Abstract
Objective:To establish the time course and extent of remodeling of terminal microcirculation in ischemic rat skeletal muscle during prolonged low flow that does not lead to inflammation. Methods:One common iliac artery was ligated vialaparotomy in adult Sprague-Dawley rats and extensor digitorum longus (EDL) muscles removed at intervals (1, 2, and 5 weeks) postsurgery. Serial frozen EDL sections were stained to show capillaries (alkaline phosphatase), cell proliferation (antibody to proliferating cell nuclear antigen [PCNA]), terminal microvessels (antibodies to α-smooth muscle actin (α-SMA) or endothelial nitric oxide synthase [eNOS]), and macrophages (antibodies to infiltrating and resident macrophages). Total muscle eNOS protein was quantified by standard Western blotting techniques. Results:Capillary proliferation was very limited in ischemic EDLs, with a modest 12% increase in the capillary/fiber ratio after 5 weeks, preceded at 2 weeks by increased numbers of PCNA-positive nuclei at capillary sites. There was no muscle necrosis or evidence of inflammation, based on macrophage staining. The number of terminal microvessels that were positive for α-SMA and <10 µm in diameter was fewer in ischemic EDLs at all time points, whereas the number of larger positive vessels was unchanged. eNOS-positive vessels <10 µm in diameter were stained similarly throughout ischemic muscles as the controls, and showed a similar increase in vessel/fiber ratio as the capillaries. The total eNOS protein level was similar to that in controls in ischemic EDLs after 1 and 2 weeks, but was 28% lower after 5 weeks. Conclusions:Prolonged, moderate flow reduction to skeletal muscles does not necessarily lead to inflammation or extensive capillary growth. Based on eNOS staining, the terminal microcirculation remains intact, but the loss of α-SMA immunoreactivity may indicate remodeling involving the “deinvestment” of microvessels by smooth muscle. Microcirculation(2003) 10,179–191. doi:10.1038/sj.mn.7800183