Prehypertensive Spontaneously Hypertensive Research Articles

Dapagliflozin Attenuates Sympathetic and Pressor Responses to Stress in Young Prehypertensive Spontaneously Hypertensive Rats.

SGLT2i (sodium-glucose cotransporter 2 inhibitor), a class of anti-diabetic medications, is shown to reduce blood pressure (BP) in hypertensive patients with type 2 diabetes. Mechanisms underlying this action are unknown but SGLT2i-induced sympathoinhibition is thought to play a role. Whether SGLT2i reduces BP and sympathetic nerve activity (SNA) in a nondiabetic prehypertension model is unknown. Accordingly, we assessed changes in conscious BP using radiotelemetry and alterations in mean arterial pressure and renal SNA during simulated exercise in nondiabetic spontaneously hypertensive rats during chronic administration of a diet containing dapagliflozin (0.5 mg/kg per day) versus a control diet. We found that dapagliflozin had no effect on fasting blood glucose, insulin, or hemoglobin A1C levels. However, dapagliflozin reduced BP in young (8-week old) spontaneously hypertensive rats as well as attenuated the age-related rise in BP in adult spontaneously hypertensive rat up to 17-weeks of age. The rises in mean arterial pressure and renal SNA during simulated exercise (exercise pressor reflex activation by hindlimb muscle contraction) were significantly reduced after 4 weeks of dapagliflozin (Δmean arterial pressure: 10±7 versus 25±14 mm Hg, Δrenal SNA: 31±17% versus 68±39%, P<0.05). Similarly, rises in mean arterial pressure and renal SNA during mechanoreflex stimulation by passive hindlimb stretching were also attenuated by dapagliflozin. Heart weight was significantly decreased in dapagliflozin compared with the control group. These data demonstrate a novel role for SGLT2i in reducing resting BP as well as the activity of skeletal muscle reflexes, independent of glycemic control. Our study may have important clinical implications for preventing hypertension and hypertensive heart disease in young prehypertensive individuals.

Evidence for a Prehypertensive Water Dysregulation Affecting the Development of Hypertension: Results of Very Early Treatment of Vasopressin V1 and V2 Antagonism in Spontaneously Hypertensive Rats.

In addition to long-term regulation of blood pressure (BP), in the kidney resides the initial trigger for hypertension development due to an altered capacity to excrete sodium and water. Betaine is one of the major organic osmolytes, and its betaine/gamma-aminobutyric acid transporter (BGT-1) expression in the renal medulla relates to interstitial tonicity and urinary osmolality and volume. This study investigated altered water and sodium balance as well as changes in antidiuretic hormone (ADH) activity in female spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats from their 3–5 weeks of age (prehypertensive phase) to SHR’s 28–30 weeks of age (established hypertension-organ damage). Young prehypertensive SHRs showed a reduced daily urine output, an elevated urine osmolarity, and higher immunostaining of tubule BGT-1, alpha-1-Na-K ATPase in the outer medulla vs. age-matched WKY. ADH circulating levels were not different between young prehypertensive SHR and WKY, but the urine aquaporin2 (AQP2)/creatinine ratio and labeling of AQP2 in the collecting duct were increased. At 28–30 weeks, hypertensive SHR with moderate renal failure did not show any difference in urinary osmolarity, urine AQP2/creatinine ratio, tubule BGT-1, and alpha-1-Na-K ATPase as compared with WKY. These results suggest an increased sensitivity to ADH in prehypertensive female SHR. On this basis, a second series of experiments were set to study the role of ADH V1 and V2 receptors in the development of hypertension, and a group of female prehypertensive SHRs were treated from the 25th to 49th day of age with either V1 (OPC21268) or V2 (OPC 41061) receptor antagonists to evaluate the BP time course. OPC 41061-treated SHRs had a delayed development of hypertension for 5 weeks without effect in OPC 21268-treated SHRs. In prehypertensive female SHR, an increased renal ADH sensitivity is crucial for the development of hypertension by favoring a positive water balance. Early treatment with selective V2 antagonism delays future hypertension development in young SHRs.

