Propofol Sedation Is Reduced by Δ9-Tetrahydrocannabinol in Mice

BACKGROUND: A9-Tetrahydrocannabinol (A9-THC) induces analgesic effects and alterations of alertness. It has been reported that propofol increases endocannabinoid levels in the brain, but the effects of A9-THC on propofol sedation remain unclear. Our aim was to characterize the interaction between A9-THC and propofol in terms of sedation and analgesia. METHODS: Sedation was monitored by a rota-rod and analgesia by tail-flick latencies. Twenty mice received intraperitoneal injections of 50 mg/kg A9-THC with 50, 75 and 100 mg/kg propofol after baseline values were established for each drug. Control experiments were performed with A9-THC and thiopental or Intralipid. RESULTS: Injection of 50 mg/kg propofol caused a rapid onset of sedation with a minimum of 24 s on the rota-rod. Fifty mg/kg A9-THC alone had no sedative effects. Administration of A9-THC significantly reduced the sedative effect of propofol to at least 60 s on the rota-rod (P < 0.001). After increasing the propofol dose to 100 mg/kg in the presence of A9-THC, sedation was re-established with 27 s on the rota-rod. Thiopental sedation was significantly reduced (P < 0.01) in the presence of A9-THC. CONCLUSION: The results indicate a dose-dependent antagonistic interaction between A9-THC and propofol, and also between A9-THC and thiopental.