studies are needed with the aim of optimizing the lidocaine concentration and also to examine the effect of the combination of lidocaine with a long-acting local anaesthetic agent, e.g. bupivacaine.     

The influence of pre-anaesthetic administration of buprenorphine on the anaesthetic effects of ketamine/medetomidine and pentobarbitone in rats and the consequences of repeated anaesthesia

Rats received pentobarbitone (60, 48 and 36 mg/kg i.p.) or ketamine/medetomidine (75/100, 60/80 and 45/60 mg/microg/kg i.p.) alone, or one hour following buprenorphine (0.5 mg/kg s.c.). Animals were anaesthetized once per week for 6 weeks with one of three anaesthetic doses according to a randomized block design. In the pentobarbitone group, animals which received buprenorphine had longer sleep times (236 +/- 22 cf. 204 +/- 21 min) and longer durations of surgical anaesthesia (83 +/- 14 cf. 27 +/- 8 min) (P<0.01), these effects being potentiated with increasing anaesthetic doses (P<0.01). A greater degree of respiratory depression was found in animals that received buprenorphine (P<0.01) although this was judged clinically acceptable in all cases. Unexpectedly high mortality and a high incidence of anaesthetic complications (nine of 16 animals) in the ketamine/medetomidine group made statistical analysis of these data impossible. We conclude that for pentobarbitone, pre-anaesthetic administration of buprenorphine reduces the dose of anaesthetic required to produce surgical anaesthesia, in addition to the presumed benefits of pre-emptive analgesia. In view of the high mortality encountered, we advise caution when considering pre-anaesthetic use of opioids in combination with ketamine/medetomidine in rats.     

Metomidate, etomidate and fentanyl as injectable anaesthetic agents in mice

Light surgical anaesthesia lasting 12-15 min was produced by metomidate at 50 mg/kg and by etomidate at 30 mg/kg after intraperitoneal injection. Full surgical anaesthesia lasting about 160 min was achieved after subcutaneous injection of a metomidate-fentanyl mixture (60 mg/kg: 0.06 mg/kg) and this proved superior to etomidate-fentanyl given subcutaneously or intraperitoneally. It was concluded that metomidate-fentanyl is superior to pentobarbitone and tribromoethanol as an injectable anaesthetic for mice.     

Four methods for general anaesthesia in the rabbit: a comparative study

The efficacy and safety of pentobarbitone, ketamine/xylazine, fentanyl/fluanisone/diazepam, and halothane/nitrous oxide anaesthesia were compared in 4 groups of six New Zealand White rabbits. Heart and respiratory rates, body temperature, reflexes, blood pressure and blood gases were measured. Pentobarbitone appeared to be unsuitable for anaesthesia in rabbits, as 5 of the 6 rabbits to whom it was administered, required artificial respiration or died. The combinations of ketamine/xylazine and fentanyl-fluanisone/diazepam both produced unpredictable levels of anaesthesia together with a substantial decline in arterial blood pressure and PO2. Despite a severe drop in blood pressure (up to 37.5%), anaesthesia with halothane and nitrous oxide was found to be superior to the other anaesthetic agents.     

The effect of alphaxalone-alphadolone, propofol, and pentobarbitone anaesthesia on the β-endorphin and ACTH response to haemorrhage in the pig

In the literature there appears to be variability in reported levels of certain hormones during haemorrhage, specifically adrenocorticotrophic hormone (ACTH) and β-endorphin. It is possible that this variability may be due to the choice of anaesthetic. Therefore, the effect of 3 common research-only anaesthetic agents (alphaxalone-alphadolone, propofol, and pentobarbitone) on ACTH and β-endorphin levels during haemorrhage was assessed in pigs. Animals were divided into 3 groups: group I received alphaxalone-alphadolone (n = 5), group II received propofol (n = 6), and group III received pentobarbitone (n = 6). Pigs were subjected to a continuous fixed-volume haemorrhage under one of the above anaesthetics while being mechanically ventilated. ACTH and β-endorphin levels increased significantly during haemorrhage under propofol and pentobarbitone anaesthesia but not with alphaxalone-alphadolone. For ACTH there was no significant difference between the groups, whereas for β-endorphin there was a significant difference between the propofol- and pentobarbitone-anaesthetized pigs. The increase in heart rate during haemorrhage was significantly different between the alphaxalone-alphadolone and propofol as well as between the propofol and pentobarbitone groups. The drop in blood pressure was only significantly different between the alphaxalone-alphadolone- and propofol-anaesthetized pigs. These results indicate that the choice of anaesthetic agent can affect the hormone response to haemorrhage and may account for the variable hormone levels reported in the published literature to date.     

