[Effects of gamma-hydroxybutyrate on monoamine metabolism and protein synthesis after transient global cerebral ischemia].

The effects of gamma-hydroxybutyrate (GHB) on 1) monoamine metabolism, and 2) protein synthesis were examined in a gerbil stroke model. The monoamine metabolism was studied by occluding bilateral common carotid arteries for 15 minutes followed by GHB administered intravenously 3 hours later. Tissue monoamine concentration was examined up to 8 hours after recirculation. Three hours after GHB administration, dopamine (DA) had increased to almost twice that of the non-treated group, whereas homovanillic acid, a metabolite of DA, did not show any significant difference. These results may mean that GHB will facilitate DA synthesis but that it has no influence on its release. Therefore, a DA-mediated increase in cerebral blood flow in the cerebral cortex cannot be expected. Tryptophan, a precursor of 5-hydroxytryptamine (5HT), started to increase just after recirculation reaching a level of over four times that of the control value at 2 to 3 hours, and then starting to decrease in the non-treated group. This decline in tryptophan was markedly facilitated by GHB administration within 1 hour. On the other hand, 5HT administration within 1 hour. On the other hand, 5HT increased only very slightly in the cerebral cortex 1 hour after GHB administration, the change ratio being 1/30 of tryptophan. It can therefore be speculated, that the decrease in tryptophan brought about by GHB administration is due to the improvement in disturbed protein synthesis rather than to stimulation of 5HT synthesis. Protein synthesis was studied by administering GHB 2 minutes prior to a 5-minute temporal common carotid artery occlusion. Ninety minutes after recirculation animals were given a single dose of 14C-leucine and further 60 minutes were allowed to pass before sacrifice. Autoradiographs of the GHB-treated group were compared with those of the non-treated group. With GHB pretreatment, autoradiographs showed an increased uptake of 14C-leucine in at least the hippocampus, thalamus, and hypothalamus, and in two out of three animals, there was diffusely increased uptake. Thus, it is speculated that GHB is effective in improving the protein synthesis in the postischemic period. The favorable function of GHB during cerebral ischemia is regarded by many to be prevention of energy failure by reducing cerebral metabolism. On the other hand, the results derived from the present study suggest that GHB may improve protein synthesis in the postischemic period. Thus, we suggest that GHB is useful if given at the acute stage of cerebral ischemia such as during internal carotid artery or middle cerebral artery occlusion.