Myointimal hyperplasia and sympathetic reinnervation following local cold injury and rapid rewarming in the rabbit central ear artery

Background: Functional and pathological improvements following rapid rewarm ing in 42 degreesC water was compared with alterations following slow thawi ng at room temperature (22 degreesC) after frostbite (-9 degreesC, 15 minut es) in vivo of the rabbit central ear artery. Methods: Following two to ten weeks of in vivo regeneration, vascular segme nts were tested in vitro. Maximal and dose-dependent isometric contractions were induced by, exogenous noradrenaline. Sympathetic nerves in the vascul ar wall were stained with glyoxylic acid. Vascular ring segments were stain ed with haematoxylin and eosin. Results: Following slow thawing, the total uptake, the K+ evoked and the sp ontaneous release of [H-3]no-radrenaline in the sympathetic nervous si,stei n were strongly reduced two weeks after freezing, with a subsequent increas e to control level within 3-4 weeks. After rapid rewarming the total uptake , the spontaneous release and the K+ evoked release of [H-3]noradrenaline c ommenced earlier such that after ten weeks the level was twice as high as f ollowing slow rewarming. The glyoxylic acid induced catecholamine fluoresce nce in sympathetic nerves, revealed an earlier regeneration after rapid rew arming. Haematoxylin and eosin-stained segments revealed less intimal hyper plasia three to 20 weeks after rapid rewarming than after slow thawing. Conclusion: Rapid rewarming of in vivo frozen arteries in warm water (42 de greesC) did not prevent immediate vasoparalysis and degeneration of sympath etic nerves. However, nerve regeneration occurred earlier and with higher t issue nerve densities as compared to tissue that had been slowly rewarmed. Myointimal hyperplasia was less pronounced after rapid rewarming. Abnormal sympathetic nerve function and myointimal hyperplasia, as observed in this study, may contribute to a greater understanding of sequelae in the human b ody following frostbite.