Intraperitoneal pentobarbitone anaesthesia of Mystromys albicaudatus

Anaesthesia trials with intraperitoneal (i.p.) pentobarbitone sodium in Mystromys albicaudatus indicated that the optimum dose is between 4 and 5 mg/100 g bodyweight. No differences were detected in duration of anaesthesia associated with sex or time of day.     

Is nebulized saline a placebo in COPD?

Background

Many trials of nebulized therapy have used nebulized saline as a "placebo". However, nebulized isotonic saline is sometimes used to assist sputum expectoration and relieve breathlessness in COPD patients. We designed this study to establish if nebulized saline had a placebo effect or a clinical effect.

Methods

40 patients were studied following hospital admission for exacerbated COPD (mean FEV1 30% predicted). Patients were randomised to single-blind administration of either 4 mls of nebulized isotonic saline using an efficient nebulizer (active group n = 20) or an inefficient nebulizer (placebo group n = 20). Spirometry and subjective breathlessness scores (Modified Likert Scale) were measured before nebulized treatment and 10 minutes after treatment.

Results

There was no significant change in FEV1 after active or placebo nebulized saline treatment. Patients reported a 4% improvement in mean breathlessness score following placebo (Wilcoxon test; p = 0.37) compared with 23% improvement following active nebulized saline (p = 0.0001). 65% of patients given active nebulized saline but only 5% of the placebo group reported that mucus expectoration was easier after the treatment.

Conclusions

This study lends support to the current use of nebulized saline to relieve breathlessness (possibly by facilitating sputum clearance) in COPD patients. Lung function was not affected. Nebulized saline can therefore be used as a placebo in bronchodilator studies involving COPD patients but it cannot be used as a placebo in trials assessing symptom relief.     

Production of corticosterone in male homozygous Brattleboro rats

Plasma concentration, metabolic clearance rate and in vitro adrenal production of corticosterone were measured in Brattleboro male rats homozygous for diabetes insipidus (DI) and in Long-Evans male rats (LE) as controls in resting conditions, under stress caused by pentobarbitone anesthesia and surgery and after three days water deprivation. In resting animals, plasma concentrations and in vitro adrenal production of corticosterone were higher in DI rats than in LE rats. Under pentobarbitone anesthesia and surgery, plasma concentrations and metabolic clearance rate of corticosterone were slightly but not statistically lower in DI rats; however, the in vivo production rate of corticosterone was significantly lower. After three days water deprivation, increasing plasma corticosterone level was consistently higher in DI than in Le rats. These results are not in favour of a reduced glucocorticoid activity of the adrenal of DI rats and of an important role played by vasopressin on the stimulation of the hypothalamopituitary adrenal activity at least in resting conditions; its role may depend upon stressful circumstances.     

Beta-adrenergic agonist therapy accelerates the resolution of hydrostatic pulmonary edema in sheep and rats.

To determine whether beta-adrenergic agonist therapy increases alveolar liquid clearance during the resolution phase of hydrostatic pulmonary edema, we studied alveolar and lung liquid clearance in two animal models of hydrostatic pulmonary edema. Hydrostatic pulmonary edema was induced in sheep by acutely elevating left atrial pressure to 25 cmH(2)O and instilling 6 ml/kg body wt isotonic 5% albumin (prepared from bovine albumin) in normal saline into the distal air spaces of each lung. After 1 h, sheep were treated with a nebulized beta-agonist (salmeterol) or nebulized saline (controls), and left atrial pressure was then returned to normal. beta-Agonist therapy resulted in a 60% increase in alveolar liquid clearance over 3 h (P < 0.001). Because the rate of alveolar fluid clearance in rats is closer to human rates, we studied beta-agonist therapy in rats, with hydrostatic pulmonary edema induced by volume overload (40% body wt infusion of Ringer lactate). beta-Agonist therapy resulted in a significant decrease in excess lung water (P < 0.01) and significant improvement in arterial blood gases by 2 h (P < 0.03). These preclinical experimental studies support the need for controlled clinical trials to determine whether beta-adrenergic agonist therapy would be of value in accelerating the resolution of hydrostatic pulmonary edema in patients.     

