Selective vasodilators redistribute intestinal blood flow and depress oxygen uptake

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Abstract
The effects of adenosine and isoproterenol on intestinal O2 consumption are reported. Using the recently developed technique of laser-Doppler velocimetry (LDV), the effects of these 2 agents on regional blood flow were also studied in the canine intestinal mucosa and muscularis. In isolated gut loops perfused at constant blood flow, both vasodilators depressed O2 uptake, but isoproterenol increased Rb extraction while adenosine depressed Rb extraction. Under constant pressure perfusion both dilators depressed O2 uptake but increased total flow. Isoproterenol increased the capillary filtration coefficient (Kf), but adenosine depressed Kf. LDV flowmetry showed adenosine increased muscularis flow and depressed mucosal flow. Both LDV flowmetry and radioactive microspheres showed isoproterenol increased mucosal but depressed muscularis flow. The deleterious effects of isoproterenol and adenosine in depressing intestinal oxygen uptake may be explained by the ability of these agents to selectively vasodilate one of the regional circulations within the gut wall and by a vascular steal mechanism to reduce blood flow in the other vascular bed not as sensitive to the agent in question. The reduction in the regional blood flow depresses the O2 consumption of the gut as a whole. By comparing regional laser-Doppler blood flow data with a simple analog model, the seemingly paradoxical effect of vasodilators in depressing a regional blood flow while increasing total perfusion is explicable by a vascular steal mechanism.

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