Minimally-invasive approach to posterior fossa decompression: Initial experience in Adult Chiari Type 1 Malformation patients.

We report our initial experience using Minimally-Invasive Surgery (MIS) technique for Posterior Fossa Decompression (PFD) in Adult Chiari 1 Malformation (C1M) patients. Five subjects who were treated with MIS PFD at our center and followed up over a 5-year period. Another nine subjects who were treated with Open PFD and follow up over the same period were used for comparison. This study suggests that there are little differences in efficacy and safety between MIS and Open PFD. Larger series and prospective randomized trials comparing the two methods would provide higher-quality evidence and clarify the role of either technique in the treatment of C1M.

Predicting primary outcomes of brain tumor patients with advanced neuroimaging MRI measures.

BACKGROUND: Advanced neuroimaging measures along with clinical variables acquired during standard imaging protocols provide a rich source of information for brain tumor patient treatment and management. Machine learning analysis has had much recent success in neuroimaging applications for normal and patient populations and has potential, specifically for brain tumor patient outcome prediction. The purpose of this work was to construct, using the current patient population distribution, a high accuracy predictor for brain tumor patient outcomes of mortality and morbidity (i.e., transient and persistent language and motor deficits). The clinical value offered is a statistical tool to help guide treatment and planning as well as an investigation of the influential factors of the disease process. METHODS: Resting state fMRI, diffusion tensor imaging, and task fMRI data in combination with clinical and demographic variables were used to represent the tumor patient population (n = 62; mean age = 51.2 yrs.) in a machine learning analysis in order to predict outcomes. RESULTS: A support vector machine classifier with a t-test filter and recursive feature elimination predicted patient mortality (18-month interval) with 80.7% accuracy, language deficits (transient) with 74.2%, motor deficits with 71.0%, language outcomes (persistent) with 80.7% and motor outcomes with 83.9%. The most influential features of the predictors were resting fMRI connectivity, and fractional anisotropy and mean diffusivity measures in the internal capsule, brain stem and superior and inferior longitudinal fasciculi. CONCLUSIONS: This study showed that advanced neuroimaging data with machine learning methods can potentially predict patient outcomes and reveal influential factors driving the predictions.

Regulation of the common carotid arterial blood flow by nicotinic receptors in the medulla of cats.

BACKGROUND AND PURPOSE: Actions of glutamate and serotonin on their respective receptors in the dorsal facial area (DFA) of the medulla are known to regulate common carotid arterial (CCA) blood flow in cats. Less is known about acetylcholine action on its nicotinic receptor (nAChR) subtypes in the DFA for regulation of CCA blood flow and this aspect was investigated. EXPERIMENTAL APPROACH: Nicotinic and muscarinic agonists and antagonists were microinjected into the DFA through a three-barrel tubing in anesthetized cats. RESULTS: CCA blood flow was dose-dependently increased by nicotine (a non-selective nAChR agonist) and choline (a selective alpha7-nAChR agonist). These effects of nicotine were attenuated by alpha-bungarotoxin (an alpha7-nAChR antagonist), methyllycaconitine (an alpha7-nAChR antagonist), mecamylamine (a relatively selective alpha3beta4-nAChR antagonist) and dihydro-beta-erythroidine (a relatively selective alpha4beta2-nAChR antagonist). The choline-induced flow increase was attenuated by alpha-bungarotoxin and mecamylamine, but not by dihydro-beta-erythroidine. Muscarinic agonists (muscarine and methacholine) and antagonist (atropine) affected neither the basal nor the nicotine-induced increase in the CCA blood flow. CONCLUSIONS AND IMPLICATIONS: Functional alpha7, alpha4beta2, and alpha3beta4 subunits of the nAChR appear to be present on the DFA neurons. Activations of these receptors increase the CCA blood flow. The present findings do not preclude the presence of other nAChRs subunits. Muscarinic receptors, if any, on the DFA are not involved in regulation of the CCA blood flow. Various subtypes of nAChRs in the DFA may mediate regulation of the CCA and cerebral blood flows.

Consequences of opiate agonist and antagonist in myocardial ischaemia suggest a role of endogenous opioid peptides in ischaemic heart disease.

