Blood Pressure In Rodents Research Articles

Gut bacteria contribute to rodent hypertension via modulation of colonic serotonin and gut vagal 5ht3aRs

Hypertension is associated with gut dysbiosis and autonomic dysfunction in humans and rodent models. While hypertension-associated gut dysbiosis elevates blood pressure in rodents, the precise mechanisms are unknown. In our model gut dysbiosis-induced hypertension, fecal matter transplant from hypertensive SHR reduced colonic serotonin and relative expression of serotonergic 5ht3a receptors (5ht3aRs) on vagal afferents in the control WKY rats. To investigate the role of serotonergic gut vagal axis in regulation of blood pressure, in a cre-dependent manner we first overexpressed channelrhodopsin 2 in the 5ht3aR-expressing gut-projecting vagal afferents (NG5ht3Ar) in 5ht3aR Cre rats. Acute bilateral optic stimulation of NG5ht3Ar produced an immediate decrease in blood pressure and heart rate. Conversely, chronic ablation of NG5ht3Ar by cre-dependent expression of caspase elevated blood pressure in 5ht3aR Cre rats. This effect was potentiated both by the infusion of low dose of angiotensin II and exposure to acute restraint stress separately. On the other hand, overexpression of 5ht3aRs in NG5ht3Ar reduced blood pressure in the SHR, the effect that was further potentiated by dietary tryptophan supplementation. Altogether, these data propose that hypertension-associated microbiota contribute to rodent hypertension via modulation of colonic serotonin and gut vagal 5ht3aRs. NIHR01HL152162. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

ClC-K2 in the collecting duct intercalated cells contributes to blood pressure regulation during variations in dietary Cl-intake

Hypertension is the major clinically relevant problem affecting millions of people in the US. The renal collecting duct is known to play a critical role in setting salt-sensitivity of blood pressure. Originally, the majority of clinical and basic effort has been devoted to defining the detrimental roles of elevated dietary Na + in pathophysiology of hypertension. However, emerging evidence indicates that the dietary Cl - is as important for blood pressure control. The collecting duct has two independent types of cells: principal and intercalated having different functions and physiological roles. Principal cells regulate Na + reabsorption, whereas intercalated cells are responsible for transport of Cl - . ClC-K2 is a Cl - permeable channel abundantly expressed on the basolateral membrane of several distal nephron segments from the thick ascending limb to the collecting duct. Loss-of-function mutations in ClC-Kb (human orthologue of ClC-K2) cause Bartter’s syndrome type 3, which is associated with urinary salt wasting and hypotension. While the function of ClC-Kb in the thick ascending limb and distal convoluted tubule are thought to be responsible for the salt-wasting phenotype in patients with Bartter’s syndrome, the role of the channel in the collecting duct intercalated cells is not known. To address this critical gap, we compared the blood pressure phenotype and systemic Cl - balance in newly created mice with deletion of ClC-K2 in the renal nephron (RN-KO) and selectively in intercalated cells (IC-KO) using cre-loxP strategy. Since the commonly used Na + deficient diet only partially reduces chloride content and does not lead to appreciable reduction in blood pressure in rodents, we used the diet lacking both Na + and Cl - . As anticipated, RN-KO ClC-K2 mice had lower blood pressure on both regular and NaCl deficient diets when compared to the respective genetic controls (WT). In addition, the mutants exhibited larger urinary volume and Cl - wasting in response to dietary Cl - restriction. Importantly, IC-KO ClC-K2 mice had comparable blood pressure on regular diet, but became more hypotonic when compared to WT in response to dietary NaCl deficiency. Moreover, patch clamp studies in freshly isolated collecting ducts from WT mice revealed that ClC-K2 activity is proportionally increased to the amount of Cl - reduction in a diet suggesting that ClC-K2 is instrumental in augmenting Cl - reabsorption during Cl - deficiency.In conclusion, our results demonstrate, for the first time, the significance of ClC-K2 function in the collecting duct intercalated cells in setting salt sensitivity of blood pressure. This research was supported by NIH-NIDDK DK117865, DK119170, AHA EIA35260097 (to O. Pochynyuk) and AHA-19CDA34660148 (to V. N. Tomilin). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Perinatal intermittent hypoxia increases early susceptibility to ANG II-induced hypertension in adult male but not in female Sprague-Dawley rats.

