Abstract
To test whether extracellular adenosine participates in the local regulation of intestinal blood flow during nutrient absorption, the serosa of the jejunum was continuously suffused with adenosine deaminase (7 μg protein/ml) or theophylline (10-4 M) in Ringerʼs solution. Using video microscopy, blood flow was calculated in submucosal arterioles from diameter and red cell velocity measurements. After a steady-state baseline, oleic acid (20 mM) + glucose (56 mM) were added to a bile salt solution suffusing the mucosa. Baseline arteriolar diameters and blood flows were 52 ± 2 μm and 20 ± 2 nl/sec with the serosal suffusate containing Ringerʼs; these values were not significantly altered by theophylline or deaminase treatment. During suffusion of the mucosa with a nutrient solution, diameter and blood flow transiently increased and these responses were not altered by deaminase or theophylline. Thereafter, diameter and blood flow stabilized at lower values for the duration of absorption. Diameter and blood flow were increased to 111 ± 1% and 134 ± 5% of control during absorption with Ringerʼs; the corresponding values were significantly lower with deaminase or theophylline. After absorption, diameter and blood flow stabilized near baseline with Ringerʼs within 7–12 minutes; the corresponding values were significantly lower with deaminase or theophylline for at least 30 minutes. Since deaminase and theophylline produced similar effects on absorptive hyperemia, adenosine might participate with other factors in the local regulation of that response. Adenosine applied to the serosa caused dose-dependent increases in calculated blood flow with a threshold near 10-5 M and a maximum near 10-3 M. In contrast, even 10-2 M adenosine in the mucosal suffusate did not increase blood flow above baseline. Until the mechanism for this regional difference between the mucosa and serosa is defined, it will be difficult to localize the site of action of adenosine within the intestinal wall or estimate its concentration in the perivascular space of intestinal arterioles.
