Sympathetic activation in adipose tissue and skeletal muscle of hypertensive rats

5-Aminolevulinic acid hydrochloride enhances bupivacaine-induced hypotension in spontaneously hypertensive rats

PURPOSE

Oral administration of 5-aminolevulinic acid hydrochloride (5-ALA-HCl) has been reported to enhance the hypotensive effects associated with anesthetics, especially in elderly hypertensive patients treated with antihypertensive agents. The present study aimed to clarify the effects of antihypertensive-agent- and anesthesia-induced hypotension by 5-ALA-HCl in spontaneously hypertensive rats (SHRs).

METHODS

We measured blood pressure (BP) of SHRs and normotensive Wistar Kyoto (WKY) rats treated with amlodipine or candesartan before and after administration of 5-ALA-HCl. We also investigated the change in BP following intravenous infusion of propofol and intrathecal injection of bupivacaine in relation to 5-ALA-HCl administration.

FINDINGS

Oral administration of 5-ALA-HCl significantly reduced BP in SHRs and WKY rats with amlodipine and candesartan. Infusion of propofol significantly reduced BP in SHRs treated with 5-ALA-HCl. Intrathecal injection of bupivacaine significantly declined SBP and DBP in both SHRs and WKY rats treated with 5-ALA-HCl. The bupivacaine-induced decline in SBP was significantly larger in SHRs compared with WKY rats.

CONCLUSION

These findings suggest that 5-ALA-HCl does not affect the antihypertensive agents-induced hypotensive effect, but enhances the bupivacaine-induced hypotensive effect, especially in SHRs, indicating that 5-ALA may contribute to anesthesia-induced hypotension via suppression of sympathetic nerve activity in patients with hypertension.

Effects of voluntary exercise on the expression of browning markers in visceral and subcutaneous fat tissue of normotensive and spontaneously hypertensive rats

High physical activity is important to optimize the function of adipose tissue. Dysfunctional adipose tissue contributes to the development of metabolic stress, chronic inflammation, and hypertension. To improve our current understanding of the interaction between physical exercise and adipose tissue, we analyzed the effect of 10 months voluntary running wheel activity of rats on uncoupling protein (UCP) 1 negative white adipose tissue (visceral and subcutaneous adipose tissue, VWAT and SWAT). Analysis was performed via RT-PCR and immunoblot from adipose tissues depicted from adult normotensive and spontaneously hypertensive female rats. UCP1 negative VWAT differed from UCP1 positive WAT and brown adipose tissue (BAT) from interscapular fat depots, by lacking the expression of UCP1 and low expression of Cidea, a transcriptional co-activator of UCP1. High physical activity affected the expression of five genes in SWAT (Visfatin (up), RBP5, adiponectin, Cidea, and Nrg4 (all down)) but only one gene (Visfatin, up) in VWAT. Furthermore, the expression of these genes is differentially regulated in VWAT and SWAT of normotensive and spontaneously hypertensive rats (SHR) under sedentary conditions (UCP2) and exercise (Visfatin, Cidea, Nrg4). Keeping the animals after 6 months of voluntary exercise under observation for an additional period of 4 months without running wheels, Visfatin, Cidea, and Nrg4 were stronger expressed in VWAT of SHRs than in sedentary control rats. In summary, our study shows that SWAT is more responsible to exercise than VWAT.

Black Soybean and Adzuki Bean Extracts Lower Blood Pressure by Modulating the Renin-Angiotensin System in Spontaneously Hypertensive Rats

Hypertension, causing cardiovascular disease, stroke, and heart failure, has been a rising health issue worldwide. Black soybeans and adzuki beans have been widely consumed throughout history due to various bioactive components. We evaluated the antihypertensive effects of black soybean and adzuki bean ethanol extracts on blood pressure, renin-angiotensin system (RAS), and aortic lesion in spontaneously hypertensive rats. A group of WKY (normal) and six groups of spontaneously hypertensive rats were administered with saline (SHR), 50 mg/kg of captopril (CAP), 250 and 500 mg/kg of black soybean extracts (BE250 and BE500), 250 and 500 mg/kg of adzuki bean extracts (AE250 and AE500) for eight weeks. BE250, BE500, AE250, and AE500 significantly (p < 0.05) reduced relative liver weight, AST, ALT, triglyceride, total cholesterol, systolic blood pressure, and angiotensin-converting-enzyme level compared to SHR. The angiotensin II level in AE500 and renin mRNA expression in BE500 and AE500 were significantly (p < 0.05) decreased compared to SHR. The lumen diameter was significantly (p < 0.05) reduced in only CAP. Furthermore, systolic and diastolic blood pressure and angiotensin II level in AE500 were lower than those of BE500. These results suggest that AE exhibit more antihypertensive potential than BE in spontaneously hypertensive rats.

The influence of hypertensive environment on adipose tissue remodeling measured by fluorescence lifetime imaging in spontaneously hypertensive rats

There is a lack of information correlating low adiposity with hypertension experienced by Spontaneous Hypertensive Rats (SHR) or overweight and normotension in Wistar-Kyoto (WKY). We aimed to investigate this lipodystrophy phenomenon by measuring fluorescence lifetime (FLIM), optical redox ratio (ORR), serum levels of hypothalamic-pituitary-adrenal (HPA) and/or hypothalamic-pituitary-thyroid (HPT) hormones axes between Wistar, WKY and SHR before and after establishment of hypertension. Under high blood pressure, we evaluated serum adipokines. Brown adipose tissue was characterized as lower ORR and shorter FLIM compared to white adipose tissue. HPT axis showed a crucial role in the SHR adipose tissue configuration by attenuating whitening. The increased adiposity in WKY may act as a preventive agent for hypertension, since SHR, with low adiposity, establishes the disease. The hypertensive environment can highlight key adipokines that may result in new therapeutic approaches to the treatment of adiposity dysfunctions and hypertension.

