Resting heart rate variability and plasma noradrenaline level as a measurement of autonomic nervous system activity in mature, aging rats

Aging is a process that also affects the autonomic nervous system (ANS) making it less adaptable to environmental and intrinsic stimuli and affecting its ability to maintain body homeostasis. The aim of this study was to estimate the resting ANS function using heart rate variability (HRV) method and by noradrenaline measurement in aging, 2-12-months-old rats. Materials and method. Resting 15-minute-long ECG recordings were performed in anaesthetized rats with a subsequent spectral HRV analysis. Basic non-normalized HRV components in the range of very low (VLF), low (LF) and high (HF) frequency, along with the total HRV spectrum power (TP) were estimated. Moreover, normalized LF (nLF) and normalized HF (nHF) were calculated. Blood samples were also collected to assay plasma noradrenaline (NA) level. Results. In the overall assessment, plasma noradrenaline level as well as both TP and all non-normalized HRV components demonstrated a tendency for reduction when compared the first (2 nd ) and last (12 th ) months. In the case of nLF and nHF, a trend of nLF predominance in the 2 nd and 3 rd month was revealed while an inverse relation was observed from the 6 th month on, with nHF superiority. Overall, males reached comparable or slightly higher NA and non-normalized HRV values compared to females, although most differences were not statistically significant. A parallel decline of LF (starting from the 10 th month) and HF (from the 6 th month) was demonstrated in both male and female animals. Female rats had a little more stable nLF and nHF course in the study time. Conclusions. Rat ANS aging is associated with global HRV decrease with parallel plasma NA decline, although without selective impairment of individual (sympathetic/parasympathetic) ANS components.