Direct comparison of magnetic resonance imaging and conductance microcatheter in the evaluation of left ventricular function in mice.

The aim of the present work was to study the reliability of conductance microcatheter volumetric measurements as compared to magnetic resonance imaging (MRI) in the same set of mice. Mice left ventricular (LV) volumes were monitored under basal conditions and in a hypertrophy model induced by transverse aortic constriction (TAC). Cardiac function was evaluated in isoflurane anesthetized mice (n = 8) by MRI followed by 1.4 F Millar microtip catheter measurements. The second group of mice with TAC-induced cardiac hypertrophy was studied eight weeks after surgery. Reliability of 3D-reconstructed MRI data was confirmed by comparison with autopsy masses (autopsy LV mass = 73.6 +/- 3.4 mg; MRI LV mass = 76.9 +/- 3.7 mg). Conduction catheter was found to greatly underestimate end-diastolic and end-systolic volumes and thus stroke volume as well as cardiac output in control mice (MRI: EDV = 79 +/- 8 microl, ESV = 27+/-9 microl, SV = 51 +/- 9 microl, CO = 25 +/- 6 ml/min; Catheter: EDV = 28 +/- 5 microl, ESV = 8 +/- 4 microl, SV = 19 +/- 4 microl, CO = 10 +/- 2 ml/min). However, values for ejection fraction showed no significant differences between the two methods. In the hypertrophy model, stroke volume and cardiac output were increased when measured with MRI (SV: +19 +/- 20%; CO: +28 +/- 27%), whereas catheter data showed opposite directional changes (SV: -22 +/- 37%; CO: -31 +/- 37%). Ejection fraction was found to be reduced only in catheter measurements (-31 +/- 26%). In summary, our data demonstrate that absolute volumetric values are strikingly underestimated by conduction catheter measurements and that even detection of directional changes with this method may not always be feasible.

Targeted disruption of cd73/ecto-5'-nucleotidase alters thromboregulation and augments vascular inflammatory response.

To investigate the role of adenosine formed extracellularly in vascular homeostasis, mice with a targeted deletion of the cd73/ecto-5'-nucleotidase were generated. Southern blot, RT-PCR, and Western blot analysis confirmed the constitutive knockout. In vivo analysis of hemodynamic parameters revealed no significant differences in systolic blood pressure, ejection fraction, or cardiac output between strains. However, basal coronary flow measured in the isolated perfused heart was significantly lower (-14%; P<0.05) in the mutant. Immunohistochemistry revealed strong CD73 expression on the endothelium of conduit vessels in wild-type (WT) mice. Time to carotid artery occlusion after ferric chloride (FeCl3) was significantly reduced by 20% in cd73-/- mice (P<0.05). Bleeding time after tail tip resection tended to be shorter in cd73-/- mice (-35%). In vivo platelet cAMP levels were 0.96+/-0.46 in WT versus 0.68+/-0.27 pmol/106 cells in cd73-/- mice (P<0.05). Under in vitro conditions, platelet aggregation in response to ADP (0.05 to 10 micromol/L) was undistinguishable between the two strains. In the cremaster model of ischemia-reperfusion, the increase in leukocyte attachment to endothelium was significantly higher in cd73-/- compared with WT littermates (WT 98% versus cd73-/- 245%; P<0.005). The constitutive adhesion of monocytes in ex vivo-perfused carotid arteries of WT mice was negligible but significantly increased in arteries of cd73-/- mice (P<0.05). Thus, our data provide the first evidence that adenosine, extracellularly formed by CD73, can modulate coronary vascular tone, inhibit platelet activation, and play an important role in leukocyte adhesion to the vascular endothelium in vivo.

A hemodynamic response to intravenous adenovirus vector particles is caused by systemic Kupffer cell-mediated activation of endothelial cells.

Intravascular injection of adenoviral vectors may result in a toxic and potentially lethal reaction, the mechanism of which is poorly understood. We noted that mice demonstrated a transient change in behavior that was characterized by inactivity and lethargy within minutes after intravenous injection of relatively low doses of adenoviral vectors (including high-capacity gutless vectors). Moreover, immediately after vector injection a significant drop in blood pressure was measured that most probably was caused by the systemic activation of endothelial cells as monitored by detection of phosphorylated Akt/PKB kinase, activated endothelial nitric oxide synthase (eNOS), and nitrotyrosine. The activation of the endothelium was the result of the interaction of viral particles with Kupffer cells, which are resident macrophages of the liver representing the first line of defense of the innate immune system. Surprisingly, the uptake of vector particles by Kupffer cells not only resulted in their strong activation, but also in their nearly complete disappearance from the liver. Our results suggest that the toxicity of intravenously injected adenoviral vectors may be directly linked to the activation and destruction of Kupffer cells.