Carotid baroreceptor stimulation in obese rats affects white and brown adipose tissues differently in metabolic protection

The sympathetic nervous system (SNS) regulates the functions of white adipose tissue (WAT) and brown adipose tissue (BAT) tightly. Carotid baroreceptor stimulation (CBS) efficiently inhibits SNS activation. We hypothesized that CBS would protect against obesity. We administered CBS to obese rats and measured sympathetic and AMP-activated protein kinase (AMPK)/ PPAR pathway responses as well as changes in perirenal WAT (PWAT), epididymal WAT (EWAT), and interscapular BAT (IBAT). CBS alleviated obesity-related metabolic changes, improving insulin resistance; reducing adipocyte hypertrophy, body weight, and adipose tissue weights; and decreasing norepinephrine but increasing acetylcholine in plasma, PWAT, EWAT, and IBAT. CBS also downregulated fatty acid translocase (CD36), fatty acid transport protein (FATP), phosphorylated and total hormone sensitive lipase, phosphorylated and total protein kinase A, and PPARγ in obese rats. Simultaneously, CBS upregulated phosphorylated adipose triglyceride lipase, phosphorylated and total AMPK, and PPARα in PWAT, EWAT, and IBAT. However, BAT and WAT responses differed; although many responses were more sensitive in IBAT, responses of CD36, FATP, and PPARγ were more sensitive in PWAT and EWAT. Overall, CBS decreased chronically activated SNS and ameliorated obesity-related metabolic disorders by regulating the AMPK/PPARα/γ pathway.

Blockade of Rostral Ventrolateral Medulla Apelin Receptors Does Not Attenuate Arterial Pressure in SHR and L-NAME-Induced Hypertensive Rats

Dysfunction of the apelinergic system, comprised of the neuropeptide apelin mediating its effects via the G protein-coupled apelin receptor (APJ), may underlie the onset of cardiovascular disease such as hypertension. Apelin expression is increased in the rostral ventrolateral medulla (RVLM) in spontaneously hypertensive rats (SHRs) compared to Wistar-Kyoto (WKY) normotensive rats, however, evidence that the apelinergic system chronically influences mean arterial blood pressure (MABP) under pathophysiological conditions remains to be established. In this study we investigated, in conscious unrestrained rats, whether APJ contributes to MABP and sympathetic vasomotor tone in the progression of two models of hypertension - SHR and _L-NAME-treated rats - and whether APJ contributes to the development of hypertension in pre-hypertensive SHR. In SHR we showed that APJ gene (aplnr) expression was elevated in the RVLM, and there was a greater MABP increase following microinjection of [Pyr¹]apelin-13 to the RVLM of SHR compared to WKY rats. Bilateral microinjection of a lentiviral APJ-specific-shRNA construct into the RVLM of WKY, SHR, and _L-NAME-treated rats, chronically implanted with radiotelemeters to measure MABP, decreased aplnr expression in the RVLM and abolished acute [Pyr¹]apelin-13-induced increases in MABP. However, chronic knockdown of aplnr in the RVLM did not affect MABP in either SHR or _L-NAME-treated rats. Moreover, knockdown of aplnr in the RVLM of prehypertensive SHR did not protect against the development of hypertension. These results show that endogenous apelin, acting via APJ, is not involved in the genesis or maintenance of hypertension in either animal model used in this study.

Median preoptic nucleus excitatory neurotransmitters in the maintenance of hypertensive state

The crucial role of the median preoptic nucleus (MnPO) in the maintenance of hydroelectrolytic balance and autonomic regulation have been highlighted. Recently, the participation of the MnPO in the control of sympathetic nerve activity was demonstrated in essential hypertension model. However, peculiarities on the neurochemical changes underlying the differential role of MnPO during hypertension remain to be clarified. Therefore, this study aimed to investigate the main excitatory pathways that modulate MnPO neurons in hypertensive rats. Spontaneously hypertensive rats (SHR) and rats submitted previously to the Goldblatt protocol (two kidneys; one clip; 2K1C) were used. Rats of both groups (250 to 350 g, n = 6) were anesthetized with urethane (1.2 g/kg,i.v.) and instrumented to record mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA). Nanoinjection (100 nl) of saline (NaCl, 150 mM), losartan (AT1 receptor antagonist; 10 mM) and kynurenic acid (glutamate receptor antagonist; 50 mM) into the MnPO were performed. In 2K1C rats, glutamatergic blockade promoted decreases in MAP and RSNA (-19.1 ± 0.9 mmHg, -21.6 ± 2.8%, p < 0.05) when compared to saline (-0.4 ± 0.6 mmHg, 0.2 ± 0.7%, p < 0.05). Angiotensinergic inhibition also reduced these parameters (-11.5 ± 1.2 mmHg, -10.5 ± 1.0%, p < 0.05) in 2K1C. In SHR, Kynurenic acid nanoinjections produced hypotension and sympathoinhibition (-21.0 ± 2.5 mmHg, -24.7 ± 2.4%, p < 0.05), as well losartan nanoinjections (-9.7 ± 1.2 mmHg; p < 0.05) and RSNA (-12.0 ± 2.4%, p < 0.05). These findings support the conclusion that a tonic excitatory neurotransmission exerted by angiotensin II, and mostly by glutamate in the MnPO could participate in the modulation of blood pressure and RSNA independent on whether hypertension is primarily neurogenic or is secondary to stenosis in renal artery.

