Age-related changes in control of blood pressure and heart rate during sleep in the rat

Study Objectives: The aim of this study was to determine age-related changes in the control of mean arterial pressure (MAP) and heart rate (HR) during sleep, and its relationship to the baroreflex in aging. Design: MAP, HR, body temperature (TP), spontaneous activity (ACT), and sleeping/waking duration were monitored for 24 hours in groups of young (10-12 wk old) and old (23-24 mo old) rats. Setting: The sleep laboratory at the University of Tokushima. Participants: Subjects were 8 young (10-12 wk old) and 7 old (23-24 mo old) Wistar rats. Interventions: Reflex control of HR was evaluated by examining various pressure responses to an intravenous bolus injection of phenylephrine and sodium nitroprusside. Measurements and Results: MAP and TP were recorded by a radiotelemetry system. HR was detected from the AP signal. ACT was counted by a photo-sensor system. In the case of old rats, the sensitivity of baroreflex control of HR was significantly depressed, and the spontaneous increase of MAP and HR during REM sleep and the MAP drop at the end of REM sleep were significantly enhanced. The old rats showed no large deterioration of the circadian profiles of MAP, HR, TP, and the amount of sleep. Conclusions: The baroreflex dysfunction is considered to appear in an early stage of the aging process, and to affect the control of MAP and HR during sleep.