OBJECTIVE: The aim was to evaluate the effects of an opiate agonist (U50,488H) and an opiate antagonist (naloxone) in myocardial ischaemia. METHODS: A left thoracotomy was performed and the left coronary artery was ligated in adult Sprague-Dawley rats of either sex (350-400 g). Blood pressure, heart rate and electrocardiogram were measured before and after injections of U50,488H or naloxone and throughout the 30 min postligation period. RESULTS: Following coronary artery occlusion, all rats in the control group developed arrhythmias, bradycardia, and hypotension. U50,488H potentiated and naloxone attenuated the ischaemia induced arrhythmias, bradycardia, and hypotension. CONCLUSIONS: The potentiating and blocking effects of U50,488H and naloxone, respectively, suggest that endogenous opioid peptides are involved in the pathophysiology of myocardial ischaemia and play an important role in ischaemic heart disease.

P2 purinergic receptor activation of neuronal nitric oxide synthase and guanylyl cyclase in the dorsal facial area of the medulla increases blood flow in the common carotid arteries of cats.

In the dorsal facial area (DFA) of the medulla, an activation of either P2 purinergic receptor or nitric oxide synthase (NOS) results in the release of glutamate, leading to an increase in blood flow of the common carotid artery (CCA). It is not known whether activation of the P2 receptor by ATP may mediate activation of NOS/guanylyl cyclase to cause glutamate release and/or whether L-Arg (nitric oxide (NO) precursor) may also cause ATP release from any other neuron, to cause an increase in CCA flow. We demonstrated that microinjections of P2 receptor agonists (ATP, α,ß-methylene ATP) or NO precursor (L-arginine) into the DFA increased CCA blood flow. The P2-induced CCA blood flow increase was dose-dependently reduced by pretreatment with NG-nitro-arginine methyl ester (L-NAME, a non-specific NOS inhibitor), 7-nitroindazole (7-NI, a relatively selective neuronal NOS inhibitor) or methylene blue (MB, a guanylyl cyclase inhibitor) but not by that with D-NAME (an isomer of L-NAME) or N5-(1-iminoethyl)-L-ornithine (L-NIO, a potent endothelial NOS inhibitor). Involvement of glutamate release in these responses were substantiated by microdialysis studies, in which perfusions of ATP into the DFA increased the glutamate concentration in dialysates, but co-perfusion of ATP with L-NAME or 7-NI did not. Nevertheless, the arginine-induced CCA blood flow increase was abolished by combined pretreatment of L-NAME and MB, but not affected by pretreatment with a selective P2 receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). In conclusion, ATP activation of the P2 receptor in the DFA induced activation of neuronal NOS/guanylyl cyclase, which causes glutamate release leading to an increase in CCA blood flow. However, arginine activation of neuronal NOS/guanylyl cyclase, which also caused glutamate release and CCA blood flow increase, did not induce activation of P2 receptors. These findings provide important information for drug design and/or developing therapeutic strategies for the diseases associated with CCA blood flow that supplies intra- and extra-cranial tissues.

Translational inhibition by 5'-polycytidine tracts in Xenopus embryos and in vitro.

Introduction of in vitro transcribed mRNA into Xenopus laevis embryos is a useful technique for analyzing gene function. In order to optimize expression of cDNA constructs from in vitro transcribed mRNAs, we examined the translational efficiency of reporter genes that simulated cDNAs synthesized by tailing with deoxyguanosine (dG) before second strand cDNA synthesis. When transcribed in vitro, these cDNAs give rise to RNAs containing a 5'-homopolymeric cytidine (poly(C)) stretch. We observed that the presence of a 5'-poly(C) tract depressed translation of a CAT reporter gene at least 100-fold in Xenopus embryos and up to 5-fold in vitro. This effect was not seen when a 5'-polyadenosine tract was tested. Translational depression was dependent on the phage polymerase used for in vitro transcription: RNAs transcribed by T7 polymerase translated far more poorly than those transcribed by SP6 polymerase. These results have general implications for optimizing expression of cDNA constructs.

Elevated extracellular glutamate levels increased the formation of hydroxyl radical in the striatum of anesthetized rat.

