Analysis of cardiovascular autonomic function from telemetric blood pressure recordings: effects of age, high fat diet and angiotensin II

Abstract

Assessments of sympathetic/parasympathetic nervous activity and baroreceptor reflex gain (BRG) are important for understanding neural mechanisms of cardiovascular diseases, and evaluation of heart rate variability (HRV) as well as spontaneous BRG from telemetric blood pressure recordings provides a useful tool in experimental rat models. We analyzed changes in these parameters in response to 60% high fat diet feeding and to central infusion of angiotensin II (AngII, 10nmol/h) or losartan (LOS, 15µg/h) in young (5 mo) and old (27mo) F344xBN rats that were equipped with telemetric BP transmitters. Spontaneous BRG was significantly higher in young rats vs. old. High fat feeding, as well as central infusions of both AngII and LOS, reduced BRG in young rats, but were ineffective in old animals. Both low frequency power (LF) of pulse interval data, which reflects sympathetic tone to the heart, and high frequency power (HF), which reflects parasympathetic tone, were significantly lower in old rats compared with young. AngII increased LF in young, but not in old rats, whereas HF remained unchanged in both groups. In contrast, LOS had no effect on either parameter. In response to high fat feeding, LF increased in young, but decreased in old rats, while HF decreased both in young and old animals. These data show that analysis of BRG and HRV can be used to detect age‐, diet‐ and AngII‐induced changes in autonomic function, and that age has a significant effect on how the autonomic nervous system reacts to these stimuli.