Grape pomace extract induced beige cells in white adipose tissue from rats and in 3T3-L1 adipocytes

This study investigated the effects of a grape pomace extract (GPE) rich in phenolic compounds on brown-like adipocyte induction and adiposity in spontaneously hypertensive (SHR) and control normotensive Wistar-Kyoto (WKY) rats fed a high-fat diet (HFD). HFD consumption for 10 weeks significantly increased epididymal white adipose tissue (eWAT) in WKY but not in SHR rats. Supplementation with GPE (300 mg/kg body weight/day) reduced adipocyte diameter and increased levels of proteins that participate in adipogenesis and angiogenesis, i.e., peroxisome-proliferator activated receptor gamma (PPARγ), vascular endothelial grow factor-A (VEGF-A) and its receptor 2 (VEGF-R2), and partially increased the uncoupling protein 1 (UCP-1) in WKY. In both strains, GPE attenuated adipose inflammation. In eWAT from SHR, GPE increased the expression of proteins involved in adipose tissue "browning," i.e., PPARγ-coactivator-1α (PGC-1α), PPARγ, PR domain containing 16 (PRDM16) and UCP-1. In primary cultures of SHR adipocytes, GPE-induced UCP-1 up-regulation was dependent on p38 and ERK activation. Accordingly, in 3T3-L1 adipocytes treated with palmitate, the addition of GPE (30 μM) activated the β-adrenergic signaling cascade (PKA, AMPK, p38, ERK). This led to the associated up-regulation of proteins involved in mitochondrial biogenesis (PGC-1α, PPARγ, PRDM16 and UCP-1) and fatty acid oxidation (ATGL). These effects were similar to those exerted by (-)-epicatechin and quercetin, major phenolic compounds in GPE. Overall, in HFD-fed rats, supplementation with GPE promoted brown-like cell formation in eWAT and diminished adipose dysfunction. Thus, winemaking residues, rich in bioactive compounds, could be useful to mitigate the adverse effects of HFD-induced adipose dysfunction.

Effect of γ-aminobutyric acid and nattokinase-enriched fermented beans on the blood pressure of spontaneously hypertensive and normotensive Wistar-Kyoto rats

In this study we have evaluated the changes in arterial blood pressure in spontaneously hypertensive rats (SHR) caused by the short-term intake of Bacillus subtilis B060-fermented beans with significant γ-aminobutyric acid (GABA) and nattokinase activity. After being weaned, 7-week-old male SHR and 7-week-old male Wistar–Kyoto (WKY) rats were randomized into seven groups. Until the 8^th week of life, the rats in each group were given one of the following: Group 1, high dose of GABA and nattokinase in the SHR (SHD); Group 2, medium dose of GABA and nattokinase in the SHR (SMD); Group 3, low dose of GABA and nattokinase in the SHR (SLD); Group 4, negative control in the SHR (SD); Group 5, positive control in the SHR (SM); Group 6, high dose of GABA and nattokinase in the WKY (WHD); and Group 7, negative control in the WKY (WD). Distilled water served as the negative control, and captopril (50 mg/kg), a known ACE inhibitor, served as the positive control. Systolic blood pressure and diastolic blood pressure values were measured weekly from the 8^th week to the 16^th week of life using the tail-cuff method. A definite decrease in systolic and diastolic blood pressure values could be observed in the rats treated with captopril and in the rats that received GABA and nattokinase. The greatest antihypertensive effect was observed when the pharmacological treatment was administered. The effect of the daily intake of fermented beans containing GABA and nattokinase may be helpful in controlling blood pressure levels in hypertensive model animals. The fermentation of beans with B. subtilis B060 may therefore constitute a successful strategy for producing a functional food with antihypertensive activity.

Decreased diabetes-induced glycemic impairment in WKY and SHR involves enhanced skeletal muscle Slc2a4/GLUT4 expression

BACKGROUND

Hypertension has been associated to diabetes, and participates in the development of diabetic complications. The spontaneously hypertensive rat (SHR) is the gold standard model for the study of hypertension, and experimental diabetes has been currently investigated in SHR. Wistar-Kyoto rat is usually taken as control for SHR, however, regarding the glycemic homeostasis, WKY may be similar to SHR, when compared to the standard Wistar rat, importantly affecting the interpretation of data. Slc2a4 gene, which encodes the GLUT4 protein, is expressed in insulin-sensitive tissues, such as muscle cells and adipocytes, and alteration in Slc2a4/GLUT4 expression is inversely related to glycemic levels. We investigated the effect of diabetes on the expression of Slc2a4/GLUT4 and glycemic control in Wistar-Kyoto and SHR.

FINDINGS

Slc2a4 mRNA (Northern-blotting) and GLUT4 protein (Western-blotting) were investigated in skeletal muscles (soleus and extensor digitorum longus) of Wistar, Wistar-Kyoto and SHR, rendered or not diabetic for 1 month. Non-diabetic SHR shows hyperinsulinemia, and unaltered GLUT4 expression. The hyperglycemia was significantly attenuated in diabetic Wistar-Kyoto and SHR, compared to that observed in diabetic Wistar, although all of them presented the same hypoinsulinemic levels. Besides, diabetes significantly reduced Slc2a4/GLUT4 in Wistar, as expected; however, that was not observed in diabetic Wistar-Kyoto and SHR.

CONCLUSIONS

Non-diabetic SHR is insulin resistant, despite unaltered GLUT4 expression. Diabetic Wistar-Kyoto and diabetic SHR presented high Slc2a4/GLUT4 expression in skeletal muscle, as compared to diabetic Wistar. This Slc2a4/GLUT4 regulation does not depend on insulin level and possibly protects the WKY and SHR from severe glycemic impairment.

