Effect of etomidate on in vivo ischemia-induced dopamine release in the corpus striatum of the rat: a study using cerebral microdialysis.

Dopamine (DA) is released in large quantities into the corpus striatum during cerebral ischemia and may exacerbate tissue damage. Using cerebral microdialysis, we studied the effect of etomidate on in vivo ischemia-induced DA release in rat corpus striatum. Reversible cerebral ischemia was induced by using carotid ligatures and hypovolemic hypotension, and monitored with laser Doppler flowmetry. After baseline measurements, 20 normothermic, anesthetized rats were subjected to three separate periods of cerebral ischemia, interrupted by 45- to 75-min periods of reperfusion. The rats were randomized into two groups. All rats received 400 mg/kg of intraperitoneal chloral hydrate for induction of anesthesia. In Group I (n = 10) anesthesia was maintained using additional intraperitoneal chloral hydrate 100 mg/kg every 2 h. Group II received etomidate 0.6 mg/kg 10 min before the first episode of cerebral ischemia, followed by an infusion of 60 micrograms.kg-1 x min-1. Before each subsequent period of induced ischemia, an additional dose of etomidate (0.6 mg/kg) was administered. DA levels were approximately 350 times above baseline in Group I during the three ischemic episodes (IS1, IS2, and IS3). In Group II, ischemia-induced DA release was significantly attenuated (by 79%) during IS1, IS2, and IS3 compared to Group I (P < 0.01). DA levels did not significantly change in magnitude during the three ischemic episodes in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of isoflurane and halothane on in vivo ischemia-induced dopamine release in the corpus striatum of the rat. A study using cerebral microdialysis.

BACKGROUND: Dopamine is released in large quantities into the corpus striatum during cerebral ischemia and may exacerbate tissue damage. METHODS: Using cerebral microdialysis, the effect of isoflurane on in vivo ischemia-induced dopamine release was studied in rat corpus striatum. Reversible cerebral ischemia was induced using carotid ligatures and induced hypovolemia and was monitored with laser-Doppler flowmetry. Following baseline measurements, 28 normothermic, anesthetized rats were subjected to cerebral ischemia followed by reperfusion. The rats were divided into four groups. Group 1 (n = 10) was anesthetized using chloral hydrate. Groups 2 and 3 received 1.5% end-tidal isoflurane. In group 2 (n = 6), hypotension was left untreated during the reperfusion period, and in group 3 (n = 6), mean arterial pressure was maintained using phenylephrine. Group 4 (n = 6) received 1-1.2% end-tidal halothane. RESULTS: Compared with pre-ischemic levels, large quantities of dopamine (350 x baseline levels) were released in group 1 animals during cerebral ischemia. Compared with group 1, ischemia-induced dopamine release was significantly reduced in group 2 (by 58%) and in group 3 (by 56%), but not in group 4. Group 2 animals were uniformly hypotensive during reperfusion and continued to release substantial amounts of dopamine (8 x baseline levels). In groups 1, 3, and 4, dopamine release decreased to near baseline levels during reperfusion. In group 3, dopamine metabolite production was significantly increased during ischemia, suggesting that enzymatic function and neuronal reuptake of dopamine was preserved. CONCLUSIONS: Isoflurane, compared with chloral hydrate and halothane, inhibits the release of the neurotransmitter dopamine during cerebral ischemia.

Increase in extracellular dopamine in the striatum during cerebral ischemia: a study utilizing cerebral microdialysis.

Unilateral ligation of the left common carotid artery in anesthetized Mongolian gerbils resulted in a steep rise in extracellular dopamine in the ipsilateral striatum in 9 out of 19 animals. Extracellular dopamine was measured by cerebral dialysis in vivo and reached a peak of 0.19 mM at 40 min. At the same time, the level of homovanillic acid fell, whereas the levels of ascorbate and 3,4-dihydroxyphenylacetic acid remained relatively constant. In a separate group of animals studied with a combined dialysis/electrochemistry probe, a rise in the in vivo chronoamperometric signal in three out of six animals correlated with a rise in extracellular dopamine. The number of animals responding in these experiments (roughly 50%) corresponds to the frequency of incompetent Circle of Willis, as well as literature reports of the frequency of signs of stroke in unanesthetized gerbils. These results show a remarkable accumulation of dopamine in extracellular fluid in response to cerebral ischemia. Released dopamine appears to be responsible for the elevated in vivo electrochemical signal previously reported.

Amine-mediated toxicity. The effects of dopamine, norepinephrine, 5-hydroxytryptamine, 6-hydroxydopamine, ascorbate, glutathione and peroxide on the in vitro activities of creatine and adenylate kinases in the brain of the rat.

