ENOS‐derived NO promotes microvascular hyperpermeability in ischemia‐reperfusion (I‐R) njury

Abstract

The role of NO in I-R injury is controversial. We tested the hypothesis that eNOS-derived NO plays a significant role in microvascular hyperpermeability in I-R. We induced ischemia for 2-h in cremaster muscles of wild-type (eNOS+/+) and eNOS −/− mouse knockout (KO) mice, and reperfused them for 1−h. We performed two experimental protocols. 1) We evaluated integrated optical intensity (IOI, an index of permeability) of FITC-dextran-70 kDa by digital image analysis. I-R increased net peak IOI significantly in wild-type muscle (2 ± 1 to 68.5 ± 21.3 units; mean ± SE), while I-R impact on permeability was reduced in muscles of KO mice (2 ± 1 vs. 16.4 ± 3.1 units). 2) We measured NO concentration with a NO-electrode near arterioles (40–50 μm diameter). We administered ACh (10 μM, 5-min) topically to the cremaster before and after I-R period. Interestingly, ACh stimulated similar periarteriolar net NO production in cremaster of eNOS+/+ (baseline 246 ± 116 to 502 ± 235 nM; p<0.05, paired t-test) and eNOS −/ − mice (baseline 341 ± 228 to 619 ± 354 nM; p<0.05). ACh-stimulated NO production was reduced after I-R in wild-type and KO mice (372 ± 193 to 451 ± 188; 187 ± 61 to 240 ± 72 nM, respectively; p<0.05). Our data support the hypothesis that eNOS- derived NO plays an important role in microvascular hyperpermeability in I-R. We also demonstrate that ACh stimulates NO production from other NOS isoforms in mouse cremaster muscle (supported by 5RO1 HL70634).