Baroreflex control of heart rate and cardiac hypertrophy in angiotensin II-induced hypertension in rabbits

The probiotic Lactobacillus fermentum 296 attenuates cardiometabolic disorders in high fat diet-treated rats

BACKGROUND AND AIM

High-fat (HF) diet consumption has been associated with gut dysbiosis and increased risk of dyslipidemia, type 2 diabetes mellitus and hypertension. Probiotic administration has been suggested as a safe therapeutic strategy for the treatment of cardiometabolic disorders. This study was designed to assess the effects of probiotic Lactobacillus (L.) fermentum 296, a fruit-derived bacteria strain, against cardiometabolic disorders induced by HF diet.

METHODS AND RESULTS

Male Wistar rats were divided into control diet (CTL); HF diet; and HF diet treated with Lactobacillus fermentum 296 (HF + Lf 296). The L. fermentum 296 strain at 1 × 10⁹ colony forming units (CFU)/ml were daily administered by oral gavage for 4 weeks. The results showed that rats fed with HF diet displayed insulin resistance, reduced Lactobacillus spp. counts in feces, serum lipids, and oxidative profile. Rats fed on HF diet also demonstrated augmented blood pressure associated with sympathetic hyperactivity and impaired baroreflex control. The administration of L. fermentum 296 for 4 weeks recovered fecal Lactobacillus sp. counts and alleviated hyperlipidemia, sympathetic hyperactivity, and reduced systolic blood pressure in HF rats without affecting baroreflex sensibility.

CONCLUSION

Our results suggest the ability of L. fermentum 296 improve biochemical and cardiovascular parameters altered in cardiometabolic disorders.

A Newly Isolated Carboxymethyl-Glucan (CM-G) Restores Depressed Baroreflex Sensitivity in Renovascular Hypertensive Rats

This study was designed to investigate the effects of a newly synthesized carboxymethyl-glucan (CM-G) on blood pressure (BP), baroreflex sensitivity (BRS) and sympathetic vascular modulation in renovascular hypertensive rats. Male Wistar rats were divided into four groups: Sham (n = 10); 2K1C (subjected to renal artery clipping to induce renovascular hypertension, n = 10); Sham + CM-G (treated with CM-G, n = 7) and 2K1C + CM-G (treated with CM-G, n = 7). The daily treatment with CM-G (40 mg/kg) was performed for 2 weeks. Blood pressure, heart rate (HR), systolic BP variability, baroreflex sensitivity (BRS) and sympathetic vascular tone were evaluated. After six weeks of renal artery clipping, 2K1C rats exhibited arterial hypertension (171 ± 11 vs. 118 ± 4 mmHg, p < 0.05), impaired BRS (-1.30 ± 0.10 vs. -2.59 ± 0.17 bpm.mmHg-1, p < 0.05) and enhanced sympathetic activity as shown by the hexamethonium test (-60 ± 5 vs. -33 ± 2 ΔmmHg, p < 0.05) when compared to sham rats. Oral administration of CM-G in renovascular hypertensive rats reduced hypertension (126 ± 4 vs. 171 ± 11 mmHg, p < 0.05) and improved the BRS (-2.03 ± 0.16 vs. -1.30 ± 0.10 bpm.mmHg^-1, p < 0.05) in 2K1C rats when compared to placebo. Those effects seem to be caused by a reduction in sympathetic activity. The present study revealed for the first time that CM-G treatment reduces arterial hypertension and restores arterial baroreflex sensitivity via a reduction in the sympathetic tone in conscious renovascular hypertensive rats.

Effect of angiotensin II on voltage-gated sodium currents in aortic baroreceptor neurons and arterial baroreflex sensitivity in heart failure rats

BACKGROUND

Impairment of arterial baroreflex sensitivity is associated with mortality in patients with chronic heart failure (CHF). Elevation of plasma angiotension II (Ang II) contributes to arterial baroreflex dysfunction in CHF. A reduced number of voltage-gated sodium (Nav) channels in aortic baroreceptor neurons are involved in CHF-blunted arterial baroreflex.

METHOD

In this study, we investigated acute effect of Ang II on Nav currents in the aortic baroreceptor neuron and on arterial baroreflex in sham and coronary artery ligation-induced CHF rats.

