Microcirculatory adaptation to skeletal muscle transplantation

A standard whole muscle graft, in which all neural and vascular connections with the host tissue are severed, reinnervates and revascularizes spontaneously. The extent to which a standard graft regains structure and function depends largely on the degree and timing of revascularization. Whether the endothelial cells that form the first capillary tubes in a whole muscle graft originate inside or outside of the graft is unknown. Blood vessel growth into a graft proceeds in a centripetal fashion and precedes muscle fiber regeneration. Abnormalities have been observed in the structure of capillaries and of the larger vessels in stable muscle grafts. The ability of the vascular bed in large standard grafts to regulate blood flow in response to twitch contractions is impaired, as is the ability of arterioles in small grafts to respond following topical application of norepinephrine and adenosine. The dysfunction of arterioles in standard grafts may be related to structural abnormalities. Blood flow at rest and in response to twitch contractions in stable grafts in which nerves and blood vessels are left intact is not different from control muscles. The following should be investigated to provide further insights into the revascularization process in regenerating skeletal muscle and the structure and function of the microcirculation in stable muscle grafts: the origin of mitotic endothelial and smooth muscle cells; the stimulus for blood vessel growth; the overall architecture and organization of the vascular bed; the presence or absence of adrenergic innervation of blood vessels; and the development of receptors involved in blood flow regulation in muscle grafts.