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Objective: To determine if insulin‐mediated hyperemia is partially dependent on local muscle oxygen concentration. Methods: Sprague–Dawley rats were anesthetized, and the extensor digitorum longus (EDL) was reflected onto an inverted microscope. Intravital video microscopy sequences were recorded during baseline and hyperinsulinemic euglycemia. The muscle was reflected over a glass stage insert (Experiment 1a and 1b), or over a gas exchange chamber (Experiment 2), and microvascular capillary blood flow was recorded during sequential changes (7%–12%–2%–7%) of oxygen (O2) concentration. Blood flow was measured by the red blood cell supply rate (SR) in number of cells per second. All animal protocols were approved by Memorial University's Institutional Animal Care Committee. Results: In Experiment 1a, SR increased from 8.0 to 14.0 cells/s at baseline to euglycemia (p =.01), while no significant SR variation was detected after performing a sham hyperinsulinemic euglycemic clamp (Experiment 1b). In Experiment 2, SR decreased at 12% O2 and increased at 2% O2, compared to 7% O2, under both experimental conditions. Magnitude of SR responses to oxygen oscillations during euglycemia were not different to those at baseline at each O2 concentration (p >.9). Conclusions: Our results suggest that increased blood flow observed in response to insulin is eliminated if tissue oxygen microenvironment is fixed at a given oxygen concentration. [ABSTRACT FROM AUTHOR]

Objectives The objective of this study was to investigate the role of the SNS on hemodynamic, metabolic, and microvascular alterations in a rat model of HFD-induced MS with salt supplementation. Methods In total, 40 adult male Wistar rats were fed normal chow ( n = 10) or a HFD ( n = 30) for 20 weeks. Thereafter, the HFD group received the centrally acting sympatho-modulatory drugs clonidine (0.1 mg/kg) or rilmenidine (1 mg/kg) or vehicle ( n = 10/group) orally by gavage. FCD was evaluated using intravital video microscopy, and the SCD was evaluated using histochemical analysis. Results The pharmacological modulation of the SNS induced concomitant reductions in SBP, HR and plasma catecholamine levels. These effects were accompanied by a reversal of functional and structural capillary rarefaction in the skeletal muscle in both treated groups and an increase in SCD in the left ventricle only in the rilmenidine group. Improvement of the lipid profile and of glucose intolerance was also obtained only with rilmenidine treatment. Conclusions Modulation of sympathetic overactivity results in the reversal of microvascular rarefaction in the skeletal muscle and left ventricle and improves metabolic parameters in an experimental model of MS in rats. [ABSTRACT FROM AUTHOR]

Abstract: Aims: We investigated the function of major superoxide-generating enzymes after remote ischemic preconditioning (IPC) and hepatic ischemia–reperfusion (IR), with the specific aim of assessing the importance of the most relevant NADPH oxidase (NOX) isoforms, NOX2 and NOX4, in the mechanism of action. Main methods: 60-min partial liver ischemia was induced in Sprague–Dawley rats in the presence or absence of remote IPC (2×10-min limb IR), and hepatic microcirculatory variables were determined through intravital video microscopy and lightguide spectrophotometry during reperfusion. Inflammatory enzyme activities (myeloperoxidase (MPO) and xanthine oxidoreductase (XOR)), cytokine production (TNF-α and HMGB-1), liver necroenzyme levels (AST, ALT and LDH) and NOX2 and NOX4 protein expression changes (Western blot analysis) were assayed biochemically. Key findings: In this setting, remote IPC significantly decreased the IR-induced hepatic NOX2 expression, but the NOX4 expression remained unchanged. The remote IPC provided significant, but incomplete protection against the leukocyte–endothelial cell interactions and flow deterioration. Hepatocellular damage (AST, ALT and LDH release), cytokine levels, and XOR and MPO activities also diminished. Significance: Remote IPC limited the IR-induced microcirculatory dysfunction, but the protective effect did not affect all NOX homologs (at least not NOX4). The residual damage and inflammatory activation could well be linked to the unchanging NOX4 activity. [Copyright &y& Elsevier]

Objective Cells require energy to carry out their functions and they typically use oxidative phosphorylation to generate the needed ATP. Thus, cells have a continuous need for oxygen, which they receive by diffusion from the blood through the interstitial fluid. The circulatory system pumps oxygen-rich blood through a network of increasingly minute vessels, the microcirculation. The structure of the microcirculation is such that all cells have at least one nearby capillary for diffusive exchange of oxygen and red blood cells release the oxygen bound to hemoglobin as they traverse capillaries. Methods This review focuses first on the historical development of techniques to measure oxygen at various sites in the microcirculation, including the blood, interstitium, and cells. Results Next, approaches are described as to how these techniques have been employed to make discoveries about different aspects of oxygen transport. Finally, ways in which oxygen might participate in the regulation of blood flow toward matching oxygen supply to oxygen demand is discussed. Conclusions Overall, the transport of oxygen to the cells of the body is one of the most critical functions of the cardiovascular system and it is in the microcirculation where the final local determinants of oxygen supply, oxygen demand, and their regulation are decided. [ABSTRACT FROM AUTHOR]

Please cite this paper as: Al-Khazraji BK, Novielli NM, Goldman D, Medeiros PJ, Jackson DN. A simple 'Streak Length Method' for quantifying and characterizing red blood cell velocity profiles and blood flow in rat skeletal muscle arterioles. Microcirculation 19: 327-335, 2012. Abstract Objectives: To develop a valid experimental method for quantifying blood flow in continuously branching skeletal muscle arterioles, and to derive an empirical relationship between velocity ratio ( VMax/ VMean) and arteriolar diameter. Methods: We evaluated arteriolar trees using IVVM of rat gluteus maximus muscle and developed a method to acquire single fluorescent-labeled RBC velocities across arteriolar lumens to create velocity profiles. These data were used to calculate the blood flow for 37 vessel segments (diameters: 21-115 μm). Results: Mass balance at arteriolar bifurcations had 0.6 ± 3.2% error. Velocity ratios ranged from 1.35 to 1.98 and were positively correlated with diameter ( p < 0.0001), and VRBC profiles were blunted with decreasing diameter. Conclusions: We present a means for quantifying blood flow in continuously branching skeletal muscle arterioles. Further, we provide an equation for calculating velocity ratios based on arteriolar diameter, which may be used by others for blood flow calculations. [ABSTRACT FROM AUTHOR]

Red blood cell oxygen saturation (SO2) is an important indicator of oxygen supply to tissues in the body. SO2 can be measured by taking advantage of spectroscopic properties of hemoglobin. When this technique is applied to transmission microscopy, the calculation of saturation requires determination of incident light intensity at each pixel occupied by the red blood cell; this value is often approximated from a sequence of images as the maximum intensity over time. This method often fails when the red blood cells are moving too slowly, or if hematocrit is too large since there is not a large enough gap between the cells to accurately calculate the incident intensity value. A new method of approximating incident light intensity is proposed using digital inpainting. This novel approach estimates incident light intensity with an average percent error of approximately 3%, which exceeds the accuracy of the maximum intensity‐based method in most cases. The error in incident light intensity corresponds to a maximum error of approximately 2% saturation. Therefore, though this new method is computationally more demanding than the traditional technique, it can be used in cases where the maximum intensity‐based method fails (eg, stationary cells), or when higher accuracy is required. This study presents a novel use of digital image inpainting to estimate the intensity of light incident on red blood cells in intravital microscopy images to calculate red blood cell hemoglobin oxygen saturation. The new approach allows for the saturation measurement of stationary cells, which could not be accomplished with the traditional video‐based approach. [ABSTRACT FROM AUTHOR]