Prenatal, perinatal, and adulthood exposure to chronic intermittent hypoxia (IH) increases blood pressure in rodents. Males exposed to chronic IH have higher blood pressure versus females. However, it is unknown if this same-sex difference exists with acute perinatal IH. We tested the hypothesis that acute perinatal IH increases baseline blood pressure and enhances sensitivity to angiotensin II (ANG II)-induced hypertension in male Sprague-Dawley rats. Male and female pups were randomized to control (room air) or IH (10 min of ∼10% O2 for 3 times/day) for the first 8 days of life. IH decreased oxygen saturation, as confirmed via a pulse oximeter. Pups were weaned at postnatal day 21. Blood pressure was measured via telemetry beginning at 14 wk of age and analyzed separately into light and dark phases to assess circadian rhythm. Osmotic minipumps to deliver ANG II were implanted at 15 wk of age. Perinatal IH exposure did not alter baseline blood pressure. One week of ANG II treatment increased blood pressure in light and dark periods in males exposed to IH versus control; there was no effect in females. Blood pressure among the groups was comparable following 2 wk of ANG II infusion. Perinatal IH did not change the circadian rhythm. Following ANG II treatment, indexes of renal injury were measured. Perinatal IH did not alter kidney size, structure, nephron number, or creatinine clearance. These data indicate that acute perinatal IH enhances early ANG II-induced hypertension in males, independent of nephron loss or decreases in body weight or kidney function.NEW & NOTEWORTHY The impact of acute intermittent hypoxia (IH) in early life on blood pressure in adulthood is unknown. This study used a new model exposing female and male rat pups to acute IH in the first 8 days of life, without exposing the dam. Although baseline blood pressure was not altered in adulthood, IH increased susceptibility to angiotensin II hypertension only in males, supporting increased susceptibility of males exposed to IH to a second cardiovascular stressor.

The Antiarrhythmic and Hypotensive Effects of S-61 and S-73, the Pyrrolidin-2-one Derivatives with α1-Adrenolytic Properties.

Heart rhythm abnormalities are a cause of many deaths worldwide. Unfortunately, the available antiarrhythmic drugs show limited efficacy and proarrhythmic potential. Thus, efforts should be made to search for new, more effective, and safer pharmacotherapies. Several studies suggested that blocking the α1-adrenoceptors could restore normal heart rhythm in arrhythmia. In this study, we aimed to assess the antiarrhythmic potential of S-61 and S-73, two novel pyrrolidin-2-one derivatives with high affinity for α1-adrenergic receptors. First, using radioligand binding studies, we demonstrated that S-61 and S-73 did not bind with β1-adrenoceptors. Next, we assessed whether S-61 and S-73 could protect rats against arrhythmia in adrenaline-, calcium chloride- and aconitine-induced arrhythmia models. Both compounds showed potent prophylactic antiarrhythmic properties in the adrenaline-induced arrhythmia model, but the effect of S-61 was more pronounced. None of the compounds displayed antiarrhythmic effects in calcium chloride- or aconitine-induced arrhythmia models. Interestingly, both derivatives revealed therapeutic antiarrhythmic activity in the adrenaline-induced arrhythmia, diminishing heart rhythm irregularities. Neither S-61 nor S-73 showed proarrhythmic potential in rats. Finally, the compounds decreased blood pressure in rodents. The hypotensive effects were not observed after coadministration with methoxamine, which suggests the α1-adrenolytic properties of both compounds. Our results confirm that pyrrolidin-2-one derivatives possess potent antiarrhythmic properties. Given the promising results of our experiments, further studies on pyrrolidin-2-one derivatives might result in the development of a new class of antiarrhythmic drugs.

