EARLY STRUCTURAL CHANGES OF AORTIC WALL IN SINOAORTIC-DENERVATED RATS

Characteristic enhancement of blood pressure V-shaped waves in sinoaortic-denervated rats in a conscious and quiet state

A hemodynamic feature of chronic sinoaortic-denervated (SAD) rats is the increase in blood pressure variability (BPV) without significant changes in the average level of blood pressure (BP). The current study was designed to investigate the changes in BP V-shaped waves (V waves) in SAD rats. Sprague-Dawley (SD) rats were divided into 2 groups: SAD rats and sham-operated rats (n=13). Hemodynamics measurements were obtained in conscious, freely moving rats, four weeks after sinoaortic denervation or sham operation. V wave indices were evaluated in rats in both conscious and quiet states. Additionally, normal and high BPV was simulated by the production of V waves with different amplitudes. The results showed that the V wave amplitude was dramatically increased, with a significantly prolonged duration and reduced frequency in SAD rats. V wave BPV in SAD rats was significantly increased, though BP remained unchanged. The twenty-four hour BPV in all rats was positively correlated with amplitude, duration time and V wave BPV and negatively correlated with frequency. The systolic BP spectral powers in the low frequency range (0.38-0.45 Hz) were significantly reduced in the V waves of SAD rats. Moreover, there was a remarkable increase in mean BPV and a normal mean BP after simulating high BPV in SAD rats. These results suggest that enhancement of V waves might be a waveform character of BP in SAD rats in both the conscious and quiet states. These types of V waves appear to be related to a depression of sympathetic regulation of BP induced by sinoaortic denervation.

Baroreflex and cerebral autoregulation are inversely correlated

BACKGROUND

The relative stability of cerebral blood flow is maintained by the baroreflex and cerebral autoregulation (CA). We assessed the relationship between baroreflex sensitivity (BRS) and CA in patients with atherosclerotic carotid stenosis or occlusion.

METHODS AND RESULTS

Patients referred for assessment of atherosclerotic unilateral >50% carotid stenosis or occlusion were included. Ten healthy volunteers served as a reference group. BRS was measured using the sequence method. CA was quantified by the correlation coefficient (Mx) between slow oscillations in mean arterial blood pressure and mean cerebral blood flow velocities from transcranial Doppler. Forty-five patients (M/F: 36/9), with a median age of 68 years (IQR:17) were included. Thirty-four patients had carotid stenosis, and 11 patients had carotid occlusion (asymptomatic: 31 patients; symptomatic: 14 patients). The median degree of carotid steno-occlusive disease was 90% (IQR:18). Both CA (P=0.02) and BRS (P<0.001) were impaired in patients as compared with healthy volunteers. CA and BRS were inversely and strongly correlated with each other in patients (rho=0.58, P<0.001) and in healthy volunteers (rho=0.939; P<0.001). Increasing BRS remained strongly associated with impaired CA on multivariate analysis (P=0.004).

CONCLUSIONS

There was an inverse correlation between CA and BRS in healthy volunteers and in patients with carotid stenosis or occlusion. This might be due to a relative increase in sympathetic drive associated with weak baroreflex enhancing cerebral vasomotor tone and CA.

Arterial baroreflex dysfunction impairs ischemia-induced angiogenesis

Background

Endothelium‐derived acetylcholine (eACh) plays an important role in the regulation of vascular actions in response to hypoxia, whereas arterial baroreflex (ABR) dysfunction impairs the eACh system. We investigated the effects of ABR dysfunction on ischemia‐induced angiogenesis in animal models of hindlimb ischemia with a special focus on eACh/nicotinic ACh receptor (nAChR) signaling activation.