Dapagliflozin Attenuates Sympathetic and Pressor Responses to Stress in Young Prehypertensive Spontaneously Hypertensive Rats

Sodium‐glucose cotransporter 2 inhibitor (SGLT2i) is a class of anti‐diabetic medications approved for lowering blood glucose in type 2 diabetes mellitus (T2DM) and reducing cardiovascular risks in heart failure patients with or without T2DM. SGLT2i is also known to reduce blood pressure (BP) in hypertensive patients with T2DM. Mechanisms underlying these benefits of SGLT2i are unclear, but sympathetic overactivation is known to play a major role in the pathogenesis and progression of hypertension and heart failure. Whether SGLT2i reduces sympathetic nerve activity (SNA) and BP in a non‐diabetic prehypertension model is undetermined. Therefore, we conducted studies to determine effects of a SGLT2i, dapagliflozin (DAPA), on conscious BP as well as SNA in prehypertensive spontaneously hypertensive rats (SHRs) during physical stress. Accordingly, we randomly assigned 4‐week‐old non‐diabetic SHRs to either a normal powdered food treated (control) group or a normal powdered food containing DAPA treated (0.5mg/kg/day) group. After 4 weeks on the diet, we measured conscious BP in both groups of rats using radiotelemetry. We also assessed changes in mean arterial pressure (MAP) and renal SNA (RSNA) in response to hindlimb muscle contraction (ie, activation of the exercise pressor reflex, EPR), passive muscle stretch (ie, activation of the mechanically sensitive component of the EPR, known as the mechanoreflex), and intra‐arterial capsaicin injection (ie, activation of the metabolically sensitive component of the EPR, known as the metaboreflex) in a separate group of decerebrate control and DAPA SHRs. We found that fasting blood glucose levels were not significantly different between DAPA and control groups (65±27 vs. 78±20 mg/dL). Heart weight and heart weight‐to‐tibial length was significantly (all P&lt;0.01) decreased by 19% and 16%, respectively in DAPA rats compared to control rats. We also found that daytime/nighttime MAP were markedly lower in DAPA SHRs than control SHRs (daytime: 120±5 vs. 130±6 mmHg, nighttime: 123±6 vs. 132±6 mmHg, P&lt;0.05). A significant reduction in HR in DAPA rats was also observed compared to control rats (daytime: 299±15 vs. 337±20 bpm, nighttime: 320±12 vs. 357±12 bpm, P&lt;0.01). Similarly, the rises in MAP and RSNA during EPR activation were significantly attenuated in DAPA SHRs compared to control SHRs (ΔMAP: 10±5 vs. 29±15 mmHg, ΔRSNA: 43±17 vs. 96±48 %, P&lt;0.05). The pressor and sympathetic responses to mechanoreflex stimulation were also markedly lower in DAPA than control (ΔMAP: 10±7 vs. 25±14 mmHg, ΔRSNA: 31±17 vs. 68±39 %, P&lt;0.05). There was a tendency for MAP and RSNA responses to metaboreflex activation to be lower in the DAPA group, but the difference did not reach statistical significance (ΔMAP: 38±18 vs. 58±24 mmHg, P=0.07, ΔRSNA: 58±29 vs. 95±45 %, P=0.08). In conclusion, our data demonstrate a novel role for SGLT2i in reducing resting BP as well as the activity of skeletal muscle reflexes, independent of blood glucose. Our study may have important clinical implications for preventing hypertension and related cardiovascular damage in young prehypertensive individuals.

Haemodynamic effects of the flavonoid quercetin in rats revisited.

Background and PurposeThe flavonoid quercetin increased the in vitro potency of the α1‐antagonist tamsulosin to reduce phenylephrine‐dependent arterial contractions by 10‐fold. To examine if this supplement–drug interaction luxates hypotensive and orthostatic events in vivo, several set of studies were conducted in spontaneously hypertensive (SHR) and normotensive (Wistar Kyoto [WKY]) rats.Experimental ApproachFirst, in rats pretreated with quercetin or its vehicle, responses to phenylephrine and tamsulosin were examined. Second, tamsulosin‐induced changes in renal, mesenteric, hindquarter and carotid conductance were compared in quercetin‐ and vehicle‐treated rats instrumented with Doppler flow probes. Animals were also placed on a tilt table to record regional haemodynamic changes to orthostatic challenges. Third, adult SHR were instrumented with telemeters to measure 24‐hr patterns of BP. Recordings were made before and during a 5‐week oral treatment of quercetin. Finally, pre‐hypertensive SHR were treated with quercetin from 4 to 8 weeks of age and arterial pressure was measured at 8 and 12 weeks.Key ResultsPretreatment with quercetin did not influence the responses to phenylephrine and tamsulosin, in neither WKY nor SHR. While tamsulosin treatment and tilting lowered BP and increased conductance in all vascular beds, effect size was not influenced by pretreatment with quercetin. Prolonged treatment with quercetin, in either prehypertensive SHR or adult SHR with established hypertension did not lower BP.Conclusions and ImplicationsCumulatively, these data demonstrate that quercetin does not amplify haemodynamic effects of tamsulosin or tilting in vivo in rats and has no effect on BP development in SHR.

