Brain Interstitial Adenosine and Sagittal Sinus Blood Flow during Systemic Hypotension in Piglet

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Abstract
We sampled, using the brain dialysis technique, interstitial fluid adenosine from the frontal cortex of newborn piglets subjected to hemorrhagic hypotension while measuring sagittal sinus blood flow, cerebrovascular resistance (CVR), and cerebral O2 delivery. In group 1 (n = 8), MABP was reduced in successive steps from 76 to 30 mm Hg with decrements of ∼ 10 mm Hg. At 60 mm Hg, CVR decreased by 19% (p < 0.001), but sagittal sinus blood flow and interstitial fluid adenosine remained unchanged. At 50 mm Hg, both sagittal sinus blood flow and CVR decreased by 19% (p < 0.001) and interstitial fluid adenosine rose 4.7-fold (p < 0.05). At 40 and 30 mm Hg, sagittal sinus blood flow decreased further but CVR remained steady, whereas interstitial fluid adenosine rose 10- and 16-fold, respectively. In group 2 (n = 7), an abrupt reduction of MABP from 80 to 47 mm Hg produced no change in sagittal sinus blood flow and a 29% decrease in CVR (p < 0.01). Interstitial fluid adenosine increased twofold (p < 0.01). In group 3 (n = 7), an abrupt reduction of MABP from 79 to 40 mm Hg decreased sagittal sinus blood flow and CVR by 24 and 30%, respectively (p < 0.01). Interstitial fluid adenosine rose threefold (p < 0.01). In groups 1, 2, and 3, the increases in interstitial fluid adenosine accompanied decreases in cerebral O2 delivery. In group 4 (n = 7), artificial CSF with a Po2 of 152 mm Hg was perfused through the brain dialysis cannula during graded hypotension. In this group, interstitial fluid adenosine rose only at an MABP of 20 mm Hg. These data support the concept that adenosine participates in the regulation of CBF during hypotension in piglets.