Blood Pressure In Conscious Mice Research Articles

Vasodilators activate the anion channel TMEM16A in endothelial cells to reduce blood pressure.

Systemic blood pressure is acutely controlled by total peripheral resistance as determined by the diameter of small arteries and arterioles, the contractility of which is regulated by endothelial cells lining the lumen of blood vessels. We investigated the physiological functions of the chloride (Cl-) channel TMEM16A in endothelial cells. TMEM16A channels generated calcium (Ca2+)-activated Cl- currents in endothelial cells from control (TMEM16Afl/fl) mice that were absent in those from mice with tamoxifen-inducible, endothelial cell-specific knockout of TMEM16A (TMEM16A ecKO). TMEM16A currents in endothelial cells were activated by the muscarinic receptor agonist acetylcholine and an agonist of the Ca2+ channel TRPV4, which localized in nanoscale proximity with TMEM16A as assessed by single-molecule localization imaging of endothelial cells. Acetylcholine stimulated TMEM16A currents by activating Ca2+ influx through surface TRPV4 channels without altering the nanoscale properties of TMEM16A and TRPV4 surface clusters or their colocalization. In pressurized arteries, activation of TMEM16A channels in endothelial cells induced by acetylcholine; TRPV4 channel stimulation; or intraluminal ATP, another vasodilator, produced hyperpolarization and dilation. Furthermore, deficiency of TMEM16A channels in endothelial cells resulted in increased systemic blood pressure in conscious mice. These data indicate that vasodilators stimulate TRPV4 channels, leading to Ca2+-dependent activation of nearby TMEM16A channels in endothelial cells to produce arterial hyperpolarization, vasodilation, and reduced blood pressure. Thus, TMEM16A is an anion channel in endothelial cells that regulates arterial contractility and blood pressure.

β 3-Adrenergic Receptor Agonist Prevents Diastolic Dysfunction in an Angiotensin II-Induced Cardiomyopathy Mouse Model.

β3-Adrenergic receptor expression is enhanced in the failing heart, but its functional effects are unclear. We tested the hypothesis that a β3-agonist improves left ventricular (LV) performance in heart failure. We examined the chronic effects of a β3-agonist in the angiotensin II (Ang II)-induced cardiomyopathy mouse model. C57BL/6J mice were treated with Ang II alone or Ang II + BRL 37344 (β3-agonist, BRL) for 4 weeks. Systolic blood pressure in conscious mice was significantly elevated in Ang II and Ang II + BRL mice compared with control mice. Heart rate was not different among the three groups. Systolic performance parameters that were measured by echocardiography and an LV catheter were similar among the groups. LV end-diastolic pressure and end-diastolic pressure-volume relationships were higher in Ang II mice compared with control mice. However, the increase in these parameters was prevented in Ang II + BRL mice, which suggested improvement in myocardial stiffness by BRL. Pathologic analysis showed that LV hypertrophy was induced in Ang II mice and failed to be prevented by BRL. However, increased collagen I/III synthesis, cardiac fibrosis, and lung congestion observed in Ang II mice were inhibited by BRL treatment. The cardioprotective benefits of BRL were associated with downregulation of transforming growth factor-β1 expression and phosphorylated-Smad2/3. Chronic infusion of a β3-agonist has a beneficial effect on LV diastolic function independent of blood pressure in the Ang II-induced cardiomyopathy mouse model. SIGNIFICANCE STATEMENT: Chronic infusion of a β3-adrenergic receptor agonist attenuates cardiac fibrosis and improves diastolic dysfunction independently of blood pressure in an angiotensin II-induced hypertensive mouse model. This drug might be an effective treatment of heart failure with preserved ejection fraction.

