Abstract 17108: Exercised-Induced eNOS-NO Modulation of Microvascular Permeability in Mouse Hindlimb by MicroCT Imaging

Abstract

Introduction: There are controversies as to whether eNOS-derived NO functions as a permeability-increasing or -decreasing factor. These disputes might result from a lack of in vivo imaging system to monitor the dynamic changes of permeability. We hypothesized that microCT (μ CT) imaging would enable noninvasive in vivo spatial, temporal, and quantitative monitoring of permeability in the hindlimb. Methods: To test this hypothesis, we longitudinally monitored micro-molecular leakage in hindlimb ischemic (HLI) models of wild-type (WT, n=12) and eNOS −/− mice (n=12) at rest [sedentary (SED)] or with physiological stimulation [swimming (SW) training] on day 3 and 14. The same animals were subsequently evaluated by specimen μ CT with 20% Bismuth gelatin as a contrast agent for arteriogenesis and macromolecular leakage. Blood flow was assessed by laser Doppler Imaging in another group of mice (n=8/group). Immunohistochemical staining for capillary density was performed in additional mice (n = 4/group). Result: eNOS deficiency altered the pattern of microvascular permeability in the hindlimb. On day 3 in vivo μ CT showed WT-HLI-SED mice had a marked increase of late contrast enhancement (20 min) in the calf region. Swimming training reduced severity. In contrast, eNOS -/- -HLI-SED mice exhibited late enhancement at the site of pre-existing collaterals. Swimming resulted in a large area of increased permeability in the upper calf region. On day 14, eNOS -/- mice showed a shift of extravasation from the thigh to the calf and worsened after swimming compared to remarked recovery in WT mice. Moreover specimen μ CT demonstrated eNOS deletion resulted in bismuth particles leaking outside the vasculature in eNOS-HLI-SED mice and more serious in eNOS-HLI-SW mice while WT mice kept their vascular integrity on day 14. This enhanced leakage in eNOS -/- -HLI-SW mice was associated with decreased angiogenesis and dysfunctional arteriogenesis (increased arterioles with less perfusion). Conclusion: μ CT allowed longitudinally spatial and quantitative monitoring of in vivo permeability in model of murine hindlimb ischemia, and predicted matured arteriogenesis with exercise training and is eNOS-NO dependent.