Anticontractile Effect of Perivascular Adipose Tissue and Leptin are Reduced in Hypertension

Leptin causes vasodilatation both by endothelium-dependent and -independent mechanisms. Leptin is synthesized by perivascular adipose tissue (PVAT). The hypothesis of this study is that a decrease of leptin production in PVAT of spontaneously hypertensive rats (SHR) might contribute to a diminished paracrine anticontractile effect of the hormone. We have determined in aorta from Wistar-Kyoto (WKY) and SHR (i) leptin mRNA and protein levels in PVAT, (ii) the effect of leptin and PVAT on contractile responses, and (iii) leptin-induced relaxation and nitric oxide (NO) production. Leptin mRNA and protein expression were significantly lower in PVAT from SHR. Concentration-response curves to angiotensin II were significantly blunted in presence of PVAT as well as by exogenous leptin (10⁻⁹ M) only in WKY. This anticontractile effect was endothelium-dependent. Vasodilatation induced by leptin was smaller in SHR than in WKY, and was also endothelium-dependent. Moreover, release of endothelial NO in response to acute leptin was higher in WKY compared to SHR, but completely abolished in the absence of endothelium. In conclusion, the reduced anticontractile effect of PVAT in SHR might be attributed to a reduced PVAT-derived leptin and to an abrogated effect of leptin on endothelial NO release probably due to an impaired activation of endothelial NO synthase.

Anticontractile Effect of Perivascular Adipose Tissue and Leptin are Reduced in Hypertension

Leptin causes vasodilatation both by endothelium-dependent and -independent mechanisms. Leptin is synthesized by perivascular adipose tissue (PVAT). The hypothesis of this study is that a decrease of leptin production in PVAT of spontaneously hypertensive rats (SHR) might contribute to a diminished paracrine anticontractile effect of the hormone. We have determined in aorta from Wistar-Kyoto (WKY) and SHR (i) leptin mRNA and protein levels in PVAT, (ii) the effect of leptin and PVAT on contractile responses, and (iii) leptin-induced relaxation and nitric oxide (NO) production. Leptin mRNA and protein expression were significantly lower in PVAT from SHR. Concentration-response curves to angiotensin II were significantly blunted in presence of PVAT as well as by exogenous leptin (10(-9) M) only in WKY. This anticontractile effect was endothelium-dependent. Vasodilatation induced by leptin was smaller in SHR than in WKY, and was also endothelium-dependent. Moreover, release of endothelial NO in response to acute leptin was higher in WKY compared to SHR, but completely abolished in the absence of endothelium. In conclusion, the reduced anticontractile effect of PVAT in SHR might be attributed to a reduced PVAT-derived leptin and to an abrogated effect of leptin on endothelial NO release probably due to an impaired activation of endothelial NO synthase.

Overview of endocrine systems in primary hypertension

Multiple hormonal factors play a major role in the functional and structural abnormalities of hypertension (HT). At present, the kidneys and, in particular, renal Na(+) retention are thought to constitute a primary and sustaining mechanism in the development of HT. However, the precise renal and hormonal mechanisms leading to increased Na(+) reabsorption and HT remain unknown. Because the vast majority of HT is primary, this article focuses on the major endocrine systems, the RAS, aldosterone, and the SNS, that play a prominent role in the pathogenesis of HT.

A current view of brain renin-angiotensin system: Is the (pro)renin receptor the missing link?

The renin-angiotensin system (RAS) plays a central role in the brain to regulate blood pressure (BP). This role includes the modulation of sympathetic nerve activity (SNA) that regulates vascular tone; the regulation of secretion of neurohormones that have a critical role in electrolyte as well as fluid homeostasis; and by influencing behavioral processes to increase salt and water intake. Based on decades of research it is clear that angiotensin II (Ang II), the major bioactive product of the RAS, mediates these actions largely via its Ang II type 1 receptor (AT1R), located within hypothalamic and brainstem control centers. However, the mechanisms of brain RAS function have been questioned, due in large part to low expression levels of the rate limiting enzyme renin within the central nervous system. Tissue localized RAS has been observed in heart, kidney tubules and vascular cells. Studies have also given rise to the hypothesis for localized RAS function within the brain, so that Ang II can act in a paracrine manner to influence neuronal activity. The recently discovered (pro)renin receptor (PRR) may be key in this mechanism as it serves to sequester renin and prorenin for localized RAS activity. Thus, the PRR can potentially mitigate the low levels of renin expression in the brain to propagate Ang II action. In this review we examine the regulation, expression and functional properties of the various RAS components in the brain with particular focus on the different roles that PRR may have in BP regulation and hypertension.

Vasodilating dipeptide Trp-His can prevent atherosclerosis in apo E-deficient mice

Most of the investigations for an alternative medicinal treatment on atherosclerosis have been focused on natural or dietary compounds including phytochemicals. So far, few studies regarding anti-atherosclerotic small peptides except for tetrapeptide of Lys-Arg-Glu-Ser have been reported. The present study was, thus, to investigate whether dipeptide Trp-His, which is one of vasodilating small peptides, could reduce atherosclerotic lesions in apo E-deficient mice fed a high-fat diet. The animal study involved a 9-week-successive administration of Trp-His at a dose of 0, 10 or 100 mg/kg per d. After 9-week administration, en face analyses provided the first direct evidence that the atherosclerotic lesion area was significantly reduced by 27 and 38 % for Trp-His dosed at 10 and 100 mg/kg per d, respectively, compared with the control group. Administration of Trp-His did not affect growth parameters such as body weight and feeding efficiency (P>0·1). Total serum cholesterol and HDL-cholesterol as well as lipid profiles in the liver did not differ between the tested groups. Taken together, the anti-atherosclerotic effect of dipeptide Trp-His should be addressed into physiological functions of bioactive peptides, in which the dipeptide may elicit the power by alternative mechanism(s), not by the regulation of lipid metabolism.