Abstract 075: Sex Differences in the Development of Autoimmune-Associated Hypertension

Systemic lupus erythematosus (SLE) is an autoimmune disorder with prevalent hypertension and is a novel disease model to study the link between chronic inflammation and hypertension. Because SLE is female-dominant, studies are usually conducted in female NZBWF1 mice, a well-established model of SLE. However, men are also diagnosed with SLE and the late onset and different clinical features draws interest. We hypothesize that sex differences exist in SLE and that female SLE mice have heightened disease, hypertension, and renal injury earlier than males. Female and male SLE and control ( NZW ) mice were monitored for albuminuria starting at 30 weeks of age and then at 35 weeks implanted with vascular catheters to allow measurement of blood pressure in conscious mice. At 30 weeks, female SLE mice had elevated plasma dsDNA autoantibodies, the hallmark of SLE, compared to male SLE (4.6e5 ± 1.3e5 vs. 6.3e4 ± 2.7e4 U/mL; n=3-5; all p<0.05), female controls (8.9e4 ± 3.3e4), and male controls (4.8e4 ± 9.3e3). At this same time point, 32% (7 out of 22) of female SLE mice had albuminuria versus 5% (1 out of 20) of male SLE, 5% (1 out of 22) of female controls, and no male controls. Although male SLE mice did not reach similar levels of dsDNA autoantibodies as SLE females (2.0e5 ± 4.6e4 vs. 3.9e5 ± 4.3e4; n=8-13; p=0.015), by 35 weeks, the autoantibodies were increasing in SLE males (2.0e5 ± 4.6e4 vs. 6.3e4 ± 2.7e4; p=0.157) and higher than male controls (4.3e4 ± 9.3e3; p=0.046). At 35 weeks, 63% (10 out of 16) of female SLE mice had albuminuria versus 5% (1 out of 19) of male SLE, 5% (1 out of 22) of female controls, and no male controls. Importantly, both female and male SLE mice were hypertensive at 35 weeks: blood pressure was higher in female SLE than female controls (152 ± 5 vs. 126 ± 3 mmHg; n=6-8; p=0.003) and in male SLE compared to male controls (152 ± 4 vs. 136 ± 4 mmHg; n=6-11; p=0.041). These data confirm the development of hypertension and renal injury in female SLE mice and suggest that male SLE mice develop hypertension with no renal involvement. Future studies will allow us to investigate the divergent mechanisms involved in autoimmune-induced hypertension in female and male mice, which will ultimately provide clues in sex differences in hypertensive humans with underlying chronic inflammation.

Abstract 070: The Prostaglandin Ep4 Receptor in Endothelium Modulates eNos Expression and Aortic Integrity

Prostaglandin EP4 receptor (EP4R) plays pivotal role in mediating PGE2-induced vasodilation and blood pressure homeostasis. Our previous work demonstrated that absence of EP4R in all tissues was associated with salt sensitivity and exaggerated Ang II-dependent hypertension. While cell-specific elimination of EP4R from vascular smooth muscle cells (VSMCs) attenuated EP4-dependent vasodilation, but the severity of Ang II-dependent hypertension was not affected. These findings indicate the effects of EP4R to resist hypertension are not attributable to the compensatory vasodilation mediated by EP4R in VSMCs and must be mediated by other cell lineages. Within the vasculature, endothelial cells (ECs) also express high levels of EP4R. To assess the role of EP4R in ECs, we generated conditional EC-specific EP4R knockout mice mice using Tie2-CreERT2 and EP4 flox/flox mouse lines (ECKO). After pre-treatment with tamoxifen, we measured the blood pressure in conscious mice using radiotelemetry. At baseline, there were no significant differences in blood pressure between ECKO and controls 107.9±1.7 VS 109.3±1 mmHg). The response of ECKOs to Ang II infusion was variable. In one cohort, MAP during Ang II infusion was significantly lower than controls (142.8±3.1 vs 133.2±1.9 mmHg, p=0.02) whereas in a second cohort there was no difference in MAP with Ang II infusion between groups (131.7±2.3 vs 135.6±2.1 mmHg). Interestingly, the incidence of aortic aneurysm was significantly higher in ECKOs (12/27) compared to controls (2/25; p=0.01 by Fisher exact test). As urine sodium excretion during Ang II infusion was increased in ECKOs, we considered the possibility that aneurysm formation may have impacted the blood pressure. We also found the ECs isolated from ECKOs have significantly higher eNOS mRNA expression compared to control (fold change: 1.35±0.13; p=0.046). To determine whether this difference in eNOS expression have a functional impact, we compared blood pressure responses to L-NAME following Ang II infusion. ECKOs showed exaggerated response to L-NAME compared to controls (MAP increases +5.2±1.4 mmHg in ECKO vs. +0.5±1.5 mmHg in control; p=0.03). Thus, EP4R in ECs play important role in regulating EC function, impacting blood pressure and aortic integrity.

