Targeted disruption of the nitric oxide synthase 2 gene protects against ischaemia/reperfusion injury to skeletal muscle

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Abstract
To provide definitive insight into the complicated roles of the nitric oxide synthase (NOS) enzymes in ischaemia/reperfusion (I/R) injury of skeletal muscle, experiments were undertaken in mice with targeted disruption of the inducible NOS (NOS‐2 KO) isoform, compared with the wild‐type mouse strain. The degree of I/R injury in the NOS‐2 KO mice was attenuated relative to that in the wild‐type strain. After 70 min of ischaemia (24 h reperfusion), nitroblue tetrazolium (NBT) staining of skeletal muscle showed significant necrosis (40%) in wild‐type mice, whilst in NOS‐2 KO mice, ischaemia could be prolonged to 90 min before significant necrosis (38%) was apparent. Specific enzyme activities of the mitochondrial respiratory chain enzymes, measured in skeletal muscle homogenates, suggested that direct inhibition of the enzymes is not causal in the I/R injury. Immunohistological examination of skeletal muscle for NOS‐2 showed its induction selectively in mast cells. In vitro experiments using bone marrow‐derived mast cells showed that NOS‐2 induction was associated with increased degranulation of mast cells. These findings suggest that NO generated by induction of NOS‐2 has a deleterious effect in I/R injury of skeletal muscle and that NO exerts its damaging effect through factors released by degranulation of mast cells. Copyright © 2001 John Wiley & Sons, Ltd.