RESULTS

Using Ang II I radioimmunoassay, real-time reverse transcription-PCR and western blot, we found that Ang II levels, and mRNA and protein expression of angiotension II type 1 receptor in nodose ganglia from CHF rats were higher than that from sham rats. Local microinjection of Ang II (0.2  nmol) into the nodose ganglia decreased the arterial baroreflex sensitivity in sham rats, whereas losartan (1  nmol, an angiotension II type 1 receptor antagonist) improved the arterial baroreflex sensitivity in CHF rats. Data from patch-clamp recording showed that Ang II (100  nmol/l) acutely inhibited Nav currents in the aortic baroreceptor neurons from sham and CHF rats. In particular, inhibitory effect of Ang II on Nav currents in the aortic baroreceptor neurons was larger in CHF rats than that in sham rats. Losartan (1  μmol/l) totally abolished the inhibitory effect of Ang II on Nav currents in sham and CHF aortic baroreceptor neurons.

CONCLUSION

These results suggest that elevation of endogenous Ang II in the nodose ganglia contributes to impairment of the arterial baroreflex function in CHF rats through inhibiting Nav channels.

Dual implantation of a radio-telemeter and vascular access port allows repeated hemodynamic and pharmacological measures in conscious lean and obese rats

Expansion of physiological knowledge increasingly requires examination of processes in the normal, conscious state. The current study describes a novel approach combining surgical implantation of radio-telemeters with vascular access ports (VAPs) to allow repeated hemodynamic and pharmacological measures in conscious rats. Dual implantation was conducted on 16-week-old male lean and obese Zucker rats. Continued viability one month after surgery was observed in 67% of lean and 44% of obese animals, giving an overall 54% completion rate. Over the five-week measurement period, reliable and reproducible basal mean arterial pressure and heart rate measures were observed. VAP patency and receptor-independent vascular reactivity were confirmed by consistent hemodynamic responses to sodium nitroprusside (6.25 µg/kg). Acutely, minimal hemodynamic responses to repeated bolus administration of 0.2 mL saline indicated no significant effect of increased blood volume or administration stress, making repeated acute measures viable. Similarly, repeated administration of the β-adrenoceptor agonist dobutamine (30 µg/kg) at 10 min intervals resulted in reproducible hemodynamic changes in both lean and obese animals. Therefore, our study demonstrates that this new approach is viable for the acute and chronic assessment of hemodynamic and pharmacological responses in both lean and obese conscious rats. This technique reduces the demand for animal numbers and allows hemodynamic measures with minimal disruption to animals' welfare, while providing reliable and reproducible results over several weeks. In conclusion, dual implantation of a radio-telemeter and VAP introduces a valuable technique for undertaking comprehensive studies involving repeated pharmacological tests in conscious animals to address important physiological questions.

Revealing the role of the autonomic nervous system in the development and maintenance of Goldblatt hypertension in rats

Despite extensive use of the renovascular/Goldblatt model of hypertension—2K-1C, and the use of renal denervation to treat drug resistant hypertensive patients, autonomic mechanisms that underpin the maintenance of this hypertension are important yet remain unclear. Our aim was to analyse cardiovascular autonomic function by power spectral density analysis of both arterial pressure and pulse interval measured continuously by radio telemetry for 6 weeks after renal artery clipping. Mean arterial pressure increased from 106 ± 5 to 185 ± 2 mm Hg during 5 weeks post clipping when it stabilized. A tachycardia developed during the 4th week, which plateaued between weeks 5 and 6. The gain of the cardiac vagal baroreflex decreased immediately after clipping and continued to do so until the 5th week when it plateaued (from − 2.4 ± 0.09 to − 0.8 ± 0.04 bpm/mm Hg; P < 0.05). A similar time course of changes in the high frequency power spectral density of the pulse interval was observed (decrease from 13.4 ± 0.6 to 8.3 ± 0.01 ms²; P < 0.05). There was an increase in both the very low frequency and low frequency components of systolic blood pressure that occurred 3 and 4 weeks after clipping, respectively. Thus, we show for the first time the temporal profile of autonomic mechanisms underpinning the initiation, development and maintenance of renovascular hypertension including: an immediate depression of cardiac baroreflex gain followed by a delayed cardiac sympathetic predominance; elevated sympathetic vasomotor drive occurring after the initiation of the hypertension but coinciding during its mid-development and maintenance.