The effects of several concentrations of amines and reducing agents on the activity of creatine (CK) and adenylate (AK) kinases were determined in homogenates of the brain of the rat at 0 and 37 degrees C. The order of decreasing irreversible inhibition of the enzymes was peroxide, 6-hydroxydopamine, dopamine, norepinephrine, 5-hydroxytryptamine. At 37 degrees C, approx. 50% of the activity of creatine kinase was lost in 30 min in the presence of 20 microM dopamine. 5-Hydroxytryptamine was several orders of magnitude less toxic. The action of dopamine was not prevented by inhibition of monoamine oxidase, chelation of metals or the addition of a catalase, indicating that formation of peroxide by monoamine oxidase was not the primary cause of the loss of enzyme. Although auto-oxidation of dopamine to a toxic quinone was considered, the degree of inhibition of creatine kinase was not affected when auto-oxidation was prevented under anaerobic conditions. Glutathione (GSH), present during the incubation, protected the enzymes but could not restore activity after exposure to amine. Concentrations of glutathione above 5 mM and of oxidized glutathione as low as 10 microM inhibited creatine kinase. Ascorbate protected the enzymes even when present at a concentration much less than that of the amine, but ascorbate was itself toxic. The findings indicate that dopamine, at concentrations attained after drug-induced release or ischemia, can be toxic to a metabolic enzyme present in the synaptosomal membrane.

The effects of BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) and CCNU (1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea) on glutathione reductase and other enzymes in mouse tissue.

BCNU has been reported to cause a rapid, irreversible inhibition of human erythrocyte glutathione reductase (GR) at chemotherapeutic dosage, without affecting metabolic enzymes. This inhibition may mediate some of the therapeutic and toxic effects of BCNU. Thiol containing agents such as reduced glutathione can protect cells against BCNU and a change in glutathione concentrations could modify BCNU effectiveness. At doses of 50 mg/kg (LD-50) and 100 mg/kg, i.p., BCNU decreased the activity of GR in mouse kidney, liver, brain, and heart with a greater loss in those animals which died from drug administration. GR activity tended to recover but still remained below control at 96 hours. Erythrocyte GR activity was reduced only at the higher BCNU dose. CCNU (100 mg/kg, i.p.) did not affect GR activity. BCNU also decreased creatine kinase, malate dehydrogenase, and lactate dehydrogenase activities. The inhibition of GR in vitro occurred only after biochemical reduction of the enzyme with NADPH. The oxidation state of GR may determine its sensitivity to BCNU in the human erythrocyte but we were unable to demonstrate an unusually high sensitivity or a specific effect of BCNU on GR in mouse tissues.

Norepinephrine stimulation of pentose cycle in rat brain prisms.

Using the C1/C6 14CO2 ratio as a relative measure of pentose shunt metabolism, rat brain prisms were incubated with (1-14C) or (6-14C) glucose and respired 14CO2 collected. Shunt metabolism was stimulated with 10-4M but not 10-5M norepinephrine. MAO inhibitors and reserpine blocked norepinephrine stimulation but uptake inhibition did not. These data demonstrate that, under the tested conditions, MAO mediated norepinephrine metabolism does stimulate shunt activity but not at physiological concentrations.

Postmortem stability of enzymes detoxifying peroxide in brain.

Glutathione peroxidase, glutathione reductase, and catalase activities were measured to 48 h after death in mouse brains held at temperatures replicating the cooling occurring in human cadaver brain. Glutathione peroxidase was stable for 48 h; catalase was stable for 24 h and then declined 20% in activity. Glutathione reductase was stable for 4 h and then decreased to 55% of its initial activity by 48 h. Perfusion of mouse brain with 0.9% (wt/vol) NaCl did not decrease enzyme activities, indicating that erythrocyte contamination has little effect on measured brain activities. The results suggest that glutathione peroxidase would not be affected by moderate time delays in obtaining human postmortem brains but catalase activity may be affected if brains are not promptly removed. Glutathione reductase is not stable and measurements would require controls carefully matched for postmortem conditions.

The activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase in rat tissues.

The activity of the myelin-associated enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) was measured in 14 rat tissues and in subcellular fractions of rat liver by a sensitive fluorometric method, using cyclic NADP as substrate. CNP activity in brain (339 mumol/h/mg protein) was fourfold that of the sciatic nerve. The activities in tissues outside the nervous system ranged from a low of 0.42 mumol/h/mg protein in the unwashed red blood cell to a high of 9.96 in the spleen. The activity was highest in tissues containing cells with membranes capable of undergoing transformation and elaboration (spleen and thymus) and low in those in which the cell membranes are morphologically stable (muscle and red cell). The enzyme was found in all major liver subfractions, with the highest activities in the microsomal and nuclear fractions. Despite the large difference in the maximal velocities of CNP in brain and liver, the affinity of the liver enzyme for the substrate (km) was similar to that of brain enzyme. Brain CNP was stable over a 48-h postmortem period.

