Possible role for adenosine in local regulation of absorptive hyperemia in rat intestine.

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 micrograms protein/ml) or theophylline (10(-4) M) in Ringer's 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 micron and 20 +/- 2 nl/sec with the serosal suffusate containing Ringer's; 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 Ringer's; the corresponding values were significantly lower with deaminase or theophylline. After absorption, diameter and blood flow stabilized near baseline with Ringer's 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.(ABSTRACT TRUNCATED AT 250 WORDS)