The vascular Ca2+-sensing receptor regulates blood vessel tone and blood pressure.

The extracellular calcium-sensing receptor CaSR is expressed in blood vessels where its role is not completely understood. In this study, we tested the hypothesis that the CaSR expressed in vascular smooth muscle cells (VSMC) is directly involved in regulation of blood pressure and blood vessel tone. Mice with targeted CaSR gene ablation from vascular smooth muscle cells (VSMC) were generated by breeding exon 7 LoxP-CaSR mice with animals in which Cre recombinase is driven by a SM22α promoter (SM22α-Cre). Wire myography performed on Cre-negative [wild-type (WT)] and Cre-positive (SM22α)CaSR(Δflox/Δflox) [knockout (KO)] mice showed an endothelium-independent reduction in aorta and mesenteric artery contractility of KO compared with WT mice in response to KCl and to phenylephrine. Increasing extracellular calcium ion (Ca(2+)) concentrations (1-5 mM) evoked contraction in WT but only relaxation in KO aortas. Accordingly, diastolic and mean arterial blood pressures of KO animals were significantly reduced compared with WT, as measured by both tail cuff and radiotelemetry. This hypotension was mostly pronounced during the animals' active phase and was not rescued by either nitric oxide-synthase inhibition with nitro-l-arginine methyl ester or by a high-salt-supplemented diet. KO animals also exhibited cardiac remodeling, bradycardia, and reduced spontaneous activity in isolated hearts and cardiomyocyte-like cells. Our findings demonstrate a role for CaSR in the cardiovascular system and suggest that physiologically relevant changes in extracellular Ca(2+) concentrations could contribute to setting blood vessel tone levels and heart rate by directly acting on the cardiovascular CaSR.

Xuebijing attenuates hypotension through the upregulation of angiotensin II type 1 receptor-associated protein 1 in rats suffering from heat stroke.

In our previous study, we demonstrated that Xuebijing (XBJ), a traditional Chinese medicine, attenuates hypotension in rats suffering from heatstroke (HS). However, the underlying mechanisms have not yet been fully elucidated. Thus, the current study was carried out to investigate the mechanisms underlying the effects of XBJ on hypotension n rats suffering from HS. For this purpose, 72 anesthetized rats were randomized into 3 groups and intravenously injected twice daily for 3 days with XBJ (4 ml/kg body weight, XBJ group) or phosphate­buffered saline (PBS) (HS and sham-operated groups). Models of HS were established in the HS and XBJ groups by placing the rats in a simulated climate chamber with a temperature of 40˚C and a humidity of 60%. Rectal temperature, arterial pressure and heart rate were monitored and recorded. Angiotensin Ⅱ (Ang Ⅱ) levels were increased during HS (shown by ELISA), and XBJ had no apparent effect on Ang Ⅱ levels. The levels of Ang Ⅱ type 1 (AT1) receptor surface expression and AT1 receptor-associated protein 1 (Arap1) were decreased during HS; however, these effects were attenuated by pre-treatment with XBJ (shown by RT-qPCR and western blot analysis). For in vitro experiments, rat macrophages pre-treated with XBJ were stimulated with lipopolysaccharide (LPS). Pre-treatment with XBJ induced a marked inhibitory effect on the release of pro-inflammatory cytokines in the LPS-stimulated macrophages. Furthermore, XBJ inhibited the activation of nuclear factor κB (NF-κB) induced by LPS in the macrophages. Taken together, our data demonstrate that XBJ promotes Arap1 expression by inhibiting the activation of the NF-κB signaling pathway and the release of pro-inflammatory cytokines, which may be the molecular mechanisms through which XBJ alleviates blood pressure reduction in rats suffering from HS.

The cardiovascular actions of fractalkine/CX3CL1 in the hypothalamic paraventricular nucleus are attenuated in rats with heart failure.

The paraventricular nucleus (PVN) of the hypothalamus plays an important role in the regulation of sympathetic nerve activity, which is significantly elevated in chronic heart failure (CHF). Fractalkine (FKN) and its cognate receptor, CX3CR1, are constitutively expressed in the central nervous system, but their role and physiological significance are not well known. The aims of the present study were to determine whether FKN plays a cardiovascular role within the PVN and to investigate how the actions of FKN might be altered in CHF. We show that both FKN and CX3CR1 are expressed on neurons in the PVN of rats, suggesting that they may have a physiological function in this brain nucleus. Unilateral microinjection of FKN directly into the PVN of anaesthetized rats elicited a significant dose-related decrease in blood pressure (1.0 nmol, -5 ± 3 mmHg; 2.5 nmol, -13 ± 2 mmHg; 5.0 nmol, -22 ± 3 mmHg; and 7.5 nmol, -32 ± 3 mmHg) and a concomitant increase in heart rate (1.0 nmol, 6 ± 3 beats min(-1); 2.5 nmol, 11 ± 3 beats min(-1); 5 nmol, 18 ± 4 beats min(-1); and 7.5 nmol, 27 ± 5 beats min(-1)) compared with control saline microinjections. In order to determine whether FKN signalling is altered in rats with CHF, we first performed quantitative RT-PCR and Western blot analysis and followed these experiments with functional studies in rats with CHF and sham-operated control rats. We found a significant increase in CX3CR1 mRNA and protein expression, as determined by quantitative RT-PCR and Western blot analysis, respectively, in the PVN of rats with CHF compared with sham-operated control rats. We also found that the blood pressure effects of FKN (2.5 nmol in 50 nl) were significantly attenuated in rats with CHF (change in mean arterial pressure, -6 ± 3 mmHg) compared with sham-operated control rats (change in mean arterial pressure, -16 ± 6 mmHg). These data suggest that FKN and its receptor, CX3CR1, modulate cardiovascular function at the level of the PVN and that the actions of FKN within this nucleus are altered in heart failure.

