ABSTRACT
Intestinal circulation is important in its own right due to its immense capacity for demand-related regulation of blood flow. As such, intestinal blood flow is influenced by well-developed neural regulatory mechanisms involving extrinsic nerves (sympathetic and sensory) as well as the intrinsic submucosal plexus of the enteric nervous system. The submucosal nerves subserve a vasodilator role as illustrated by studies on postprandial hyperaemia of the small intestine. However, the activity of the intrinsic nerves can be modified by extrinsic sympathetic nerves which act as a “brake” and serve to divert blood away from the intestine, when required. Although the mechanisms underlying sympathetic nerve transmission in the intestinal vessels have been a focus of study for the past two decades, it is only in the last decade that our understanding of mechanisms underlying responses to stimulation of sensory and intrinsic nerves has increased. It is clear from recent work that endothelial paracrine factors, the electrical connectivity between endothelium and vascular smooth muscle, a direct action on the vascular smooth muscle plus the interaction between vasomotor pathways are all involved in the neural regulation of vascular tone of the intestinal vessels. Despite substantial progress, we still do not know which particular subclasses of nerves are involved in normal physiological responses, nor do we have much understanding of changes in neural control resulting from diseased states such as diabetes, which is associated with widespread neuropathy and dysfunction of the enteric nervous system. Evaluating the roles of intrinsic and extrinsic nerves is an essential step towards understanding the neural regulation of intestinal arterioles in normal and pathophysiological states. The next decade promises to be both exciting and challenging as we piece together the jigsaw of neural control of intestinal vessels.
