44 ADENOSINE ACCUMULATION IN HEMORRHAGIC CEREBROSPINAL FLUID

Abstract

Although adenosine (Ado) may play a critical regulatory role in brain, little information is available with respect to its metabolism in cerebrospinal fluid (CSF). In normal, cell-free CSF from children of various ages, degradation of 1 μM Ado reached only 0.028 ± 0.010 nmol/h/ml at 25 °C (mean ± SEM for n = 9). Both intact and hemolysed red blood cells (RBC, ~ 50,000/mm3 of test volume) produced no or negligible Ado when incubated in the absence of CSF. Incubation of intact RBC with CSF similarly did not result in Ado accumulation. However, incubation of a hemolysate with CSF resulted in buildup of Ado at rates that were proportional to both amount of hemolysate and of CSF. Accumulation was enhanced in the presence of the adenosine deaminase inhibitor deoxycoformycin (1μM). Further studies showed that CSF contains a 5′-nucleotidase (activity : 7.4 ± 1.8 nmol/h/ml at 25 °C, n = 11) with the kinetic characteristics of an ecto-5′-nucleotidase (high affinity for AMP, inhibition by adenosine 5′-methylene diphosphonate, no stimulation by 2,3-bisphosphoglycerate). It is concluded that Ado may accumulate in hemorrhagic CSF as a result of the combination of red cell hemolysis providing AMP, the presence of a membrane-derived 5′-nucleotidase, and the low activity of adenosine deaminase.