Results from various in vitro experiments have indicated that excitotoxicity and oxidative stress are two interrelated major mechanisms in causing neuronal damage in brain disorders such as cerebral ischemia/reperfusion. Thus, we have conducted experiments to investigate whether in the striatum of anesthetized rats the elevated brain extracellular concentrations of glutamate could increase the formation of hydroxyl radical. Elevation of glutamate levels and trapping of hydroxyl radical were accomplished by perfusing Ringer solutions containing both glutamate and salicylic acid through microdialysis probes implanted in rat striatum. The formation of hydroxyl radical was quantitated as the increased amounts of 2,3 and 2,5 dihydroxybenzoic acid (DHBA) which were the hydroxylative products of salicylic acid. Eluted microdialysates were directly injected onto high performance liquid chromatography (HPLC) with electrochemical detector via an on-line automatic injector. This method was authenticated by in vitro studies employing Fenton-type hydroxyl radicals generation system. Our results indicated that elevated glutamate concentrations (15 mM, 1.5 mM, and 150 microM glutamate in perfusing solutions) would significantly increased both the concentrations of 2,3 and 2,5 DHBA. In conclusion, we have obtained direct evidence showing that the elevated glutamate concentrations in brain extracellular space would increase the formation of hydroxyl radical, and these results implied that oxidative stress occurring in brain disorders might be induced by excitotoxicity.

In vivo evidence of hydroxyl radical formation induced by elevation of extracellular glutamate after cerebral ischemia in the cortex of anesthetized rats.

The in vivo interrelation between excitotoxicity and oxidative stress following cerebral ischemia in the cortex of anesthetized rats was investigated. Cerebral ischemia was induced by ligation of the bilateral common carotid arteries and the unilateral middle cerebral artery. Microdialysis perfusion with on-line high-performance liquid chromatography was used to monitor the hydroxyl radical levels. Extracellular hydroxyl radical levels were quantitated as the increased formation of 2.3 and 2.5 dihydroxybenzoic acid (DHBA), the hydroxylative products of salicylic acid contained in the microdialysis perfusion solutions. Elevated cortex extracellular glutamate content, resulting from the cerebral ischemia, caused an increase in the formation of hydroxyl radicals. Exogenous perfusion of authentic glutamate solutions through implanted microdialysis probes also resulted in increased hydroxyl radical formation in the cortex. The 2.3 and 2.5 DHBA levels remained elevated for an entire 80-min ischemic period. These results suggest that, after cerebral ischemia, increased oxidative stress did occur in anesthetized rats, and the oxidative stress may result from increased excitotoxicity.

The roles of reactive oxygen species and endogenous opioid peptides in ischemia-induced arrhythmia of isolated rat hearts.

Although the formation of oxygen-derived free radicals (or reactive oxygen species; ROS) and the release of endogenous opioid peptides (EOP) have been independently reported to be the major arrhythmogenic factors in ischemic hearts, possible relations between these two factors have seldom been investigated. Thus, we studied whether the ROS and EOP were related in the progression of ischemia-induced arrhythmias. Isolated rat hearts perfused in the Langendorff mode were treated with dynorphin A1-13 (kappa EOP receptor agonist), and/or allopurinol (xanthine oxidase inhibitor), before the onset of ischemia induced by ligating the left coronary arteries. Ischemic period lasted for 30 min, during which cardiac rhythms were recorded. At the end of ischemia, hearts were analyzed for the glutathione and ascorbate levels. Allopurinol (100 nmoles/heart) was effective in reducing the severity of arrhythmia (arrhythmia score: Mean +/- SEM 3.00 +/- 0.80 for allopurinol, 5.75 +/- 0.41 for placebo, p < 0.01), while dynorphin (10 micrograms/heart) potentiated the arrhythmia (6.71 +/- 0.52, p < 0.05 vs. placebo). Coadministration of allopurinol and dynorphin was capable of reducing arrhythmia (5.57 +/- 0.65) when compared with the administration of dynorphin alone (6.71 +/- 0.52, p < 0.05). Tissue oxidative stress was evaluated by the concentrations of glutathione (GSH) and ascorbate. Allopurinol did not significantly elevate tissue GSH concentrations (1.46 +/- 0.05 mumoles/g wet wt) in ischemic hearts, while dynorphin alone significantly decreased the GSH concentrations (0.96 +/- 0.08, p < 0.05) when compared with the placebo (1.32 +/- 0.03). The dynorphin-induced GSH decrease cannot be reversed by coadministration with allopurinol (0.90 +/- 0.104). Allopurinol significantly elevated tissue ascorbate levels (0.16 +/- 0.01) when compared with placebo (0.10 +/- 0.01, p < 0.05). Interestingly, dynorphin alone also elevated the tissue ascorbate concentrations (0.16 +/- 0.02). Coadministration of allopurinol and dynorphin further spiked the ascorbate levels (0.28 +/- 0.05, p < 0.01). In conclusion, the results suggested that ischemia-induced arrhythmia mechanisms might involve the formation of superoxide and other ROS, which were probably generated from the release of EOP (or EOP/EOP receptor interactions). Superoxide, the formation of which can be inhibited by allopurinol that exerted antiarrhythmic effect, was probably scavenged by ascorbate in myocardial ischemia. The ROS resulting from EOP/EOP receptor interactions were probably scavenged by glutathione system. Elevated ascorbate levels in dynorphin-treated hearts might result from the compensatory synthesis induced by decreased glutathione levels.

