Intramural blood flows and flow distribution in the feline small intestine during arterial hypotension

The vascular reactions of the parallel-coupled vascular sections of the small intestine were studied during hypotension at two different levels of intestinal arterial inflow pressure, using a 85Kr elimination technique. The regional hypotension was accomplished by partially occluding the superior mesenteric artery with a clamp and maintained for 2 h. At the higher level (50-55 mmHg) total intestinal blood flow decreased but not to the same relative extent as blood pressure due to the autoregulatory capacity of the intestinal vascular bed. The flow autoregulation was also reflected in a decreased blood flow resistance. The distribution of blood to the muscularis and mucosa-submucosa layer, respectively, did not change significantly during or after hypotension as compared to the prehypotensive level, since the relative flow decrease was the same in the mucosa-submucosa and in themuscularis. At the lower arterial pressure level (30-35 mmHg) a more marked decrease of intestinal blood flow and flow resistance was observed as compared to the experiments performed at the 50-55 mmHg pressure level. Moreover, muscularis blood flow was relatively more decreased than blood flow in the mucosa-submucosa implying the fraction of total blood flow diverted to the muscularis was significantly decreased. Despite this redistribution of blood flow, a histological damage was apparent only in the mucosa, particularly at the villous tips.