EFFECTS OF EXCITATION AND ANAESTHESIA ON THE GLUTAMINE CONTENT OF THE RAT BRAIN WITH A REFERENCE TO THE ADMINISTRATION OF GLUTAMINE

Abstract— A study of the factors affecting the ghtamine content in brain of rats showed that it was significantly decreased by intraperitoneal injection of physiological saline and by the stimulus of decapitation. It fell markedly at the stage of delirium (excitement) of pentobarbitone sodium anaesthesia and returned to the original value in light and deep surgical anaesthesia; after pentylenetetrazol injection the glutamine content showed a tendency to decrease but this change was only significant in relation to its post-saline level when the convulsant and 0.9 % NaCl were given to lightly-anaesthetized animals.
The i.p. administration of glutamine temporarily abolished the decrease in its concentration in the brain caused by injection and decapitation but never raised it above the original level. Many rats previously treated with glutamine showed no signs of excitement during the induction period of pentobarbitone sodium anaesthesia, and those which were excited showed a comparatively smaller decrease of brain glutamine content. whereas in the anaesthetic state there was no change in the content of brain glutamine after glutamine had been administered. Pentylenetetrazol given at the dose level of 200 mg/kg, but not at that of 100 mg/kg, resulted in the uptake of the added glutamine by the brain up to its normal concentration. Hence, the added glutamine did not readily enter normal or anaesthetized brain, but did penetrate the hyperactive brain where its level had fallen.
The brain levels of free glutamic and aspartic acids were not affected, in general, by procedures which increased cerebral activity. Glutamate was decreased by deep anaesthesia, whereas aspartate was not significantly altered in any of the conditions which were tested.
The significance of these results in relation to cerebral ammonia metabolism and possible changes of the permeability of the tissue to glutamine in different functional states is discussed.     

Convulsive properties of various organoselenium compounds]

Three organo-selenium compounds have been synthetized : methyl seleno-2 benzoic acid, acetylseleno-2 benzoic acid and diselenosalicylic acid. These compounds induce convulsive seizures in the rat, the most active of them being methyl seleno 2 benzoic acid. Convulsions are stopped after anaesthesia with pentobarbitone.     

Alterations in pituitary gland sensitivity in ram lambs to physiological doses of gonadotrophin-releasing hormone (GnRH), after divergent selection based on the luteinizing hormone response to a pharmacological GnRH challenge.

Divergent selection in 10-week-old Finn-Dorset ram lambs was based on the luteinizing hormone (LH) response to a pharmacological dose of GnRH (5 micrograms). After eight generations of selection, the LH responses of the two lines (low and high) to GnRH differed by a factor of five. This study investigates the pituitary sensitivity of the two lines to exogenous GnRH. Initially, two pilot studies were performed: one to determine the range of doses of GnRH which would stimulate LH pulses of similar amplitude to those seen endogenously, and the other to confirm that sodium pentobarbitone prevents pulsatile LH secretion in prepubertal ram lambs. The results indicated that barbiturate anaesthesia suppressed pulsatile LH secretion in castrated and intact ram lambs. A model system was therefore constructed in 18 10-week-old intact ram lambs (high n = 7, low n = 11), whereby endogenous pulsatile LH secretion was prevented by sodium pentobarbitone anaesthesia and the amplitudes of LH pulses produced in response to different doses of exogenous GnRH could be measured. The GnRH dose-response curves demonstrated that there was a five-fold difference in the sensitivity of the pituitary glands of the two lines to stimulation with GnRH. The projected minimum concentration of GnRH required to produce a measurable pulse of LH was 4.75 ng for the high-line animals and 26.6 ng for the low-line animals. The results indicated that the low-line animals required five times more GnRH than the high-line lambs to stimulate LH pulses of similar amplitude (high line 43.67 ng; low line 206.55 ng). These results demonstrate that selection has produced two lines of sheep which differ in the control of LH secretion at the level of the hypothalamus-pituitary gland.     

Neurophysiological alterations following fluvalinate administration in mice.

