Effect of stimulation frequency on angiogenesis and gene expression in ischemic skeletal muscle of rabbit

To examine the comparative effects of different frequencies of electrical stimulation (ES) on angiogenesis and gene expression, New Zealand white rabbits with femoral artery ligation in one hindlimb and electrode implantation on the sciatic nerve of the same hindlimb were randomly assigned to 4 groups: control group, 1 Hz group, 10 Hz group, and 40 Hz group. The ES procedure involved 5 min stimulation, followed by 5 min rest, repeated 8 times daily for 4 consecutive weeks. The resting blood flow (RBF) was measured via the microspheres technique. Collateralization was evaluated by immunohistochemistry. Angiogenic factors were analyzed by real-time RT-PCR. Both RBF and capillary density were significantly increased in the 10 Hz and 40 Hz groups, but were not changed in the 1 Hz group. Vascular endothelial growth factor (VEGF) mRNA was highest in the 40 Hz group. Hypoxia-inducible factor 1 alpha (HIF-1 alpha) mRNA was significantly elevated only in the 40 Hz group. VEGF receptor fetal liver kinase 1 (Flk-1) mRNA was upregulated equally in the 10 Hz and 40 Hz groups, but fibroblast growth factor 2 (FGF-2) mRNA did not change in any group. Our results suggest that the optimal frequency of ES for angiogenesis is within the 10-40 Hz range.