Inhibitory effects of losartan and azelnidipine on augmentation of blood pressure variability induced by angiotensin II in rats

Effects of vasodilators on beat-to-beat and every fifteen minutes blood pressure variability induced by noradrenaline infusion in rats

Increased blood pressure variability (BPV) was shown to be associated with cardiovascular morbidities and/or mortalities. There are various types of BPV depending on time intervals of BP measurements, ranging from beat-to-beat to visit-to-visit or year-to-year. We previously found that continuous infusion of noradrenaline (NA) for 14 days increased short-term BPV every 15 min in rats. The aims of this study were to examine (1) whether NA infusion increases very short-term beat-to-beat BPV, (2) the effects of azelnidipine and hydralazine on NA-induced BPV, and (3) whether baroreceptor reflex sensitivity (BRS) is affected by NA or NA plus those vasodilators. Nine-week-old Wistar rats infused subcutaneously with 30 μg/h NA were orally treated with or without 9.7 mg/day azelnidipine or 5.9 mg/day hydralazine over 14 days. BP levels were continuously monitored via abdominal aortic catheter with a telemetry system in an unrestrained condition. Standard deviations (SDs) were used to evaluate beat-to-beat BPV and BPV every 15 min which was obtained by averaging BP levels for 10-s segment at each time point. BRS was determined by a sequence analysis. Continuous NA infusion over 14 days increased average BP, beat-to-beat BPV, and BPV every 15 min, lowering BRS. Comparing the two vasodilators, hydralazine reduced BP elevation by NA; meanwhile, azelnidipine alleviated BPV augmentation, preserving BRS, despite a smaller BP reduction. Thus, NA infusion increased both very short- and short-term BPV concomitantly with impaired BRS, while azelnidipine had an inhibitory effect, possibly independent of BP-lowering, on those types of BPV and impairment of BRS.

Changes in Blood Pressure Variability in Children with Postural Tachycardia Syndrome

(1) Objective: In this research, we explored the difference in blood pressure variability (BPV) between children with postural tachycardia syndrome (POTS) and healthy children. Furthermore, we tried to investigate the effect of BPV on POTS and its relationship with prognosis of POTS. (2) Methods: 47 children with POTS (11.2 ± 1.8 years, 23 males) were enrolled in the POTS group and 30 healthy children (10.9 ± 1.9 years, 15 males) were matched for the control group. All participants completed 24 h ambulatory blood pressure monitoring (24hABPM). Thirty-three children with POTS were followed up for 52.0 (30.5, 90.5) days and were divided into a response group and a non-response group after evaluation. (3) Results: The 24 h diastolic blood pressure standard deviation (24hDSD), daytime diastolic blood pressure standard deviation (DDSD), nighttime systolic blood pressure standard deviation (NSSD), daytime diastolic blood pressure variation coefficient (DDCV) and nighttime systolic blood pressure variation coefficient (NSCV) in the control group were lower than those in the POTS group (p < 0.05). Percentage of females, age and height were lower in the response group than in the non-response group in children with POTS (p < 0.05). Univariate analysis showed that 24hDSD, DDSD, NSSD, DDCV and NSCV were potential risk factors for POTS, and sex and height were potential risk factors for poor prognosis of POTS. After adjusting for covariates, the risk of POTS increased by 48%, 53% and 49% when DDSD, NSSD and NSCV increased by 1 mmHg, 1 mmHg and 1%, respectively. The risk of poor prognosis in females was 12.99 times higher than that in males. (4) Conclusions: The results suggest that children with POTS may have an abnormal circadian rhythm in blood pressure and increased BPV. DDSD, NSSD and NSCV are independent risk factors for POTS, and being female is an independent risk factor for poor prognosis of POTS.

Analysis of Mechanisms for Increased Blood Pressure Variability in Rats Continuously Infused with Angiotensin II

Objective

We reported that rats infused with angiotensin II (Ang II) are not only a model of hypertension but also of augmented 24 h blood pressure variability (BPV). In this study, we examined the mechanisms for Ang II-induced BPV, focusing on BP, heart rate (HR), baroreceptor reflex sensitivity (BRS), and medial area of the aortic arch.

Methods

Nine-week-old male Wistar rats were infused with subcutaneous 5.2 μg/kg/h Ang II with or without oral administration with 30 mg/kg/day azelnidipine for 14 days. BP and HR were recorded every 15 min under an unrestrained condition by a radiotelemetry system, while BPV was evaluated by standard deviation of BP. BRS was quantified by a sequence analysis, and medial thickness of the aortic arch was measured by microscopic examination.

Results

BPV increased at days 7 and 14 following continuous infusion of Ang II. Before the infusion, a positive correlation was found between BP and HR, but it became negative at day 7 and then weakened or disappeared at day 14. BRS was slightly impaired at day 7 and significantly lowered at day 14, a phenomenon accompanied by thickened medial area of the aortic arch in Ang II-infused rats. Those Ang II-induced alterations were all significantly attenuated by azelnidipine.

Conclusions

The present findings suggest sequential changes in the mechanisms behind augmented BPV in rats continuously infused with Ang II over 14 days.

Augmented blood pressure variability following continuous infusion of noradrenaline in rats

OBJECTIVE

Augmented blood pressure (BP) variability has been shown to be associated with cardiovascular diseases. Activity of the sympathetic nervous system is an important determinant factor of the 24-h profile of BP variability, although it is unknown whether persistent adrenergic activation causes augmented BP variability or not. Here we report that continuous infusion of noradrenalin augments 24-h BP variability in rats.

METHODS

Nine-week-old male Wistar rats were continuously infused with subcutaneous 30 μg/h noradrenalin, 150 μg/h of the α1-adrenergic agonist phenylephrine, or 30 μg/h of the β-agonist isoproterenol, for 14 days. Noradrenalin-infused rats were also administered either oral 5 mg/day prazosin or 50 mg/day atenolol during the infusion period. BP variability was evaluated before and after 7 and 14 days of the infusion, using a coefficient of variation of BP recorded every 15 min under an unrestrained condition via an abdominal aortic catheter by a radiotelemetry system.

RESULTS

Continuous infusion of noradrenalin significantly increased 24-h BP variability at 7 and 14 days, slightly elevating BP levels, while this increase in BP variability was partially attenuated by prazosin, but not by atenolol. Continuous infusion of phenylephrine augmented BP variability, but isoproterenol had no effect on the variability.

CONCLUSION

Continuous infusion of noradrenalin augmented 24-h BP variability partly through an α1-adrenergic receptor-mediated mechanism in rats, suggesting that the noradrenalin-infused rat is an animal model of augmented BP variability induced by persistent adrenergic activation.