Methods and Results

Male Sprague‐Dawley rats were randomly assigned to 1 of 3 groups that received (1) sham operation (control group), (2) sinoaortic denervation (SAD)‐induced ABR dysfunction (SAD group), or (3) SAD rats on diet with an acetylcholinesterase inhibitor pyridostigmine (30 mg/kg per day, SAD+Pyr group). After 4 weeks of the SAD intervention, unilateral limb ischemia was surgically induced in all animals. At postoperative day 14, SAD rats exhibited impaired angiogenic action (skin temperature and capillary density) and decreased angiogenic factor expressions (vascular endothelial growth factor [VEGF] and hypoxic inducible factor [HIF]‐1α) in ischemic muscles. These changes were restored by acetylcholinesterase inhibition. Rats with ABR dysfunction had lower eACh levels than did control rats, and this effect was recovered in SAD+Pyr rats. In α7‐nAChR knockout mice, pyridostigmine improved ischemia‐induced angiogenic responses and increased the levels of VEGF and HIF‐1α. Moreover, nicotinic receptor blocker inhibited VEGF expression and VEGF receptor 2 phosphorylation (p‐VEGFR2) induced by ACh analog.

Conclusions

Thus, ABR dysfunction appears to impair ischemia‐induced angiogenesis through the reduction of eACh/α7‐nAChR‐dependent and ‐independent HIF‐1α/VEGF‐VEGFR2 signaling activation.

Activation of receptor for advanced glycation end products contributes to aortic remodeling and endothelial dysfunction in sinoaortic denervated rats

OBJECTIVE

The aim of present study was to test the hypothesis that activation of receptor for advanced glycation end products (RAGE) pathway contributes to aortic remodeling and endothelial dysfunction in sinoaortic denervated (SAD) rats.

METHODS AND RESULTS

Experiment 1: 8 weeks after sinoaortic denervation, aortas were removed for measurement of AGE/RAGE pathway. Sinoaortic denervation in rats resulted in enhanced activity of aldose reductase, reduced activity of glyoxalase 1, accumulation of methylglyoxal and AGE, and upregulated expression of RAGE in aortas. Experiment 2: 5 weeks after sinoaortic denervation, the rats received intraperitoneal injections of 500 μg soluble RAGE (sRAGE) daily for 3 weeks. Treatment of SAD rats with sRAGE attenuated aortic remodeling, marked by reduction in AW/length, wall thickness, proliferation of SMC, and collagen deposition, and improvement of endothelial function. Treatment of SAD rats with sRAGE abated aortic oxidative stress, marked by reduction in formation of malondialdehyde, reactive oxygen species, superoxide, peroxynitrite and 3-nitrotyrosine, and enhancement of ratio of GSH/GSSG. Treatment of SAD rats with sRAGE attenuated aortic mitochondrial dysfunction. Treatment of SAD rats with sRAGE suppressed aortic NFκB nuclear translocation and inflammation. Treatment of SAD rats with sRAGE restored aortic NO formation through upregulating eNOS and dimethylarginine dimethylaminohydrolase-2 and downregulating protein arginine methyltransferase-1.

CONCLUSION

Activated RAGE contributed to aortic remodeling and endothelial dysfunction in SAD rats, possibly via induction of oxidative stress and inflammation, impairment of mitochondrial function, and reduction in NO bioavailability.

Role of Kir6.2 subunits of ATP-sensitive potassium channels in endotoxemia-induced cardiac dysfunction

Background

Cardiac dysfunction is well-described in endotoxemia and diagnosed in up to 60% of patients with endotoxic shock. ATP-sensitive potassium (K_ATP) channels are critical to cardiac function. This study investigates the role of Kir6.2 subunits of K_ATP channels on cardiac dysfunction in lipopolysaccharide (LPS)-induced endotoxemia.

Methods

Kir6.2 subunits knockout (Kir6.2^−/−) and wild-type (WT) mice were injected with LPS to induce endotoxemia. Cardiac function was monitored by echocardiography. Left ventricles were taken for microscopy (both light and electron) and TUNEL examination. Serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities, and tumor necrosis factor-α (TNF-α) levels in both serum and left ventricular tissues were determined.