The influence of wasabi on the gut microbiota of high-carbohydrate, high-fat diet-induced hypertensive Wistar rats.

The human gut microbiota plays a critical role in the regulation of adiposity, obesity and metabolic and cardiovascular disease. Wasabi is a pungent spice and its active component, allyl isothiocyanate, improves plasma triacylglycerol, cholesterol and high blood pressure in rodents, but it is unclear if this occurs through alterations to the composition of the microbiota. The aim of this study was to determine the effectiveness of Wasabi japonica stem and rhizome blend on ameliorating cardiovascular disease parameters including plasma sodium concentration, systolic blood pressure (SBP), plasma endothelin-1 and angiotensin II concentrations by altering the gut microbiota in a Wistar rat model of obesity and metabolic syndrome. Rats were randomized to receive a corn starch or high-carbohydrate/high-fat diet for 8 weeks before being allocated to supplementation with wasabi powder (5% (w/w) in food) or not for an additional 8 weeks. At the end of the trial, rats were grouped according to blood pressure status. Wasabi supplementation prevented the development of hypertension and was also associated with significantly increased abundance of Allobaculum, Sutterella, Uncl. S247, Uncl. Coriobacteriaceae and Bifidobacterium. Hypertension was positively correlated with higher abundance of Oscillospira, Uncl. Lachnospiraceae and Uncl. Clostridiales, Uncl. Bacteroidales and Butyricimonas. Oscillospira and Butyricimonas abundances were specifically positively correlated with systolic blood pressure. Overall, the improved host cardiovascular health in diet-induced obese rats supplemented with wasabi powder may involve changes to the gut microbiota composition.

Under pressure—how to assess blood pressure in rodents: tail-cuff?

Under pressure—how to assess blood pressure in rodents: tail-cuff?

Does leptin cause an increase in blood pressure in animals and humans?

Cardiovascular diseases (CVDs) are the number one cause of death globally. The risk for the development of CVDs is significantly increased in obesity. Leptin, the product of white adipose tissue, appears to contribute to the development of CVDs in obesity. Here, we discuss the premise that leptin engages the sympathetic nervous system and contributes to elevated blood pressure (BP) developing in obesity. The long-term regulation of BP is dependent on the activity of the autonomic nervous system and specifically the sympathetic nervous system. Sympathetic nerve activity is significantly increased in obese rodents and humans. Leptin increases sympathetic nerve activity in rodents and humans; however, leptin only consistently increases BP chronically in rodents. The ability of leptin to increase BP in rodents is via both hypothalamic and extrahypothalamic regions. In leptin-deficient and leptin receptor-deficient humans, leptin appears to be the key reason for decreased systolic BP. However, in other research conducted in humans, chronic administration of leptin does not elevate BP. Further research into the role of leptin in the development of CVDs, especially in humans, needs to be conducted.

Differential synergy with nitric oxide across a panel of soluble guanylate cyclase stimulators

Soluble guanylate cyclase (sGC) is the endogenous receptor for nitric oxide (NO). Upon binding of NO, sGC catalyzes the synthesis of cGMP which is involved in numerous downstream processes, including vasorelaxation, fibrosis, and inflammation. Dysregulation of this pathway has been implicated in multiple pathologies. sGC stimulators are a class of molecules which are capable of increasing the activity of the enzyme. While these stimulators are capable of activating the enzyme in the absence of NO, their effect is greatly amplified in the presence of NO. However, it is unclear if all stimulators synergize with NO equally. To examine differences in NO synergy across stimulators, we assessed a panel of compounds for their ability to stimulate cGMP synthesis with or without NO in a human whole cell assay. All compounds selected for this analysis were potent in vitro under high NO conditions (with EC50 values ranging from 10 to 200nM) and were effective at lowering blood pressure in rodents at doses between 1 and 10 mg/kg. We found that all compounds tested had similar EC50 values (~5µM) when examined in the absence of NO. However, in the presence of high NO the compounds exhibited a wide range of potency shifts relative to the NO‐free state (16‐320 fold). Emax values for the compounds were also differentially affected by NO, with some compounds reaching the same Emax regardless of the presence of NO, and others exhibiting a 4‐6 fold increase in Emax upon addition of NO. These data suggest that synergy between NO and sGC stimulators is complex and varies considerably between compounds. We hypothesize that differences between compounds in NO synergy may be harnessed to maximize their therapeutic value in a variety of disease states and patient populations.