The molecular basis of blood pressure variation.

Advances in genetic mapping and sequencing techniques have led to substantial progress in the study of rare monogenic (Mendelian) forms of abnormal blood pressure. Many disease-defining pathways for hypertension have been identified in the past two decades. Perturbations in renal salt handling appear to be a common mechanism underlying these rare syndromes of hypertension. Excess activation at various points in the mineralocorticoid signaling pathway and malfunctioning of the autonomic (specifically sympathetic) nervous system have both been implicated in inducing hypertension, while complementary studies examining low blood pressure phenotypes have identified novel pathways exclusively linked to renal salt wasting in either the thick ascending limb or the distal nephron. The genetic defects and the physiological and cellular pathways affected in these various disorders are reviewed here. Importantly, studies have suggested that genetic variation affecting these same genes and pathways may play an important role in explaining the variation of blood pressure levels in the general population. The investigation of rare syndromes of human blood pressure variation has important implications for improving the diagnosis and treatment of hypertension.

BK large conductance Ca²+-activated K+ channel-deficient mice are not resistant to hypotension and display reduced survival benefit following polymicrobial sepsis.

Nitric oxide-mediated activation of large conductance calcium-activated potassium (BK) channels is considered an important underlying mechanism of sepsis-induced hypotension. Indeed, the nonselective K-channel inhibitor, tetraethylammonium chloride (TEA), has been proposed as a potential treatment to raise blood pressure in septic shock by virtue of its ability to inhibit BK channels. As experimental evidence has so far relied on pharmacological inhibition, we examined the effects of channel deletion using BKα subunit knockout (α, Slo) mice in two mouse models of polymicrobial sepsis, namely, intraperitoneal fecal slurry and cecal ligation and puncture. Comparison was made against TEA treatment in wild-type (WT) mice. Following slurry, BKα and WT mice developed similar degrees of hypotension over 10 h with no difference in cardiac output as assessed by echocardiography between groups. Tetraethylammonium chloride raised blood pressure significantly in septic WT mice, but had no effect on survival. However, following cecal ligation and puncture, a significantly reduced survival was seen in both BKα mice and (high-dose) TEA-treated WT mice compared with untreated WT animals. In conclusion, the BK channel does not appear to be integral to sepsis-induced hypotension but does affect survival through other mechanisms. The pressor effect of TEA may be related to effects on other potassium channels.

Subjects heterozygous for genetic loss of function of the thiazide-sensitive cotransporter have reduced blood pressure.

Gitelmans syndrome (GS) is an inherited recessive disorder caused by homozygous or compound heterozygous loss of function mutations of the NaCl cotransporter (NCCT) gene encoding the kidney-expressed NCCT, the pharmacological target of thiazide diuretics. An observational study estimated the prevalence of GS to 19/1,000,000, in Sweden, suggesting that approximately 1% of the population carries one mutant NCCT allele. As the phenotype of GS patients, who always carry two mutant alleles, is indistinguishable from that seen in patients treated with high-dose thiazide diuretics, we aimed at investigating whether subjects carrying one mutated NCCT allele have a phenotype resembling that of treatment with low-dose thiazide diuretics. We screened first-degree relatives of 18 of our patients with an established clinical end genetic diagnosis of GS for NCCT loss of function mutations and identified 35 healthy subjects carrying one mutant allele (GS-heterozygotes). Each GS-heterozygote was assigned a healthy control subject matched for age, BMI and sex. GS-heterozygotes had markedly lower blood pressure (systolic 103.3 +/- 16.4 versus 123.2 +/- 19.4 mmHg; diastolic 62.5 +/- 10.5 versus 73.1 +/- 9.4 mmHg; P < 0.001) than controls. There was no significant difference between the groups either in plasma concentration or urinary excretion rate of electrolytes, however, GS-heterozygotes had higher fasting plasma glucose concentration. Similar to patients being treated with low-dose thiazide diuretics, GS-heterozygotes have markedly lower blood pressure and slightly higher fasting plasma glucose compared with control subjects. Our findings suggest that GS-heterozygotes, the prevalence of which can be estimated to 1%, are partially protected from hypertension through partial genetic loss of function of the NCCT. However, as our study had a case-control design, it is important to underline that any potential effects on population blood pressure and risk of future cardiovascular disease need to be examined in prospective and population-based studies.

