Regulation of intestinal blood flow with increased intraluminal pressure

To better characterize the mechanisms which regulate intestinal blood flow (IBF), we studied the effects of gradual and rapid increases in intraluminal pressure (LP) in anesthetized canines. Polarographic measurements of hydrogen washout allowed repeated assessment of IBF (ml/min X g) in control (CL) and distended (DL) autoperfused small intestinal loops. In group I (n = 7) graded increases in LP (mm Hg) were produced by saline inflation. In group II (n = 4), IBF was measured before and after intraarterial aminophylline (adenosine blockade); LP was then rapidly raised to 24 mm Hg. IBF was unchanged by time (CL 0.64 +/- 0.24) or gradual distension (DL 0.65 +/- 0.28 at mean maximal LP = 26). Aminophylline did not change IBF at LP = 0. Rapid distension after adenosine blockade was accompanied by immediate increases in IBF (0.96 +/- 0.41, P less than 0.05) and decreased resistance (50 +/- 25% control). IBF is maintained despite gradual increases in luminal pressure. Blockade of adenosine, an intestinal vasodilator, does not inhibit this response; hyperemia associated with rapid distension is not impaired. We conclude that autoregulation of IBF during distension is not accomplished by an adenosine mediated metabolic mechanism.