Median lethal dose (LD50) of fluvalinate (Marvik 25EC) was 105 (94.6-116.5 mg/kg, ip) in albino mice. Gross observable signs were dose dependent and indicative of central and peripheral nervous system stimulation. Fluvalinate, at 10.5 and 21.0 mg/kg, ip doses in mice, facilitated maximal electroshock seizures, reduced reaction time in analgesic test and enhanced duration of ether anaesthesia. Acute and subacute (7 days) treatment at lower and higher doses enhanced pentobarbitone sleeping time. Acute and subacute treatment (7 days) with phenobarbitone (50 mg/kg, ip) prior to fluvalinate enhanced toxicity of fluvalinate.     

The effects of inhaled house dust mite on airway barrier function and sensitivity to inhaled methacholine in mice

Asthma is functionally characterized by increased airway sensitivity and reactivity. Multiple mechanisms are believed to underlie these functional disorders, including impairment of airway wall barrier function. One proposed mechanism of impaired barrier function is through the direct consequence of proteolytic properties of inhaled allergens, including house dust mite (HDM). Here, we have observed the direct effects of HDM on airway barrier function and response to nebulized or intravenous methacholine. HDM na?ve BALB/c mice were anesthetized, exposed to intranasal or intratracheal HDM (15 or 100 μg), and allowed to recover for 30 min or 2 h before methacholine challenge. A separate group of mice was exposed to intratracheal poly-L-lysine (PLL; 100 μg) for a duration of 30 min. This group served as a positive control for the presence of impaired barrier function and airway hypersensitivity. Negative control mice received saline challenges. Outcomes included assessment of lung mechanics in response to nebulized or intravenous methacholine as well as clearance of intratracheally instilled technetium-labeled ((99m)Tc) DTPA to evaluate airway epithelial barrier function. We found that PLL produced a leftward shift in the dose-response curve following nebulized but not intravenous methacholine challenge. This was associated with a significantly faster clearance of (99m)Tc-DTPA, indicating impairment in airway barrier function. However, HDM exposure did not produce changes in these outcomes when compared with saline-exposed mice. These findings suggest that direct impact on airway barrier function does not appear to be a mechanism by which HDM produces altered airway sensitivity in airway disease.     

High-frequency oscillatory ventilation increases canine pulmonary epithelial permeability

To investigate the effect of high-frequency oscillatory ventilation (HFOV) on the pulmonary epithelial permeability, we measured the clearance rate of nebulized sodium pertechnetate (99mTcO4-) and diethylenetriaminepentaacetate (99mTc-DTPA) before and after a 4-h period of mechanical ventilation in anesthetized mongrel dogs. The animals also underwent experiments with 4 h of spontaneous breathing (SB) and intermittent positive-pressure ventilation (IPPV) with and without addition of positive end-expiratory pressure (PEEP) for comparison. After IPPV and SB there was no change in the clearance rate of either 99mTcO4- or 99mTc-DTPA. After IPPV + PEEP and HPOV (8 and 16 Hz), there was an increase in the clearance rate of 99mTc-DTPA, but an increase in clearance rate of 99mTcO4- was seen after IPPV + PEEP only. In a separate group of dogs an increase in end-tidal lung volume was demonstrated after 4 h of ventilation with IPPV + PEEP (but not after HFOV), and this may account for the measured increase in 99mTcO4- clearance. We conclude that an increase in 99mTc-DTPA clearance rate after HFOV signifies an increase in pulmonary epithelial permeability, possibly through the mechanism of damage to the intercellular junctions during HFOV.     

Noradrenaline thermogenesis in conscious and anaesthetised pouched mice (Saccostomus campestris)

1. The metabolic response to injections of noradrenaline (NA) and saline (control) was investigated in conscious and anaesthetised (sodium pentobarbitone) pouched mice, Saccostomus campestris. 2. NA injection produced a calorigenic response which was significantly greater than that elicited by saline injection in both conscious and anaesthetised animals. 3. This calorigenic response was enhanced by motor activity in conscious pouched mice, but the exclusion of measurements recorded during visible activity eliminated the influence of movement. 4. Anaesthetised pouched mice underwent mild Hypothermia and displayed a retarded metabolic response to NA injection which suggests that anaesthesia affects the expression of NA-induced thermogenesis. 5. The validity of proposed techniques for the measurement of NA thermogenesis is further discussed.