Long-term Mercury Exposure Accelerates the Development of Hypertension in Prehypertensive Spontaneously Hypertensive Rats Inducing Endothelial Dysfunction: the Role of Oxidative Stress and Cyclooxygenase-2.

Mercury is a metal widely dispersed in nature that when in contact with human organism, it damages the cardiovascular system. Long-term mercury exposure for 30days induces endothelial dysfunction without blood pressure changes in normotensive adult rats. However, it is not known whether exposure to mercury can exacerbate endothelial dysfunction and hypertension development in predisposed animals. Thus, we aimed to investigate the effects of long-term mercury exposure on the blood pressure (BP) and in the isolated aortas of young normotensive and prehypertensive spontaneously hypertensive rats (SHRs). Four-week-old male Wistar rats and SHRs were treated daily with mercury chloride (HgCl2) (1st dose, 4.6μg/kg; subsequent dose, 0.07μg/kg/day, im, 30days) or vehicle. BP was assessed weekly and the vascular reactivity to phenylephrine was evaluated in isolated aorta from rats exposed or not to mercury. Mercury exposure did not affect BP in young Wistar rats but accelerated the development of hypertension in young SHRs. Vascular reactivity to phenylephrine increased only in the aorta from mercury-exposed SHRs. While HgCl2 exposure in SHRs did not alter nitric oxide production, we observed increased superoxide anion production and decreased superoxide dismutase-1 protein expression, and enhanced cyclooxygenase-2 (COX-2) participation with increased prostaglandin (PGE2) production and decreased prostacyclin. In the Wistar group, mercury exposure did not alter superoxide anion production or the COX-2 pathway. Mercury exposure accelerated the natural course of hypertension in young SHRs and increased oxidative stress associated with reduced participation of antioxidant enzymes, an activated COX-2 pathway, thereby producing endothelial dysfunction, which is a risk factor in prehypertensive individuals.

Defective Renal Angiotensin III and AT2 Receptor Signaling in Prehypertensive Spontaneously Hypertensive Rats.

BackgroundPrevious studies demonstrated that angiotensin (Ang) III, not Ang II, is the predominant endogenous agonist for Ang type‐2 receptor (AT 2R)‐induced natriuresis in normal rats, and that hypertensive 12‐week‐old spontaneously hypertensive rats (SHR) lack natriuretic responses to Ang III. This study tested whether prehypertensive SHR already have defective Ang III‐induced natriuresis and determined possible mechanisms.Methods and ResultsFemale and male normotensive 4‐week‐old SHR and Wistar Kyoto rats were studied after 24‐hour systemic AT 1R blockade. Left kidneys received 30 minute renal interstitial infusions of vehicle followed by Ang III (3.5, 7.0, 14, and 28 nmol/kg per min; each dose for 30 minutes). Right kidneys received vehicle infusions. In 4‐week‐old Wistar Kyoto rats, renal interstitial Ang III increased urine sodium (Na+) excretion but failed to induce natriuresis in 4‐week‐old SHR. Renal Ang III levels were similar between Wistar Kyoto rats and SHR, making increased Ang III degradation as a possible cause for defective natriuresis in SHR unlikely. In Wistar Kyoto rats, renal interstitial Ang III induced translocation of AT 2Rs to apical plasma membranes of renal proximal tubule cells. Simultaneously, Ang III induced retraction of the major Na+ transporter Na+‐H+ exchanger‐3 (NHE‐3) from apical membranes and internalization of Na+/K+ ATPase (NKA) from basolateral membranes of renal proximal tubule cells. Consistent with NHE‐3 and NKA retraction, Ang III increased pSer552‐NHE‐3 and decreased pSer23‐NKA. In contrast, in SHR, intrarenal Ang III failed to induce AT 2R translocation, NHE‐3 or NKA retraction, pSer552‐NHE‐3 phosphorylation, or pSer23‐NKA dephosphorylation.ConclusionsThese results indicate impaired Ang III/AT 2R signaling as a possible primary defect in prehypertensive SHR.

