Recovery of blood flow regulation in microvascular resistance networks during regeneration of mouse gluteus maximus muscle

Abstract

Skeletal muscle regenerates after injury, however the recovery of its microvascular supply is poorly understood. We injured the gluteus maximus muscle in mice aiming to investigate the recovery of blood flow regulation in microvascular resistance networks. We hypothesized that blood flow regulation recovers in concert with myofibre regeneration. Microvascular perfusion ceased within 1day post injury and was restored at 5days coincident with the appearance of new myofibres; however, the resistance network was dilated and unresponsive to vasoactive agents. Spontaneous vasomotor tone, endothelium-dependent dilatation and adrenergic vasoconstriction increased at 10days in concert with myofibre regeneration. Vasomotor control recovered at 21days, when regenerated myofibres matured and active force production stabilized. Functional vasodilatation in response to muscle contraction recovered at 35days. Physiological integrity of microvascular smooth muscle and endothelium recovers in parallel with myofibre regeneration. Additional time is required to restore the efficacy of signalling between myofibres and microvascular networks controlling their oxygen supply. Myofibre regeneration after skeletal muscle injury is well-studied, although little is known about how microvascular perfusion is restored. The present study aimed to evaluate the recovery of blood flow regulation during skeletal muscle regeneration. In anaesthetized male C57BL/6J mice (aged 4 months), the gluteus maximus muscle (GM) was injured by local injection of barium chloride solution (1.2%, 75μL). Functional integrity of the resistance network was evaluated at 5, 10, 21 and 35 days post-injury vs. Control by measuring internal diameter of feed arteries, first-, second- and third-order arterioles supplying the GM using intravital microscopy. The resting diameters of all branch orders were significantly greater (P<0.05) than Control at 5 and 10days and recovered to Control by 21days, as did spontaneous vasomotor tone. Vasodilatation to ACh and vasoconstriction to phenylephrine (10-9 to 10-5 m) were absent at 5days, increased at 10days and recovered to Control by 21days; reactivity improved in a distal-to-proximal gradient. Across branch orders, functional vasodilatation to single tetanic contraction (100Hz, 500ms) and to rhythmic twitch contractions (4Hz, 30s) was impaired at 5days, improved through 21days and was not different from Control at 35days. Peak force development (g) was 60% of Control at 10days and recovered by 21days. Diminished vasomotor tone during the initial stages of regeneration promotes tissue perfusion as myofibre recovery begins. Recovery of tone and vasomotor responses to agonists occur in concert with myofibre regeneration. Delayed recovery of functional vasodilatation indicates that additional time is required to restore signalling between contracting myofibres and their vascular supply.