Analysis of the ghrelin receptor-independent vascular actions of ulimorelin

Ulimorelin (TZP101) is a ghrelin receptor agonist that stimulates intestinal motility, but also reduces blood pressure in rodents and humans and dilates blood vessels. It has been proposed as a treatment for intestinal motility disorders. Here we investigated the mechanisms through which ulimorelin affects vascular diameter. Actions of ulimorelin on wall tension of rodent arteries were investigated and compared with other ghrelin receptor agonists.Saphenous, mesenteric and basilar arteries were obtained from Sprague-Dawley rats (male, 8 weeks) and saphenous arteries were obtained from wild type or ghrelin receptor null mice. These were mounted in myography chambers to record artery wall tension.Ulimorelin (0.03–30µM) inhibited phenylephrine-induced contractions of rat saphenous (IC50=0.6µM; Imax=66±5%; n=3–6) and mesenteric arteries (IC50=5µM, Imax=113±16%; n=3–4), but not those contracted by U46619, ET-1 or 60mM [K+]. Relaxation of phenylephrine-constricted arteries was not observed with ghrelin receptor agonists TZP102, capromorelin or AZP-531. In rat saphenous and basilar arteries, ulimorelin (10–100µM) and TZP102 (10–100µM) constricted arteries (EC50=9.9µM; Emax=50±7% and EC50=8µM; Emax=99±16% respectively), an effect not attenuated by the ghrelin receptor antagonist YIL 781 3µM or mimicked by capromorelin or AZP-531. In mesenteric arteries, ulimorelin, 1–10µM, caused a surmountable rightward shift in the response to phenylephrine (0.01–1000µM; pA2=5.7; n=3–4). Ulimorelin had similar actions in mouse saphenous artery from both wild type and ghrelin receptor null mice.We conclude that ulimorelin causes vasorelaxation through competitive antagonist action at α1-adrenoceptors and a constrictor action not mediated via the ghrelin receptor.

Leptin Mediates the Increase in Blood Pressure Associated with Obesity

SummaryObesity is associated with increased blood pressure (BP), which in turn increases the risk of cardiovascular diseases. We found that the increase in leptin levels seen in diet-induced obesity (DIO) drives an increase in BP in rodents, an effect that was not seen in animals deficient in leptin or leptin receptors (LepR). Furthermore, humans with loss-of-function mutations in leptin and the LepR have low BP despite severe obesity. Leptin’s effects on BP are mediated by neuronal circuits in the dorsomedial hypothalamus (DMH), as blocking leptin with a specific antibody, antagonist, or inhibition of the activity of LepR-expressing neurons in the DMH caused a rapid reduction of BP in DIO mice, independent of changes in weight. Re-expression of LepRs in the DMH of DIO LepR-deficient mice caused an increase in BP. These studies demonstrate that leptin couples changes in weight to changes in BP in mammalian species.

Impact of bisphenol a on the cardiovascular system - epidemiological and experimental evidence and molecular mechanisms.