Brainstem projections to the ventromedial medulla in cat: retrograde transport horseradish peroxidase and immunohistochemical studies.

Stimulation of the nucleus magnocellularis (NMC) of the medulla produces changes in locomotion, muscle tone, heart rate, and blood pressure. Glutamatergic input has been found to modulate muscle tone, whereas cholinergic input has been found to mediate cardiovascular changes produced by stimulation of the NMC. The current study was designed to identify the brainstem afferents to NMC by using retrograde transport of wheat germ agglutinin and horseradish peroxidase (WGA-HRP) combined with glutamate and choline acetyltransferase (ChAT) immunohistochemical and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical techniques. Fifty nanoliters of 2.5% WGA-HRP were microinjected into the NMC in the cat. A heavy density of WGA-HRP-labeled neurons was found in the ipsilateral mesencephalic reticular formation (MRF), periaqueductal gray, Kolliker-Fuse nucleus, and pontis centralis caudalis (PoC), in the contralateral pontis centralis oralis (PoO), and bilaterally in the nucleus paragigantocellularis lateralis. A moderate density of retrogradely labeled neurons was found in the ipsilateral side of the nuclei parvocellularis, retrorubral (RRN), PoO, and vestibular complex, in the contralateral PoC and nucleus gigantocellularis, and bilaterally in the inferior vestibular nucleus. Retrograde HRP/glutamate-positive cells could be found throughout the brainstem, with a high percentage in RRN, PoO, PoC, and MRF. Double-labeled WGA-HRP/ChAT neurons were found in the pedunculopontine nucleus. Double-labeled WGA-HRP/NADPH-d-positive neurons could be seen in many nuclei of the brainstem, although the number of labeled neurons was small. The dense glutamatergic projections to the NMC support the hypothesis that rostral brainstem glutamatergic mechanisms regulate muscle activity and locomotor coordination via the NMC, whereas the pontine cholinergic projections to the NMC participate in cardiovascular regulation.

Supplementation with vitamins C and E enhances cytokine production by peripheral blood mononuclear cells in healthy adults.

The effect of supplementation with vitamins C and E on cytokine production of healthy adult volunteers was studied in a single-blind trial. Ten subjects in each group received daily vitamin C (1 g ascorbic acid), vitamin E (400 mg dl-alpha-tocopheryl acetate), or vitamins C and E for 28 d. Plasma concentrations of alpha-tocopherol, ascorbate, and lipid peroxides as well as the production of cytokines by peripheral blood mononuclear cells (PBMCs) were measured before, during, and at the end of the supplementation and 1 wk later. PBMCs were cultured in the presence of absence of lipopolysaccharide for 24 h. The interleukin 1 (IL-1), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-alpha) in the culture supernates were assayed by enzyme-linked immunosorbent assay methods. Production of IL-1 beta and TNF-alpha in the group supplemented with vitamins C and E was significantly higher (P < 0.05) than that of the groups given vitamin E or vitamin C alone. The enhancing effect of supplementation with a combination of vitamins E and C coincided with peak plasma alpha-tocopherol and ascorbate concentrations and the lowest plasma lipid peroxide concentrations (P < 0.05) on day 14. In addition, an in vitro experiment with PBMCs showed that vitamins E and C reduced lipopolysaccharide-induced prostaglandin E2 production and enhanced TNF-alpha production. These results indicate that combined supplementation with vitamins C and E is more immunopotentiating than supplementation with either vitamin alone in healthy adults.