Experimental Autoimmune Encephalomyelitis Potentiates Mouse Mast Cell Protease 4-Dependent Pressor Responses to Centrally or Systemically Administered Big Endothelin-1.

Multiple sclerosis is a neurodegenerative disease affecting predominantly female patients between 20 and 45 years of age. We previously reported the significant contribution of mouse mast cell protease 4 (mMCP-4) in the synthesis of endothelin-1 (ET-1) in healthy mice and in a murine model of experimental autoimmune encephalomyelitis (EAE). In the current study, the cardiovascular effects of ET-1 and big endothelin-1 (big-ET-1) administered systemically or intrathecally were assessed in the early preclinical phase of EAE in telemetry instrumented/conscious mice. Chymase-specific enzymatic activity was also measured in the lung, brain, and mast cell extracts in vitro. Finally, the impact of EAE immunization was studied on the pulmonary and brain mRNA expression of different genes of the endothelin pathway, interleukin-33 (IL-33), and monitoring of immunoreactive tumor necrosis factor-α (TNF-α). Systemically or intrathecally administered big-ET-1 triggered increases in blood pressure in conscious mice. One week post-EAE, the pressor responses to big-ET-1 were potentiated in wild-type (WT) mice but not in mMCP-4 knockout (KO) mice. EAE triggered mMCP-4-specific activity in cerebral homogenates and peritoneal mast cells. Enhanced pulmonary, but not cerebral preproendothelin-1 and IL-33 mRNA were found in KO mice and further increased 1 week post-EAE immunization, but not in WT animals. Finally, TNF-α levels were also increased in serum from mMCP-4 KO mice, but not WT, 1 week post-EAE. Our study suggests that mMCP-4 activity is enhanced both centrally and systemically in a mouse model of EAE.

Cardiac manifestations of inherited metabolic disease linked to cellular vitamin B12 (cobalamin) uptake: Study in murine model of invalidation of Mtr gene in the heart

Heart failure is one of the most common cause of death in Western societies. Deficiency in folates and vitamin B12 during gestation and lactation causes foetal programming effect with metabolic cardiomyopathy related to decreased synthesis of methionine by methionine synthase encoded by MTR Gene. Methionine is the precursor for S-adenosyl methionine (SAM) the universal methyl donor. Mutations in MTR gene causes cardiac decompensation in new-borns by unknown mechanisms. To investigate cardiac metabolic and functional consequences of inhibition of methionine synthesis in conditional knock out of Mtr gene in the heart of C57BL/6 mice. Systolic Blood Pressure in conscious mice was measured using tail-cuff plethysmography. Left ventricular (LV) functions were assessed by Mini-PET and Echocardiography. Transcriptomics analysis was achieved by RNA deep sequencing and proteomic study by LC-MS/MS. Systolic hypertension, decreased LV ejection fraction, increased LV mass and heart/body weight ratio were observed in Mtr KO compared to control. RT-qPCR confirmed upregulated expression of natriuretic peptides (ANP and BNP) and decreased alpha MHC/beta MHC ratio in Mtr KO. Biochemical studies revealed decreased SAM/SAH ratio, elevated plasma acylcarnitine and cardiac fibrosis in Mtr KO. The whole heart transcriptome consisted of 16540 expressed genes which were clustered by K-means into three signatures, these signatures were correlated to proteomic results. Dysregulated genes and proteins in Mtr KO were implicated in cardiac contraction, cell growth and energy metabolism. Our results suggest that silencing of Methionine synthase in the heart induces hypertension, hypertrophic cardiomyopathy with LV systolic dysfunction. The related mechanisms were dysregulation of energy metabolism and fibrosis. This data provides a novel insight on physiopathological mechanisms of cardiomyopathies of inherited disorders of cobalamin metabolism.

Glutamatergic neurons of the paraventricular nucleus are critical contributors to the development of neurogenic hypertension.

