Free radicals, together with the disintegrity of biological membranes and cellular
structures come out with the results of the changes in enzyme activities followed
by the damages of cellular function and metabolism. This condition was attributed
to the initiative effect of some anaesthetic agents and drugs which were used
throughout general anaesthesia on oxidation (Khinev and
Dafinova, 1993). General anaesthesia can impair immunological defence mechanisms
and release inflammatory mediators and free Oxygen Radicals (OFRs) (Goode
et al., 1995). Damage to membrane lipids by free radicals is implied
by the appearance of lipid peroxidation products during general anaesthesia
(Halliwell et al., 1992; Kotani
et al., 1995). In this respect, it is important to know whether an
anesthetic or a sedative drug has antiradical properties and this feature provides
a potential benefit in critically ill patients. Some anesthetic agents were
investigated in the sense of antioxidative effects and effects on OFRs production
(Murphy et al., 1992; Davidson
et al., 1995; Chinev et al., 1995; Weiss
et al., 1997). It was indicated in many researches that phagocytic
and cytotoxic activities of alveolar macrophages were suppressed by using volatile
anaeshetic agents in animals. In a research in which oxidative stress were investigated,
it was observed that desfloran increased the MDA concentration and increase
in gluthathione peroxidase activity however sevofloran did not induce the production
of free oxigen radicals in sera and bronco-alveolar lavage taken from pigs (Allaouchiche
et al., 2001). It was indicated that free radicals were formed by
metabolized halothane via NADPH-sitokrom P-450 system and produced free radicals
initiates lipid peroxidation in cell membranes. It was also emphasized that
isoflurane which is less metabolized and produces few amounts of free radicals
is less toxic than halothane. This hypothesis was supported by the research
in which the damages of anaesthesia with halothane and isoflurane in blood cells
and its effect on lipid peroxidation and antioxidant enzymes were investigated
(Yesilkaya et al., 1998). Halothane, one of the
volatile anaesthetic agents used for general anaesthesia has the structure of
2-bromo-2-chloro-1,1,1-trifloroetan is a clear and sweet odor fluid. It is absorbed
rapidly throughout respiratory system and accumulated in especially connective
tissue. Few amount of it subject to biotransformation.
It is converted to the trifluoracetic acid from trifluor acetyl aldehyde as forced to the oxidative non-halojenization with metabolic enzymes. Additionally, organic bromide and chloride are released. Halothane is converted to difluorobromochloroetilene by facing to oxidative defluorination in a very small level and by loosing one of its fluor atom.
This substance leads to the some of the unwanted side effects of this drugas
it is bound the phospholipids covalently in the cells. Isoflurane has the structure
of 1-chloro-2,2,2-trifluoroethyldifluoromethylether is an isomer of enflorane.
As very few amount of this drug subject to biotransformation, very small amount
of flour and trifluor acetic acid produced. The amounts of these substances
are not enough to cause a cellular damage (Kaya, 2000).
The aim of this study was to investigate the production of possible free radicals
and lipid peroxidation before, during and after the anaesthesia of healthy dogs
with halothane and isoflurane.
MATERIALS AND METHODS
Animals and experimental procedures: This experiment was conducted on 14 mongrel, 10-36 month aged dogs admitted to the clinics of Kirikkale University, Faculty of Veterinary Medicine of for various reasons and required to have anaesthesia and determined to be healthy according to the clinical and hematologic inspection. Dogs were divided into two groups randomly. Body temperatures, respiration and hearth rates and blood oxygen saturations values were recorded in all dogs before and during anaesthesia. Protocol of the experiment was approved by The Animal Health Care Committee of the Faculty of Veterinary Medicine in Kirikkale University (10/21).
Induction and inhalation anaesthesia procedures: Following placement of a catheter in cephalic vein, 0.3 mg kg-1 diazepam (Diazem ampul, DEVA, Istanbul, Turkey) was administered for premedication. Intubation was performed after 10 mg kg-1 thiopental (Pental sodium, I.E.Ulagay, Istanbul, Turkey) was administered for induction of anesthesia. Each animal was randomly assigned to two groups of seven animals each. They were considered to be healthy based on physical and haematological examination. Anaesthesia was maintained with halothane (Halotan, Hoechst, Istanbul, Turkey) in the first group and isoflurane (Isoflurane, Adeka, Samsun, Turkey) in the second group. The fresh gas flow was 2 l min-1. Halothane (1-2.5%) and isoflurane (1-3%) were administered in 100% oxygen. Heart rate, respiration rate, oxygen saturation (SpO2) and body temperature were recorded (Peta°, KMA 800) during anesthesia. The clinical assessment of the depth of anaesthesia was evaluated by the anesthesist as presence of eyelid, pedal and anal reflexes and increase in the jaw tone. The anesthesia was maintained with spontaneous ventilation during 1 h, afterwards all dogs were recovered.