Oxidative stress exaggerates skeletal muscle contraction-evoked reflex sympathoexcitation in rats with hypertension induced by angiotensin II

Muscle contraction stimulates thin fiber muscle afferents and evokes reflex sympathoexcitation. In hypertension, this reflex is exaggerated. ANG II, which is elevated in hypertension, has been reported to trigger the production of superoxide and other reactive oxygen species. In the present study, we tested the hypothesis that increased ANG II in hypertension exaggerates skeletal muscle contraction-evoked reflex sympathoexcitation by inducing oxidative stress in the muscle. In rats, subcutaneous infusion of ANG II at 450 ng·kg(-1)·min(-1) for 14 days significantly (P < 0.05) elevated blood pressure compared with sham-operated (sham) rats. Electrically induced 30-s hindlimb muscle contraction in decerebrate rats with hypertension evoked larger renal sympathoexcitatory and pressor responses [+1,173 ± 212 arbitrary units (AU) and +35 ± 5 mmHg, n = 10] compared with sham normotensive rats (+419 ± 103 AU and +13 ± 2 mmHg, n = 11). Tempol, a SOD mimetic, injected intra-arterially into the hindlimb circulation significantly reduced responses in hypertensive rats, whereas this compound had no effect on responses in sham rats. Tiron, another SOD mimetic, also significantly reduced reflex renal sympathetic and pressor responses in a subset of hypertensive rats (n = 10). Generation of muscle superoxide, as evaluated by dihydroethidium staining, was increased in hypertensive rats. RT-PCR and immunoblot experiments showed that mRNA and protein for gp91(phox), a NADPH oxidase subunit, in skeletal muscle tissue were upregulated in hypertensive rats. Taken together, hese results suggest that increased ANG II in hypertension induces oxidative stress in skeletal muscle, thereby exaggerating the muscle reflex.

Status epilepticus produces chronic alterations in cardiac sympathovagal balance

PURPOSE

Status epilepticus (SE) activates the autonomic nervous system, increasing sympathetic nervous system control of cardiac function during seizure activity. However, lasting effects of SE on autonomic regulation of the heart, which may contribute to mortality following seizure activity, are unknown. Therefore, autonomic control of cardiac function was assessed following SE.

METHODS

Using Sprague-Dawley rats after 1-2 weeks of recovery from lithium-pilocarpine-induced SE or control procedures, we tested overall sympathovagal control of the heart, the individual contributions of the sympathetic and parasympathetic components of the autonomic nervous system, and baroreflex sensitivity.

RESULTS

SE induced a chronic shift in sympathovagal balance toward sympathetic dominance resulting from decreased parasympathetic activity. Baroreflex sensitivity to increased blood pressure was also decreased, likely resulting from diminished vagal activation.

DISCUSSION

Chronic alterations in autonomic regulation of cardiac function, characterized by increased sympathetic dominance, occur following SE and likely contribute to subsequent increased cardiac risk and mortality.

Baroreflex mechanisms regulating mean level of SNA differ from those regulating the timing and entrainment of the sympathetic discharges in rabbits

The arterial baroreflex pathway provides the fundamental basis for the short-term control of blood pressure via the rapid regulation of the mean level of sympathetic nerve activity (SNA) in response to changes in blood pressure. A central tenet in the generation and regulation of bursts of SNA is that input from the arterial baroreceptors also regulates the timing of the bursts of sympathetic activity. With the use of an implantable telemetry-based amplifier, renal SNA was recorded in intact and arterial baroreceptor-denervated (SAD) conscious rabbits. Data were collected continuously while animals were in their home cage. Mean levels of SNA were not different between SAD and baroreceptor-intact animals. Whereas SNA was unresponsive to changes in blood pressure in SAD rabbits, the timing of the bursts of SNA relative to the arterial pulse wave was maintained (time between the diastolic pressure and the next maximum SNA voltage averaged 107 ± 12 ms SAD vs. 105 ± 7 ms intact). Transfer function analysis between blood pressure and SNA indicates the average gain at the heart rate frequency was not altered by SAD, indicating strong coupling between the cardiac cycle and SNA bursts in SAD animals. Further experiments in anesthetized rabbits showed that this entrainment is lost immediately after performing baroreceptor denervation surgery and remained absent while the animal was under anesthesia but returned within 20 min of turning off the anesthesia. We propose that this finding indicates the regulation of the mean level of SNA requires the majority of input from baroreceptors to be functional; however, the regulation of the timing of the bursts in the conscious animal requires only minimal input, such as a sensitive trigger mechanism. This observation has important implications for understanding the origin and regulation of SNA.

Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.

LONG-TERM RECORDING OF SYMPATHETIC NERVE ACTIVITY: THE NEW FRONTIER IN UNDERSTANDING THE DEVELOPMENT OF HYPERTENSION?

1. With increasing evidence that the sympathetic nervous system plays a critical role in the development of hypertension, focus is turning to how these signals translate to a chronic increase in arterial pressure. 2. The kidney's role in the control of salt and water homeostasis makes it an obvious target for such investigations. However, to date, many studies have been restricted to experiments lasting only a few hours or, at most, a few days, whereas others may use indirect methods of assessing sympathetic activity rather than direct recordings. 3. We review current approaches used to determine the effects of renal sympathetic nerve activity (SNA) on arterial pressure and suggest possible avenues of future investigation. We propose that although afferent inputs, such as from chemoreceptors and baroreceptors, are important for the short-term control of blood pressure via regulation of SNA to multiple organs, it is highly likely that alternative signals are important for setting the long-term level of renal SNA. 4. Emerging evidence indicates circulating angiotensin II is hormone that may act on the central nervous system to regulate renal SNA, renal function and, thus, blood pressure. 5. We propose that an integral part of future studies seeking an understanding of the genesis of hypertension should include chronic direct recordings of renal SNA.

Association between cardiovascular autonomic neuropathy and left ventricular hypertrophy in diabetic haemodialysis patients

BACKGROUND

Patients with diabetic nephropathy are likely to have neurological complications including cardiovascular autonomic dysfunction, which is related to increased risk of mortality. We investigated whether cardiovascular autonomic neuropathy is associated with left ventricular hypertrophy (LVH) in diabetic haemodialysis patients.

METHODS

Holter electrocardiography was carried out for 24 h with time and frequency domain analyses of heart rate variability in 154 diabetic (age 62+/-11 years) and 63 non-diabetic haemodialysis patients (62+/-10 years). The left ventricular mass index (LVMI) was determined by echocardiography. We used the percentage of differences exceeding 50 ms between adjacent normal RR intervals (pNN50) in time domain analysis and the power in the high-frequency range (HF: 0.15-0.40 Hz) in frequency domain analysis as indicators of parasympathetic activity.

RESULTS

The mean LVMI was greater in diabetic than in non-diabetic patients (168+/-63 vs 144+/-54 g/m(2), P<0.01). LVMI inversely correlated with pNN50 (r = -0.270, P = 0.0007, n = 154) and HF (r = -0.277, P = 0.0005, n = 154) in diabetic patients, but not in non-diabetic patients. By multiple logistic analysis, LVH was strongly associated with pNN50 (odds ratio 0.088; 0, <2%; 1, >/=2%) and HF (odds ratio 0.058; 0, <500 ms(2); 1, >/=500 ms(2)) in diabetic patients.

CONCLUSIONS

Impaired parasympathetic activity, which indicates cardiovascular autonomic neuropathy, was associated with the presence of LVH in diabetic haemodialysis patients. The co-existence of cardiovascular autonomic neuropathy and LVH may be one of the key factors for the high incidence of cardiovascular events in diabetic haemodialysis patients.

