To date, there is no safe and effective hemoglobin-based oxygen carrier (HBOC) to substitute for erythrocyte transfusion. It is uncertain whether a deficiency of endothelial nitric oxide ...bioavailability (endothelial dysfunction) prevents or augments HBOC-induced vasoconstriction.
Hemodynamic effects of infusion of PolyHeme (1.08 g hemoglobin/kg; Northfield Laboratories, Evanston, IL) or murine tetrameric hemoglobin (0.48 g hemoglobin/kg) were determined in awake healthy lambs, awake mice, and anesthetized mice. In vitro, a cumulative dose-tension response was obtained by sequential addition of PolyHeme or tetrameric hemoglobin to phenylephrine-precontracted murine aortic rings.
Infusion of PolyHeme did not cause systemic hypertension in awake lambs but produced acute systemic and pulmonary vasoconstriction. Infusion of PolyHeme did not cause systemic hypertension in healthy wild-type mice but induced severe systemic vasoconstriction in mice with endothelial dysfunction (either db/db mice or high-fat fed wild-type mice for 4-6 weeks). The db/db mice were more sensitive to systemic vasoconstriction than wild-type mice after the infusion of either tetrameric hemoglobin or PolyHeme. Murine aortic ring studies confirmed that db/db mice have an impaired response to an endothelial-dependent vasodilator and an enhanced vasoconstrictor response to HBOC.
Reduction in low molecular weight hemoglobin concentrations to less than 1% is insufficient to abrogate the vasoconstrictor effects of HBOC infusion in healthy awake sheep or in mice with reduced vascular nitric oxide levels associated with endothelial dysfunction. These findings suggest that testing HBOCs in animals with endothelial dysfunction can provide a more sensitive indication of their potential vasoconstrictor effects.
When activated by the sympathetic nervous system, brown adipose tissue (BAT) increases energy expenditure to produce heat. Augmenting BAT mass or increasing BAT activation could potentially be used ...to decrease obesity. Noninvasive methods to detect and monitor BAT mass are needed. Contrast ultrasound can estimate BAT blood flow and is able to measure the perfused volume of an organ and thus its mass. The objective of this study was to evaluate whether contrast ultrasound could characterize BAT mass in two mouse models of obesity: wild-type mice fed a high-fat diet and mutant db/db mice.
Contrast ultrasound of BAT (Definity 2 μL/min; 14-MHz linear probe) was performed before and after stimulation of BAT with norepinephrine (NE). BAT replenishment curves were obtained, and blood flow was estimated by the product of the curve's plateau and slope. Additionally, consecutive two-dimensional images of perfused BAT were acquired at 1-mm intervals after stimulation with NE and used to assess BAT volume and mass.
BAT blood flow increased after NE infusion in all mice studied. Blood flow response to NE was similar in wild-type mice fed either a low-fat diet or a high-fat diet. BAT blood flow was lower in db/db mice than in wild-type mice (P = .02). Contrast ultrasound-derived BAT mass was correlated with BAT mass obtained at necropsy (R(2) = 0.83, P < .001). BAT mass was higher in mice fed a high-fat diet than in those fed a low-fat diet.
Contrast ultrasound can be used to estimate BAT mass in mice when BAT vascularization is not significantly impaired. This noninvasive technique may potentially allow the serial evaluation of therapies designed to augment BAT mass.
Obesity is associated with an increased incidence and severity of asthma, as well as other lung disorders, such as pulmonary hypertension. Adiponectin (APN), an antiinflammatory adipocytokine, ...circulates at lower levels in the obese, which is thought to contribute to obesity-related inflammatory diseases. We sought to determine the effects of APN deficiency in a murine model of chronic asthma. Allergic airway inflammation was induced in APN-deficient mice (APN(-/-)) using sensitization without adjuvant followed by airway challenge with ovalbumin. The mice were then analyzed for changes in inflammation and lung remodeling. APN(-/-) mice in this model develop increased allergic airway inflammation compared with wild-type mice, with greater accumulation of eosinophils and monocytes in the airways associated with elevated lung chemokine levels. Surprisingly, APN(-/-) mice developed severe pulmonary arterial muscularization and pulmonary arterial hypertension in this model, whereas wild-type mice had only mild vascular remodeling and comparatively less pulmonary arterial hypertension. Our findings demonstrate that APN modulates allergic inflammation and pulmonary vascular remodeling in a model of chronic asthma. These data provide a possible mechanism for the association between obesity and asthma, and suggest a potential novel link between obesity, inflammatory lung disease, and pulmonary hypertension.
Flavoprotein reductases are involved in the generation of reactive oxygen species by doxorubicin. The objective of the present study was to determine whether or not one flavoprotein reductase, ...endothelial nitric oxide synthase (nitric oxide synthase 3 NOS3), contributes to the cardiac dysfunction and injury seen after the administration of doxorubicin.
