Abstract
OBJECTIVE: The aim of this study is to investigate the effects of light and administration time of isoflurane on circadian gene expression in the brains and liver tissues of rats kept in light-dark cycle. METHODS: Seventy two 15-days-old rats pups were divided into four groups. All animals were exposed to 1.5% concentration of isoflurane or to 6 L min(-1) O(2) for six hours between Zeitgeber Time (ZT) 0-ZT06 (day-time administration) or ZT12-ZT18 (night-time administration). Rats were sacrificed after six hours of anaesthesia with four-hour time intervals. Total RNA was isolated from brains and liver tissues. Circadian gene expression was examined using quantitative real-time Reverse transcription polymerase chain reaction (RT-PCR). RESULTS: BMAL1, CLOCK, PER2 and CRY2 gene expression levels were markedly suppressed after day-time anaesthesia in the both brain and liver, but night-time administration caused only temporary suppression of gene expression. CONCLUSION: The effect of isoflurane on the circadian clock is time-dependent, and administered isoflurane anaesthesia at night had minimal effect on clock gene expression. Additionally, when the treated animals were kept in a regular light-dark cycle, isoflurane-induced phase shift was not observed, possibly because of the light.