Recurrent periods of over-excitation in the paraventricular nucleus (PVN) of the hypothalamus could contribute to chronic over-activation of this nucleus and thus enhanced sympathetic drive. Stimulation of the PVN glutamatergic population utilizing channelrhodopsin-2 leads to an immediate frequency-dependent increase in baseline blood pressure. Partial lesions of glutamatergic neurons of the PVN (39.3%) result in an attenuated rise in blood pressure following Deoxycorticosterone acetate (DOCA)-salt treatment and reduced index of sympathetic activity. These data suggest that stimulation of PVN glutamatergic neurons is sufficient to cause autonomic dysfunction and drive the increase in blood pressure during hypertension. Neuro-cardiovascular dysregulation leads to increased sympathetic activity and neurogenic hypertension. The paraventricular nucleus (PVN) of the hypothalamus is a key hub for blood pressure (BP) control, producing or relaying the increased sympathetic tone in hypertension. We hypothesize that increased central sympathetic drive is caused by chronic over-excitation of glutamatergic PVN neurons. We tested how stimulation or lesioning of excitatory PVN neurons in conscious mice affects BP, baroreflex and sympathetic activity. Glutamatergic PVN neurons were unilaterally transduced with channelrhodopsin-2 using an adeno-associated virus (CamKII-ChR2-eYFP-AAV2) in wildtype mice (n= 7) to assess the impact of acute stimulation of excitatory PVN neurons selectively on resting BP in conscious mice. Stimulation of the PVN glutamatergic population resulted in an immediate frequency-dependent (2, 10 and 20Hz) increase in BP from baseline by ∼9mmHg at 20Hz stimulation (P< 0.001). Additionally, in vGlut2-cre mice glutamatergic neurons of the PVN were bilaterally lesioned utilizing a cre-dependent caspase (AAV2-flex-taCASP3-TEVp). Resting BP and urinary noradrenaline (norepinephrine) levels were then recorded in conscious mice before and after DOCA-salt hypertension. Partial lesions of glutamatergic neurons of the PVN (39.3%, P< 0.05) resulted in an attenuated rise in BP following DOCA-salt treatment (P< 0.05 at 7day time point, n= 8). Noradrenaline levels as an index of sympathetic activity between the lesion and wildtype groups showed a significant reduction after DOCA-salt treatment in the lesioned animals (P< 0.05). These experiments suggest that stimulation of PVN glutamatergic neurons is sufficient to cause autonomic dysfunction and drive the increase in BP.

Abstract 21022: Increasing Cav1.2 in Smooth Muscle Cells Induces Both Systemic and Pulmonary Hypertension via Inhibiting Endothelium-Dependent Relaxation

Introduction: Local activation of the L-type Ca 2+ channel (Cav1.2) in smooth muscle cells (SMCs) may activate big- and small- conductance K + channels, leading to hyperpolarization of the cell and vascular relaxation; however, large-scale activation of Cav1.2 increases cytosolic Ca 2+ to enhance muscle contraction. Hypothesis: We are testing if and how increasing Cav1.2 in SMCs causes systemic and pulmonary hypertension. Methods: Systemic blood pressure in conscious mice were measured with telemetric blood pressure system. Intra-ventricular hemodynamics of the LV and RV were determined in 6-month old SMC-specific Cavβ2a transgenic and control mice. Whole heart, LV and the right ventricular (RV) hypertrophy was assessed by heart weight (HW)/body weight (BW), LV weigth/BW, RV weight/BW, and RV-to-left ventricle+septum (RV/LV+S) ratio. Lung and heart sections were stained with H&amp;E. Mesenteric arteries were isolated for evaluating small arterial contractility and relaxation. Results: SMCs from the cerebral iddle arteries of TG mice had increased ICa (by 98.5±5.4%) vs. control. Conscious TG mice had significantly higher systemic systolic (TG vs. control: 145.4±12.1mmHg, n=45 vs. 115.2±7.4mmHg, n=16 ) and diastolic (TG vs control: 116.7±9.1mmHg, n=45 vs. 87.8±8.2mmHg, n=16) pressure (telemetry). Intra-ventricular hemodynamics (anesthestized) showed significantly increased systolic and diastolic pressure in both the LV (systolic: TG vs control: 120.2±7.3mmHg, n=17 vs. 82.3±7.2mmHg, n=16) and RV (systolic: TG vs control: 60.5±6.8mmHg, n=10 vs. 20.4±4.9mmHg, n=9). HW/BW, LV/BW, RV/BW, and RV/LV+S was higher in TG mice than in control mice. Small arteries in the lungs and the heart had increased wall thickness. Mesenteric arteries from TG mice had similar maximum contractility upon 40mM KCl stimulation. Acetylcholine induced relaxation but not NO-depedent relaxation was impaired in TG mesenteric arteries. Western blot and immunostaining showed less small- and large-conductance Ca 2+ -activated K + channels in the TG endothelium. Conclusions: Excessive calcium ion (Ca 2+ ) influx through L-type Ca 2+ channels can lead to both systemic and pulmonary arterial hypertension due to impairment of endothelium-dependent relaxation.

