MacDonald P H, Dinda P K, Beck I T
Department of Medicine, Queen's University, Kingston, Ontario, Canada.
Gastroenterology. 1992 Jul;103(1):57-64. doi: 10.1016/0016-5085(92)91095-l.
It was previously shown that the vasoconstrictory response to hypotension was similar in the mucosa of the small bowel and the colon but was significantly higher in the muscularis of the latter than that of the former. To understand the mechanism of this differential response of the muscularis of the small bowel and the colon, the present study investigated the effect of an angiotensin II inhibitor (saralasin) on the hypotension-induced vasoconstriction of the mucosa and the muscularis of these two locations of the gastrointestinal tract. Dogs were used. Hypotension was induced by hemorrhage to reduce blood pressure by 40 mm Hg. Blood flow was measured by 15-microns radiolabeled microspheres. Saralasin was infused intravenously for 20 minutes at a rate of 0.05 mg.kg-1 bolus followed by 1 microgram.kg-1.min-1. Saralasin had no effect on the basal blood flow of the mucosa or the muscularis of the small bowel or on the hypotension-induced vasoconstriction of these two layers of the small bowel. In contrast, saralasin decreased blood flow to the mucosa (-28%; P less than 0.001) and increased blood flow to the muscularis (+140%; P less than 0.001) of the colon under basal conditions and also reduced the hypotension-induced vasoconstriction of the colonic muscularis (P less than 0.01). These and supplementary data indicate that there is a difference between the small bowel and the colon in local activity of vascular angiotensin system and that this system is most active in the colonic muscularis where it plays a significant role in the vasoconstrictory response to hypotension.
先前的研究表明，小肠和结肠黏膜对低血压的血管收缩反应相似，但结肠肌层的反应明显高于小肠肌层。为了解小肠和结肠肌层这种差异反应的机制，本研究调查了血管紧张素II抑制剂（沙拉新）对胃肠道这两个部位黏膜和肌层低血压诱导的血管收缩的影响。实验用犬。通过出血诱导低血压，使血压降低40 mmHg。用15微米放射性标记微球测量血流量。沙拉新以0.05 mg·kg-1推注，随后以1微克·kg-1·min-1的速率静脉输注20分钟。沙拉新对小肠黏膜或肌层的基础血流量以及小肠这两层低血压诱导的血管收缩均无影响。相比之下，在基础条件下，沙拉新使结肠黏膜血流量减少（-28%；P<0.001），使结肠肌层血流量增加（+140%；P<0.001），并且还降低了结肠肌层低血压诱导的血管收缩（P<0.01）。这些及补充数据表明，小肠和结肠在血管紧张素系统的局部活性方面存在差异，且该系统在结肠肌层最为活跃，在对低血压的血管收缩反应中起重要作用。