Multiple effects of hyperbaric oxygen on the expression of HIF-1 alpha and apoptotic genes in a global ischemia-hypotension rat model.

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor specifically activated by hypoxia. Activation of proapoptotic caspase-9 and caspase-3 pathways, by binding with tumor suppressor p53, HIF-1alpha could lead to harmful actions such as apoptosis. We examined whether increasing oxygen levels by hyperbaric oxygen (HBO) offers neuroprotection, at least partially by suppression of HIF-1alpha and apoptotic genes. Male SD rats (n = 78) were randomly divided into 13 groups: 1 sham group, 6 groups of global ischemia-hypotension (GI), and 6 groups of HBO treatment after global ischemia-hypotension (GI + HBO). HBO (3 ATA for 2 h) was applied at 1 h after global ischemia-hypotension. Rats were sacrificed at 6, 12, 24, 48, and 96 h and 7 days. Global ischemia-hypotension (10 min ischemia, 30-35 mm Hg) produced a marked increase of HIF-1alpha expressions in the hippocampus and cortex at 6 h and peaked at 48-96 h. The expressions of p53, caspase-9, and caspase-3 were all increased in a similar time course. These molecular changes were accompanied by massive cell loss in the hippocampal regions and to a lesser degree in the cortex, with features of apoptosis. HBO treatment reduced expressions of HIF-1alpha, p53, caspase-9, and caspase-3 and decreased cell death. The protein levels of proapoptotic caspase-8 and antiapoptotic bcl-2 were increased after global ischemia-hypotension and HBO potentiated the expression of caspase-8 and decreased expression of bcl-2. These results indicate that HBO has multiple actions on apoptotic genes even though the overall effect of HBO was decreased HIF-1alpha expression and reduced apoptosis after global ischemia-hypotension.

Hypertension in a patient with Gitelman's syndrome.

Gitelman's syndrome is an autosomal recessive disorder characterized by sodium wasting and hypotension. A middle-aged woman was diagnosed with Gitelman's syndrome because of typical clinical manifestations in the youth and homozygous mutations of 18-base-pair insertion in exon 6 of thiazide-sensitive NaCl-cotransporter gene. It was unusual that she showed hypertension with advancing age. Her serum potassium levels remained low at around 3.5 mEq/l despite potassium supplementation. This case demonstrates that hypertension could result in spite of the extremely decreased sodium reabsorption in Gitelman's syndrome and that essential hypertension is genetically heterogeneous, and abnormality of all genes may not be necessarily required to cause blood pressure rise.

Malignant hyperthermia phenotype: hypotension induced by succinylcholine in susceptible swine.

BACKGROUND: Succinylcholine causes immediate and severe arterial hypotension in swine with the malignant hyperthermia phenotype. The underlying mechanisms are unknown. METHODS: Malignant hyperthermia-susceptible (MHS; n = 10) and normal swine (n = 5) were anesthetized with thiopental. The following were monitored: electrocardiogram; arterial blood pressure; pulmonary artery, central venous, and left and right ventricular pressure; cardiac output; end-tidal carbon dioxide; core temperature; peripheral-blood flows; and arterial blood gases. After a control period, 2 mg/kg succinylcholine was given intravenously. Three MHS animals received 1 mg/kg vecuronium and two MHS animals received 2.5 mg/kg dantrolene intravenously. The effects of succinylcholine on left and right ventricular pressure and contractility were analyzed in isolated hearts. The effects of 0.06 mm succinylcholine on isometric tension development were recorded in isolated femoral artery rings. RESULTS: Succinylcholine caused an early, severe decrease in blood pressure, cardiac output, left ventricular pressure, and left ventricular contractility in MHS swine but not in normal swine; no significant differences were found in heart rate, right ventricular parameters, systemic vascular resistance, and preload (pulmonary diastolic pressure, central venous pressure). The succinylcholine-induced hypotension and associated effects were not prevented by dantrolene. However, pretreatment with high-dose vecuronium prevented not only the cardiovascular depression, but also MH. In addition, no phenotypic differences of succinylcholine on contractility or left ventricular pressure were observed in the isolated working hearts. Similary, succinylcholine did not cause a significantly different relaxation in rings in either phenotype. CONCLUSION: Succinylcholine-induced hypotension occurred before muscle hypermetabolism in MHS swine. Succinylcholine had no differential physiologic effects on either the isolated heart or on isolated arteries. This hypotension could not be prevented by dantrolene but was prevented by pretreatment with high-dose vecuronium. Thus, an indirect mechanism such as the release of a cardiac depressant from skeletal muscle may have caused this hypotensive response.

Norepinephrine level in the hypothalamus of the genetically hypertensive mouse.

The norepinephrine content of the hypothalamus of young mice with high blood pressure was statistically lower than that of mice with low blood pressure. The difference was not evident in older mice from these same strains. No differences in dopamine content were found suggesting a genetic difference in the activity of the converting enzyme.