Abstract P268: Extracellular Vesicles from Wistar Kyoto and Spontaneously Hypertensive Rats Have Differential Vasodilatory Effects on Resistance Arteries

Extracellular vesicles (EVs) have been described as novel bio-markers and bio-activators in vascular dysfunction in HTN. However, the exact mechanism how EVs affect vascular function is not known. We hypothesized that hypertensive and normotensive EVs have differential vasodilatory effects on resistance arteries. To examine the effects of EVs on acetylcholine (ACh)-mediated vasodilation, we freshly isolated 3 rd /4 th order mesenteric arteries and circulating EVs from 6 and 12-week-old normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Arteries were cannulated on a pressure myograph and pressurized to 80 mmHg. EVs (~6x10 7 EV/mL) from hypertensive and normotensive 6 and 12 week old rats were added to the vessel lumen and circulating bath solutions and equilibrated for 10 min. We also added EVs after delipidation with Chloroformmethanol. Inner diameter was measured as cumulative concentrations of ACh were applied to the bath following a preconstruction with 10 μM phenylephrine (PE). No significant difference in ACh vasodilation was observed in arteries from WKY and SHR rats, although SHR arteries were more vasoconstrictive to PE. Interestingly, EVs from WKY had an anti-vasodilatory effect on WKY arteries, whereas EVs from SHR had no effect compared to control condition without EVs. This differential effect was not observed in arteries from SHR rats treated with WKY or SHR EVs. The anti-vasodilatory effect on WKY arteries was also achieved by infusing either delipidated EVs from 12 week-old SHR, or intact EVs from 6 week old SHR rats that have not yet developed hypertension. Together, these data suggest that EVs from normotensive WKY rats and pre-hypertensive SHR rats have anti-vasodilatory effects on healthy resistance arteries. Additionally, the anti-vasodilatory effect of pre-hypertensive SHR EVs is dependent on intact vesicles, but not that of WKY EVs. The effect of normotension on EV cargo might be more important to vasodilatory response than EV species source. This data supports the functional role of EVs in vascular regulation in HTN. Further studies are needed to delineate the effector cargo of these functional EVs.

Differences in autonomic innervation to the vertebrobasilar arteries in spontaneously hypertensive and Wistar rats.

Essential hypertension is associated with hyperactivity of the sympathetic nervous system and hypoperfusion of the brainstem area controlling arterial pressure. Sympathetic and parasympathetic innervation of vertebrobasilar arteries may regulate blood perfusion to the brainstem. We examined the autonomic innervation of these arteries in pre-hypertensive (PHSH) and hypertensive spontaneously hypertensive (SH) rats relative to age-matched Wistar rats. Our main findings were: (1) an unexpected decrease in noradrenergic sympathetic innervation in PHSH and SH compared to Wistar rats despite elevated sympathetic drive in PHSH rats; (2) a dramatic deficit in cholinergic and peptidergic parasympathetic innervation in PHSH and SH compared to Wistar rats; and (3) denervation of sympathetic fibres did not alter vertebrobasilar artery morphology or arterial pressure. Our results support a compromised vasodilatory capacity in PHSH and SH rats compared to Wistar rats, which may explain their hypoperfused brainstem. Neurogenic hypertension may result from brainstem hypoperfusion. We previously found remodelling (decreased lumen, increased wall thickness) in vertebrobasilar arteries of juvenile, pre-hypertensive spontaneously hypertensive (PHSH) and adult spontaneously hypertensive (SH) rats compared to age-matched normotensive rats. We tested the hypothesis that there would be a greater density of sympathetic to parasympathetic innervation of vertebrobasilar arteries in SH versus Wistar rats irrespective of the stage of development and that sympathetic denervation (ablation of the superior cervical ganglia bilaterally) would reverse the remodelling and lower blood pressure. Contrary to our hypothesis, immunohistochemistry revealed a decrease in the innervation density of noradrenergic sympathetic fibres in adult SH rats (P<0.01) compared to Wistar rats. Unexpectedly, there was a 65% deficit in parasympathetic fibres, as assessed by both vesicular acetylcholine transporter (α-VAChT) and vasoactive intestinal peptide (α-VIP) immunofluorescence (P<0.002) in PHSH rats compared to age-matched Wistar rats. Although the neural activity of the internal cervical sympathetic branch, which innervates the vertebrobasilar arteries, was higher in PHSH relative to Wistar rats, its denervation had no effect on the vertebrobasilar artery morphology or persistent effect on arterial pressure in SH rats. Our neuroanatomic and functional data do not support a role for sympathetic nerves in remodelling of the vertebrobasilar artery wall in PHSH or SH rats. The remodelling of vertebrobasilar arteries and the elevated activity in the internal cervical sympathetic nerve coupled with their reduced parasympathetic innervation suggests a compromised vasodilatory capacity in PHSH and SH rats that could explain their brainstem hypoperfusion.