Results

Compared to WT, Kir6.2^−/− mice showed significantly declined cardiac function 360 min after LPS administration, aggravated myocardial damage and elevated serum LDH and CK activities. Apoptotic cells were obviously increased in heart tissues from Kir6.2^−/− mice at 90, 180 and 360 min. TNF-α expression in both serum and heart tissues of Kir6.2^−/− mice was significantly increased.

Conclusions

We conclude that Kir6.2 subunits are critical in resistance to endotoxemia-induced cardiac dysfunction through reducing myocardial damage by inhibition of apoptosis and inflammation. K_ATP channels blockers are extensively used in the treatment of diabetes, their potential role should therefore be considered in the clinic when patients treated with antidiabetic sulfonylureas are complicated by endotoxemia.

Contribution of hydrogen sulfide and nitric oxide to exercise-induced attenuation of aortic remodeling and improvement of endothelial function in spontaneously hypertensive rats

It is well known that exercise training attenuates aortic remodeling and improves endothelial function in spontaneously hypertensive rats (SHR). However, the underlying molecular mechanism remains unclear. Hydrogen sulfide (H(2)S) and nitric oxide (NO), as two established physiologic messenger molecules, have important roles in the development of aortic remodeling and endothelial dysfunction in hypertensive animals and patients. In this work, it was found that exercise training had no significant effect on blood pressure, but effectively attenuated baroreflex dysfunction in SHR. Exercise training in SHR attenuated aortic remodeling and improved endothelium-mediated vascular relaxations of aortas in response to acetylcholine. Interestingly, exercise training in SHR restored plasma H(2)S levels and aortic H(2)S formation and enhanced levels of mRNA for cystathionine γ-lyase in aortas. Furthermore, exercise training in SHR resulted in augmentation of nitrite and nitrate (NOx) contents and reduction of asymmetric dimethylarginine contents of aortas, upregulation of dimethylarginine dimethylaminohydrolase 2, and phosphorylation of nitric oxide synthase 3, but had no significant effect on protein levels of NOS3. In addition, exercise training could effectively reduce malondialdehyde production and suppressed formation of O(2) (-), and OONO(-) in aortas of SHR through enhancing activities of superoxide dismutase and catalase, and suppressing NADPH oxidase activity. In conclusion, exercise training ameliorates aortic hypertrophy and endothelial dysfunction, possibly via restoring bioavailabilities of hydrogen sulfide and nitric oxide in SHR.

Down-regulation of DDAH2 and eNOS induces endothelial dysfunction in sinoaortic-denervated rats

The aim of present study was to investigate whether downregulation of dimethylarginine dimethylaminohydrolase (DDAH2) and endothelial nitric oxide synthase (eNOS) induced endothelial dysfunction in sinoaortic-denervated (SAD) rats. SAD rats exhibited significantly higher blood pressure (BP) variability and markedly lower baroreflex sensitivity. However, there was no significant difference in BP between SAD rats and sham-operated rats. In SAD rats, ultrastructural analysis revealed that endothelial cells were degenerated and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) study showed that apoptotic aortic endothelial cells increased. Circulating angiotensinII (AngII), asymmetric dimethylarginine (ADMA) and malondialdehyde (MDA) levels in SAD rats were similar to sham-operated rats, but aortic AngII and MDA levels locally increased. Endothelium-mediated relaxation of thoracic aorta isolated from SAD rats was impaired compared to sham-operated rats, whereas the sodium nitroprusside-induced relaxation was quite similar. Western blotting results showed that DDAH2 and eNOS expressions decreased significantly in the aortae of SAD rats. Treatment of primary cultured rat aortic endothelial cells with AngII (1 μM) resulted in a marked reduction of DDAH2 and eNOS expressions, and coadministration of losartan (1 μM), an AT(1) receptor antagonist, abolished the effect. In conclusion, downregulation of DDAH2 and eNOS induced endothelial dysfunction in SAD rats. DDAH2 and eNOS may be the potential targets for treatment of endothelial dysfunction.