Activity of antioxidant enzymes: About five blood samples from each
dog; prior to premedication, just before gas anaeshesia administered and 1,
3 and 24 h after the anaeshesia were taken into the lithium-heparinized vacuum
tubes (Venosafe, Terumo Europe N.V. Leuven, Belgium) and transferred to the
laboratory. Plasma and erythrocytes were separated by centrifugation at 3000
rpm for 15 min (+4°C) immediately and the erythrocytes were stored at -70°C
until enzyme assays were performed. Malondialdehyde levels in the plasma samples
were determined spectrophotometrically by reaction with 2-Thiobarbituric Acid
(TBA) as described by Yoshioka et al. (1979).
Statistical analysis: When the main effects of the means between the treatment groups or between different times were significant then the pairwise comparisons of LSD means seperation was administered. p<0.05 was considered to be significant, unless otherwise noted.
RESULTS AND DISCUSSION
In this study, the effects of halothane and isoflurane on malondialdehyde levels
were investigated. Malondialdehyde levels were measured in the plasma of the
blood samples taken before premedication, after induction and 1, 3 and 24 h
after volatile anaesthesia administered.
|| Malondialdehyde levels of halothane and isoflurane groups
|| Body temperature, respiration and heart rate values of the
animals before and during anaesthesia
It was determined that MDA levels during the anaesthesia were decreased in
both anaesthesia groups when compared with prior to the anaesthesia. Additionally,
it was determined that MDA levels at 24 h after anaesthesia were elevated to
the levels prior to the anaesthesia in both anaesthesia groups (Table
Additionally, body temperature, respiration and heart rates were recorded at before anaesthesia and 10, 20, 30, 40, 50 and 60 min of the anaesthesia (Table 2).
The researchers have been reported that some hypnotics and sedatives had antioxidant
properties (Krumholz et al., 1995; Weiss
et al., 1997). Propofol, thiopental, midazolam and ketamine at clinical
plasma concentrations have minimal effects on OFRs production (Davidson
et al., 1995). Krumholz et al. (1995)
investigated the effects of thiopental, etomidate, ketamine and midazolam on
the generation of superoxide anion and hydrogen peroxide by polymorphonuclear
leukocyte in vitro. Thiopental inhibited superoxide anion as well as hydrogen
peroxide production. Neither etomidate nor ketamine influenced, midazolam suppressed
superoxide anion generation but only if a concentration far beyond clinical
relevance was used.
In another study, midazolam is reported to decrease superoxide anion production
in doses higher than those of clinical use (Krumholz
et al., 1995). However, it was found ineffective by the others (Weiss
et al., 1997; Erol et al., 2002).
Only thiopental and propofol have efficient oxygen scavenging properties (Weiss
et al., 1997). Superoxide dismutase is a prominent defence against
the lipid peroxidation products during general anaesthesia (Mercer
et al., 1994; McCord, 2000). Nitrous oxide,
fentanyl and droperidol increase lipid peroxidation in rat liver (Chinev
et al., 1995).
Propofol, thiopental, midazolam and ketamine at clinical plasma concentrations
have minimal effects on OFRs production (Davidson et
al., 1995). More recent studies have tried to show the potential antioxidant
activity of other anaesthetic agents such as propofol, midazolam, ketamine and
vecuronium (Kang et al., 1998; Tsuchiya
et al., 2002). These researches are commonly associated with MDA
measurement during different surgery procedures such as ischemia and reperfusion
injury. At the present time, there are only a few reports concerning the effects
of volatile anaesthetics on the antioxidant enzyme activities. Inhalation of
volatile anesthetics under mechanical ventilation induces an inflammatory response.
Allaouchiche et al. (2001), evaluated the bronchoalveolar
and systemic oxidative stress in swine during exposure to propofol, desflurane
and sevoflurane. They show that desflurane produces a systemic and a local oxidative
stress in comparison with the sevoflurane and propofol. The same researchers
also observed that animals exposed to desflurane have increased MDA concentrations
and enhanced glutathione peroxidase consumption in serum. Conversely, animals
exposed to propofol have lower circulating and local measurements of MDA levels
and reduced glutathione peroxidase consumption. Sevoflurane did not induce a
chemical reaction leading to the generation of oxygen free radicals. Hence,
propofol and sevoflurane were more likely to have antioxidant properties.
In a study conducted by Koksal et al. (2004),
it was determined that desflorane caused more lipid peroxidation systemically
and locally than sevoflorane, in healthy humans on whom laparoscopic cholecystotomy
operation was performed. In a study conducted on dogs to investigate the effects
of anaesthetic agents on liver, it was indicated that both isoflurane and sevoflorane
anaesthesia were safer than halothane anaesthesia (Topal
et al., 2003). Malondialdehyde is one of the important indicators
of oxidative metabolism that it was measured in the course of this study. It
was indicated in many scientific studies that there were changes in the activity
of the drugs with various doses and anaesthesia types and that they affected
In this study, it was determined that halothane and isoflurane did not cause any negative effect on oxidative metabolism under applied anaesthesia procedure.
Researchers would like to thank Dr. Mehmet Basalan for linguistic revision of the manuscript and statistical interpretation.