Blood flow distribution, villous tissue osmolality and fluid and electrolyte transport in the cat small intestine during regional hypotension

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Abstract
The hemodynamic reactions of the parallel coupled vascular circuits in the cat small intestine was studied before, during and after a 2 h period of intestinal hypotension induced by lowering the intestinal arterial inflow pressure by partially occluding the superior mesenteric artery during a continuous stimulation of the postganglionic nerves to the small intestine. Fluid and electrolyte transport and villous tissue osmolality were measured. A histological examination of biopsies taken during and after the hypotensive period was also carried out. The animals were divided into 2 groups (undamaged and damaged) according to the histological appearance of the intestinal mucosa. The hemodynamic reactions were investigated with a method that made it possible to study total intestinal, absorptive site (villous), nonabsorptive site (crypt) and muscle layer blood flow. Total intestinal blood flow was lower in the damaged group than in the undamaged group during the arterial hypotension. Absorptive site blood flow was similar in the 2 groups. A significantly larger fraction of blood flow was distributed to the villi in the damaged group. Absorptive site red blood cell flow was only slightly reduced despite the development of mucosal ulcerations. These findings are discussed in relation to the pathophysiology of the mucosal lesions. Net fluid, net Na and net Cl absorption was unchanged in the undamaged group; in the damaged group a marked decrease was observed after lowering the perfusion pressure. The decrease in net Na absorption was due to a decrease in the lumen to tissue transport of Na. The capacity of the small intestine to absorb fluid and electrolytes is unchanged even during a marked arterial hypotension with a pronounced decrease of intestinal blood flow as long as no mucosal damage has developed.