Vascularization of the Arteriovenous Loop in a Rat Isolation Chamber Model-Quantification of Hypoxia and Evaluation of Its Effects.

The aim of this study was to analyze the three-dimensional distribution of hypoxia in the arteriovenous (AV) loop model in rats, by examining the distribution of hypoxia-inducible factor-1 alpha (HIF-1α). AV loops were created from the femoral artery and vein of male Lewis rats and an interpositional graft from the contralateral femoral vein. This AV fistula was embedded in a fibrin-filled isolation chamber and subcutaneously implanted into the thigh. The specimens were harvested after 7 days (n = 4), 10 days (n = 5), and 14 days (n = 4). The fibrin clots were stained for lectin, HIF-1α, and ectodysplasin 1 (ED1). The distribution of positive and negative cells was analyzed in three dimensions and at different points in time. The HIF-1α-positive rate increased from the proximity of the central vessel to the distant regions. From day 7 to 10, we noted a decrease in the HIF-1α-positive rate in the proximity of the vessels and an increase in the periphery. A global decrease in positive cells was seen at day 14. HIF-1α and macrophage (ED1) double staining indicated that macrophages accounted for a significant fraction of the cells. Double staining for endothelium (with lectin) demonstrated that no HIF-1α was detectable in well-vascularized areas. In the AV loop model, the HIF-1α-positive cell distribution is highly related to the vascularization process. The onset of rapid vessel outgrowth follows the increase of the HIF-1α rate closely, indicating that HIF-1α may be a driving force for vascularization.