Abstract 208: Excessive Autophagy Contributes to Microvascular Endothelial Dysfunction in Prehypertensive Spontaneously Hypertensive Rats

Autophagy exists in vascular endothelial cells, however, the exact role of autophagy in hypertensive-associated vascular endothelial dysfunction remains largely elusive. We assessed the hypothesis that autophagy is one of the mechanisms of endothelial dysfunction in normotensive spontaneously hypertensive rats (SHRs). Age-matched male SHRs and Wistar Kyoto rats (WKY) aged 4 weeks (young) and 12 weeks (adult) were randomized into 2 groups and treated daily for 2 weeks by a) gavage with vehicle alone (normal saline) or b) intraperitoneally injection of rapamycin (1 mg/kg/day), and the vascular function of their isolated aorta and mesenteric artery was assessed in vitro . Furthermore, human umbilical vein endothelial cells (HUVECs) were incubated serum-starved for 6 h to induce excessive cell autophagy, and then incubated with DMEM containing 10% FBS and a) treated with 10 nmol/L insulin-like growth factor 1 (IGF-1) for 12 h, b) treated with 100 nmol/L Rapamycin for 1 h for 37°C. Compared with WKY, young and adult SHRs showed endothelial dysfunction of the aorta and mesenteric artery, along with decreased phosphorylated (p)-Akt, p-mTOR, and autophagic marker protein p62 and increased LC3 II/I in microvascular but not aortic tissues. Treatment of young SHRs with the mTOR inhibitor rapamycin aggravated the endothelial autophagy and subsequent impaired endothelial function. Moreover, IGF-1 significantly activated Akt/mTOR signaling in HUVECs and reduced autophagic levels, while rapamycin inhibited p-mTOR and increased autophagic levels. In conclusion, mesenteric endothelial dysfunction in prehypertensive SHRs is at least partly attributable to excessive autophagy in vascular tissues, and is likely mediated by the underactive Akt/mTOR signaling pathway; however, autophagy appears not to be responsible for the macrovascular endothelial dysfunction.

Tetrahydroxystilbene Glucoside Inhibits Excessive Autophagy and Improves Microvascular Endothelial Dysfunction in Prehypertensive Spontaneously Hypertensive Rats.

Autophagy exists in vascular endothelial cells, but the relationship between autophagy and blood vessel dysfunction in hypertension remains elusive. This study aimed to investigate role of autophagy in vascular endothelial dysfunction in prehypertension and hypertension and the underlying mechanisms involved. Furthermore, we sought to determine if and how tetrahydroxystilbene glucoside (TSG), a resveratrol analogue and active ingredient of Polygonum multiflorum Thunb used for its cardiovascular protective properties in traditional Chinese medicine, influences vascular endothelial function. Male spontaneously hypertensive rats (SHRs) aged 4 weeks (young) and 12 weeks (adult) were studied and the vascular function of isolated aorta and mesenteric artery was assessed in vitro. Compared with Wistar Kyoto rats (WKY), young and adult SHRs showed endothelial dysfunction of the aorta and mesenteric artery, along with decreased pAkt, pmTOR, and autophagic marker protein p62 and increased LC3 II/I in microvascular but not aortic tissues. TSG administration for 14 days significantly improved mesenteric vascular endothelial function, increased levels of pAkt and pmTOR, and decreased autophagy. Pretreatment of young SHRs with the mTOR inhibitor rapamycin blocked the antiautophagic and vasodilative effects of TSG. Moreover, TSG significantly activated Akt-mTOR signaling in HUVECs and reduced the autophagic levels in vitro, which were almost completely blocked by rapamycin. In summary, mesenteric endothelial dysfunction in prehypertensive SHRs was at least partly attributable to excessive autophagy in vascular tissues. TSG partly restored microvascular endothelial dysfunction through activating the Akt/mTOR pathway, which consequently suppressed autophagy, indicating that TSG could be potentially applied to protect vascular function against subclinical changes in prehypertension.

Protein disulfide isomerase expression increases in resistance arteries during hypertension development. Effects on Nox1 NADPH oxidase signaling.

