Authors: Pavol Švorc, Darina Petrášová, Pavol ŠvorcJr.
Background: It is known that general anesthesia weakens autonomic function and baroreflex control. Intravenous anesthetics may have different qualitative and quantitative effects on the peripheral autonomic nervous system (ANS) and, can thus, alter the activity of sympathetic or parasympathetic divisions of the ANS. Presently, there are relatively little data regarding sex differences in ANS activity or sex differences in ANS activities during anesthesia. The primary goal of the present study was to assess sex differences in ANS activity in dependence on the light-dark (LD) cycle in healthy, sexually mature, spontaneously breathing zoletil-anesthetized rats.
Methods: Experiments were performed using zoletil-anesthetized (30 mg/kg [intraperitoneal]) female and male Wistar rats after a four-week adaptation to an LD cycle (12h:12h). The animals were divided into four experimental groups according to sex and light period (n=20). Heart rate variability (HRV) was evaluated 20 min after administration of anesthesia.
Results: Sympathetic and baroreceptor activity were decreased, parasympathetic activity was increased in both sexes and in both lighted periods. LD differences were preserved mainly in the HF component; thus, circadian rhythm in parasympathetic activity probably persists in both sexes. Taking into account sex differences, HRV was significantly lower in females versus males in the light period. In the dark period, females exhibited higher HRV than males. Taking into account LD differences, in females, HRV was lower in the light versus the dark period, unlike males, in which HRV was higher in the dark versus light period of the rat regimen day.
Conclusions: It is concluded that the sex differences exist in rat ANS activity, persist in general anesthesia and depend on the LD cycle, what can be also related to its regulatory effect on the cardiovascular system. Future studies should address this issue and try to include females into the experiment if it is possible.