Bisphenol A (BPA) is a ubiquitous plasticizing agent used in the manufacturing of polycarbonate plastics and epoxy resins. There is well-documented and broad human exposure to BPA. The potential risk that BPA poses to the human health has attracted much attention from regulatory agencies and the general public, and has been extensively studied. An emerging and rapidly growing area in the study of BPA’s toxicity is its impact on the cardiovascular (CV) system. Recent epidemiological studies have shown that higher urinary BPA concentration in humans is associated with various types of CV diseases, including angina, hypertension, heart attack and coronary and peripheral arterial disease. Experimental studies have demonstrated that acute BPA exposure promotes the development of arrhythmias in female rodent hearts. Chronic exposure to BPA has been shown to result in cardiac remodeling, atherosclerosis, and altered blood pressure in rodents. The underlying mechanisms may involve alteration of cardiac Ca2+ handling, ion channel inhibition/activation, oxidative stress, and genome/transcriptome modifications. In this review, we discuss these recent findings that point to the potential CV toxicity of BPA, and highlight the knowledge gaps in this growing research area.

G-protein coupled receptor 35 activation mediates human vascular smooth muscle migration

Introduction: GPR35 is a poorly characterised G protein-coupled receptor endogenously activated by kynurenic acid and selectively coupled to Gα13, a G protein involved in regulation of cellular motility and proliferation via the Rho kinase pathway. The role of GPR35 in cardiovascular disease (CVD) is poorly explored, though it has been proposed to regulate blood pressure in rodents. Ligands which activate GPR35 are orthologue selective however, we have identified potent novel human GPR35 specific ligands; agonist pamoic acid and antagonists, CID-2745687 and ML145 for further dissection of GPR35 pharmacology. Based on GPR35's coupling to Gα13, here we investigated the role of GPR35 in primary human saphenous vein vascular smooth muscle cell (HSVSMC) migration and proliferation; a pathological process integral to the development of vein graft failure and restenosis. Methods: Human selective GPR35 ligands were pharmacologically characterised in β-arrestin translocation assays via bioluminenscence resonence energy transfer (BRET) in cells stably expressing FLAG-hGPR35-eYFP (Flp-In TREx 293). Endogenous expression of GPR35 was quantified in HSVSMC via QRT-PCR and migration was measured in HSVSMCs stimulated with 10-500nM pamoic acid, +/- CID-2745687 and ML145 (100nM) or ROCK1/2 inhibitor Y-27632 (10μM) in scratch wound assays using ImageJ. HSVSMC proliferation was assessed via MTS assay. Changes in HSVSMC morphology and actin-cytoskeletal structure were assessed via tetramethyl rhodamine isothiocyanate (TRITC) actin phalloidin staining. Results: BRET assays in FLAG-hGPR35-eYFP cells demonstrated that pamoic acid was a potent, human selective GPR35 agonist (pEC50 7.28±0.007) while CID-2745687 (pIC50 7.16±0.12) and ML145 (pIC50 8.08±0.12) were potent antagonists. QRT-PCR demonstrated HSVSMC endogenously express GPR35 (ΔCT=19.97±0.23, normalised to 18s). Analysis of the actin cytoskeleton revealed GPR35 activation induced a rearrangement of actin filaments consistent with HSVSMC migration. Quantification of HSVSMC migration revealed the GPR35 agonist pamoic acid induced a 30% increase in migration (p 0.05 vs -serum control). GPR35 activation did not affect HSVSMC proliferation. Conclusion: Here, we have described a novel role for GPR35 activation in the migratory capacity of HSVSMC via its downstream effector ROCK1/2. This suggests GPR35 might be a therapeutic target in the setting of vein graft failure and restenosis.

A low-carbohydrate/high-fat diet reduces blood pressure in spontaneously hypertensive rats without deleterious changes in insulin resistance

