Tail cuff system

The non-invasive component detection analysis tail-cuff system was used to measure heart rate and blood pressure (Kent Scientific Corporation, Torrington, CT) [24 (link)]. Only the control group was used for this study. This system uses volume pressure recording to measure the flow of the blood in the tail. One day prior to the experiment, rats (n = 6) were put in restrainers with darkened nose cones in a warm environment for 30 minutes. This was done twice during the day. Two cuffs were put on the tail, an occlusion and a volume-pressure recording cuff, on the day of recording. Values of blood pressure (systolic and diastolic) and heart rate were displayed in the accompanying software. Readings were taken under basal condition and at 2 hours and days 1, 3, and 5 after incision (1,000–1,200 hr). The rats were housed individually. The average invasive systolic and diastolic blood pressure in the caudal venous artery is 95.9 ± 12.9 mmHg and 73 ± 13.7 mmHg, respectively, whereas the mean heart rate is 305 beats/min [25 (link)].

Blood pressure and heart rate were monitored by noninvasive tail-cuff system (Kent Scientific Corporation Coda, Torrington, CT, USA), described previously [32] (link), [33] (link) accordingly to the manufacturer's protocol. After training, baseline measurements were taken and subsequently the rats were anesthetized by spontaneous inhalation of isoflurane (Forene®, Abbott Scandinavia AB, Solna, Sweden) in air (~ 2.2%). Osmotic minipumps (Alzet®, Durect™, CA, USA) were implanted subcutaneously to deliver ANG II (120 ng/kg/min) (Sigma-Aldrich, Stockholm, Sweden) for 14 days, as described previously [34] (link). After implantation all rats were given L-NAME (0.5 g/L; drinking water) and treated with either NDHP (10 mg/kg i.p.) or vehicle (cremophor in saline) twice per day (8 a.m. and 8 p.m.). Blood pressure and heart rate were monitored again on Day 10–14 following implantation.

All experimental animals were purchased from Vital River Laboratories (Beijing, China). Male WKY and SHRs were randomly divided into 4 groups: 16-week-old WKY, 16-week-old SHRs, 49-week-old WKY, and 49-week-old SHRs. Conscious rats were instrumented with tail-cuff system (Kent Scientific) to record the blood pressure. Systolic blood pressure, diastolic blood pressure, and mean blood pressure were measured with the rat tails at 31°C as previously described.^{15 (link)} The investigation conforms to the Guidelines for the Care and Use of Laboratory Animals, and the procedures for care and use of animals were approved by the Ethics Committee of Chinese PLA General Hospital.