Effects of low-dose ketanserin on atherosclerosis in rats and rabbits

The present study was designed to test the hypothesis that a small dose of ketanserin, which enhances baroreflex activity, prevents the early lesions of atherosclerosis. In experiment 1, baroreflex sensitivity (BRS) was measured in 31 spontaneously hypertensive rats (SHRs) in a conscious state using a computerized blood pressure monitoring system. Four weeks later, the rats were administered vitamin D3 and fed a high-cholesterol diet for 8 weeks to induce atherosclerosis. Then their hearts and aortae were removed for pathological examination. A negative correlation was found between BRS and the scores of coronary (r = -0.460, P < 0.01) and aortic atherosclerosis (r = -0.448, P < 0.05) in SHR. In experiment 2, SHRs were divided into 3 groups (n = 10 in each group) and received a dose of ketanserin of 0.3, 1.0, and 3.0 mg/kg (i.g.), respectively. At the smallest dose (0.3 mg/kg), ketanserin did not lower blood pressure but enhanced BRS. In experiment 3, SHRs were administered vitamin D3, fed a high-cholesterol diet, and simultaneously treated with low-dose ketanserin. The atherosclerosis scores of the treatment group were significantly lower than those of the control group (coronary score: 0.90 ± 0.14 vs. 1.76 ± 0.27, P < 0.05; aortic scores: 1.00 ± 0.39 vs. 2.18 ± 0.41, P < 0.05). In experiment 4, male New Zealand White rabbits were fed a high-cholesterol diet and treated with low-dose ketanserin at the same time. The atherosclerosis scores of the treatment group were significantly lower than those of the control group (aortic scores: 0.26 ± 0.20 vs. 0.60 ± 0.31, P < 0.05). In conclusion, the present study demonstrated, for the first time, that low-dose ketanserin prevented the development of atherosclerosis independent of its blood pressure lowering action in SHRs and New Zealand White rabbits at least in part via enhancement of arterial baroreflex function.

The combination of atenolol and amlodipine is better than their monotherapy for preventing end-organ damage in different types of hypertension in rats

Combinations therapy is often used in hypertensive patients whether combination therapy is necessary for preventing end-organ damage is not known. The objective of this study was to determine in four different hypertensive animal models the necessity of adding the calcium channel blocker amlodipine to therapy with the ß-blocker atenolol to modulate end-organ damage. Spontaneously hypertensive rats, DOCA-salt hypertensive rats, two-kidney, one-clip renovascular hypertensive rats and Lyon genetically hypertensive rats were used to study this objective. These animal models have different sensitivities to atenolol and amlodipine. The dosages of therapy employed were 10 mg/kg atenolol alone, 1 mg/kg amlodipine, 10 mg atenolol + 1 mg/kg amlodipine and 5 mg/kg atenolol+0.5 mg/kg amlodipine. BP was continuously recorded in all animals. After determination of baroreflex sensitivity, rats were sacrificed for end-organ damage evaluation. The combination of amlodipine and atenolol had a synergistic inhibitory effect on blood pressure and blood pressure variability, and end-organ damage as compared with monotherapy with atenolol or amlodipine in all animal models. Baroreflex sensitivity also improved with the combination therapy more than with monotherapy. In conclusion, atenolol and amlodipine combination exerts a superior effect on blood pressure, blood pressure variability, baroreflex sensitivity and end-organ damage. The superior effect of the combination was observed in all four models of hypertension.

Fosinopril prevents the pulmonary arterial remodeling in sinoaortic-denervated rats by regulating phosphodiesterase

AIM

To study the effects of fosinopril on sinoaortic denervation (SAD)-induced pulmonary vascular remodeling and on phosphodiesterases (PDE) 1 in rats.