Visualization of the transport pathways of low density lipoproteins across the endothelial cells in the branched regions of rat arteries.

The transport pathways of low density lipoproteins (LDL) across the endothelium at the branched and unbranched regions of the artery were studied in high cholesterol diet-fed rats. Rat tissues were analyzed by perfusing in situ human or rat LDL labeled with colloidal gold or fluorescein 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Results indicated that more LDL-DiI accumulated in the branched regions than in the unbranched regions of the artery. LDL-gold conjugates were observed in the plasmalemmal vesicles, multivesicular bodies and in the subendothelial space in both the branched and the unbranched regions of the arteries. Quantitative study revealed that the volume densities of plasmalemmal vesicles which contained the LDL-gold particles in the branched regions of the aortic arch were significantly (P < 0.05) higher than the density value in the unbranched regions of the thoracic aorta, whereas there was no marked difference in the density value of multivesicular bodies between these two regions. The open junctions with gap widths of 30-450 nm between adjacent endothelial cells were only observed in the branched regions of the aortic arch, whereas no open junctions were present in the unbranched regions of the thoracic aorta. Moreover, the LDL-gold conjugates were present within most of these open junctions. In all specimens examined, no gold particles were found in the normal intercellular channels (i.e., 25 nm and less) of both regions. These results indicated that the major visible routes for transport of LDL across the endothelium in the branched regions of the arteries are open junctions as well as plasmalemmal vesicles. The region-associated permeability changes of LDL might account for the incidence of atherosclerosis in the branched areas of arteries.

A radioactive antigen-binding assay for the measurement of antibody to Haemophilus influenzae type b capsular polysaccharide.

A new polyethylene glycol (PEG) radioimmunoprecipitation assay was developed for the detection of antibody to Haemophilus influenzae b capsular polysaccharide, polyribosylribitol phosphate (PRP). The radioactive antigen, [3H]PRP, with a high specific activity, was produced by growing the organism in the presence of [3H]ribose and was purified by hydroxylapatite and Sepharose 4B column chromatography. In the assay, PEG (12.5%) was used to separate antibody-bound [3H]PRP from free [3H]PRP. The assay covered the range of 0.5 and 20 ng antibody/assay at a maximum sensitivity of 0.5 approximately 1.0 ng antibody/assay. With various dilutions (1-20 ng antibody/assay) of S. Klein reference antiserum, the within-run coefficient of variation (CV) of 10 replicates ranged from 3.5 to 8.5%. Average CVs of 8.9% and 11.0% were obtained in the between-run and day-to-day reproducibility studies. The binding of [3H]PRP to S. Klein reference antiserum was severely inhibited by a minute amount of non-radioactive PRP; however, no significant interference was found in the presence of high concentrations of polysaccharides from Escherichia coli K100 and Streptococcus pneumoniae indicating that the RIA was highly specific for antibody to H. influenzae b PRP. The present RIA is a simple, specific, sensitive and reproducible procedure for the evaluation of antibody responses of young animals and infants to H. influenzae b vaccines and infections.

Resveratrol inhibits interleukin-6 production in cortical mixed glial cells under hypoxia/hypoglycemia followed by reoxygenation.

Reactive oxygen intermediates (ROIs) are important mediators of a variety of pathological processes, including inflammation and ischemia/reperfusion injury. Cytokines and chemokines are detected at mRNA level in human and animal ischemic brains. This suggests that hypoxia/reoxygenation may induce cytokine production through generation of ROIs. In this study, we investigated the cytokine induction and inhibition by antioxidants in rat cortical mixed glial cells exposed to in vitro ischemia-like insults (hypoxia plus glucose deprivation). The results showed that interleukin-6 (IL-6) mRNA and protein, but not tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta (IL-1beta), were induced during hypoxia/hypoglycemia followed by reoxygenation in the mixed glial cells. The accumulation of IL-6 mRNA was induced as early as 15 min after hypoxia/hypoglycemia and its level was further increased after subsequent reoxygenation. Among the antioxidants studied, only resveratrol suppressed IL-6 gene expression and protein secretion in mixed glial cultures under hypoxia/hypoglycemia followed by reoxygenation. These findings suggest that resveratrol might be useful in treating ischemic-induced inflammatory processes in stroke.

