Effects of adrenomedullin on acute ischaemia-induced collateral development and mobilization of bone-marrow-derived cells

Adrenomedullin exerts not only vasodilatory effects, but also angiogenic effects. In the present study, we investigated the effects of adrenomedullin on collateral formation and circulating bone-marrow-derived cells after acute tissue ischaemia. Bone marrow of 8-10-week-old female C57BL/6J mice was replaced with that from GFP (green fluorescent protein) transgenic mice (GFP mice). At 8 weeks after transplantation, hindlimb ischaemia was induced by resecting the right femoral artery and a plasmid expressing human adrenomedullin (50 mu g) was injected into the ischaemic muscle, followed by in vivo electroporation on a weekly basis. Overexpression of adrenomedullin significantly enhanced the blood flow recovery compared with controls (blood flow ratio, 1.0 +/- 0.2 compared with 0.6 +/- 0.3 respectively, at week 4; P < 0.05) and increased capillary density in the ischaemic leg as determined by anti-CD31 immunostaining of the ischaemic muscle (567 +/- 40 compared with 338 +/- 65 capillaries/mm(2) respectively, at week 5; P < 0.05). There were more GFP-positive cells in the thigh muscle of the mice injected with adrenomedullin than in that of the control mice (29.6 +/- 4.5 compared-with 16.5 +/- 3.3 capillaries/mm(2) respectively, at week 5; P < 0.05). We repeated the same experiments using LacZ-knock-in mice instead of GFP mice, and obtained similar results. These findings suggest that adrenomedullin may augment ischaemia-induced collateral formation with some effects on circulating bone-marrow-derived cells.