NADPH oxidases derived reactive oxygen species (ROS) play an important role in vascular function and remodeling in hypertension through redox signaling processes. Previous studies demonstrated that protein disulfide isomerase (PDI) regulates Nox1 expression and ROS generation in cultured vascular smooth muscle cells. However, the role of PDI in conductance and resistance arteries during hypertension development remains unknown. The aim of the present study was to investigate PDI expression and NADPH oxidase dependent ROS generation during hypertension development. Mesenteric resistance arteries (MRA) and thoracic aorta were isolated from 6, 8, and 12 week-old spontaneously hypertensive (SHR) and Wistar rats. ROS production (dihydroethidium fluorescence), PDI (WB, imunofluorescence), Nox1 and NOX4 (RT-PCR) expression were evaluated. Results show a progressive increase in ROS generation in MRA and aorta from 8 to 12 week-old SHR. This effect was associated with a concomitant increase in PDI and Nox1 expression only in MRA. Therefore, suggesting a positive correlation between PDI and Nox1 expression during the development of hypertension in MRA. In order to investigate if this effect was due to an increase in arterial blood pressure, pre hypertensive SHR were treated with losartan (20 mg/kg/day for 30 days), an AT1 receptor antagonist. Losartan decreased blood pressure and ROS generation in both vascular beds. However, only in SHR MRA losartan treatment lowered PDI and Nox1 expression to control levels. In MRA PDI inhibition (bacitracin, 0.5 mM) decreased Ang II redox signaling (p-ERK 1/2). Altogether, our results suggest that PDI plays a role in triggering oxidative stress and vascular dysfunction in resistance but not in conductance arteries, increasing Nox1 expression and activity. Therefore, PDI could be a new player in oxidative stress and functional alterations in resistance arteries during the establishment of hypertension.

Neurohormonal Modulation of the Innate Immune System Is Proinflammatory in the Prehypertensive Spontaneously Hypertensive Rat, a Genetic Model of Essential Hypertension

Inflammation and autonomic dysfunction contribute to the pathophysiology of hypertension. Cholinergic stimulation suppresses innate immune responses. Angiotensin II (Ang II) induces hypertension and is associated with proinflammatory immune responses. Our goal was to define the innate immune response in a model of genetic hypertension and the influences of cholinergic stimulation and Ang II. Studies were conducted on 4- to 5-week-old prehypertensive spontaneously hypertensive rats (SHRs) and age-matched normotensive control, Wistar Kyoto (WKY) rats. Isolated splenocytes were preexposed to nicotine or Ang II before Toll-like receptor (TLR) activation. Culture supernatants were tested for cytokines (tumor necrosis factor-α, interleukin [IL]-10, and IL-6). TLR-mediated cytokine responses were most pronounced with TLR7/8 and TLR9 activation and similar between WKY rats and SHRs. Nicotine and Ang II enhanced this TLR-mediated IL-6 response in prehypertensive SHR splenocytes. In contrast, nicotine suppressed the TLR-mediated IL-6 response in WKY rats, whereas Ang II had no effect. In vivo, nicotine enhanced plasma levels of TLR7/8-mediated IL-6 and IL-1β responses in prehypertensive SHRs but suppressed these responses in WKY rats. Flow cytometry revealed an increase in a CD161+ innate immune cell population, which was enhanced by nicotine in the prehypertensive SHR spleen but not in WKY. There is a pronounced anti-inflammatory nicotinic/cholinergic modulation of the innate immune system in WKY rats, which is reversed in prehypertensive SHRs. The results support the novel concept that neurohormonal regulation of the innate immune system plays a role in the pathogenesis of genetic hypertension and provide putative molecular targets for treatment of hypertension.

Angiotensin-(1–7) attenuates the chronotropic response to angiotensin II via stimulation of PTEN in the spontaneously hypertensive rat neurons

Several studies have focused on the beneficial effects of peripheral angiotensin-(1-7) [Ang-(1-7)] in the regulation of cardiovascular function, showing its counterregulatory effect against the actions of angiotensin II (ANG II). However, its actions in the central nervous system are not completely understood. In the present study, we investigated the intracellular mechanisms underlying the action of ANG-(1-7) using the patch-clamp technique in neurons cultured from the hypothalamus of neonatal spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Superfusion of neurons with ANG II (100 nM) significantly increased neuronal firing in both strains of rats, and this chronotropic effect of ANG II was significantly enhanced in prehypertensive SHR neurons compared with WKY rat neurons. The enhanced chronotropic effect of ANG II was attenuated by a phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, LY 294002 (10 μM). Superfusion of neurons with ANG-(1-7) (100 nM) did not alter the neuronal firing rate in either SHR or WKY neurons; however, it significantly attenuated the chronotropic action of ANG II exclusively in prehypertensive SHR neurons. This counterregulatory effect of ANG-(1-7) on ANG II action in prehypertensive SHR neurons was attenuated by cotreatment with either A-779, a Mas receptor antagonist, or bisperoxovanadium, a phosphatase and tensin homologue deleted on chromosome ten (PTEN) inhibitor. In addition, incubation of WKY and prehypertensive SHR neurons with ANG-(1-7) significantly increased PTEN activity. The data demonstrate that ANG-(1-7) counterregulates the chronotropic action of ANG II via a PTEN-dependent signaling pathway in prehypertensive SHR neurons.

