Sympathetic Nervous Control of Intestinal O2 Extraction
All three of the functionally defined series-coupled elements within the intestinal microcirculation respond to sympathetic nerve stimulation: the resistance vessels, the precapillary sphincters which govern the exchange vessels, and the capicitance vessels(1). In our computor model of the intestinal circulation (2,3), oxygen delivery to the intestinal tissues is regulated by arteriolar resistance to blood flow while the precapillary sphincters determine the number of open perfused capillaries; thus they control the diffusion parameters for oxygen (i.e., capillary surface area and mean capillary-to-cell diffusion distance). The model predicts that sympathetic-induced reductions in the density of the perfused capillary bed will depress intestinal oxygen extraction. Therefore, the purpose of this work has been to test that prediction in an animal model. Since oxygen delivery is the product of the arteriovenous oxygen difference (A–V ∆O2) and blood flow, we have studied the effects of norepinephrine infusion and sympathetic stimulation on intestinal oxygen extraction under constant-flow conditions in order to eliminate blood flow as a variable.
KeywordsOxygen Extraction Sympathetic Stimulation Norepinephrine Infusion Sympathetic Nerve Stimulation Perivascular Nerve
Unable to display preview. Download preview PDF.