| Propofol (2,6-diisopropylphenol) has been the most common intravenous anesthetic as an induction and maintenance agent and is widely used as a sedative agent in the intensive care unit (ICU). Many researches have been done to investigate the anesthetic mechanism of propofol, but the mechanism has not been made out very clearly until today.In the past decade, a large body of experimental observations have accumulated that the central GABAA receptors represent an important target in mediating the anesthetic mechanism of propofol. The central GABAA receptors scatter in the brain, but it is more intensive in some cerebral tissues than the others. As we know, Positron emission tomography (PET) allows researchers to study brain function in vivo, and it has been applied to investigate the nature of the action of propofol in the brain. Using this technique, it has been found that the regional cerebral glucose metabolism and regional cerebral blood flow is depressed by propofol more significantly in some of the cerebral tissues. Based on these researches, it can be assumed that propofol concentrations are discordant in various cerebral tissues. Therefore, the cerebral uptake and regional distribution of propofol must be investigated to understand its anesthetic mechanism.The research of cerebral uptake of propofol usually bases on mass balance principles. By determinations of propofol concentrations in arterial and venous blood of cerebral circulation using high-pressure liquid chromatrography(HPLC), we can evaluate indirectly the cerebral uptake of propofol by calculating the areas between the arterial and venous concentration-time curves. However, the concentrations of propofol at its site of action in the brain can't be accurately counted and the character of regional cerebral distribution of propofol can't be revealed by this method. To improve the research of cerebral uptake, the concentrations of propofol in different parts of the brain must be detected directly by anatomy.Sufentanil has many advantages combining with propofol in clinical anesthesia,but no evidence can prove whether other anesthetics such as sufentanil can influence the cerebral uptake and regional distribution of propofol . Recently, it has been found that sufentanil has different effect on various cerebral tissues and can disturb the cerebral metabolism and cerebral blood flow. Because cerebral blood flow is involved in the cerebral uptake of propofol, it can be assumed that sufentanil may have effect on the cerebral uptake and regional distribution of propofol.This study is firstly aimed to investigate the cerebral uptake and distribution of propofol in different cerebral tissues (frontal lobe, parietal lobe, temporal lobe, cingulated gyrus, midbrain, pons, cerebellum, thalamus and hippocampus) after a single bolus or a constant rate intravenous infusion. Secondly, the aim of this study is to explore the effect of sufentanil on the cerebral uptake and regional distribution of propofol. Meanwhile, we improved the method of HPLC analysis for determination of propofol concentration of cerebral tissue and blood plasma. Part One The cerebral uptake and distribution of propofol after a single bolus intravenous injection in dogsObjectiveTo investigate the cerebral uptake and distribution of propofol in different cerebral tissues after a single bolus intravenous injection of propofol or combined with sufentanil in dogs.Material and methodsTwelve male dogs aged 12-18 months weighing 10-12 kg were divided randomly into two groups (group A and B). The venous channel was established in the great saphenous vein of the right hind leg in every animal. Animals were anesthetized with propofol via the venous channel at a single bolus (7mg·kg-1) in 15 sec in group A. After sufentanil (1μg·kg-1) was intravenously injected, propofol (7mg·kg-1) was infused in 15 sec in group B.As the eyelid reflex disappeared,blood samples were collected by right internal carotid and internal jugular vein respectively for determination the plasma concentration of propofol in two groups. Then the animal was scarificed immediately by decapitation. The frontal lobe, parietal lobe, temporal lobe, cingulated gyrus, midbrain, pons, cerebellum, thalamus and hippocampus were dissected for determination the concentration of propofol.Propofol concentration was determined by modified HPLC-UV. External standard was a control article of propofol. The analysis was performed with a Dikma Diamonsil C18 reverse-phase column (200×4.6mm, 5μm) and a 2996 Waters ultraviolet detector (270nm). The solvent system was acidum aceticum-methanol-ammonium acetate at flow rate of 1ml·min-1. The brain tissue samples were extracted with acetonitrile (2ml·g-1) and homogenized. The blood samples were extracted with acetonitrile (di-volume). After being centrifuged, the supernatant was submitted to HPLC analysis.Measurement data were expressed as mean±standard deviation. All statistical calculations were performed using SPSS 13.0 for windows. The One-Way ANOVA ,factorial analysis and paired t-test were used to test the differences for measurement data. Multiple comparisons were analyzed by using Student-Newman-Keuls (SNK) test. Differences were considered statistically significant when P was less than 0.05.ResultsIn group A and B, the blood plasma concentration of propofol in internal carotid artery (11.711±1.634,11.700±1.585μg·ml-1) was higher than that in internal jugular vein (5.424±0.802,5.444±0.780μg·ml-1) respectively (P<0.05).The propofol concentration in internal carotid artery of group A was the same as that of group B (P >0.05).In group A, the propofol concentrations in frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, thalamus, midbrain, pons, cerebellum were 8. 