Elevated vertebrobasilar artery resistance in neonatal spontaneously hypertensive rats

There is a strong correlation between increased vertebral artery resistance and arterial blood pressure in humans. The reasons for this increased resistance at high systemic pressure remain unknown, but may include raised sympathetic activity. With the recent finding that prehypertensive spontaneously hypertensive (PHSH) rats, which have raised sympathetic nerve activity, but a blood pressure comparable to normotensive rat strains, we hypothesized that its vertebrobasilar vascular resistance would already be raised and, as a consequence, would exhibit a more responsive Cushing response (e.g., brain ischemia evoked sympathoexcitation and a pressor response). We report that PHSH rats exhibited a remodeling of the basilar artery (i.e., increased wall thickness and lower lumen-to-wall thickness ratio) that occurred before the onset of hypertension. In a novel in vitro vascularly isolated, arterially perfused brain stem preparation of PHSH rats of 4-5 wk of age, brain stem vascular resistance was raised by ∼35% relative to age- and sex-matched normotensive rats (P < 0.05). In the in situ arterial perfused working heart-brain stem preparation, occlusion of both vertebral arteries in the PHSH rat resulted in a significantly greater increase in sympathetic activity (57 vs. 20%, PHSH vs. control; P < 0.01) that triggered a greater increase in arterial perfusion pressure (8 vs. 3 mmHg, PHSH vs. control; P < 0.01) compared with normotensive rats. These data indicate raised vertebrobasilar artery resistance before the onset of hypertension in the PHSH rat. With the raised responsiveness of the Cushing response in the PHSH rat, we discuss the possibility of brain stem perfusion as a central nervous system determinant of the set point of vasomotor sympathetic tone in the hypertensive condition.

Calcium Handling in Postganglionic Sympathetic Neurons is enhanced in Prehypertensive Spontaneously Hypertensive rat

Noradrenergic hyperactivity is associated with hypertension that may precede the developing of hypertension itself. We hypothesized that Ca2+ signalling in sympathetic neurons is enhanced in young pre‐hypertensive spontaneously hypertensive rats (SHR). We measured depolarisation (high [K+]0) evoked Ca2+ transient ([Ca2+]i) with fluorescence imaging using fura‐2 in superior cervical ganglia from age and gender matched hypertensive and normotensive Wistar‐Kyoto (WKY) rats. In 4‐7 day old rats, no difference was observed in [Ca2+]i between the SHR and WKY. In contrast, among young pre‐hypertensive (4‐5 weeks old) rats, [Ca2+]i were higher in the SHR (male: 1.39±0.11 μM; female: 1.21±0.05 μM) compared with the gender matched WKY (male: 1.08±0.13 μM, p&lt;0.05; female: 1.07±0.05 μM, p&lt;0.05). In adult (16‐18 weeks old) rats the [Ca2+]i were also increased in the SHR (male: 1.82±0.06 μM; female: 1.58±0.07 μM) compared with the gender matched WKY (male: 1.59±0.09 μM, p&lt;0.01; female: 1.12±0.06 µM, p&lt;0.001). Interestingly, in the adult SHR and WKY, [Ca2+]i was significantly higher in male. The overall responses are consistent with the hypothesis that enhanced Ca2+ signalling may contribute to the noradrenergic hyperactivity that is seen before the onset of hypertension itself.This work was supported by British Heart Foundation and Welcome Trust.

Mechanoreceptors and central command

static exercise increases mean arterial pressure, heart rate, and ventilation. Central command and the exercise pressor reflex are the two neural mechanisms causing these responses to static exercise. Central command is defined as the parallel activation of the locomotor and autonomic circuits in

Functional and Structural Postglomerular Alterations in the Kidney of Prehypertensive Spontaneously Hypertensive Rats

