CAPILLARY ULTRASTRUCTURE AND FUNCTIONAL CAPILLARY DENSITY

We briefly summarize our findings on alterations in capillary structur e in skeletal muscle and heart in response to up to 30 min of ischemia . In frog sartorius muscle, reactive hyperemia was absent in atrophy. Increased spatial heterogeneity of red cell velocity in individual cap illaries was observed, as were increases in the percentage of capillar ies with damaged endothelium and white cell volume density in capillar ies. Examination of the effect of aging on the response of the vascula r bed to 30 min ischemia in extensor digitorum longus muscle of Fisher 344 rats suggested that the lack of postischemic hyperemia and struct ural alterations in frog muscle were related to disuse rather than agi ng per se. However, the specific study of disuse in rat extensor digit orum longus muscle after chronic application of tetrodotoxin revealed both capillary damage and a postischemic hyperemic response. It sugges ted an effect of the degree of tissue deterioration on the hyperemic r esponse after short-term disuse in rat muscle, compared to longer-term atrophy in frog. Morphometric data in isolated rabbit heart suggested a link between microvascular compression as a result of tissue edema and decreased perfusion after 30 min total ischemia.