Regional distribution of catalase in the adult rat brain.

Catalase activity was measured in 11 areas of perfused adult rat brain. The hypothalamus and substantia nigra contained the highest activities. The corpus callosum, a white-matter structure, contained intermediate activity. The caudate-putamen and frontal cortex contained the lowest activities. Regional catalase bears some relationship to the reported distribution of microperoxisomes, but considerable activity is present in areas with few microperoxisomes. Catalase may function as one of the systems detoxifying H2O2 formed in CNS amine metabolism.

Developmental study of rat brain glutathione peroxidase and glutathione reductase.

Glutathione peroxidase and glutathione reductase activities were measured in whole rat brains at selected ages from birth to adulthood. On a wet weight basis glutathione peroxidase activity increased 70% during development and glutathione reductase activity increased 160%. On a protein basis glutathione peroxidase declined slightly in activity during the first two weeks of life and then maintained the 14-day activity into adulthood while glutathione reductase showed a 30% increase in activity. While less than the developmental changes in many enzyme involved in aerobic glycolysis or catecholamine metabolism, these increases do suggest a role in CNS metabolism.

Regional distribution of glutathione reductase in the adult rat brain.

Glutathione reductase was measured in 10 selected areas of the adult rat brain. Activitives varied over a 2.5-fold range. The caudate-putamen and cortical areas contained the highest activities. Several gray matter structures contained intermediate activities. The substantia nigra and the corpus callosum, a white matter structure, contained the lowest activities. The caudate-putamen, a catecholamine rich area, may produce H2O2 via MAO and would require glutathione reductase to recycle glutathione oxidized by glutathione peroxidase. However, the distribution of glutathione reductase activity also suggests a role in reducing oxidants formed during tissue respiration.

Regional distribution of glutathione peroxidase in the adult rat brain.

Glutathione peroxidase activity was measured in 10 areas of perfused adult rat brain with the use of a fluorometric assay coupled to NADPH oxidation. The caudate-putamen and the substantia nigra had the highest activities. Cortical areas and several nuclear areas had somewhat lower activity. Activity was lowest in a white matter structure (corpus callosum). High activity of glutathione peroxidase may be related to the need to reduce hydrogen peroxide arising in the course of monoamine metabolism.

Bilateral basal ganglia calcifications visualised on CT scan.

Thirty-eight cases of basal ganglia calcification imaged on computed axial tomography were reviewed. Most cases were felt to represent senescent calcification. The possibility of a vascular aetiology in this group is discussed. A less common group of patients was identified with calcification secondary to abnormalities in calcium metabolism or radiation therapy. Three cases of basal ganglia calcifications were detected in juvenile epileptic patients receiving chronic anticonvulsants. These cases may be related to abnormalities in calcium metabolism and alkaline phosphatase activity. Clinical evidence of basal ganglia abnormality was generally absent demonstrating the preservation of neuronal pathways in most cases.

Aldose reductase and sorbitol dehydrogenase distribution in rat kidney.

The sorbitol pathway catalyzes the conversion of glucose to fructose via the intermediate sorbitol. It consists of aldose reductase (AR) and sorbitol dehydrogenase (SDH). In adult (44 day) kidney zones, AR was highest in the outer medulla. In substructures AR was highest in distal convoluted tubule. The AR was greatest in newborn and 8-day zones of developing rat kidney. Acute alloxan diabetes was associated with decreased AR in small arteries, but not glomeruli. The SDH was lowest in outer medulla. It was most active in glomeruli and distal convoluted tubules. The diabetic state leads to no change of SDH in arteries but an increase in glomeruli. SDH increased with development. This study demonstrates AR and SDH in substructures of the kidney. The pathway is present in developing kidney. In diabetes the enzymatic changes would tend to decrease accumulation of sorbitol.

Histochemical measurements of rat kidney hexokinase.

HK has been measured in substructures of the developing rat nephron. Reactions were carried on samples dissected from freeze dried kidney and assayed in 1 mul reaction volume utilizing the "oil-well" technique. Samples from 4 days prenatal to 44-day adult were analyzed. Activity during development decreased in G, PCT, and it increased in ALH. There was little change in PRT, DCT and CT. Activity in small arteries decreased.