doses of DLL4 (500ng/ml and above), the pro-angiogenic effect waslost. Growth factor depleted Matrigel basement membrane plugsimplanted in mouse subcutaneous tissue were vascularized in re-sponse to optimum dose DLL4, with several large caliber vesselscontaining blood cells in them, suggestive of integration into nativecirculation. DLL4 containing pellets also induced vessel formation inthe otherwise avascular mouse cornea.

CONCLUSIONS: DLL4 has potent pro-angiogenic properties atsites of neovascularization in the adult.

Altered inflammation increases intramuscular fataccumulation and impairs skeletal muscleregeneration following ischemic injury in CCR2�/�miceOscar Ochoa MD, Paula, K Shireman MD, Linda M McManus PhDUTHSCSA, The South Texas Veterans Health Care System, SanAntonio, TX

INTRODUCTION: Monocyte chemotactic protein-1 (MCP-1)and its receptor, CCR2, are essential in macrophage chemotaxisand activation, yet their role in muscle regeneration is poorlyunderstood. CCR2�/� mice have normal restoration of perfu-sion and delayed macrophage accumulation post-femoral arteryexcision (FAE). This study evaluated neutrophil accumulationand skeletal muscle regeneration following ischemic injury inCCR2�/� mice.

METHODS: Right FAE was performed on CCR2�/� and wild-type (WT) mice (both on a C57Bl/6J background). Myeloperoxidase(MPO) and lactate dehydrogenase (LDH) activities in muscle lysateswere determined. Light microscopic histomorphometry was used toquantitate muscle fiber size and percent intramuscular fat accumula-tion.

RESULTS: MPO, a marker of neutrophil accumulation, was signif-icantly elevated over baseline at 1 and 3 days post-FAE in CCR2�/�mice and at 1 and 7 days post-FAE in WT mice. Furthermore, MPOlevels were significantly increased in CCR2�/� vs WT mice at day1 (p�0.001). LDH, an indicator of muscle injury and regeneration,was minimal at day 3 post-FAE in both groups and increased there-after. In CCR2�/� mice, LDH was significantly decreased at day 14compared to WT mice (3262�/�382 vs 4667�/�426 U/mg,p�0.004); fiber size was also decreased in CCR2�/� mice (672�/�29 vs 1079�/�58 �m2; p�0.001). In addition to impaired mus-cle fiber regeneration, intramuscular fat accumulation was signifi-cantly higher in CCR2�/� mice compared to WT (18.2�/�3.6 vs3.3�/�0.2%; p�0.003).

CONCLUSIONS: CCR2-dependent events modulate the local,post-ischemic inflammatory microenvironment in skeletal muscle.In the absence of CCR2-mediated inflammation, muscle regenera-tion is impaired in parallel with the intramuscular accumulation ofadipose tissue.

Fetal artery healing: Changes in IL-8 geneexpression may not explain lack of acuteinflammationJean E Hsu MD, Roma Patel BS, Oluyinka O Olutoye MD, PhD,C Wayne Smith MD, Darrell L Cass MDBaylor College of Medicine and Texas Children’s Hospital,Houston, TX

INTRODUCTION: Compared to adults, fetal arteries heal with re-duced inflammation and a lack of late neointimal hyperplasia (NIH)and scar. We hypothesize that reduced fetal NIH results from de-creased neutrophil infiltration and reduced expression of IL-8, aknown neutrophil chemoattractant.

METHODS: A segment of common carotid artery of fetal lambs(n�16; 80-85 days gestation; term�145 days) was injured with apressure-distention, air-dry technique. Blood flow was re-estab-lished; fetuses were returned to the uterus, and harvested at 1(n�5),3(n�6), or 28(n�5) days after injury. The mothers (n�13) under-went the same carotid injury and served as adult controls. At harvest,sections of injured and uninjured carotid arteries were snap frozen(RNA) or paraffin embedded. Leukocyte infiltrate was quantitatedby immunohistochemistry (CD18) and cell-counts. Ovine IL-8 wascloned and IL-8 mRNA levels were determined by quantitative, real-time PCR.

RESULTS: At day 1 and 3 postinjury fetal arteries showed no sig-nificant leukocyte infiltration whereas adult arteries showed markedinfiltration from both the intima and adventitia (Table 1). At day 1after injury, both fetal and adult arteries showed marked upregula-tion of IL-8 mRNA levels compared to uninjured arteries. At day 3,adult arteries showed an 18-fold increase in IL-8 mRNA, whereasfetal arteries showed no significant difference above baseline values(Table 2).

Table 1. Neutrophils/hpfDay 1 Day 3

Adult 63.5�41.2 15.1�7.9Fetus 0.9�0.5 0.8�0.3

p value p�.001 p�.01

Table 2. IL-8 gene expressionDay 1 Day 3

Fetus: uninjured 1.3�10e-5�8.9�10e-6 1.0�10e-4�1.3�10e-4

Fetus: injured 4.1�10e-3�4.8x10e-3 1.6�10e-4�1.1�10e-4p value 237 fold increase; p�.02 n.s.

Adult: uninjured 9.7�10e-5�1.1�10e-4 5.2�10e-6�2.1�10e-6Adult: injured 8.1�10e-3�7.6�10e-3 9.4�10e-5�6.7�10e-5

p value 421 fold increase; p�.007 18 fold increase; �.001

CONCLUSIONS: Compared to those in adults, fetal arteries healwith a striking lack of early neutrophil infiltrate. This lack ofinflammation does not appear to be due to reduced upregulationof IL-8.

S101Vol. 203, No. 3S, September 2006 Vascular Surgery I