Effects of biological rhythm disturbance on sedation induced by propofol in rats

Objective To evaluate the effects of biological rhythm disturbance on sedation induced by propofol in rats. Methods Thirty-two adult male Sprague-Dawley rats, weighing 180-220 g, were randomly divided into 4 groups(n=8 each)using a random number table: circadian rhythm+ administration during night-time group(group CN), circadian rhythm+ administration during day-time group(group CD), biological rhythm+ administration during night-time group(group BN), and biological rhythm+ administration during day-time group(group BD). In CN and CD groups, the rats were fed for 2 weeks in the experimental boxes in a 12(7: 00–19: 00): 12 h(19: 00–7: 00)light: dark cycle.While the rats were fed for 2 weeks in the experimental boxes in a 24 h light cycle.Propofol 75 mg/kg was intraperitoneally injected at 14: 00 in CN and BN groups, or at 22: 00 in CD and BD groups.The duration of loss of righting reflex was recorded.At 20 min after recovery of righting reflex, the cognitive function was assessed.The latency of passive avoidance was measured at 6, 12, 24 and 48 h after training. Results Compared with group CN, the duration of loss of righting reflex was significantly shortened, and the latency of passive avoidance was prolonged at 12 and 24 h after training in group CD, and the duration of loss of righting reflex and latency of passive avoidance at 12 and 24 h after training were shortened in group BN.Compared with group CD, no significant change was found in the duration of loss of righting reflex, and the latency of passive avoidance was significantly shortened at 24 h after training in group BD.There was no significant change between BN group and BD group in the duration of loss of righting reflex and latency of passive avoidance. Conclusion Biological rhythm disturbance can counteract circadian rhythm-produced effects on sedation induced by propofol in rats. Key words: Biorhythms; Propofol; Conscious sedation