METHODS

SAD was performed in male Sprague-Dawley rats at the age of 10 weeks. The experiment included sham-operated (Sham), SAD, and fosinopril-treated SAD groups. Fosinopril (15 mg/kg/d) was given in rat chow. After 16 weeks of treatment, the pulmonary arteries were taken for investigations, including pharmacological study, measurement of cGMP, light microscopy, immunohistochemistry, Western blotting, and quantitative real-time RT-PCR.

RESULTS

Compared with Sham rats, blood pressure variability (BPV) was significantly increased in the SAD group. However, the mean pulmonary artery pressure (mPAP) was not significant change among 3 groups. After SAD, maximal contraction of pulmonary artery rings to phenylephrine was markedly decreased; the most prominent morphological change in the lung included thickening vascular walls, increasing number of smooth muscle cells, and greater wall-to-lumen ratio; the tissue concentrations of cGMP was reduced significantly; PDE1A or PDE1C expression was upregulated significantly, and endothelial nitric oxide synthase (eNOS) expression was downregulated significantly. Fosinopril treatment prevented these changes induced by SAD.

CONCLUSION

Pulmonary artery remodeling (structural and functional abnormalities) was induced by SAD. Fosinopril, an angiotensin-converting enzyme inhibitor, mainly via potentiating eNOS pathway and inhibiting AngII formation, effectively prevented increased blood pressure variability and vascular remodeling of the pulmonary artery after SAD by regulating the activity levels or expression of eNOS, cGMP, and PDE1s.

Effects of K+ channel modulators on oscillatory contractions in sinoaortic denervated rat aortas

Sinoaortic denervated (SAD) rats present arterial pressure lability without sustained hypertension. We investigated the relation between sinoaortic denervation and the occurrence of oscillatory contractions in SAD rat aortas, as well as the effect of various K(+) channel modulators on these oscillations. Aortas were removed and concentration-effect curves to phenylephrine (0.01 to 10 muM) were constructed in arteries from SAD and Sham-operated rats in order to verify the occurrence of oscillations. We also evaluated the effects of various K(+) channel modulators on these oscillations. Only SAD rat aortas exhibited oscillatory contractions. Tetraethylammonium increased the frequency (28.5+/-3.5 to 41.5+/-4.5 counts/5 min) and amplitude (0.435+/-0.07 to 0.630+/-0.09 g) of the oscillations. Apamin and 4-aminopyridine did not alter the oscillations. Barium chloride converted the oscillatory contractions to a tonic contraction. Pinacidil rapidly blocked the oscillatory contractions and glibenclamide evoked reduction in amplitude from 0.410+/-0.07 to 0.180+/-0.06 g. Iberiotoxin increased the frequency of oscillatory contractions (from 28.0+/-3.5 to 51.5+/-7.5 counts/5 min) but decreased the amplitude (from 0.410+/-0.08 to 0.195+/-0.2 g). Our results demonstrate that SAD rat aortas exhibit oscillatory contractions and K(+) channels, mainly K(ATP) and BK(Ca), play a dominant role in these oscillations.

Effects of combination therapy with atenolol and amlodipine on blood pressure control and stroke prevention in stroke-prone spontaneously hypertensive rats

AIM

To test the effects of atenolol and amlodipine, either alone or in combination, on blood pressure, blood pressure variability (BPV), baroreflex sensitivity (BRS), and the prevalence of stroke in stroke-prone spontaneously hypertensive rats (SHR-SP).

METHODS

In the first set of the study, 24 8-month-old, female SHR-SP rats were randomly divided into 3 groups. Blood pressure, heart period, and BRS were determined before and after the intragastric administration of atenolol (10 mg/kg) and amlodipine (1.0 mg/kg), either alone or in combination. In the second set of the study, 40 male and 40 female rats were randomly assigned to 1 of the following 4 groups: control, atenolol (10 mg.kg(-1).d(-1)), amlodipine (1.0 mg.kg(-1).d(-1)), and both (10 male and 10 female in each group). The stroke incident and survival time were recorded.