Smooth Muscle Specific Deletion of Ndst1 Leads to Decreased Vessel Luminal Area and No Change in Blood Pressure in Conscious Mice

Heparan sulfate proteoglycans are abundant matrix and membrane molecules. Smooth muscle specific deletion of one heparan sulfate biosynthetic enzyme, N-deacetylase-N-sulfotransferase1 leads to decreased vascular smooth muscle cell proliferation, and vascular wall thickness. We hypothesized that this may lead to changes in blood pressure in conscious mice. Blood pressure was measured via telemetry in SM22αCre(+)Ndst1(-/-)(n = 4) and wild type (n = 8) mice. Aorta and thoracodorsal artery luminal area is significantly smaller in SM22αCre(+)Ndst1(-/-) (n = 4-8, P = 0.02, P = 0.0002) compared to wild type (n = 7) mice. Diurnal differences were observed in both cohorts for systolic, diastolic, mean arterial blood pressure, and heart rate (P < 0.001 from T test). No significant differences were found in the above parameters between the cohorts in either light or dark times using a linear mixed model. In conclusion, deletion of N-deacetylase-N-sulfotransferase1 in smooth muscle did not influence any of the blood pressure parameters measured despite significant decrease in aorta and thoracodorsal artery luminal area.

Adenosine elicits an eNOS-independent reduction in arterial blood pressure in conscious mice that involves adenosine A2A receptors

Adenosine plays an important role in the regulation of heart rate (HR) and vascular reactivity. However, the mechanisms underlying the acute effect of adenosine on arterial blood pressure in conscious mice are unclear. Therefore, this study investigated the effect of the nucleoside on mean arterial blood pressure (MAP) and HR in conscious mice. Chronic indwelling catheters were placed in C57Bl/6J (WT) and endothelial nitric oxide synthase knockout (eNOS(-/-)) mice for continuous measurements of MAP and HR. Using PCR and myograph analysis, involvement of adenosine receptors was investigated in human and mouse renal blood vessels. Bolus infusion of 0.5 mg kg(-1) adenosine elicited significant transient decreases in MAP (99.3 ± 2.3 to 70.4 ± 4.5 mmHg) and HR (603.2 ± 18.3 to 364.3 ± 49.2 min(-1)), which were inhibited by the A(2A) receptor antagonist ZM 241385. Activation of adenosine A(2A) receptors with CGS 21680 (0.02 mg kg(-1)) caused a significant reduction in MAP from 99.6 ± 1.2 to 73.1 ± 3.6 mmHg accompanied by tachycardia (610.5 ± 9.3 to 677.5 ± 9.5 min(-1)). The reduction in MAP observed after adenosine or CGS 21680 administrations was not significantly different in WT and eNOS(-/-) mice. In isolated human and mouse intrarenal arteries, adenosine caused a relaxation dependent on A(2A) adenosine receptor activation. A(2A) receptors were present in both human and mouse arteries whereas A(1) and A(2B) receptors were only present in mouse arteries. In conclusion, acute adenosine administration and selective stimulation of adenosine A(2A) receptors results in an immediate, transient eNOS-independent reduction in MAP. A(2A) receptor activation causes relaxation of human and mouse arteries.

