The effect of experimental frost‐bite on the responses of the rabbit ear‐artery to adrenergic and electrical stimulation

Publisher Website
Google Scholar
Abstract
The aim of the present investigation was to study the effect of sub‐zero temperatures on the adrenergic activated, smooth muscle‐contraction of a peripheral blood‐vessel. The central ear‐artery of the rabbit was used for this purpose. The artery was stimulated to contractin vitroby activation of phentolamine sensitive, post‐junctional, a‐adrenoceptors by use of noradrenaline, or by noradrenaline released from noradrenergic nerves in the blood‐vessel following electrical field stimulation. The effect of freezing the tissuein vivofor 15 min at sub‐zero temperatures (–4, ‐ 6 and – 9oC) was studiedin vitro.Exposure to – 4 and – 6oC did not alter the apparent affinity (ED60) of noradrenaline significantly, when measured immediately, or 2 or 6 days after exposure. The maximal response to noradrenaline was reduced by approximately 54, 74 and 100% following exposure to –4, – 6 and – 9oC, respectively. The response was completely restored after 2 and 6 days of regenerationin vivofollowing exposure to – 6oC, whereas the response after exposure to – 9oC was restored by only about 8 and 30% after 2 and 6 days regeneration, respectively. The maximal response to electrical field stimulation, which was completely inhibited by tetrodotoxin and phentolamine, was reduced by approximately 92% after exposure for 15 min to –4 and – 6oC, while it was completely inhibited after exposure to – 9oC. The response was restored by only 15–20% following 2 and 6 daysin vivoafter exposure to – 6oC. No regeneration of the contraction induced by the electrical stimulation was observed after 2 or 6 days following exposure to –9oC. The results of the present study suggest that noradrenergic nerves in the central ear‐artery of the rabbit are more sensitive to subzero temperatures than are the post‐junctional, noradrenergic α‐receptors and the smooth muscle of the blood‐vessel. The damage induced by freezing appeared to be both time and temperature dependent and there was only limited restoration of the nervous function 6 days after severe freezing.