The kidney plays a major role in the development of hypertension. Following the Borst‐Guyton theory of an altered set‐point for fluid and electrolyte homeostasis we aim to investigate functional and structural renal parameter during the development of hypertension. Therefore we focus on counter current exchange related factors. We compared 4 and 8 weeks old Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) concerning basic renal parameters as creatinine and phosphorus clearance and urinary osmolality. Mean arterial pressure (MAP) was measured intra‐arterially. Vasa recta were investigated using immunohistochemistry for α‐smooth‐muscle actin (ASMA) and plastification for geometric analyses. Blood pressure was not yet significantly elevated in SHR at 4 weeks but at 8 weeks it was higher in SHR (116 ± 7 vs. 102 ± 4 mm Hg; p < 0.01). Kidney weight/body weight ratio was lower in SHR at both ages. In 4 weeks old SHR, phosphorus clearance and urinary osmolality were decreased compared to WKY [0.02 ± 0.01 vs. 0.05 ± 0.02 (ml/min*100 g BW) p < 0.03; 14.2 ± 2.2 vs. 18.9 ± 2.9 (osmol/kg*24 h urine) p < 0.05] indicating reduced tubular reabsorption. At 8 weeks phosphorus clearance and urinary osmolality were comparable to WKY. α‐Actin was found in vasa recta in a 4‐times higher degree in SHR with a predominant location in the outer medulla. Radii of vasa recta in the outer medulla decreased during development. In plastificated sections vasa recta of SHR revealed sphincter‐like pattern. Functional and structural alterations related to the counter current exchanger are already evident in prehypertensive SHR. During development of hypertension both factors get adapted to higher blood pressure level. Sphincter‐like structures in vasa recta suggest contractility of pericytes/vascular smooth muscle cells (vSMC). As these were just seen in SHR that might allude to a higher potential to contract. We conclude that differences in postglomerular structure and function may contribute to the development of hypertension in SHR.

Alterations in heme oxygenase/carbon monoxide system in pulmonary arteries in hypertension.

Enhancement of the heme oxygenase/carbon monoxide (HO/CO) system has been shown to lower blood pressure (BP) in young (8 weeks), but not in adult (20 weeks) spontaneously hypertensive (SHR) rats. The reasons for this selective effect still remain puzzling. We investigated the effects of hemin on the HO/CO system of the pulmonary artery (PA) in SHR and Wistar-Kyoto (WKY) rats at different ages and evaluated the hemin-dependent changes in sGC and cGMP pathways. Hemin administration resulted in an evident reduction of BP (from 148.6 +/- 3.2 to 125.8 +/- 2.6 mmHg, P < 0.01) in young, but not in prehypertensive (4 weeks) or adult SHR or WKY rats at all ages. Coadministration of the HO inhibitor, chromium mesoporphyrin, with hemin, cancelled the BP-lowering effect of hemin. Remarkably, lower expression levels of HO-1, HO-2, and sGC paralleled with reduced HO activity and cGMP content were observed in PA from 8-week SHR rats, but not from adult SHR or WKY rats of all ages. Interestingly, hemin treatment restored these deficiencies, although the expression level of non-inducible HO-2 protein remained unchanged. We conclude that in young and prehypertensive SHR rats, an impaired HO/CO-sGC/cGMP system in the PA might be indicative of the pathogenesis and development of hypertension. In contrast, the HO/CO system in the PA of adult SHR rats was upregulated as a compensatory reaction to elevated BP and desensitization of the downstream targets of the sGC/cGMP pathway occurred.

Primary and adaptive changes of A-type K+ currents in sympathetic neurons from hypertensive rats.

The A-type K+ current (IA) of superior cervical ganglion neurons acutely isolated from spontaneously hypertensive (SHR) and age-matched Wistar-Kyoto (WKY) rats was compared under whole cell voltage clamp. Activation parameters were similar in each strain. Steady-state inactivation was shifted approximately -6 mV in SHR, where one-half inactivation occurred at -81 mV vs. -75 mV in WKY rats. The shift was not present in prehypertensive SHR but remained in adult enalapril-treated SHR and, therefore, may represent a primary alteration of IA properties. IA amplitudes evoked from physiological potentials were similar, despite inactivation of a greater fraction of the current in the SHR. Comparing maximal IA densities revealed that current density is elevated in the SHR, which compensates for the inactivation shift. Current density decreased with age in WKY neurons but did not significantly decline in SHR neurons unless hypertension was prevented with enalapril. Thus adult SHR neurons may retain a high IA density as an adaptive response to offset potential hyperexcitability resulting from the hyperpolarized IA inactivation.

Functional evidence of alpha1D-adrenoceptors in the vasculature of young and adult spontaneously hypertensive rats.

The role of alpha1D-adrenoceptors in the vasculature of spontaneously hypertensive (SHR) and normotensive Wistar Kyoto rats (WKY), of different ages was assessed in pithed rats by the use of the selective alpha1D-adrenoceptor antagonist BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-8-azaspiro [4.5]decane-7,9-dione dihydrochloride). BMY 7378 displaced the pressor effect of phenylephrine in young pre-hypertensive pithed SHR rats, but produced no effect in young WKY rats (dose ratio of 3.4 and 1.6, respectively), while in adult rats BMY 7378 produced a greater shift in the phenylephrine response curve than in younger animals (dose ratio of 3.2 and 6.2 in WKY and SHR, respectively). The presence of alpha1D-adrenoceptors in the vasculature of pre-hypertensive rats, suggests its role in the pathogenesis/maintenance of increased blood pressure.