Metabolic consequences and vulnerability to diet-induced obesity in male mice under chronic social stress

Social and psychological factors interact with genetic predisposition and dietary habit in determining obesity. However, relatively few pre-clinical studies address the role of psychosocial factors in metabolic disorders. Previous studies from our laboratory demonstrated in male mice: 1) opposite status-dependent effect on body weight gain under chronic psychosocial stress; 2) a reduction in body weight in individually housed (Ind) male mice. In the present study these observations were extended to provide a comprehensive characterization of the metabolic consequences of chronic psychosocial stress and individual housing in adult CD-1 male mice. Results confirmed that in mice fed standard diet, dominant (Dom) and Ind had a negative energy balance while subordinate (Sub) had a positive energy balance. Locomotor activity was depressed in Sub and enhanced in Dom. Hyperphagia emerged for Dom and Sub and hypophagia for Ind. Dom also showed a consistent decrease of visceral fat pads weight as well as increased norepinephrine concentration and smaller adipocytes diameter in the perigonadal fat pad. On the contrary, under high fat diet Sub and, surprisingly, Ind showed higher while Dom showed lower vulnerability to obesity associated with hyperphagia. In conclusion, we demonstrated that social status under chronic stress and individual housing deeply affect mice metabolic functions in different, sometime opposite, directions. Food intake, the hedonic response to palatable food as well as the locomotor activity and the sympathetic activation within the adipose fat pads all represent causal factors explaining the different metabolic alterations observed. Overall this study demonstrates that pre-clinical animal models offer a suitable tool for the investigation of the metabolic consequences of chronic stress exposure and associated psychopathologies.

Chronic blockade of phosphatidylinositol 3-kinase in the nucleus tractus solitarii is prohypertensive in the spontaneously hypertensive rat

Phosphatidylinositol 3-kinase (PI3K) within brain stem neurons has been implicated in hypertension in the spontaneously hypertensive rat (SHR). Previously, we demonstrated elevated expression of PI3K subunits in rostral ventrolateral medulla and paraventricular nucleus of SHRs compared with Wistar-Kyoto rats. Here, we considered expression levels of PI3K in the nucleus tractus solitarii, a pivotal region in reflex regulation of arterial pressure, and determined its functional role for arterial pressure homeostasis in SHRs and Wistar-Kyoto rats. We found elevated mRNA levels of p110beta and p110delta catalytic PI3K subunits in the nucleus tractus solitarii of adult (12 to 14 weeks old) SHRs relative to the age-matched Wistar-Kyoto rats (fold differences relative to beta-actin: 1.7+/-0.2 versus 1.01+/-0.08 for p110beta, n=6, P<0.05; 1.62+/-0.15 versus 1.02+/-0.1 for p110delta, n=6, P<0.05). After chronic blockade of PI3K signaling in the nucleus tractus solitarii by lentiviral-mediated expression of a mutant form of p85alpha, systolic pressure increased from 175+/-3 mm Hg to 191+/-6 mm Hg (P<0.01) in SHRs but not in Wistar-Kyoto rats. In addition, heart rate increased (from 331+/-6 to 342+/-6 bpm; P<0.05) and spontaneous baroreflex gain decreased (from 0.7+/-0.07 to 0.5+/-0.04 ms/mm Hg; P<0.001) in the SHRs. Thus, PI3K signaling in the nucleus tractus solitarii of SHR restrains arterial pressure in this animal model of neurogenic hypertension.

A reduction in the amount and anti-contractile effect of periadventitial mesenteric adipose tissue precedes hypertension development in spontaneously hypertensive rats

The aim of this study was to determine whether alterations in periadventitial adipose tissue and its anti-contractile effect precede hypertension development. We used 4-week-old male Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), which were pre-hypertensive. Vascular function was studied in the perfused mesenteric bed (MB, 1.5 mL/min). MB weight was lower in SHR (8.0 +/- 0.3 mg/g body weight) than in WKY (9.0 +/- 0.3 mg/g body weight) rats. Concentration-response curves to KCI (6 to 75 mmol/L) and to acetylcholine (10(-9) to 10(-5) mol/L) were similar between groups. Contractile responses to serotonin (10(-9) to 10(-5) mol/L) were significantly higher in SHR compared to WKY. 4-Aminopyridine (4-AP, 2 mmol/L), a blocker of Kv channels, induced a similar increase in perfusion pressure in both strains. However, 4-AP (2 mmol/L) significantly increased the contractile response to serotonin (10(-9) to 10(-5) mol/L) only in WKY. The anti-contractile effect of fat was confirmed by a comparison of (+) fat and (-) fat mesenteric arteries, which revealed that 4-AP significantly enhanced contractions only in (+) fat rings from WKY. These results show that alterations in visceral periadventitial fat mass and function in SHR precede hypertension, suggesting a constitutive mechanism independent of age and the hypertensive state.

Plasticity of pre- and postsynaptic GABAB receptor function in the paraventricular nucleus in spontaneously hypertensive rats

GABA(B) receptor function is upregulated in the paraventricular nucleus (PVN) of the hypothalamus in spontaneously hypertensive rats (SHR), but it is unclear whether this upregulation occurs pre- or postsynaptically. We therefore determined pre- and postsynaptic GABA(B) receptor function in retrogradely labeled spinally projecting PVN neurons using whole cell patch-clamp recording in brain slices in SHR and Wistar-Kyoto (WKY) rats. Bath application of the GABA(B) receptor agonist baclofen significantly decreased the spontaneous firing activity of labeled PVN neurons in both SHR and WKY rats. However, the magnitude of reduction in the firing rate was significantly greater in SHR than in WKY rats. Furthermore, baclofen produced larger membrane hyperpolarization and outward currents in labeled PVN neurons in SHR than in WKY rats. The baclofen-induced current was abolished by either including G protein inhibitor GDPbetaS in the pipette solution or bath application of the GABA(B) receptor antagonist in both SHR and WKY rats. Blocking N-methyl-d-aspartic acid receptors had no significant effect on baclofen-elicited outward currents in SHR. In addition, baclofen caused significantly greater inhibition of glutamatergic excitatory postsynaptic currents (EPSCs) in labeled PVN neurons in brain slices from SHR than WKY rats. By contrast, baclofen produced significantly less inhibition of GABAergic inhibitory postsynaptic currents (IPSCs) in labeled PVN neurons in SHR than in WKY rats. Although microinjection of the GABA(B) antagonist into the PVN increases sympathetic vasomotor tone in SHR, the GABA(B) antagonist did not affect EPSCs and IPSCs of the PVN neurons in vitro. These findings suggest that postsynaptic GABA(B) receptor function is upregulated in PVN presympathetic neurons in SHR. Whereas presynaptic GABA(B) receptor control of glutamatergic synaptic inputs is enhanced, presynaptic GABA(B) receptor control of GABAergic inputs in the PVN is attenuated in SHR. Changes in both pre- and postsynaptic GABA(B) receptors in the PVN may contribute to the control of sympathetic outflow in hypertension.