Involvement of catecholamines in recall of the conditioned NK cell response.

The primary goal of the study was to identify the types of catecholamines and the associated receptors which might be involved in the recall of the conditioned NK cell response. Specific catecholamine receptor antagonists were selected to block the conditioned NK cell response at the recall step. The regional contents of dopamine (DA), norepinephrine (NE), and epinephrine were determined in the brain of the conditioned animals by using the high performance liquid chromatography with electrochemical detection (HPLC/ED). Results showed that pre-disruption of the central alpha1-, alpha2-, beta1-, beta2-, D1-, or D2-receptors at the conditioned recall stage, interrupted the conditioned enhancement in NK cell activity. The NE contents at the cerebellum, and DA contents at the striatum and hippocampus, were significantly higher in the brain of the conditioned animals when compared to that of the control animals. These information indicated the possible roles of the central noradrenergic and dopaminergic systems in regulating the recall of the conditioned NK cell response.

The involvement of glutamate in recall of the conditioned NK cell response.

The molecular mechanisms responsible for the conditioned enhancement of natural killer (NK) cell activity were investigated. The primary goal of the study was to examine the roles of glutamate and gamma-aminobutyric acid (GABA) in recall of the conditioned NK cell response. Both neurochemical blocking assay and high performance liquid chromatography (HPLC) technique were used in the study. Results from the neurochemical blocking assay demonstrated that glutamate but not GABA was required in recall of the conditioned NK cell response. NMDA but not the kainate/AMPA receptors, are believed to be involved. The levels of glutamate that were released and/or taken up also appeared to be critical in that interruption of glutamate release and/or uptake blocked the conditioned NK cell response. Results from the HPLC analysis, however, did not show any significant difference in the glutamate content between the conditioned and control brains.

Neurotoxic N-methyl-D-aspartate lesion of the ventral midbrain and mesopontine junction alters sleep-wake organization.

The dorsal regions of the midbrain and pons have been found to participate in sleep regulation. However, the physiological role of the ventral brainstem in sleep regulation remains unclear. We used N-methyl-D-aspartate-induced lesions of the ventral midbrain and pons to address this question. Unlike dorsal mesencephalic reticular formation lesions, which produce somnolence and electroencephalogram synchronization, we found that ventral midbrain lesions produce insomnia and hyperactivity. Marked increases in waking and decreases in slow wave sleep stage 1 (S1), stage 2 (S2) and rapid eye movement sleep were found immediately after the lesion. Sleep gradually increased, but never returned to baseline levels (baseline/month 1 post-lesion: waking, 30.6 +/- 4.58%/62.3 +/- 10.1%; S1, 5.1 +/- 0.74/3.9 +/- 1.91%; S2, 46.2 +/- 4.74%/23.1 +/- 5.47%; rapid eye movement sleep, 14.1 +/- 3.15%/7.2 +/- 5.42%). These changes are comparable in magnitude to those seen after basal forebrain lesions. Neuronal degeneration was found in the ventral rostral pons and midbrain, including the substantia nigra, ventral tegmental area, retrorubral nucleus, and ventral mesencephalic and rostroventral pontine reticular formation. We conclude that nuclei within the ventral mesencephalon and rostroventral pons play an important role in sleep regulation.

Study on the vascular reactivity and alpha 1-adrenoceptors of portal hypertensive rats.

