Rapid and complete recovery of responsiveness to adenosine and norepinephrine by regenerating arterioles of the tibialis anterior muscle of the hamster after in situ autografting

Abstract

Intravital microscopy studies of small bundles of fibers of the extensor digitorum longus muscle grafted onto the hamster cheek pouch revealed a persistent reduction in the responsiveness of regenerated arterioles to vasoactive agents. We tested the hypothesis that the recovery of responsiveness to vasoactive agents by regenerating arterioles within whole, in situ autografted tibialis anterior muscles occurs earlier and more completely than that reported for regenerating arterioles within bundles of fibers of the extensor digitorum longus muscle grafted ectopically to the hamster cheek pouch. The tibialis anterior muscles of Syrian golden hamsters were excised and soaked in bupivacaine (0.75%) for 10 minutes to ensure uniform degeneration of muscle fibers. The tendons were resutured, and the graft became revascularized spontaneously. Fluorescent intravital microscopy was used to measure the responsiveness of 10--40-μm arterioles to topically applied adenosine and norepinephrine at 7, 14, and 30 days after grafting. Nine to 25 arterioles were studied at each time period. Both intravital and light microscopy were used at each time period to characterize the structural development of the microcirculation. We found that the responsiveness of regenerated arterioles returned to control values for topically applied norepinephrine by 14 days and for adenosine by 30 days. Light microscopy showed regenerated blood vessels in the center of the grafts early in the second week after grafting. The structure of the microcirculation at 7 days was characterized by a plexiform microvascular pattern, long spiderlike capillaries, and arterioles and venules that had irregular walls and an irregular branching pattern. Rhodamine-labeled albumin extravasated spontaneously. The 14-day grafts had a more linear capillary pattern, and the arterioles and venules often contained loops that had circular flow patterns. By 30 days, a parallel capillary structure had developed, no vascular loops were present, and the arteriolar-venular pattern was nearly normal. We conclude that recovery of responsiveness to vasoactive agents by regenerating arterioles within whole, in situ autografted tibialis anterior muscles occurs earlier and more completely than that reported for regenerating arterioles within bundles of fibers of the extensor digitorum longus muscle grafted ectopically to the hamster cheek pouch. These results suggest that the intactness of the microcirculation at the time of initiation of regeneration and the local environment may have substantial effects on the nature and extent of regeneration.