A single dose of doxorubicin (20 mg/kg) was administered to wild-type (WT) mice, NOS3-deficient mice (NOS3-/-), and mice with cardiomyocyte-specific overexpression of NOS3 (NOS3-TG). Cardiac function was assessed after 5 days with the use of echocardiography. Doxorubicin decreased left ventricular fractional shortening from 57+/-2% to 47+/-1% (P<0.001) in WT mice. Compared with WT mice, fractional shortening was greater in NOS3-/- and less in NOS3-TG after doxorubicin (55+/-1% and 35+/-2%; P<0.001 for both). Cardiac tissue was harvested from additional mice at 24 hours after doxorubicin administration for measurement of cell death and reactive oxygen species production. Doxorubicin induced cardiac cell death and reactive oxygen species production in WT mice, effects that were attenuated in NOS3-/- and were more marked in NOS3-TG mice. Finally, WT and NOS3-/- mice were treated with a lower dose of doxorubicin (4 mg/kg) administered weekly over 5 weeks. Sixteen weeks after beginning doxorubicin treatment, fractional shortening was greater in NOS3-/- than in WT mice (45+/-2% versus 28+/-1%; P<0.001), and mortality was reduced (7% versus 60%; P<0.001).
These findings implicate NOS3 as a key mediator in the development of left ventricular dysfunction after administration of doxorubicin.
Although multiple echocardiographic methods exist to calculate cardiac output (CO), they have not been validated in mice using a reference method.
Echocardiographic and flow probe measurements of CO ...were obtained in mice before and after albumin infusion and inferior vena cava occlusions. Echocardiography was also performed before and after endotoxin injection. Cardiac output was calculated using left ventricular volumes obtained from an M-mode or a two-dimensional view, left ventricular stroke volume calculated using the pulmonary flow, or estimated by the measurement of pulmonary velocity time integral (VTI).
Close correlations were demonstrated between flow probe-measured CO and all echocardiographic measurements of CO. All echocardiographic-derived CO overestimated the flow probe-measured CO. Two-dimensional image-derived CO was associated with the smallest overestimation of CO. Interobserver variability was lowest for pulmonary VTI-derived CO.
In mice, CO calculated from two-dimensional parasternal long-axis images is most accurate when compared with flow probe measurements; however, pulmonary VTI-derived CO is subject to less variability.
Activin and myostatin are related members of the TGF-β growth factor superfamily. FSTL3 (Follistatin-like 3) is an activin and myostatin antagonist whose physiological role in adults remains to be ...determined. We found that homozygous FSTL3 knockout adults developed a distinct group of metabolic phenotypes, including increased pancreatic islet number and size, β cell hyperplasia, decreased visceral fat mass, improved glucose tolerance, and enhanced insulin sensitivity, changes that might benefit obese, insulin-resistant patients. The mice also developed hepatic steatosis and mild hypertension but exhibited no alteration of muscle or body weight. This combination of phenotypes appears to arise from increased activin and myostatin bioactivity in specific tissues resulting from the absence of the FSTL3 antagonist. Thus, the enlarged islets and β cell number likely result from increased activin action. Reduced visceral fat is consistent with a role for increased myostatin action in regulating fat deposition, which, in turn, may be partly responsible for the enhanced glucose tolerance and insulin sensitivity. Our results demonstrate that FSTL3 regulation of activin and myostatin is critical for normal adult metabolic homeostasis, suggesting that pharmacological manipulation of FSTL3 activity might simultaneously reduce visceral adiposity, increase β cell mass, and improve insulin sensitivity.
Aim The effects of nitric oxide (NO) in the cardiovascular system are attributed in part to cGMP synthesis by the α1β1 isoform of soluble guanylate cyclase (sGC). Because available sGC inhibitors are ...neither enzyme- nor isoform-specific, we generated knockout mice for the α1 subunit (sGCα1−/− mice) in order to investigate the function of sGCα1β1 in the regulation of blood pressure and cardiac function. Methods and results Blood pressure was evaluated, using both non-invasive and invasive haemodynamic techniques, in intact and gonadectomized male and female sGCα1−/− and wild-type (WT) mice. Cardiac function was assessed with a conductance catheter inserted in the left ventricle of male and female sGCα1−/− and WT mice. Male sGCα1−/− mice developed hypertension (147 ± 2 mmHg), whereas female sGCα1−/− mice did not (115 ± 2 mmHg). Orchidectomy and treatment with an androgen receptor antagonist prevented hypertension, while ovariectomy did not influence the phenotype. Chronic testosterone treatment increased blood pressure in ovariectomized sGCα1−/− mice but not in WT mice. The NO synthase inhibitor Nω-nitro-L-arginine methyl ester hydrochloride raised blood pressure similarly in male and female WT and sGCα1−/− mice. The ability of NO donor compounds to reduce blood pressure was slightly attenuated in sGCα1−/− male and female mice as compared to WT mice. The direct sGC stimulator BAY 41-2272 reduced blood pressure only in WT mice. Increased cardiac contractility and arterial elastance as well as impaired ventricular relaxation were observed in both male and female sGCα1−/− mice. Conclusion These findings demonstrate that sGCα1β1-derived cGMP signalling has gender-specific and testosterone-dependent cardiovascular effects and reveal that the effects of NO on systemic blood pressure do not require sGCα1β1.
