Elkhawad A O, Al-Zaid N S, Bou-Resli M N
Department of Pharmacology, Faculty of Medicine, Kuwait University, Safat.
Am J Physiol. 1990 Mar;258(3 Pt 2):R602-7. doi: 10.1152/ajpregu.1990.258.3.R602.
The reactivity of the superficial veins of the camel was investigated in vitro in response to stretch, heat, norepinephrine, and transmural nerve stimulation (TNS). Stretch at 30 degrees C or 37 degrees C produced a maintained tone and phasic contractions of the facial and nasal veins. The developed tone increased significantly with increasing the temperature (from 30 to 45 degrees C), especially in the proximal part of the buccal facial vein. Norepinephrine caused a constrictor response in the facial vein with the proximal part showing a lower maximum. TNS evoked a constrictor response in proximal segment and a dilator response in the more proximal segment of the buccal facial vein. Either responses were blocked by bretylium or tetrodotoxin. Morphological examination of the vasoactive segment of the facial vein showed a thick muscular layer and a valve in the proximal segment of the buccal facial vein. These results show functional variation in the distribution of adrenoceptors in the facial vein. The high-temperature sensitivity of the buccal facial vein suggests that this part could serve as a temperature-sensitive sphincter that diverts cool nasal blood to the brain for selective cooling of the camel brain during heat stress.
在体外研究了骆驼体表静脉对拉伸、热、去甲肾上腺素和跨壁神经刺激（TNS）的反应。在30℃或37℃下拉伸可使面部和鼻静脉产生持续的张力和相位性收缩。随着温度升高（从30℃至45℃），尤其是颊面静脉近端，所产生的张力显著增加。去甲肾上腺素可使面部静脉产生收缩反应，近端部分的最大收缩反应较低。TNS可使颊面静脉近端段产生收缩反应，而在更近端段产生舒张反应。两种反应均被溴苄铵或河豚毒素阻断。对面部静脉血管活性段的形态学检查显示，颊面静脉近端段有一层厚厚的肌肉层和一个瓣膜。这些结果表明面部静脉中肾上腺素能受体分布存在功能差异。颊面静脉对高温的敏感性表明，该部分可作为一个温度敏感括约肌，在热应激期间将凉爽的鼻腔血液分流至脑部，以选择性冷却骆驼的大脑。