Changes of Central Norepinephrine, β-Endorphin, LEU-Enkephalin, Peripheral Arginine-Vasopressin, and Angiotensin II Levels in Acute and Chronic Phases of Sino-Aortic Denervation in Rats

We and others have demonstrated that impaired arterial baroreceptor reflex (ABR) function is one of the major causes of hypertension-associated end organ damage. The goal of this study was to clarify the potential neuro-humoral mechanisms responsible for impaired ABR-induced end organ damage. The sino-aortic denervated (SAD) rat was used as an animal model of ABR dysfunction. One-week SAD rats were characterized by hypertension, tachycardia, increased norepinephrine content, and decreased beta-endorphin and leu-enkephalin content in hypothalamus and medulla oblongata, and increased plasma levels of arginine-vasopressin. In 18-week SAD rats, the 24-hour average arterial pressure, heart rate, beta-endorphin, and leu-enkephalin content in hypothalamus and medulla oblongata and plasma levels of arginine-vasopressin and angiotensin II were not different from those measured in ABR-intact rats. However, blood pressure variability and angiotensin II content in kidney and left ventricle increased. When exposed to chronic stress, exaggerated changes in arterial pressure, blood pressure variability, the levels of central norepinephrine, beta-endorphin and leu-enkephalin, plasma arginine-vasopressin and angiotensin II, and tissue angiotensin II were found in 18-week SAD rats. These data indicate that a long-term impairment of ABR leads to chronic activation of central noradrenergic neurons and tissue renin-angiotensin system, and that stress induces exaggerated responses of neuro-humoral factors and hemodynamics in SAD rats. Thus, if the present results hold true for humans, one can expect abnormal neurotransmitter/neuromodulator responses to environmental insults in patients with impaired ABR function.

Regional responsiveness of renal perfusion to activation of the renal nerves

We tested for regional differences in perfusion responses, within the renal medulla and cortex, to renal nerve stimulation in pentobarbital sodium-anesthetized rabbits. Laser-Doppler flux (LDF) was monitored at various depths below the cortical surface (1-15 mm). Basal cortical LDF (1-3 mm, approximately 200-450 U) was greater than medullary LDF (5-15 mm, approximately 70-160 U), but there were no statistically significant differences in basal LDF within these regions. The background LDF signal during aortic occlusion was similar in the cortex (2 mm, 31 U) and outer medulla (7 mm, 31 U), but slightly greater in the inner medulla (12 mm, 44 U). During electrical stimulation of the renal nerves (0.5-8 Hz), cortical LDF and total renal blood flow were similarly progressively reduced with increasing stimulus frequency. Medullary LDF (measured between 5 and 15 mm) was overall less responsive than cortical LDF. For example, 4-Hz stimulation reduced inner medullary LDF (9 mm) by 19 +/- 6% but reduced cortical LDF (1 mm) by 54 +/- 11%. However, medullary LDF responses to nerve stimulation were similar at all depths measured. Our results indicate that while the vascular elements controlling medullary perfusion are less sensitive to the effects of electrical stimulation of the renal nerves than are those controlling cortical perfusion, sensitivity within these vascular territories appears to be relatively homogeneous.

Neural control of the renal vasculature in angiotensin II-induced hypertension

1. Chronic administration of angiotensin (Ang) II causes an increase in blood pressure via a multitude of actions, including direct vasoconstriction, hypertrophy and increased sympathetic nerve activity. In the present study, we assessed whether the hypertension resulting from chronic Ang II alters the ability of the renal vasculature to respond to sympathetic activity. 2. Angiotensin II was administered for 7 weeks via an osmotic minipump at a dose of 50 ng/kg per min, i.v., to a group of six rabbits. Blood pressure, measured at 0, 1, 2 and 6 weeks after insertion of the pump, increased from 76 +/- 2 to 104 +/- 6 mmHg at the end of 6 weeks, without any significant change in heart rate. The blood pressure in the control group remained constant at 76 +/- 2 mmHg. 3. After 7 weeks, rabbits were anaesthetized and the renal nerves were stimulated at 0.5, 1, 1.5, 2, 3, 5 or 8 Hz for 3 min at their supramaximal voltage (5.5 +/- 1.0 V in the normotensive group and 6.5 +/- 1.5 V in the hypertensive group) while the renal blood flow (RBF) response was recorded. Under anaesthesia, there was no difference in mean arterial pressure between the normotensive and hypertensive animals (77 +/- 2 and 80 +/- 7 mmHg, respectively). The resting RBF under these conditions was not significantly different in the hypertensive group (30 +/- 4 vs 26 +/- 5 mL/min in the normotensive vs hypertensive group, respectively). 4. Stimulation at increasing frequencies was associated with increasing reductions in RBF (e.g. 36 +/- 8% at 2 Hz in normotensive rabbits and 48 +/- 7% at 2 Hz in hypertensive rabbits). However, there were no significant differences between RBF responses in normotensive and hypertensive rabbits. 5. We conclude that hypertension associated with chronic Ang II administration does not alter the response in RBF to electrical stimulation of the nerves.