Whole body norepinephrine kinetics in ANG II-salt hypertension in the rat

The purpose of this study was to investigate total body norepinephrine (NE) kinetics as an index of global sympathetic nervous system (SNS) outflow in a rat model of chronic ANG II-salt hypertension. Male Sprague-Dawley rats fed a 0.4% (normal salt, NS) or 2% (HS) NaCl diet were instrumented with arterial and venous catheters. After 5 days of recovery and a 3-day control period, ANG II (150 ng.kg(-1).min(-1)) was given subcutaneously by minipump for 14 days. Plasma NE levels and total body NE spillover and clearance were determined on control day 3 and ANG II infusion days 7 and 14 using radioisotope dilution principles. To perform this analysis, 3H-NE and NE were measured in arterial plasma after a 90-min infusion of tracer amounts of 3H-NE. Mean arterial pressure (MAP) was similar during the control period in NS and HS rats; however, MAP increased to a higher level in HS rats. During the control period, plasma NE tended to be lower in rats on HS, whereas NE clearance tended to be higher in HS rats. As a result NE spillover was similar in NS and HS rats during the control period. In NS rats, plasma NE, NE spillover, and NE clearance were unchanged by ANG II. In contrast, in rats on the HS diet, plasma NE and NE spillover increased during ANG II infusion, whereas NE clearance was unchanged. In conclusion, a HS diet alone or ANG II infusion in animals fed NS do not affect global sympathetic outflow. However, the additional hypertensive response to ANG II in animals fed HS is accompanied by SNS activation.

Upregulation of angiotensin AT1 receptor and intracellular kinase gene expression in hypertensive rats

1. Activation of angiotensin II AT1 receptors (AT1R) stimulates catecholamine systems within both central and peripheral tissues that are associated with blood pressure control. In the present study, we sought to determine whether the hypertensive phenotype of the spontaneously hypertensive rat (SHR) is associated with changes in AT1R gene expression and whether gene expression of downstream signalling molecules was coupled to catecholamine gene expression, both in key brainstem nuclei and in peripheral sites implicated in cardiovascular control. 2. Gene expression levels of AT1R, extracellular signal-regulated kinase (ERK) 1 and 2 and phosphatidylinositol 3-kinase (PI3-K) were quantified in Wistar-Kyoto (WKY) rats and SHR. Messenger RNA expression levels were quantified using real time reverse transcription-polymerase chain reaction. In addition, we investigated whether there was a relationship between gene expression and systolic blood pressure. 3. The gene expression levels of AT1R, ERK2 and PI3-K were significantly higher in the paraventricular nucleus of the hypothalamus (4.12-, 1.40- and 1.38-fold, respectively), rostral ventrolateral medulla (2.71-, 1.33- and 2.73-fold, respectively), spinal cord (30.5-, 2.72- and 1.53-fold, respectively), adrenal medulla (1.68-, 1.55- and 1.76-fold, respectively) and coeliac ganglion (1.39-, 1.35- and 1.12-fold, respectively) in SHR compared with WKY rats. There was no significant difference in the level of ERK1 gene expression between the two strains. The gene expression levels of AT1R and ERK2 were positively correlated with blood pressure in all central nervous tissues investigated in the SHR, but not in WKY rats. Gene expression levels of the AT1R in the coeliac ganglion and adrenal medulla were also positively correlated with increased systolic blood pressure. 4. The present data suggest that a defect in AT1R expression (that may further alter downstream signalling pathways) in the SHR may be responsible, at least in part, for the hypertensive phenotype.

Role of γ-Aminobutyric Acid (GABA)Aand GABABReceptors in Paraventricular Nucleus in Control of Sympathetic Vasomotor Tone in Hypertension

The paraventricular nucleus (PVN) of the hypothalamus is involved in tonic regulation of sympathetic outflow. Impaired GABAergic control of PVN neurons may contribute to the elevated sympathetic drive in hypertension. In this study, we examined the function of GABA(A) and GABA(B) receptors in the PVN in control of sympathetic nerve activity and arterial blood pressure (ABP) in normotensive and hypertensive rats. Lumbar sympathetic activity (LSNA) and ABP were recorded from anesthetized spontaneously hypertensive rats (SHRs), Sprague-Dawley (SD) rats, and Wistar-Kyoto (WKY) rats. Bilateral microinjection of bicuculline (0.01-0.15 nmol), a GABA(A) receptor antagonist, into the PVN increased LSNA and ABP in normotensive WKY and SD rats in a dose-dependent manner. This response was significantly attenuated in SHRs. Furthermore, the decrease in LSNA and ABP induced by a GABA(A) receptor agonist, muscimol (0.05-1.5 nmol), in the PVN was significantly less in SHRs than in normotensive controls. In contrast, microinjection of the GABA(B) receptor agonist baclofen (0.3-4.5 nmol) into the PVN decreased LSNA and ABP in SHRs. However, in WKY and SD rats, baclofen only decreased LSNA and ABP at the highest dose tested. In addition, blockade of GABA(B) receptors in the PVN with CGP52432 (3-[[(3,4-dichlorophenyl)methyl]amino]propyl]diethoxymethyl)phosphinic acid) (0.15-3.0 nmol) dose-dependently increased LSNA and ABP in SHRs but not in normotensive controls. Collectively, this study provides new evidence that GABA(A) receptor function is attenuated, whereas the function of GABA(B) receptors is enhanced, in the PVN of SHRs.

