Intramural distribution of intestinal blood flow during sympathetic stimulation.

Recent studies indicate that the mucosal circulation of the small intestine possesses more potent local circulatory control mechanisms than the muscularis. Several lines of evidence support this assertion: the absence of reactive hyperemia in the muscularis, the confinement of glucose-induced hyperemia to the mucosal circulation, and the more effective autoregulation of villus blood flow in comparison with total blood flow. Therefore, we postulated that the mucosal circulation would exhibit a more pronounced ability to escape the vasoconstrictor influence of sympathetic nerve stimulation. To test this hypothesis, we used laser-Doppler velocimetry (LDV) to study the effects of perivascular nerve stimulation on blood flow in the muscularis and mucosa of isolated dog intestine. In two series of experiments, we measured total blood flow to a gut loop with an electromagnetic flow probe on the supply artery, while LDV measurements were made either on the mucosa or on the muscularis. Sympathetic stimulation (10 Hz) transiently reduced total blood flow to approximately 10% of control in both studies. Muscularis and mucosal blood flow both reached minimal values. Subsequently, total blood flow and the two regional perfusions exhibited "autoregulatory escape," but the propensity for blood flow to escape from sympathetic vasoconstriction was significantly greater in the mucosa than in the muscularis. These data provide more evidence that, compared with the muscularis, the intestinal mucosa possesses more potent local control mechanisms that oppose neurogenic vasoconstriction.