Biphasic Action of Inducible Nitric Oxide Synthase in a Hindlimb Ischemia Model

We investigated the influence of inducible nitric oxide synthase (iNOS) on acute ischemic injury and chronic angiogenesis. In a hindlimb ischemia model, NO produced by endothelial NO synthase (eNOS) reduces ischemic injury and promotes angiogenesis. However, the effect of the large amounts of NO generated by induced iNOS is unclear. Experimental groups of mice were as follows: (1) wild-type group (Wild), (2) iNOS-knockout group (iNOS-KO), and (3) aminoguanidine-treated wild-type group (Wild + AG), which received aminoguanidine from day 0 to day 3 after ischemia. Acute ischemic injury was evaluated by measuring the plasma CK value and ischemic score. Chronic angiogenesis was evaluated by microangiography and with a non-contact type Doppler blood flowmeter on day 3. Compared with the Wild group (251 ± 34.7 IU/l), the CK value was significantly elevated in the iNOS-KO (497 ± 126.7 IU/l) and Wild + AG (587.2 ± 128.7 IU/l) groups. The ischemic score was significantly increased in the iNOS-KO (92%) and Wild ± AG (66.6%) groups compared with the Wild group (23%). Blood flow was significantly increased in the iNOS-KO group (58.7 ± 15.3%) compared with the Wild (38.1 ± 15.9%) and Wild ± AG (43.5 ± 9.8%) groups in the chronic stage. Microangiography revealed a significantly increased number of blood vessels in the iNOS-KO (0.29 ± 0.02) group compared with the Wild (0.12 ± 0.01) and Wild + AG (0.15 ± 0.02) groups. Our findings indicate that NO generated by iNOS has a biphasic action, reducing acute ischemic injury and inhibiting angiogenesis in the chronic stage.