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 degrees C 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 Ca(2+)-dependent. One day after exposure to -6, -9 or -18 degrees C, 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 degrees C, while no alteration was observed after exposure to -9 degrees C. A reduction of 84-89% was recorded after exposure to -18 degrees C. Following this exposure to -18 degrees C, 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 degrees C. The total uptake of [3H]-NA was unchanged after freezing the tissue at -6 degrees C, but was substantially reduced after exposure to -9 and -18 degrees C. A short period of in vivo restoration (6 days, enhanced the uptake of [3H]-NA.(ABSTRACT TRUNCATED AT 250 WORDS)