1 Anesthesia Center for Critical Care Research, Department of Anesthesia and Critical Care, and 2 Cardiac Ultrasound Laboratory, Massachusetts General Hospital and Harvard Medical School, Boston, ...Massachusetts
Submitted 4 February 2008
; accepted in final form 14 July 2008
MyD88 is an adaptor protein critical for innate immune response against microbial infection and in certain noninfectious tissue injury. The present study examined the role of MyD88 in myocardial inflammation and injury after ischemia-reperfusion (I/R). I/R was produced by coronary artery ligation for 30 min followed by reperfusion. The ratios of area at risk to left ventricle (LV) were similar between wild-type (WT) and MyD88-deficient (MyD88 –/– ) mice. However, 24 h after I/R, the ratios of myocardial infarction to area at risk were 58% less in MyD88 –/– than in WT mice (14 ± 2% vs. 33 ± 6%, P = 0.01). Serial echocardiographic studies demonstrated that there was no difference in baseline LV contractile function between the two groups. Twenty-four hours after I/R, LV ejection fraction (EF) and fractional shortening (FS) in WT mice were reduced by 44% and 62% (EF, 51 ± 2%, and FS, 22 ± 1%, P < 0.001), respectively, and remained depressed on the seventh day after I/R. In comparison, EF and FS in MyD88 –/– mice were 67 ± 3% and 33 ± 2%, respectively, after I/R ( P < 0.001 vs. WT). Similarly, LV function, as demonstrated by invasive hemodynamic measurements, was better preserved in MyD88 –/– compared with WT mice after I/R. Furthermore, when compared with WT mice, MyD88 –/– mice subjected to I/R had a marked decrease in myocardial inflammation as demonstrated by attenuated neutrophil recruitment and decreased expression of the proinflammatory mediators keratinocyte chemoattractant, monocyte chemoattractant protein-1, and ICAM-1. Taken together, these data suggest that MyD88 modulates myocardial inflammatory injury and contributes to myocardial infarction and LV dysfunction during I/R.
myocardial infarction; inflammation; echocardiography; innate immune system
Address for reprint requests and other correspondence: W. Chao, Dept. of Anesthesia & Critical Care, Massachusetts General Hospital, GRJ-4-462, 55 Fruit St., Boston, MA 02114 (e-mail: wchao{at}partners.org )
1 Department of Anesthesia and Critical Care, 2 Cardiovascular Research Center, 3 Cardiac Ultrasound Laboratory, Division of Cardiology, Department of Medicine, and 4 Department of Pathology, ...Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts; and 5 Cardiovascular Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland
Submitted 7 November 2005
; accepted in final form 20 January 2006
To learn whether nitric oxide (NO) inhalation can decrease myocardial ischemia-reperfusion (I/R) injury, we studied a murine model of myocardial infarction (MI). Anesthetized mice underwent left anterior descending coronary artery ligation for 30, 60, or 120 min followed by reperfusion. Mice breathed NO beginning 20 min before reperfusion and continuing thereafter for 24 h. MI size and area at risk were measured, and left ventricular (LV) function was evaluated using echocardiography and invasive hemodynamic measurements. Inhalation of 40 or 80 ppm, but not 20 ppm, NO decreased the ratio of MI size to area at risk. NO inhalation improved LV systolic function, as assessed by echocardiography 24 h after reperfusion, and systolic and diastolic function, as evaluated by hemodynamic measurements 72 h after reperfusion. Myocardial neutrophil infiltration was reduced in mice breathing NO, and neutrophil depletion prevented inhaled NO from reducing myocardial I/R injury. NO inhalation increased arterial nitrite levels but did not change myocardial cGMP levels. Breathing 40 or 80 ppm NO markedly and significantly decreased MI size and improved LV function after ischemia and reperfusion in mice. NO inhalation may represent a novel method to salvage myocardium at risk of I/R injury.
myocardial infarction; cardiac injury; murine model
Address for reprint requests and other correspondence: M. Scherrer-Crosbie, Cardiac Ultrasound Laboratory, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114 (e-mail: marielle{at}crosbie.com )
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