Increased DNA fragmentation and altered apoptotic protein levels in skeletal muscle of spontaneously hypertensive rats

Apoptosis is a highly conserved process that plays an important role in controlling tissue development, homeostasis, and architecture. Dysregulation of apoptosis is a hallmark of numerous human pathologies including hypertension. In the present work we studied the effect of hypertension on apoptosis and the expression of several apoptotic signaling and/or regulatory proteins in four functionally and metabolically distinct muscles. Specifically, we examined these markers in soleus, red gastrocnemius, white gastrocnemius, and left ventricle (LV) of 20-wk-old normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Compared with WKY rats SHR had a significantly greater heart weight, LV weight, and mean arterial pressure. In general, SHR skeletal muscle had increased Bax protein, procaspase-3 protein, caspase-3 activity, cleaved poly(ADP-ribose) polymerase protein, and DNA fragmentation as well as decreased Bcl-2 protein and a lower Bcl-2-to-Bax ratio. Subcellular distribution studies demonstrated increased levels of apoptosis-inducing factor protein in cytosolic or nuclear extracts as well as elevated nuclear Bax protein in SHR skeletal muscle. Moreover, heat shock protein 70 in red gastrocnemius and soleus was significantly correlated to several apoptotic factors. With the exception of lower heat shock protein 90 levels in SHR no additional differences in any apoptotic markers were observed in LV between groups. Collectively, this report provides the first evidence that apoptotic signaling is altered in skeletal muscle of hypertensive animals, an effect that may be mediated by both caspase-dependent and -independent mechanisms. This proapoptotic state may provide some understanding for the morphological and functional abnormalities observed in skeletal muscle of hypertensive animals.

Plasticity of GABAergic control of hypothalamic presympathetic neurons in hypertension

Increased sympathetic outflow contributes to the pathogenesis of hypertension. However, the mechanisms of increased sympathetic drive in hypertension remain unclear. We examined the tonic GABAergic inhibition in control of the excitability of paraventricular (PVN) presympathetic neurons in spontaneously hypertensive rats (SHR) and normotensive controls, including Sprague-Dawley (SD) and Wistar-Kyoto (WKY) rats. Whole cell patch-clamp recordings were performed on retrogradely labeled PVN neurons projecting to the rostral ventrolateral medulla (RVLM) in brain slices. The basal firing rate of PVN neurons was significantly decreased in 13-wk-old SD and WKY rats but increased in 13-wk-old SHR, compared with their respective 6-wk-old controls. The GABA(A) antagonist bicuculline consistently increased the firing of PVN neurons in normotensive controls. Surprisingly, bicuculline either decreased the firing or had no effect in 59.3% of labeled cells in 13-wk-old SHR. In contrast, the GABA(B) antagonist CGP-55845 had no effect on the firing of PVN neurons in normotensive controls but significantly increased the firing of 75% of cells studied in 13-wk-old SHR. Furthermore, the evoked GABA(A) current decreased significantly in labeled PVN neurons of 13-wk-old SHR compared with that in normotensive controls. Both the frequency and amplitude of GABAergic spontaneously inhibitory postsynaptic currents were also reduced in 13-wk-old SHR. This study demonstrates an unexpected functional change in GABA(A) and GABA(B) receptors in regulation of the firing activity of PVN-RVLM neurons in SHR. This change in GABA(A) receptor function and GABAergic inputs to PVN output neurons may contribute to increased sympathetic outflow in hypertension.

Sympathetic modulation by carvedilol and losartan reduces angiotensin II-mediated lipolysis in subcutaneous and visceral fat

Advanced heart failure is characterized by increased activation of the renin-angiotensin system and the development of cachexia. Angiotensin II (Ang II) has been proposed as a lipid metabolism regulator. The effects of exogenous Ang II (osmotic minipump, 525 ng/kg/min for 12 d) on interstitial sc glycerol and norepinephrine levels, indexes of lipolysis, and sympathetic activation, respectively, were measured in Sprague Dawley rats by consecutive microdialysis performed in vivo in white adipose tissue. Higher sustained interstitial glycerol and norepinephrine levels were found after 7 and 12 d of Ang II infusion. Triglyceride to DNA content ratio and adipocyte diameter were reduced in sc and visceral (retroperitoneal and epididymal) fat tissues of Ang II-infused rats, whose body weight was lower and blood pressure higher. Losartan, an Ang II receptor 1 blocker, and carvedilol, an alpha1-nonselective-beta1,2,3-adrenergic blocker, but not doxazosin, an alpha1-selective-adrenergic blocker, lowered glycerol and norepinephrine levels, preventing lipolysis and weight loss. Our results indicate that Ang II stimulates lipolysis in sc and visceral adipocytes by sympathetic activation and beta-adrenergic-receptor stimulation. Nonselective-beta-adrenergic and Ang II-receptor1 blockade markedly attenuated the rise of norepinephrine, preventing catabolic effects. The metabolic benefits of carvedilol and losartan, in addition to recognized protective cardiovascular effects, may be relevant in cachectic patients with advanced heart failure.

