Regional protein synthesis in rat brain following acute hemispheric ischemia

Regional protein synthesis was measured in rat brain at intervals up to 48 h following occlusion of the four major arteries to the brain for either 10 or 30 min. Four-vessel occlusions produces ischemia in the cerebral hemispheres and oligemia in the midbrain-diencephalon and brainstem. During the hour following 10 min of ischemia, protein synthesis, measured by incorporation of [14C]valine into protein, was inhibited in the cerebral cortex by 67%. Normal rates of protein synthesis were attained within 4 h of recirculation. In rats subjected to 30 min of ischemia, protein synthesis was inhibited by 83% during the first hour of recirculation in the cortex, caudate-putamen, and hippocampus. Recovery of protein synthesis in these regions was slow (25-48 h). The midbrain-diencephalon showed less inhibition, 67%, and faster recovery (by 12 h). Protein synthesis was unaffected in the brainstem. [14C]Autoradiography revealed that the pyramidal neurons of the hippocampus and areas of the caudate and cortex failed to recover normal rates of protein synthesis even after 48 h. The accumulation of TCA-soluble [14C]valine was enhanced (55-65%) in the cortex, caudate, and hippocampus after 30 min of ischemia; the increase persisted for 12 h. A smaller rise in [14C]valine content (30%) and more rapid normalization of valine accumulation (by 7 h) were observed in the midbrain-diencephalon; no changes were found in the brainstem. In the cortex, recovery was more rapid when the duration of ischemia was reduced. Thus, the degree of inhibition of protein synthesis, the accumulation of valine in the tissue, and the length of time required to reestablish normal values for these processes were dependent on both the severity and the duration of the ischemic insult. Restoration of normal rates of protein synthesis after ischemia was slow compared with the normalization of cerebral energy metabolites.