OBJECTIVETo investigate the effect of propofol at doses for different anesthesia depths on γ-aminobutyric acid (GABA) in different cerebral regions at propofol uptake equilibrium in dogs.

METHODSTwelve 12-18-month-old healthy hybrid dogs weighing 10-12 kg were randomly divided into light anesthesia group (n=6) and deep anesthesia group (n=6) with a single bolus dose of propofol (5.5 and 7.0 mg/kg, respectively) completed in 15 s followed by intravenous propofol infusion at a constant rate (55 and 70 mg·kg(-1)·h(-1), respectively). Blood samples (2 ml) were taken from the internal carotid artery and jugular vein to measure plasma propofol concentrations 50 min after the start of the infusion. The dogs were then sacrificed and tissues were taken from different brain regions and the cervical cord to measure GABA concentrations using high-pressure liquid chromatography (HPLC).

RESULTSThe plasma propofol concentrations in internal carotid artery and jugular vein were similar in both light anesthesia group (3.00 ± 0.31 and 3.10 ± 0.51 µg/ml, respectively, P>0.05) and deep anesthesia group (6.41 ± 0.05 and 6.40 ± 0.11 µg/ml, respectively, P>0.05). GABA concentrations in the brain regions were significantly higher in deep anesthesia group than in light anesthesia group (P<0.05). The dorsal thalamus and hypothalamus showed greater GABA variations [(83.83 ± 2.230%) and (85.83 ± 1.72)%] compared to other brain regions at different anesthesia depths (P<0.05).

CONCLUSIONSIn both groups, plasma propofol concentrations in the internal carotid artery and internal jugular vein reach equilibrium at 50 min of propofol infusion. The variation of GABA is associated with the anesthesia depth of propofol, and GABA variation in the dorsal thalamus and hypothalamus plays an important role in propofol anesthesia.