Recanalization of the collecting lymphatics in rabbit hind leg

Objective: This study was designed to examine whether mature collecting lymphatics can regenerate in the adult tissue or not. Materials and Methods: The X-ray lymphograms were used to detect network of the collecting lymphatics in rabbit hind leg. Regeneration of the lymphatics was observed after surgical removal of the popliteal lymph node or a part of the popliteal afferent lymphatic. Structure and mechanical properties of the lymphatics were also examined by light and electron microscopes and in vitro functional experiments. Results: One week after removal of the lymph node, only an afferent lymphatic and a deposit of the contrast medium at the popliteal region were observed. Four weeks after the removal, the connection of the afferent and efferent lymphatics at the popliteal region, and collateral lymphatics were present in the leg. Further, 4 weeks after 1-mm excisions of a part of the lymphatic, recanalization was observed between the central and peripheral cut ends of the lymphatic but not after 3- and 10-mm excisions. Endothelial cells and smooth muscle cells could be observed by electron microscope, and contractile proteins, and alpha-smooth muscle actin SM1 and SM2 were immunofluorescently detected in both intact and the regenerated lymphatic walls. In both lymphatics, norepinephrine and acetylcholine induced dose-dependent constriction and dilation of the vessels, respectively. Conclusion: The present study demonstrated that mature collecting lymphatics are able to regenerate in the adult tissues.