Objectives: 

The aim of the study was to evaluate the chronobiological effects of ketamine/xylazine anaesthesia on some parameters of the cardiovascular system, the acid-base balance, ions and autonomic nervous system in spontaneously breathing rats.

Materials: 

Study was performed in female Wistar rats (10 mg/kg/15 mg/kg, i.m) after adaptation to light-dark (LD) cycle of 12 hours light:12 hours dark. Heart rate (HR), rectal temperature (RT), electrophysiological properties of the heart using electrocardiographic (ECG) parameters (PQ, QT and QTc interval, QRS complex, and P, R and T wave amplitude) were evaluated. Autonomic nervous system activity was evaluated using parameters of heart rate variability (HRV) (R-R interval duration, power HF, power LF, power VLF, relative power of HF, LF and VLF components of HRV), acid-base balance (pH, pCO2, pO2, O2 saturation, HCO3-, TCO2, BE, stHCO3-, BB) and Na+, K+, Ca2+ and Cl- plasma concentrations in arterial blood and their dependence on the active (dark) and non-active (light) parts of the LD cycle.

Results: 

Significant LD differences were found for HR (p<0,001), RT (p<0,001), RR intervals (p<0,01), PQ and QTc intervals (p<0,01), QRS complex (p<0,01), P wave (p<0,05), power HF,LF,VLF (p<0,001), pO2 and HCO3 (p<0,05), Na+, Ca2+ and Cl- (p<0,001) from all followed parameters.

Conclusions: 

Anaesthesia preserves LD differences in the electrophysiological properties of rat atria but not properties of the ventricles. Also causes respiratory distress conditions which are independent of the LD cycle and increases parasympathetic activity witout loss of LD differences. Thus, it is suitable anaesthesia for chronobiological research.