Vasomotion in critically perfused muscle protects adjacent tissues from capillary perfusion failure

We analyzed the incidence and interaction of arteriolar vasomotion and capi llary flow motion during critical perfusion conditions in neighboring perip heral tissues using intravital fluorescence microscopy. The gracilis and se mitendinosus muscles and adjacent periosteum, subcutis, and skin of the lef t hindlimb of Sprague-Dawley rats were isolated at the femoral vessels. Cri tical perfusion conditions, achieved by stepwise reduction of femoral arter y blood flow, induced capillary flow motion in muscle, but not in the perio steum, subcutis, and skin. Strikingly, blood flow within individual capilla ries was decreased (P < 0.05) in muscle but was not affected in the periost eum, subcutis, and skin. However, despite the flow motion-induced reduction of muscle capillary blood flow during the critical perfusion conditions, f unctional capillary density remained preserved in all tissues analyzed, inc luding the skeletal muscle. Abrogation of vasomotion in the muscle arteriol es by the calcium channel blocker felodipine resulted in a redistribution o f blood flow within individual capillaries from cutaneous, subcutaneous, an d periosteal tissues toward skeletal muscle. As a consequence, shutdown of perfusion of individual capillaries was observed that resulted in a signifi cant reduction (P < 0.05) of capillary density not only in the neighboring tissues but also in the muscle itself. We conclude that during critical per fusion conditions, vasomotion and flow motion in skeletal muscle preserve n utritive perfusion (functional capillary density) not only in the muscle it self but also in the neighboring tissues, which are not capable of developi ng this protective regulatory mechanism by themselves.