Previous studies reported that diets high in simple carbohydrates could increase blood pressure in rodents. We hypothesized that the converse, a low-carbohydrate/high-fat diet, might reduce blood pressure. Six-week-old spontaneously hypertensive rats (SHR; n = 54) and Wistar-Kyoto rats (WKY; n = 53, normotensive control) were fed either a control diet (C; 10% fat, 70% carbohydrate, 20% protein) or a low-carbohydrate/high-fat diet (HF; 20% carbohydrate, 60% fat, 20% protein). After 10 wk, SHR-HF had lower (P < 0.05) mean arterial pressure than SHR-C (148 ± 3 vs. 159 ± 3 mmHg) but a similar degree of cardiac hypertrophy (33.4 ± 0.4 vs. 33.1 ± 0.4 heart weight/tibia length, mg/mm). Mesenteric arteries and the entire aorta were used to assess vascular function and endothelial nitric oxide synthase (eNOS) signaling, respectively. Endothelium-dependent (acetylcholine) relaxation of mesenteric arteries was improved (P < 0.05) in SHR-HF vs. SHR-C, whereas contraction (potassium chloride, phenylephrine) was reduced (P < 0.05). Phosphorylation of eNOSSer1177 increased (P < 0.05) in arteries from SHR-HF vs. SHR-C. Plasma glucose, insulin, and homoeostatic model of insulin assessment were lower (P < 0.05) in SHR-HF vs. SHR-C, whereas peripheral insulin sensitivity (insulin tolerance test) was similar. After a 10-h fast, insulin stimulation (2 U/kg ip) increased (P < 0.05) phosphorylation of AktSer473 and S6 in heart and gastrocnemius similarly in SHR-C vs. SHR-HF. In conclusion, a low-carbohydrate/high-fat diet reduced blood pressure and improved arterial function in SHR without producing signs of insulin resistance or altering insulin-mediated signaling in the heart, skeletal muscle, or vasculature.

Fenofibrate lowers blood pressure in salt-sensitive but not salt-resistant hypertension

Peroxisome proliferator-activated receptor α agonists reduce blood pressure in rodents, but clinical trials provide conflicting data regarding their effects in humans. We tested the hypothesis that the effect of fenofibrate on blood pressure depends on salt sensitivity. Thirty-one hypertensive volunteers (17 salt-resistant, 14 salt-sensitive) completed a randomized, crossover, double-blind protocol with three dietary phases: low salt diet (10 mmol/day) followed by two consecutive high salt diets (200 mmol/day), each for 6 days. During high salt, volunteers were randomized to fenofibrate 160 mg/day or placebo. Hemodynamic and metabolic parameters were measured on the last morning of each treatment arm. Fenofibrate reduced triglycerides similarly in salt-sensitive and salt-resistant volunteers. Fenofibrate did not affect blood pressure in salt-resistant volunteers. In salt-sensitive volunteers, fenofibrate significantly decreased diastolic (P = 0.02 versus placebo) and mean arterial (P = 0.04 versus placebo) blood pressure during high salt. In all volunteers, the decrease in systolic pressure during fenofibrate correlated inversely with the salt sensitivity of mean arterial pressure as a continuous variable. Fenofibrate significantly decreased heart rate, plasma renin activity, and renal vascular resistance during high salt in salt-sensitive volunteers, but not salt-resistant volunteers. Fenofibrate did not affect sodium excretion or weight gain during high salt. The effect of salt intake and fenofibrate on plasma and urine epoxyeicosatrienoic acid concentrations differed in salt-resistant and salt-sensitive volunteers. Fenofibrate reduces blood pressure, heart rate and renal vasoconstriction in salt-sensitive volunteers, but not in salt-resistant volunteers. These findings have implications for the treatment of hyperlipidemia in hypertensive individuals.

Novel signaling mechanisms of intracellular angiotensin II-induced NHE3 expression and activation in mouse proximal tubule cells