Locomotor activity and blood pressure in conscious mice with targeted deletion of the equilibrative nucleoside transporter 1

Extracellular adenosine (ado) is regulated by transmembrane transport through both equilibrative and concentrative nucleoside transporters (ENTs and CNTs). Previous studies have reported profound effects of extracellular ado on sleep, anxiety, and locomotor activity. The present experiments were performed in ENT1‐deficient mice to assess the long term effect of impaired ado exchange on arterial blood pressure (MAP) and locomotor activity. Average daily running wheel activity (RWA, revolutions/min) under LD (12h light:12h dark) and DD (24 h dark) was markedly reduced in ENT1 −/− (LD, 3.1 ± 0.1; DD, 2.1 ± 0.1; n=4) vs. WT mice (LD, 9.4 ± 0.7; DD, 11.3 ± 0.3; n=4; p &lt; 0.001). RWA showed comparable circadian periodicity between genotypes, but the periodic strength was greater in WT than ENT1−/−. Spontaneous activity measured with radiotransmitters was also 40% lower in ENT1−/− than WT mice. Telemetric measurements of MAP showed no significant differences between genotypes although pulse pressure was lower in −/− than +/+ mice. Heart rates were lower in ENT1−/− than WT by about 40 bpm during both light and dark periods. Plasma renin concentration (ng Ang I/ml hr) tended to be lower in ENT1 −/− mice without reaching significance. Absence of ENT1 is associated with reduced locomotor activity, perhaps reflecting suppression of neuronal activities by impaired ado transporting capacity.

Influence of the adenosine A1receptor on blood pressure regulation and renin release

The present study was performed to investigate the role of adenosine A1 receptors in regulating blood pressure in conscious mice. Adenosine A1-receptor knockout (A1R-/-) mice and their wild-type (A1R+/+) littermates were placed on standardized normal-salt (NS), high-salt (HS), or salt-deficient (SD) diets for a minimum of 10 days before telemetric blood pressure and urinary excretion measurements in metabolic cages. On the NS diet, daytime and nighttime mean arterial blood pressure (MAP) was 7-10 mmHg higher in A1R-/- than in A1R+/+ mice. HS diet did not affect the MAP in A1R-/- mice, but the daytime and nighttime MAP of the A1R+/+ mice increased by approximately 10 mmHg, to the same level as that in the A1R-/-. On the SD diet, day- and nighttime MAP decreased by approximately 6 mmHg in both A1R-/- and A1R+/+ mice, although the MAP remained higher in A1R-/- than in A1R+/+ mice. Although plasma renin levels decreased with increased salt intake in both genotypes, the A1R-/- mice had an approximately twofold higher plasma renin concentration on all diets compared with A1R+/+ mice. Sodium excretion was elevated in the A1R-/- compared with the A1R+/+ mice on the NS diet. There was no difference in sodium excretion between the two genotypes on the HS diet. Even on the SD diet, A1R-/- mice had an increased sodium excretion compared with A1R+/+ mice. An abolished tubuloglomerular feedback response and reduced tubular reabsorption can account for the elevated salt excretion found in A1R-/- animals. The elevated plasma renin concentrations found in the A1R-/- mice could also result in increased blood pressure. Our results confirm that adenosine, acting through the adenosine A1 receptor, plays an important role in regulating blood pressure, renin release, and sodium excretion.

Influence of elevated renin substrate on angiotensin II and arterial blood pressure in conscious mice

The present experiments were performed to determine the influence of intravenous administration of renin substrate on plasma angiotensin II levels and mean arterial blood pressure in conscious C57BL/6J mice. Mice with chronic indwelling femoral arterial and venous catheters were acutely or chronically administered intravenous doses of a synthetic peptide corresponding to the 14 amino acids on the N-terminal of angiotensinogen. A dose-dependent increase in arterial blood pressure was observed as the intravenous bolus dose of the renin substrate was increased from 0.18 to 180 nmol kg(-1) with a maximal increase in pressure of 40 +/- 3 mmHg achieved following administration of the 18 nmol kg(-1) bolus (n = 11). Additional experiments demonstrated that a sustained intravenous infusion of the renin substrate led to a long-term increase in arterial blood pressure. The continuous infusion of renin substrate at 0.05 nmol kg(-1) min(-1) for 3 days did not alter arterial blood pressure from the control level of 119 +/- 5 mmHg (n = 5); however, arterial blood pressure significantly increased to 129 +/- 6 mmHg with an infusion rate of 0.5 nmol kg(-1) min(-1) and further increased to 141 +/- 3 mmHg when the renin substrate infusion was increased to 5.0 nmol kg(-1) min(-1). Finally, the infusion of renin substrate at 5.0 nmol kg(-1) min(-1) resulted in a significant increase in plasma angiotensin II concentration from 34 +/- 6 pg ml(-1) in vehicle-infused mice to 288 +/- 109 pg ml(-1). These results demonstrate that modulation of the circulating level of angiotensinogen can alter the plasma angiotensin II level and arterial blood pressure in normal animals.

