Effects Of Melatonin On Circadian Blood Pressure In SHR Rats

Objective: To explore the effect of circadian administration of melatonin on blood pressure in spontenous hypertension rats(SHR).Methods:(1)Sixof 20-week-old SHR rats were implanted with a PA-F40 telemetry device intraperitoneally,and the blood pressure was continuously monitored by a BW-200 auto-monitoring system for 24 hours.(2) Melatonin solution(10mg/kg/d)was injected into SHR rats one hour before the peak and trough of SBP rhythm respectively, and the blood pressure、 heart rate and motor activity were continuously monitored by a BW-200 auto-monitoring system.(3) Blood samples were taken to measure the MT、 ET、AngⅡ、NO and e NOS at 0h, 1h, and 2h after the melatonin injection.Results:(1) Sistolic blood pressure(SBP) of SHR rats was lower during the daytime(6:00-18:00) than that at the nighttime(18:00-6:00), with the trough at 11:00 and the peak at 23:00.(2) In rats injected with melatonin, the heart rate and the amplitude of SBP、diastolic blood pressure(DBP) and mean blood pressure(MBP) decreased in peak group, with an advanced acrophase. The amplitude of DBP increased in trough group, with a delayed acrophase. The acrophase of motor activity advanced only in peak group.(3) Levels of ET and AngⅡwere both decreasded, but levels of NO and e NOS were both increased after melatonin injection.Conclusion:Melatonin treatment resulted in a lower blood pressure and changed parameters in circadian rhythm of SHR rats. The melatonin effects on blood pressure,heart rate and motor activitymay probably be mediated by alterations in nitric oxide, endothelin,NO and e NOS levels in SHR rats.