Expression of a cytosolic cyan fluorescent fusion protein of angiotensin II (ECFP/ANG II) in proximal tubules increases blood pressure in rodents. To determine cellular signaling pathways responsible for this response, we expressed ECFP/ANG II in transport-competent mouse proximal convoluted tubule cells (mPCT) from wild-type (WT) and type 1a ANG II receptor-deficient (AT(1a)-KO) mice and measured its effects on intracellular ANG II levels, surrogates of Na/H exchanger 3 (NHE3)-dependent Na(+) absorption, as well as MAP kinases and NF-κB signaling. In WT mPCT cells, ECFP/ANG II expression doubled ANG II levels, increased NHE3 expression and membrane phospho-NHE3 proteins threefold and intracellular Na(+) concentration by 65%. These responses were associated with threefold increases in phospho-ERK 1/2 and phospho-p38 MAPK, fivefold increases in p65 subunit of NF-κB, and threefold increases in phospho-IKKα/β (Ser 176/180) proteins. These signaling responses to ECFP/ANG II were inhibited by losartan (AT(1) blocker), PD123319 (AT(2) blocker), U0126 (MEK1/MEK2 inhibitor), and RO 106-9920 (NF-κB inhibitor). In mPCT cells of AT(1a)-KO mice, ECFP/ANG II also increased the levels of NHE3, p-ERK1/2, and p65 proteins above their controls, but considerably less so than in WT cells. In WT mice, selective expression of ECFP/ANG II in vivo in proximal tubules significantly increased blood pressure and indices of sodium reabsorption, in particular levels of phosphorylated NHE3 protein in the membrane fraction and proton gradient-stimulated (22)Na(+) uptake by proximal tubules. We conclude that intracellular ANG II may induce NHE3 expression and activation in mPCTs via AT(1a)- and AT(2) receptor-mediated activation of MAP kinases ERK 1/2 and NF-κB signaling pathways.

Hypertensive effects of the iv administration of picomoles of ouabain

Ouabain, an endogenous digitalis compound, has been detected in nanomolar concentrations in the plasma of several mammals and is associated with the development of hypertension. In addition, plasma ouabain is increased in several hypertension models, and the acute or chronic administration of ouabain increases blood pressure in rodents. These results suggest a possible association between ouabain and the genesis or development and maintenance of arterial hypertension. One explanation for this association is that ouabain binds to the α-subunit of the Na(+) pump, inhibiting its activity. Inhibition of this pump increases intracellular Na(+), which reduces the activity of the sarcolemmal Na(+)/Ca(2+) exchanger and thereby reduces Ca(2+) extrusion. Consequently, intracellular Ca(2+) increases and is taken up by the sarcoplasmic reticulum, which, upon activation, releases more calcium and increases the vascular smooth muscle tone. In fact, acute treatment with ouabain enhances the vascular reactivity to vasopressor agents, increases the release of norepinephrine from the perivascular adrenergic nerve endings and promotes increases in the activity of endothelial angiotensin-converting enzyme and the local synthesis of angiotensin II in the tail vascular bed. Additionally, the hypertension induced by ouabain has been associated with central mechanisms that increase sympathetic tone, subsequent to the activation of the cerebral renin-angiotensin system. Thus, the association with peripheral mechanisms and central mechanisms, mainly involving the renin-angiotensin system, may contribute to the acute effects of ouabain-induced elevation of arterial blood pressure.

Mast Cells Increase Vascular Permeability by Heparin-Initiated Bradykinin Formation In Vivo

Activated mast cells trigger edema in allergic and inflammatory disease. We report a paracrine mechanism by which mast cell-released heparin increases vascular permeability invivo. Heparin activated the protease factor XII, which initiates bradykinin formation in plasma. Targeting factor XII or kinin B2 receptors abolished heparin-triggered leukocyte-endothelium adhesion and interfered with a mast cell-driven drop in blood pressure in rodents. Intravital laser scanning microscopy and tracer measurements showed heparin-driven fluid extravasation in mouse skin microvessels. Ablation of factor XII or kinin B2 receptors abolished heparin-induced skin edema and protected mice from allergen-activated mast cell-driven leakage. In contrast, heparin and activated mast cells induced excessive edema in mice deficient in the major inhibitor of factor XII, C1 esterase inhibitor. Allergen exposure triggered edema attacks in hereditary angioedema patients, lacking C1 esterase inhibitor. The data indicate that heparin-initiated bradykinin formation plays a fundamental role in mast cell-mediated diseases.

