Laser-Doppler blood flowmetry of intestinal mucosal hyperemia induced by glucose and bile

To determine whether the functional hyperemia evoked by solute transport is confined to the intestinal mucosa or whether blood flow increases throughout the bowel wall, we measured blood flow in the mucosa and muscularis-serosa with laser-Doppler velocimetry. Ileal loops were vascularly isolated in pentobarbital sodium-anesthetized dogs. Total blood flow to the loop was measured electromagnetically, while blood flow in the superficial mucosa and muscularis-serosa was monitored by laser-Doppler velocimetry. Perfusion pressures and arteriovenous oxygen difference were also recorded continuously. When a mixture of 5% bile and glucose was placed in the lumen of the isolated loop, total blood flow and oxygen uptake increased 21 and 62%, respectively. During this hypermetabolic state, laser-Doppler measurements indicated blood flow in the muscularis-serosa fell by 10%, but blood flow in the mucosa increased 42%. These findings with laser-Doppler velocimetry confirm earlier studies in which the radioactive microsphere technique indicated that low-fat, low-protein test meals induce a postprandial hyperemia confined to the mucosal circulation. These findings also demonstrate a metabolic flow-controlling mechanism closely linked to the absorptive process.