Purine levels in the intact rat brain. Studies with an implanted perfused hollow fibre

Abstract

A thin dialysis tube was implanted stereotaxically under halothane anesthesia in the caudate nucleus of Sprague-Dawley rats and perfused with Ringer solution at a rate of 2 μl/min. Initially there was a high rate of purine outflow but after 1–2 h of perfusion the rate was essentially constant (anesthetized - adenosine 0.4 ± 0.04 μM, inosine 0.8 ± 0.2 μM; non-anesthetized - adenosine 0.33 ± 0.03 μM, inosine 0.21 ± 0.07 μM). Hypoxia (9% O₂) increased the levels more than 3-fold. The adenosine deaminase inhibitor erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA) increased the adenosine level and decreased the inosine level. In vitro recovery of adenosine was about 30%. Therefore, we conclude that the free exchangable concentration of adenosine in the rat brain is likely to be 1–2 μM. This level is high enough to potentially affect central nervous function.