Nimodipine Does Not Affect Cerebral Lactate Levels following Complete Ischemia in Dogs

Abstract

Nimodipine is known to improve postischemic cerebral blood flow (CBF) and neurologic outcome in experimental animals. Whether or not the two observations are related is unknown. This study searched for a possible improved rate of brain metabolic recovery in animals treated with nimodipine postischemia. Complete cerebral ischemia was produced for 11 min in 16 dogs, followed by reperfusion for 70 min. Prior to ischemia, glucose was administered (0.75 g · kg−1) in 12 dogs. Half of the glucose-treated dogs were given i.v. nimodipine, beginning 5 min postischemia (10 μg · kg−1 bolus followed by 1 μg · kg−1 · min−1). The other half were given only saline postischemia. The remaining four dogs were given no glucose and received saline only postischemia. In all dogs, serial brain biopsies were taken at 2, 20, 40, and 70 min postischemia. In 5 dogs, the integrity of the blood–brain barrier (BBB) was tested by injection of Evans blue dye and postmortem examination of the brains. Brain biopsies were assayed for concentrations of phosphocreatine, ATP, ADP, AMP, glucose, lactate, and pyruvate. In all dogs, there was rapid restoration of a normal brain energy state following reperfusion. Brain lactate had returned to near normal in all dogs by 70 min postischemia, and the rate of lactate depletion was not different between groups. The integrity of the BBB was only minimally affected. A portion of the brain lactate was converted to pyruvate rather than crossing the BBB. If lactate is a valid marker of the washout of metabolic products postischemia, there is no apparent benefit resulting from a nimodipine-induced increase in CBF during the initial 70 min following ischemia.