007±0. 987,8. 015±1. 010,8.182±1. 051, 5. 593±0. 747, 8. 232±1. 029, 10. 644±1. 660,8. 558±1. 052, 8. 389±1. 070 and 7.836±0. 964μg·g-1 respectively. The propofol concentrations were highest in thalamus and lowest in hippocampus (P <0.05).In group B, the propofol concentrations in the frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, thalamus, midbrain, pons, cerebellum were 8.154±1. 542,8.125±1. 572, 8. 340±1. 544, 5. 605±0. 729, 8. 351±1. 738, 11. 2 40±2.111, 8. 434±1. 586, 8. 567±1. 687 and 7.968±1.323μg·g-1 respectively. The propofol concentrations were highest in thalamus and lowest in hippocampus (P <0.05).No differences were observed in propofol concentrations in brain tissues between group A and B (P >0.05).ConclusionsAs the eyelid reflex disappeared after a single bolus propofol intravenous injection in dogs,the cerebral uptake of propofol is unstable and the propofol concentrations are discordant in various cerebral tissues, highest in the thalamus, lowest in the hippocampus.Under above condition, sufentanil(1μg·kg-1) has no influence on the cerebral uptake and regional distribution of propofol.Part Two The cerebral distribution of propofol when the cerebral uptake being in equilibrium in dogsObjectiveTo investigate the cerebral distribution of propofol in different cerebral tissues (frontal lobe, parietal lobe, temporal lobe, cingulated gyrus, midbrain, pons, cerebellum, thalamus and hippocampus) when the cerebral uptake being in equilibrium after a constant rate intravenous infusion in dogs.Material and methodsSix male 12-18 months old dogs weighing 10-12kg were used in this study. Animals were anesthetized with propofol at a single bolus (7mg·kg-1) in 15s and then was infused at a constant rate of 70 mg·kg1·h-1 using a microinfusion pump via the great saphenous vein of right hind leg.Blood samples were collected by the right internal carotid and internal jugular vein at 30 min (T30) and 50 min (T50) after propofol was infused for measurement the blood plasma concentrations of propofol. Then the animal was scarificed immediately by decapitation. At T50, the frontal lobe, parietal lobe, temporal lobe, cingulated gyrus, midbrain, pons, cerebellum, thalamus and hippocampus were dissected for determination the concentration of propofol.Propofol concentration was determined by modified HPLC-UV. External standard was a control article of propofol. The analysis was performed with a Dikma Diamonsil C18 reverse-phase column (200×4.6mm, 5μm) and a 2996 Waters ultraviolet detector (270nm). The solvent system was acidum aceticum-methanol-ammonium acetate at flow rate of 1ml·min-1. The brain tissue samples were extracted with acetonitrile (2ml·g-1) and homogenized. The blood samples were extracted with acetonitrile (di-volume). After being centrifuged, the supernatant was submitted to HPLC analysis.Measurement data were expressed as mean±standard deviation. Statistical analysis was undertaken using SPSS 13.0 for windows. The One-Way ANOVA and paired t-test were used to test the differences for measurement data. Multiple comparisons were analyzed by using SNK test. Differences were considered statistically significant when P was less than 0.05.ResultsThe propofol concentrations in internal carotid artery and internal jugular vein blood plasma were 3.107±1. 067, 3. 095±1. 085μg·ml-1 at T30 and 3. 090±1.101,3.117±1.091μg·ml-1 at T50 respectively. There were no significant differences between the propofol concentrations in internal carotid artery and internal jugular vein blood plasma at T30 and T50 (P>0.05).The propofol concentrations in the frontal lobe, parietal lobe, temporal lobe, hippocampus, cingulate gyrus, thalamus, midbrain, pons, cerebellum were 3. 086±1.123, 3.116±1. 125, 3. 073±1. 158, 3.117±1. 090, 3. 075±1. 178, 3. 073±1.146,3.075±1. 151,3.102±1.174 and 3. 072±1.192μg.g-1 respectively. Propofol were evenly distributed in these cerebral tissues at T50 (P>0.05). Conclusions1. At 30min and 50 min after a constant rate intravenous infusion , the cerebral uptake of propofol is in equilibrium.2. When the cerebral uptake of propofol is in equilibrium , propofol is distributed evenly among regional cerebral tissues in dogs.SummaryThis study is to investigate the cerebral uptake and distribution of propofol in different cerebral tissues (frontal lobe, parietal lobe, temporal lobe, cingulated gyrus, midbrain, pons, cerebellum, thalamus and hippocampus) after a single bolus or a constant rate propofol intravenous infusion. We can reach conclusions as follows:1. As the eyelid reflex disappeared after a single bolus propofol intravenous injection in dogs, the cerebral uptake of propofol is unstable , and the propofol concentrations are discordant in various cerebral tissues, highest in the thalamus, lowest in the hippocampus.2. With a single bolus propofol intravenous injection, sufentanil(1μg·kg-1) has no influence on the cerebral uptake and regional distribution of propofol in dogs.3. At 30min and 50 min after a constant rate intravenous injection , the cerebral uptake of propofol is in equilibrium and propofol is distributed evenly among regional cerebral tissues in dogs.4. The HPLC- ultra-violet spectroscopy combining with precipitation method can be used appropriately to determinate the propofol concentration of blood plasma and brain tissue.
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