Early inducible nitric oxide synthase 2 (NOS 2) activity enhances ischaemic skin flap survival

A functional skin-flap model of angiogenesis in the mouse was utilized to investigate ischaemic flap survival/angiogenesis whilst under pharmacological or genetic inhibition of nitric oxide synthase (NOS). In this model, the epigastric artery was cauterized. Following a five-day angiogenic period an abdominal skin-flap supplied by the pre-existing epigastric artery was raised and resutured. After a further six days the outcome was determined by measuring the area of living skin-flap that was sustained by new vessel growth around the cauterized artery. Both pharmacological [ S-methyl-isothiourea (SMT) given via i.p. injection for the five-day angiogenic period] and genetic inhibition of NOS 2 (using NOS 2-/- mice) caused a similar and significant fall in flap survival compared to saline-treated wild-type mice ( P < 0.05). Delaying pharmacological NOS 2 inhibition for two days post-arterial cauterization increased flap survival in wild-type mice to that of saline-treated controls, whilst treating wild-type mice with SMT for only the first three days of angiogenesis produced a significant decrease in flap survival, similar to that of five-day SMT-treated wild types. Immunoreactivity for NOS 2 in NOS 2-/- knockout mice was absent in both pedicles and skin-flaps, whilst mast cells from both the pedicle and the skin-flap stained positively for NOS 2 in wild-type mice. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF 2) immunoreactivity was also strongly evident in mast cells of both wild-type and NOS 2-/- mice at both sites. These results point to a significant role for NOS 2 in promoting wound healing/angiogenesis in its early stages.