Vascular growth factor expression in a rat model of severe limb ischemia

In ischemic tissue hypoxia induces production of vascular growth factors, especially VEGF, which initiate local angiogenesis. Collateralization-or arteriogenesis-occurs at a distance from the ischemic tissue and depends on different growth factors such as FGF-2. A spatial discrepancy in endogenous growth factor production in limb ischemia may have implications for therapeutic angiogenesis. The present study elucidates if such spatial and temporal variation occurs.

A two-staged procedure was performed to generate severe long-lasting limb ischemia in 60 rats. At 1, 7, 28, and 56 days, subgroups were subjected to perfusion assessment with laser Doppler imaging and angiography. Muscle samples and foot skin were gathered to measure growth factor expression and signs of angiogenesis using immunohistochemistry.

There was an early twofold increase (P < 0.05) in both VEGF and FGF-2 levels in distal muscle from the ischemic leg, but no significant rise in the thigh. The concentrations decreased over time with an exception for VEGF in soleus and FGF-2 in anterior tibial muscle, which remained high. An increased capillarity was noted (P < 0.05) in soleus after 28 days, and the number of BrdU-positive ECs was elevated in all ischemic samples at 56 days. Collateral arteries were observed on the angiograms after 7 days.

The results suggest that in limb ischemia any major increase in vascular growth factor production is limited to ischemic tissue. The spatial and temporal distribution patterns of growth factor production are complex and to a great extent influenced by inflammation.