Decreased tyrosine hydroxylase activity in the adrenals of spontaneously hypertensive rats

Higher activity of the peripheral sympathetic nervous system, accompanied by higher tyrosine hydroxylase activity is frequently and consistently reported in human essential hypertension as well as in animal models of hypertension. However, results obtained in the adrenals, particularly in young animals before the development of hypertension, are scarce and controversial. In the present study tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats and of age-matched control Wistar Kyoto rats were evaluated before, during and after the development of hypertension (5, 12 and 22-week-old animals). Results show that both tyrosine hydroxylase activity and total amine content in the adrenals of spontaneously hypertensive rats were significantly reduced (35% reduction) at all studied ages. Determination of the kinetic parameters for tyrosine hydroxylase in the adrenals of 5 week-old spontaneously hypertensive rats revealed a 38% reduction in V(max) values (13.4 versus 21.3 nmol L-DOPA/mg prot/h in age-matched controls) accompanied by lower levels of expression of both tyrosine hydroxylase total protein and phosphoSer40 observed by Western-Blot. In contrast, norepinephrine content in both plasma and tail artery were significantly higher in the spontaneously hypertensive strain. In conclusion, contrary to the higher peripheral sympathetic activity, tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats are markedly reduced before, during and after the development of hypertension. End product, long-term feedback inhibition by the high norepinephrine plasma levels could be responsible for this reduction, establishing yet another regulatory mechanism of tyrosine hydroxylase operating in adrenal cromaffin cells.

Soyabean protein hydrolysate prevents the development of hypertension in spontaneously hypertensive rats

The aim of the present study was to investigate the anti-hypertensive and angiotensin-converting enzyme (ACE) inhibition effects of soyabean protein hydrolysate in spontaneously hypertensive rats (SHR). Soyabean protein hydrolysate was prepared by peptic hydrolysis and was added into the feed of SHR (0% for the S0 group, 0.5% for the S1 group, and 1% for the S2 group) for 12 weeks. Systolic blood pressure and mean blood pressure of the S1 (164.3 (sem 4.7); 128.0 (sem 5.0) mmHg) and S2 (156.8 (sem 1.6); 120.8 (sem 3.4) mmHg) groups were significantly lower than those of the S0 group (199.4 (sem 5.2); 158.3 (sem 7.0) mmHg) at the end of the study. In the analysis of ACE activity, plasma and heart ACE activities of the S1 and S2 groups were significantly lower than those of the S0 group, and there were no significant differences in aorta, kidney, and lung ACE activities among all SHR. Soyabean protein hydrolysate had no significant effect on plasma lipids, electrolytes, or on left ventricular wall or aorta wall thickness. The results suggest that the long-term administration of soyabean protein hydrolysate might retard the development of hypertension in SHR by its inhibitory effect on ACE in vivo.

Brain renin-angiotensin system dysfunction in hypertension: recent advances and perspectives

This review focuses on the dysfunction of the intrinsic brain renin-angiotensin system (RAS) in the pathogenesis of hypertension. Hyperactivity of the brain RAS plays a critical role in mediating hypertension in both humans and animal models of hypertension, including the spontaneously hypertensive rat (SHR). The specific mechanisms by which increased brain RAS activity results in hypertension are not well understood but include increases in sympathetic vasomotor tone and impaired arterial baroreflex function. We discuss the contribution of endogenous angiotensin (Ang) II actions on presympathetic vasomotor rostral ventrolateral medulla neurons to enhance sympathetic activity and maintain hypertension. In addition, we discuss Ang II-induced attenuation of afferent baroreceptor feedback within the nucleus tractus solitarius and its relevance to the development of hypertension. We also outline the cellular and molecular mechanisms of Ang II signal transduction that may be critical for the initiation and establishment of hypertension. In particular, we present evidence for a phosphoinositide-3-kinase-dependent signaling pathway that appears to contribute to hypertension in the SHR, possibly via augmented Ang II-induced increases in neuronal firing rate and enhanced transcriptional noradrenaline neuromodulation. Finally, we outline future directions in utilizing our understanding of the brain RAS dysfunction in hypertension for the development of improved therapeutic intervention in hypertension.

Kinin B2 receptor localization and expression in the hypothalamo-pituitary-adrenal axis of spontaneously hypertensive rats

OBJECTIVE

An enhanced hypothalamo-pituitary-adrenocortical (HPA) activity has been demonstrated during onset of high blood pressure in spontaneously hypertensive rats (SHR). Furthermore, compared to normotensive Wistar-Kyoto (WKY) rats, SHR show hypersensitivity to bradykinin (BK)-induced pressor responses which may be caused by an upregulation of B(2) receptor expression in the brain.

METHODS

We performed an immunohistochemical localization and measured gene expression of B(2) receptors in the hypothalamus, pituitary and adrenal glands of SHR at three ages corresponding to the development of hypertension, i.e. prehypertensive phase, onset of hypertension and established hypertension. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot technique, B(2) receptor mRNA and protein levels, respectively, were measured.

RESULTS

A specific immunostaining for B(2) receptors was observed in the hypothalamic nuclei paraventricularis (PVN) and supraopticus (SON). In the pituitary and adrenal glands, a strong immunostaining was observed in neurohypophysis (NH) and adrenal medulla, respectively. At all ages tested, B(2) receptor mRNA and protein levels were higher in the hypothalamus and adrenal glands of SHR compared to age-matched WKY rats. Among SHR, the mRNA level was increased in neurohypophysis with age, and no difference was found in the adenohypophysis (AH) between SHR and WKY rats.

CONCLUSION

The data demonstrate a specific localization and an upregulation of B(2) receptor expression in the hypothalamus and adrenal glands of SHR, providing an anatomical and molecular basis for a possible contributory role to bradykinin-induced hypersensitivity of cardiovascular responses. The increased B(2) receptor expression in the hypothalamus and adrenal glands may also play a role in the abnormalities of the HPA axis in SHR during the development of hypertension.