Changes in brain adenosine during bicuculline-induced seizures in rats. Effects of hypoxia and altered systemic blood pressure

We analyzed brain tissue in 139 rats for adenosine and its metabolites, inosine and hypoxanthine, during the initial 120 seconds of seizures induced by bicuculline. We also measured ATP, ADP, AMP, phosphocreatine (PCr), and lactate. We divided the rats into four groups by adjustment of their preictal arterial oxygen tension: group I, PaO2 > 200 mm Hg; group II PaO2 = 50 mm Hg; and group III: PaO2 = 100 mm Hg. We treated a fourth group whose PaO2 = 100 mm Hg with phentolamine to block the 44% rise in blood pressure which occurred with the onset of seizures. PaCO2 was maintained between 30 anf 40 mm Hg in all groups. Brain tissue was sampled rapidly after 0, 10, 20, 30, 60, and 120 seconds of seizures by the freeze-blow technique. With normoxia (PaO2 = 100 mm Hg) or hyperoxia (PaO2 > 200 mm Hg), adenosine increased within ten seconds of the onset of seizures and remained elevated even after 120 seconds. Elevations in inosine and hypoxanthine were delayed compared to the increases in adenosine. A reduction in PaO2 (50 mm Hg) or systemic blood pressure during seizures caused a further augmentation in the increase in brain adenosine levels. During the seizure period, transient changes in adenine nucleotides and energy charge were observed, but PCr remained depressed and lactate continued to rise. The rapid and sustained increase in cerebral adenosine levels, temporally paralleling the changes in cerebral blood flow, supports the role for adenosine in the regulation of cerebral blood flow.