Renal and cardiac sympathetic baroreflexes in hypertensive rabbits

1. The purpose of the present study was to assess the changes to renal sympathetic nerve activity (RSNA) baroreflexes during the development of hypertension after renal clipping in conscious rabbits. 2. Rabbits were fitted with a clip on the right renal artery or underwent a sham operation under halothane anaesthesia. A recording electrode was implanted on the left renal nerve 1 week before the experiment, 3 or 6 weeks after the initial operation. During the experiment, drug-induced ramp rises and falls in mean arterial pressure (MAP) were used to produce RSNA and heart rate (HR) baroreflex curves. The RSNA for each experiment was calibrated against maximum RSNA evoked by stimulation of baroreceptor-independent trigeminal afferents. 3. Mean arterial pressure was 20 and 36% higher 3 and 6 weeks after clip implantation, respectively. Renal sympathetic nerve activity baroreflex curves were reset rightwards accordingly, but the shape of the RSNA curves was differentially affected. 4. At both hypertensive periods, MAP-HR baroreflex gain was markedly reduced due to a reduction in curvature. The HR baroreflex range was increased. The RSNA baroreflex gain was reduced at 3 weeks, which was due to a 35% lower RSNA baroreflex range, but was similar to sham animals at 6 weeks. 5. The results show that, in established two kidney, one clip hypertension in rabbits, the sympathetic baroreflex is relatively well preserved but sensitivity of cardiac baroreflexes is attenuated. Therefore, the short-term inhibition of RSNA baroreflexes is not related to the level of blood pressure or the development of secondary changes, such as cardiac or vascular hypertrophy, but may be related to circulating angiotensin, which is known to increase at this time.

Arterial baroreflex deficit induced organ damage in sinoaortic denervated rats

To verify the independent role of the arterial baroreceptor dysfunction involved in target-organ damage in hypertension, sinoaortic denervated (SAD) rats were used as a model of arterial baroreflex (ABR) deficit. SAD, isolated aortic-denervated (AD), and isolated sinus-denervated (SD) rats were instrumented to record blood pressure (BP), heart rate (HR), BP variability (BPV), HR variability (HRV), ABR function control of heart period (ABR-HP), and BP (ABR-BP). Vascular maximum contractile/relaxant function was determined and organ damage was estimated by observation of morphologic changes. Short-term (postoperative 1 week) SAD caused hypertension and tachycardia in rats. Eighteen weeks after operation, BP and HR values in SAD and SD rats were not different from those in sham-operated rats, but AD rats were hypertensive compared with control group. Although 24-h mean BP values of long-term SAD rats were not different from those of sham-operated rats, 24-h BPV of SAD rats was significantly higher than that of sham-operated rats. Arterial baroreflex function in short-term SAD rats was significantly less than in sham-operated rats, whereas in long-term SAD rats, ABR-HP and ABR-BP were higher than those in short-term SAD rats, but were still significantly lower than those in control groups. At postoperative 18 weeks, baroreflex function in SAD and AD rats was significantly less than function in SD and control groups. SBPmax after phenylephrine and DBPmin after nitroprusside were significantly higher in SAD, AD, and SD rats than in control rats. Baroreflex function was negatively correlated to DBPmin and SBPmax in all denervated rats (n = 44). Some morphologic changes were found 18 weeks after denervation in heart, kidney, and small artery in SAD, AD, and SD rats. Baroreflex function in all denervated rats was negatively related to 24-h BPV values. In contrast, 24-h BPV values in SAD, AD, and SD rats were positively related to organ-damage score. A negative correlation between ABR function and end-organ damage score was found. Arterial baroreflex deficit played an independent and important role in organ-damage in SAD rats with significantly elevated 24-h BPV.

