Chronobiological analysis of sex differences in electrocardiographic parameters in spontaneously breathing Wistar rats under tiletamine-zolazepam anaesthesia

Introduction General anaesthesia is essential in surgical interventions because it reduces stress and restricts the animal’s movement. However, it can interfere with the circadian clock and, consequently, with several physiological functions, including the cardiovascular system. A combination of tiletamine and zolazepam is rarely used in rat studies; therefore, its effect on cardiovascular function in the context of sex and the light/dark cycle remains unknown. Aim This study analysed the effect of sex and the light/dark cycle on electrocardiographic parameters in Wistar rats anaesthetised with tiletamine-zolazepam. Methods Experiments were performed on spontaneously breathing Wistar rats of both sexes following a 4-week adaptation to a light/dark (12h/12h) cycle. After intraperitoneal administration of Zoletil 50 (30 mg/kg; Virbac; France), electrocardiographic parameters were measured in lead II using LabChart 8 (ID Instruments). Results Regarding the effect of the light/dark cycle on electrocardiographic parameters, males showed a higher heart rate and a shorter PR interval during the dark period, whereas females exhibited a longer QRS interval and a higher R wave amplitude in the dark period than in the light period. Sexual dimorphism was present during the light period, with males showing a longer QT interval and females displaying a higher T wave amplitude. In the dark period, sex differences were observed only in the PR interval, which was shorter in males. Conclusion The obtained results indicate a significant effect of sex and light/dark cycle on cardiovascular parameters in rats under tiletamine-zolazepam.