248 Brain Research, 516 (1990) 248-256 Elsevier BRES 15455 Protective effect of adenosine and a novel xanthine derivative propentofylline on the cell damage after bilateral carotid occlusion in the gerbil hippocampus Ern6 Dux 2'*, Johan Fastbom 1, Urban Ungerstedt 1, Karl Rudolphi 3 and Bertil B. Fredholm 1 ~ Department of Pharmacology, Karolinska Institutet, Stockholm (Sweden), 2Laboratory of Molecular Neurobiology, Institute of Biophysics, Biological Research Center, Szeged (Hungary), 3 Pharma Research, Hoechst AG, Werk Albert, Wiesbaden (ER. G.) (Accepted 17 October 1989) Key words: Purine metabolism; Ischemia; Theophylline; Microdialysis; Autnradiography; Electron microscopy The role of adenosine in the development of ischemia induced pathological changes has been examined in Mongolian gerbils. A dramatic increase in the concentrations of adenosine, inosine and hypoxanthine was detected by microdialysis in the dorsal part of hippocampus and in the striatum immediately after 5 min bilateral occlusion of the carotid arteries. From a resting value of about 0.5 pM the concentration of adenosine increased to more than 10 pM. The adenosine levels became normalized within 30 min after ischemia. Inosine and hypoxanthine levels were higher and they increased and also returned towards control somewhat later than adenosine. A second occlusion resulted in a similar but somewhat smaller increase in purine levels. Carotid occlusion for up to 12 min had no major, lasting effect on the binding to adenosine Al-receptors in the CA-regions of the hippocampus, as determined by autoradiography. Neuronal and vascular changes (degeneration of neurons, mitochondrial destruction and ribosomal disaggregation, astroglial oedema) due to ischemia (3-12 min, followed by 48 h recirculation) was studied with light and electron microscopy in the selectively vulnerable CA1 area of hippocampus. In one series of experiments the adenosine antagonist theophylline (20 mg/kg i.p.), given 15 min prior to a 5 min occlusion, significantly enhanced the ischemia induced changes. In another experiment the adenosine uptake inhibitor propentofylline (HWA 285, 10 mg/kg), injected 15 min before a 12 min carotid occlusion, reduced the neuronal (90%) and astroglial changes (84%) due to ischemia. The results provide further evidence that adenosine could play a role as an endogenous protective substance in ischemia by showing that ischemia leads to a massive increase in extracellular adenosine concentration with little change in adenosine receptors and by the demonstration at the ultrastructural level that the adenosine antagonist theophylline aggravates and that propentofylline, a drug known to raise levels of adenosine, decreases ischemia induced neuronal and vascular degeneration. INTRODUCTION The extracellular levels of adenosine and its metabo- lites in the rat brain increase rapidly following hypoxia 32" 40 or ischemia 2°'36. Adenosine is known to decrease transmitter release and to decrease neuronal firing 5'14'35. It also dilates cerebral blood vessels and increases cAMP levels in endothelial cells, an effect that may be related to vascular permeability 1°'25'3~. These findings suggest that adenosine may have pro- tective effects against ischemic brain damage and there is recent direct evidence that this is the case. Thus, two adenosine analogues, 2-chloroadenosine 7 and cyclohexyl- adenosine 37 were found to protect against ischemic damage. Conversely the adenosine antagonist theophyl- line was found to aggravate ischemic changes 33. A novel xanthine derivative, propentofylline (HWA 285), was shown to protect against damage induced by transient cerebral ischemia 3'4. One of the properties of this compound is to act as an inhibitor of adenosine uptake and in that way to increase the actions of adenosine 16, and there is evidence that it may enhance levels of adenosine in the intact brain following ischemia ~9. Among laboratory animals, Mongolian gerbils are frequently used to produce total transient forebrain ischemia because of the absence of arterial anastomoses between the carotid and vertebrobasilar circulations 27. The CA1 subfield of hippocampus is the most sensitive to the delayed neuronal degeneration due to ischemic hypoxia 21"22"23. Another sensitive region is the striatum. In the present study we have therefore used the gerbil model to further examine the role of adenosine in the development of ischemic brain damage, and the effects of propentofylline. In the first part we investigated, using microdialysis probes, the in situ concentration of aden- osine and its metabolites during and after transient ischemia in the dorsal part of the hippocampus, corre- sponding to the CA1 region, and in the striatum, and, * Present address: Department of Neurology, University of California, San Francisco, CA 94148, U.S.A. Correspondence: B.B. Fredholm, Dept. of Pharmacology, Karolinska Institutet, Box 60400, S-104 01 Stockholm, Sweden. 0006-8993/90/$03.50 (~) 1990 Elsevier Science Publishers B.V. (Biomedical Division)