Importance of the renin–angiotensin system in the regulation of arterial blood pressure in conscious mice and rats

The present experiments were designed to determine the mechanism(s) for increased sensitivity to blockade of the renin-angiotensin system in mice in comparison with rats. Mice and rats, with indwelling femoral arterial and venous catheters, were chronically administered angiotensin II or pharmacological inhibitors of the renin-angiotensin system as sodium intake was altered. Increasing sodium intake led to suppression of circulating renin, angiotensin II, and aldosterone in rats and mice in the absence of alterations in arterial blood pressure. Additional experiments demonstrated that continuous intravenous infusion of angiotensin II (20 ng kg(-1) min(-1)) significantly increased arterial blood pressure by approximately 35 mmHg in conscious rats at all levels of sodium intake (n = 6). In contrast, arterial pressure was unaffected by angiotensin II infusion in conscious mice under conditions of low sodium intake, although arterial pressure was increased by 16 mmHg when mice were administered a high sodium intake while infused with angiotensin II (n = 6). In comparison, blockade of the endogenous renin-angiotensin system led to significantly greater effects on arterial pressure in mice than rats. Continuous infusion of captopril (30 microg kg(-1) min(-1)) or losartan (100 microg kg(-1) min(-1)) resulted in a 55-90% greater fall in blood pressure in conscious mice in comparison with conscious rats. The present studies indicate that arterial pressure in mice is more dependent upon the endogenous renin-angiotensin system than it is in rats, but mice are more resistant to the hypertensive effects of exogenous angiotensin II.

Exercising restraint in measuring blood pressure in conscious mice.

A rat’s tail is a slender appendage on which the weight of so much research in hypertension hangs, yet blood pressure measurements recorded from it are usually taken for granted, often abused, but seldom discussed,” observed Buang in an earlier commentary.1 The same methodology has now been adapted to mice. Restraining the animals is a serious problem. A 7-day training period is recommended to accustom the animals to the restrainers.2–4 Nevertheless, heart rates recorded while mice are in a restrainer are higher than those in the resting state.3 Furthermore, blood pressures also appear to be higher, even though coaxing the animals into restrainers becomes easier day-to-day.5 A blood pressure–elevating effect of restrainers has been observed in the rat.6 Telemetric blood pressure and heart rate solves this problem.6 We made telemetric measurements of blood pressure and heart rate on four 129Sv/J mice outfitted with telemetry as described earlier.7 The purpose of our observations was to test the notion that “conditioning” might lessen the effects of restraint on blood pressure and heart rate. After an initial 120-minute control period, the mice …

Long-term measurement of arterial blood pressure in conscious mice.

This study describes a technique for the direct daily measurement of arterial blood pressure, sampling of arterial blood, and continuous intravenous infusion in free-moving, conscious, Swiss-Webster mice. Catheters were chronically implanted in the femoral artery and vein, tunneled subcutaneously, exteriorized at the back of the neck in a lightweight tethering spring, and attached to a swivel device at the top of the cage. Time-control experiments (n = 8) demonstrated stable values of mean arterial pressure (MAP, 116 +/- 1 mmHg) and heart rate (HR, 627 +/- 21 beats/min) for up to 35 days after catheter implantation. It was further observed that restraining mice (n = 7) increased MAP by 10 +/- 3 mmHg and HR by 78 +/- 8 beats/min from the values observed under free-moving conditions. To demonstrate the chronic use of the venous catheter, intravenous infusion of NG-nitro-L-arginine methyl ester (L-NAME, 8.6 mg.kg-1.day-1, n = 6) for 5 days significantly increased MAP from 117 +/- 4 to 131 +/- 4 mmHg without altering HR. In a final group of mice (n = 5), oral L-arginine (2% in drinking water) increased plasma arginine concentration from 90 +/- 7 to 131 +/- 17 microM and prevented L-NAME hypertension. These experiments illustrate the feasibility of long-term intravenous infusion, direct arterial blood pressure measurements, and arterial blood sampling in conscious mice.