Physiology and homeostasis of extracellular matrix: cardiovascular adaptation and remodeling

Tissue distensibility and extracellular matrix (ECM) including receptor integrins play significant role in the frequency of heart beat, contraction and relaxation. To meet the workload and during compensatory adaptive remodeling, the ECM restructures and transmits nuclear signals to convert fibroblasts to myofibroblasts. The matrix metalloproteinases (MMPs), a disintegrin and metalloproteinase (ADAM), and tissue inhibitor of metalloproteinases (TIMPs) control the activation of ECM remodeling and transmission of nuclear signals. This lead to the replacement of the injured muscle during wound healing in heart failure. The ECM degradation leads to apoptosis in cardiomyocytes.

Effects of central infusion of ANG II and losartan on the cardiac baroreflex in rabbits

The effect of chronic activation or inhibition of central ANG II receptors on cardiac baroreflex function in conscious normotensive rabbits was examined. Animals received a fourth ventricular (4V) infusion of ANG II (30 and 100 ng/h), losartan (3 and 30 microg/h), or Ringer solution (2 microl/h) for 2 wk. After 1 and 2 wk, ANG II (100 ng/h) decreased cardiac baroreflex gain by 20 and 37%, respectively (P = 0.015), whereas losartan (30 microg/h) increased baroreflex gain by 24 and 58%, respectively (P = 0.02). Within 1 wk of the end of the infusions, cardiac baroreflex gain had returned to control. Ringer solution or the lower doses of ANG II or losartan did not modify the cardiac baroreflex function. Blood pressure and heart rate were not altered by any treatment, nor was their variability affected. These data demonstrate a novel long-term modulation of cardiac baroreflexes by endogenous ANG II that is independent of blood pressure level.

Relationship between baroreceptor reflex function and end-organ damage in spontaneously hypertensive rats

The purpose of this study was to further illustrate the relationship between baroreceptor reflex sensitivity (BRS) and hypertensive end-organ damage (EOD) and to test the hypothesis that impairment of BRS aggravates EOD in hypertension. We studied baroreflex-mediated changes in heart rate [expressed as baroreceptor sensitivity to heart rate control (BRS(HR))] and blood pressure [expressed as baroreceptor sensitivity to blood pressure control (BRS(BP))] in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) that were used as controls, both at the age of 50-52 wk. Rats were also instrumented to record BP, HR, and BP variability (BPV) in the conscious, unrestrained state. In SHR compared with WKY, BP and BPV were significantly increased, whereas BRS(HR) and BRS(BP) were significantly decreased. SHR had remarkable EOD when compared with WKY (EOD score: 6.3 +/- 2.5 vs. 2.9 +/- 0.8, P < 0.01). Univariate regressive analysis demonstrated that EOD score was increased with BP and BPV and decreased with BRS. In multivariate analysis, EOD score was predicted by greater systolic BP and lower BRS and HR variability. These results indicate that BRS is negatively related to BPV and EOD score, and impaired BRS might be one of the major causes for hypertensive EOD.

Mechanisms of spontaneous baroreflex impairment in lyon hypertensive rats

This experiment aimed at 1) comparing the spontaneous baroreflex sensitivity (SBRS) in Lyon genetically hypertensive (LH), normotensive (LN), and low blood pressure (LL) rats and 2) assessing some aspects of the mechanisms of its impairment in LH rats. Baroreflex was studied in control animals after an early chronic converting enzyme inhibition with perindopril and after a 4-wk infusion of ANG II in perindopril-treated rats. The SBRS was determined with a previously validated method, using statistical dependence between blood pressure (BP) and heart rate values recorded in freely moving animals. LH rats exhibited high BP, cardiac hypertrophy, and decreased SBRS (LH, 1.3 +/- 0.2; LN, 2.5 +/- 0.4; LL, 2.2 +/- 0.4 beats . min-1 . mmHg-1). Perindopril prevented the development of hypertension and cardiac hypertrophy and normalized SBRS. BP rose in LH and LL rats after ANG II infusion, but only LH rats, which developed a cardiac hypertrophy, had an impaired SBRS (LH, 1.1 +/- 0.2; LN, 2.5 +/- 0.2; LL, 2.8 +/- 0.3 beats . min-1 . mmHg-1). This impairment was partially reversed by an acute ANG II blockade with losartan. These results demonstrate that high BP does not account for the decreased SBRS in LH rats. SBRS impairment could result either from cardiac hypertrophy or from the direct effect of ANG II on the baroreflex loop.