RESULTS

Atenolol and amlodipine, either alone or in combination, significantly decreased blood pressure, with the exception of the amlodipine-induced effect on diastolic blood pressure. Meanwhile, only the combination treatment significantly decreased the BPV levels for the same period. The q-values calculated by the probability sum analysis were 1.17 and 2.67 for systolic and diastolic blood pressure, respectively, and were 2.48 and 2.10 for systolic and diastolic BPV, respectively, following administration. Neither drug exhibited any significant effect on BRS. Atenolol and amlodipine, either alone or in combination, significantly increased the lifespan of SHR-SP, with the best effect elicited by the combination therapy.

CONCLUSION

A significant synergism exists between atenolol and amlodipine in lowering and stabilizing blood pressure in SHR-SP. Combination therapy may be an optimal strategy for the prevention of stroke in hypertension.

Circadian expression of clock genes and angiotensin II type 1 receptors in suprachiasmatic nuclei of sinoaortic-denervated rats

AIM

To investigate whether the circadian expression of central clock genes and angiotensin II type 1 (AT1) receptors was altered in sinoaortic-denervated (SAD) rats.

METHODS

Male Sprague-Dawley rats underwent sinoaortic denervation or a sham operation at the age of 12 weeks. Four weeks after the operation, blood pressure and heart period were measured in the conscious state in a group of sham-operated (n=10) and SAD rats (n=9). Rest SAD and sham-operated rats were divided into 6 groups (n=6 in each group). The suprachiasmatic nuclei (SCN) tissues were taken every 4 h throughout the day from each group for the determination of the mRNA expression of clock genes (Per2 and Bmal1) and the AT1 receptor by RT-PCR; the protein expression of Per2 and Bmal1 was determined by Western blotting.

RESULTS

Blood pressure levels in the SAD rats were similar to those of the sham-operated rats. However, blood pressure variabilities significantly increased in the SAD rats compared with the sham-operated rats. The circadian variation of clock genes in the SCN of the sham-operated rats was characterized by a marked increase in the mRNA and protein expression during dark periods. Per2 and Bmal1 mRNA levels were significantly lower in the SAD rats, especially during dark periods. Western blot analysis confirmed an attenuation of the circadian rhythm of the 2 clock proteins in the SCN of the SAD rats. AT1 receptor mRNA expressions in the SCN were abnormally upregulated in the light phase, changed to a 12-h cycle in the SAD rats.

CONCLUSION

The circadian variation of the 2 central clock genes was attenuated in the SAD rats. Arterial baroreflex dysfunction also induced a disturbance in the expression of AT1 receptors in the SCN.

Treatment of hypertension based on measurement of blood pressure variability: lessons from animal studies

PURPOSE OF REVIEW

Blood pressure variability, a quantitative index for the spontaneous variation in blood pressure, has been proposed as a risk factor for end-organ damage and to determine the efficacy of hypertension treatment.

RECENT FINDINGS

Animal studies indicate that blood pressure variability is as important as blood pressure level in determining end-organ damage, and that high blood pressure variability is associated with end-organ damage, including myocardial lesions, aortic hypertrophy, vascular remodeling and renal damage. Although the organ damage induced by high blood pressure variability was similar to that induced by hypertension, comparative studies in sinoaortic-denervated and spontaneously hypertensive rats revealed that aortic hypertrophy is a sensitive index of high blood pressure variability, and left ventricular hypertrophy is a sensitive index of high blood pressure level. The possible mechanisms for high blood pressure variability-induced end-organ damage include: direct endothelial lesions, renin-angiotensin system activation, inflammation initiation and cardiomyocyte apoptosis augmentation. Blood pressure variability reduction contributes importantly to the organ-protective effect of some antihypertensive drugs.

SUMMARY

Although animal studies suggest some advantages in blood pressure variability measurements, clinical trials are necessary before the widespread use of blood pressure variability as a predictor of hypertensive organ damage and a new strategy for the treatment of hypertension.