guanosine-triphosphate and Brain-Ischemia

Normovolemic hemodilution is a possible way to improve the brain recovery after ischemia and reperfusion. Therefore we have decided to examine how this process may affect the post-ischemic protein synthesis machinery. We analysed rat brains after 4-vessel-occlusion and different time intervals of reperfusion using normovolemic hemodilution. We achieved an important increase of [4,5-3H]leucine incorporation into polypeptides in vitro in the rat brain neocortex 30 minutes after ischemia, but concurrently there was no significant change in the hippocampus and striatum. By extending the time course of reperfusion we did not observe any important deviation of in vitro [4,5-3H]leucine incorporation in the studied brain areas. Thus, although hemodilution increased protein synthesis in selective vulnerable regions after ischemia, this improvement is not of significant importance.

Topics: Animals; Brain Chemistry; Brain Ischemia; Carotid Arteries; Eukaryotic Initiation Factor-2; Guanosine Triphosphate; Hematocrit; Hemodilution; Male; Nerve Tissue Proteins; Phosphorylation; Protein Biosynthesis; Rats; Rats, Wistar; Reactive Oxygen Species; Reperfusion; RNA, Transfer, Met; Vertebral Artery

The potential usefulness of adenosine receptor stimulation in the therapy for ischemic brain disease is dependent upon retention of adenosine receptors and their transduction mechanisms after ischemia. The receptors most clearly associated with adenosine-dependent cerebral inhibition are the A1-type (A1-AR), which work via a Gi protein to inhibit adenylate cyclase. In brain membranes from rats recovering at various times after 15 min of complete cardiac arrest-induced ischemia, the levels of A1-AR decreased temporarily to 60% of the control values. However, agonist affinities for A1-AR, as well as guanine nucleotide-sensitive high-affinity binding, remain unchanged. The significant decrease of agonist affinities to A1-AR produced by calcium depletion in control membranes was markedly attenuated after ischemia. Moreover, the A1-AR agonist-induced inhibition of cAMP production parallels the decrease in these receptor numbers. It was blocked in the postischemic membranes but reverts to control levels upon extending the recovery period to one week after the insult. It is concluded that in addition to the lowering of the number of A1-AR binding sites, the coupling of A1 receptor activation to adenylate cyclase response is inhibited after ischemia, but not at the level of receptor-Gi protein interaction.

Topics: Adenosine; Adenosine-5'-(N-ethylcarboxamide); Adenylyl Cyclase Inhibitors; Adenylyl Cyclases; Animals; Binding, Competitive; Brain Ischemia; Calcium; Colforsin; Cyclic AMP; Down-Regulation; Edetic Acid; Egtazic Acid; Female; GTP-Binding Proteins; Guanosine 5'-O-(3-Thiotriphosphate); Guanosine Triphosphate; Heart Arrest; Male; Models, Biological; Rats; Rats, Wistar; Receptors, Purinergic; Signal Transduction

The purpose of this study was to determine the effect of normoxic reperfusion and graded postischemic reoxygenation on cerebral protein synthesis in a cell-free system. Ischemia alone produced a relatively small decrease (15-17%) in activity in all the subcellular systems studied. After a 15-min interval of normoxic reperfusion (75-90 mmHg O2 in arterial blood), a 40% decrease (p less than 0.01) in [14C]leucine incorporation was observed. Reoxygenation with hypoxemic blood containing 37.5 mm Hg O2 at 0-5 min and 56 mm Hg O2 at 6-10 min of recirculation followed by 5 min of normoxic reperfusion resulted in a significant increase (p less than 0.05) of polypeptide chain synthesis in vitro when compared with normoxic reperfusion. The results obtained by this experimental approach tend to show that graded postischemic reoxygenation could be used as a simple and effective neuroprotective tool that substantially diminishes the secondary postischemic damage in nervous tissue, including the newly synthesized proteins.

Topics: Animals; Brain Ischemia; Cerebral Cortex; Dogs; Guanosine Triphosphate; Leucine; Nerve Tissue Proteins; Oxygen; Reperfusion

Topics: Adenosine; Animals; Brain Ischemia; Colforsin; Gerbillinae; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Hippocampus; Random Allocation; Receptors, Purinergic; Time Factors

Changes in the sensitivity of adenylate cyclase and steady-state levels of cyclic AMP (adenosine 3',5'-monophosphate) occur in mammalian brain during ischemic episodes. In our previous investigation with the gerbil model of bilateral ischemia there was an indication that ischemic conditions produced an enhancement of GTP sensitivity of adenylate cyclase within the cerebral cortex. The present study employed a kinetic analysis to evaluate further the role of this GTP modulation of adenylate cyclase in the gerbil frontal cortex during periods of bilateral ischemia and recirculation. In general, after either 15-min (with or without 15-min reflow) or 60-min ischemia the Vmax to GTP (alone or with dopamine and norepinephrine) was increased. Under these conditions the ED50 for half-maximal enzyme activation was decreased, indicating a greater affinity of the transducer site for GTP during ischemia. However, if irreversible 60-min ischemia was followed by 15-min reflow the enzyme responses to GTP were now absent. An unexpected observation showed that the ED50 for GTP activation of cortical adenylate cyclase was likewise attenuated when sham-operated animals were compared to normal gerbils.

Topics: Adenylyl Cyclases; Animals; Brain Ischemia; Cerebral Cortex; Cyclic AMP; Dopamine; Female; Gerbillinae; Guanosine Triphosphate; Kinetics; Norepinephrine

Topics: Adenylyl Cyclases; Animals; Brain Ischemia; Catecholamines; Cerebral Cortex; Enzyme Activation; Female; Frontal Lobe; Gerbillinae; Guanosine Triphosphate; Nucleotides, Cyclic; Sodium Fluoride