Responses of noradrenergic nerves in rabbit ear‐artery before and after experimental frost‐bite

Experiments were designed to determine the effects of sub‐zero temperatures on the function of the noradrenergic innervation of a peripheral blood‐vessel. The central ear‐artery of the rabbit was used for this purpose. The ear was exposed to temperatures of – 6, –9 or –18 oC in vivo for 15 min. After 1 day (24 h) or 6 days in vivo, the central ear‐artery was dissected free, incubated in [3H]‐noradrenaline (NA) and stimulated in vitro with high potassium (75 mM) for 5 min to evoke release of [3H]‐NA. The release of [3H]‐NA was Ca2+‐dependent. One day after exposure to –6, –9 or –18 CC, increases of 45–57 and 44–72% and a reduction of 12–35% were observed, respectively, in three successive potassium‐evoked NA‐releases. After 6 days in vivo an increase of 30–34% was observed following exposure to –6 oC, while no alteration was observed after exposure to –9 oC. A reduction of 84–89% was recorded after exposure to – 18 oC. Following this exposure to – 18 oC, there was also a great reduction in the evoked release of [3H]‐NA compared with the spontaneous release, whereas this correlation did not change after exposure to – 6 and – 9 oC. The total uptake of [3H]‐NA was unchanged after freezing the tissue at – 6 oC, but was substantially reduced after exposure to –9 and –18 oC. A short period of in vivo restoration (6 days, enhanced the uptake of [3H]‐NA. Rapid thawing, within approximately 3 min, after freezing at – 9 oC (1 day in vivo) resulted in a normal, potassium‐evoked, release of [3H]‐NA and a higher uptake of [3H]‐NA than after a longer, standardized, thawing procedure of approximately 10 min. These results demonstrate that both the evoked and the spontaneous releases of [3H]‐NA from the sympathetic nerves were increased after freezing at moderate freezing temperatures (±– 9 oC), while rapid thawing resulted in a normalization of the potassium evoked released of [3H]‐NA. Exposure to –18 oC reduced both the uptake and release of neurotransmitter. Restoration in vivo for 6 days improved the uptake, but not the release, of [3H]‐NA.