ketamine/xylazine; chronobiology; electrophysiology of the heart; acid-base balance; ions; autonomic nervous system

Administration of anaesthesia during the daytime is important and may influence specific aspects of in vivo animal experiments. The aim of the present study was to refer to the suitability of the use of ketamine/xylazine anaesthesia in chronobiological studies. Study was performed in ketamine-/xylazine-anaesthetized female Wistar rats ( 100 mg/kg/15 mg/kg, i.m) after adaptation to a light-dark (LD) cycle ( 12 h: 12 h). Heart rate (HR), rectal temperature, ECG parameters, autonomic nervous system activity, acid-base balance and Na+, K+, Ca2+ and Cl(-)plasma concentrations were evaluated in dependence on LD cycle. LD differences were found in the HR, rectal temperature, RR, PQ and QTc intervals, QRS complex, P wave amplitude, in power HF, LF and VLF components, in paO2 and HCO3-, and in Na+, Cl(-)and Ca2+ ions. Ketamine/xylazine anaesthesia may be applicable in chronobiological studies. It does not disturb LD differences, but it can modify them probably without loss of rhythmicity.