Melanocortin Signalling and the Regulation of Blood Pressure in Human Obesity

Obesity has reached epidemic proportions worldwide. Sympathetic nervous system activation has been shown to play a major role linking obesity to the development of associated metabolic complications, such as hypertension. Recent evidence has implicated central melanocortin signalling in the regulation of blood pressure in rodents and humans. The importance of sympathetic neural activity in mediating this association has been highlighted. Humans with loss-of-function mutations in the melanocortin 4 receptor (MC4R) are an ideal group of subjects in whom the importance of melanocortin signalling in linking obesity to hypertension can be studied. Consistent with rodent studies, it was recently demonstrated that humans with MC4R deficiency have lower blood pressure, less hypertension, lower 24-h urinary catecholamine excretion, lower resting heart rate and attenuated insulin-mediated sympathetic activation compared to equally-obese humans. In overweight and obese humans without MC4R mutations, the infusion of a highly-selective MC4R agonist led to dose-dependent increases in blood pressure and heart rate. All effects were independent of insulin. This evidence supports the notion that the melanocortin system regulates blood pressure and sympathetic neural function. The results obtained in rodent and human studies, in relation to blood pressure and sympathetic function, may limit the use of MC4R agonists for the treatment of obesity. Future studies will determine whether MC4R deficiency is associated with protection from development of the detrimental cardiovascular consequences that accompany obesity.

Modulation of blood pressure by central melanocortinergic pathways

Weight gain and weight loss are associated with changes in blood pressure through unknown mechanisms. Central melanocortinergic signaling is implicated in the control of energy balance and blood pressure in rodents, but there is no information regarding such an association with blood pressure in humans. The authors assessed blood pressure, heart rate, and urinary catecholamines in overweight or obese subjects with a loss-of-function mutation in MC4R, the gene encoding the melanocortin 4 receptor, and in equally overweight control subjects. They also examined the effects of an MC4R agonist administered for 7 days in 28 overweight or obese volunteers.

Modulation of Blood Pressure by Central Melanocortinergic Pathways

Weight gain and weight loss are associated with changes in blood pressure through unknown mechanisms. Central melanocortinergic signaling is implicated in the control of energy balance and blood pressure in rodents, but there is no information regarding such an association with blood pressure in humans. We assessed blood pressure, heart rate, and urinary catecholamines in overweight or obese subjects with a loss-of-function mutation in MC4R, the gene encoding the melanocortin 4 receptor, and in equally overweight control subjects. We also examined the effects of an MC4R agonist administered for 7 days in 28 overweight or obese volunteers. The prevalence of hypertension was markedly lower in the MC4R-deficient subjects than in the control subjects (24% vs. 53%, P=0.009). After the exclusion of subjects taking antihypertensive medications, blood-pressure levels were significantly lower in MC4R-deficient subjects than in control subjects, with mean (+/-SE) systolic blood pressures of 123+/-14 mm Hg and 131+/-12 mm Hg, respectively (P=0.02), and mean diastolic blood pressures of 73+/-10 mm Hg and 79+/-7 mm Hg, respectively (P=0.03). As compared with control subjects, MC4R-deficient subjects had a lower increase in heart rate on waking (P=0.007), a lower heart rate during euglycemic hyperinsulinemia (P<0.001), and lower 24-hour urinary norepinephrine excretion (P=0.04). The maximum tolerated daily dose of 1.0 mg of the MC4R agonist led to significant increases of 9.3+/-1.9 mm Hg in systolic blood pressure and of 6.6+/-1.1 mm Hg in diastolic blood pressure (P<0.001 for both comparisons) at 24 hours, as compared with placebo. Differences in blood pressure were not explained by changes in insulin levels; there were no significant adverse events. Results of our genetic and pharmacologic studies implicate melanocortinergic signaling in the control of human blood pressure through an insulin-independent mechanism.