1. Vascular hyporesponsiveness in portal hypertension has been demonstrated to various vasoconstrictors including noradrenaline (NA). The present study aimed to determine whether the attenuated vascular responsiveness to NA is due to a change in the affinity or the number of alpha 1-adrenoceptors. 2. Partial portal vein ligation (PVL) was performed in Sprague-Dawley rats to produce portal hypertension. Vascular responsiveness to NA was assayed in portal vein, mesenteric artery or tail artery. The affinity and number of alpha 1-adrenoceptors were determined by specific binding of [125I]-HEAT (2-beta-4-hydroxy-3-iodophenyethyl-aminomethyltetralone). 3. In the presence of yohimbine (10(-7) M, an alpha 2-adrenoceptor antagonist), propranolol (10(-6) M, a beta-adrenoceptor antagonist), and two catecholamine uptake inhibitors, desipramine (10(-7) M) and normetanephrine (10(-6) M), the maximum responses to NA were decreased in all three blood vessels of PVL rats: 45% decrease in portal vein, 25% in mesenteric artery and 18% in tail artery. 4. The EC50 values of NA and the pA2 values of prazosin, an alpha 1-adrenoceptor antagonist, in all three blood vessels were not significantly different between sham-operated and PVL rats. 5. The KD and Bmax values for specific binding of [125I]-HEAT or the Ki values for NA in the crude membrane preparations of either mesenteric artery or tail artery were also not significantly different between the two groups. 6. It is concluded that the vascular hyporesponsiveness to NA in the mesenteric artery or tail artery of PVL rats is not due to changes in the affinity or number of alpha 1-adrenoceptors.

Termination of digitalis-induced ventricular tachycardias by clonidine involves central alpha 2-adrenoceptors in cats.

1. Effects of intravenous (i.v.) and intravertebral arterial (i.a.) administration of the alpha 2-adrenoceptor agonist, clonidine (Clon) and its antagonist, yohimbine (Yoh, 0.5 mg kg-1, i.v.; 0.05 mg kg-1, i.a.), on ventricular tachycardia (VT) induced by intravenous acetylstrophanthidin (AS) were studied in cats anaesthetized with intraperitoneal chloralose. 2. AS dose-dependently produced cardiac arrhythmias including complete atrioventricular conduction block (118 +/- 14 micrograms kg-1, i.v.), junctional tachycardia (128 +/- 20 micrograms kg-1, i.v.), multiform ventricular premature beats (157 +/- 21 micrograms kg-1, i.v.) and sustained VT (220 +/- 23 micrograms kg-1, i.v.). 3. Doses of Clon (i.v.) required for termination of VT following i.v. Yoh (62.9 +/- 5.2 micrograms kg-1) or i.a. Yoh (88.5 +/- 16.3 micrograms kg-1) were higher than those for termination of VT without Yoh administration (28.3 +/- 6.2 micrograms kg-1). Doses of Clon (i.a.) required for termination of VT without or with i.a. Yoh administration were 5.8 +/- 1.0 or 14.8 +/- 3.7 micrograms kg-1, respectively, and they were significantly different. 4. These experiments demonstrate that either i.v. or i.a. Yoh antagonizes the antiarrhythmic effect of Clon on AS-induced VT. Since small doses of Clon administered i.a. act predominantly on the central nervous system, we suggest that its antiarrhythmic effect is likely to be on central alpha 2-adrenoceptors in the central nervous system.

Effect of diethylmaleate on liver extracellular glutathione levels before and after global liver ischemia in anesthetized rats.

Glutathione (GSH), present in a high concentration in the liver, serves important protective functions. We investigated the effect of lowered tissue GSH content, accomplished by diethylmaleate (DEM) administration, on liver extracellular GSH levels before and after global ischemia in anesthetized rats. Liver extracellular GSH levels were determined by microdialysis perfusion and an on-line high performance liquid chromatography system. Global liver ischemia was induced by ligation of the hepatic pedicles including the hepatic artery, portal vein, and bile duct. DEM (4 mmol/kg) significantly lowered both the liver tissue GSH levels (1.36 +/- 0.26 micromol/g wet wt vs 9.50 +/- 0.55 micromol/g wet wt for the untreated) and the liver extracellular GSH levels (4.3 +/- 2.4 microM vs 25.2 +/- 8.7 microM for the untreated). Global liver ischemia induced a dramatic increase in the liver extracellular GSH level. Although the liver tissue GSH level was lowered following DEM treatment, DEM administration did not affect significantly ischemia-induced elevation of extracellular GSH (when presented as fold increase relative to basal value). In conclusion, DEM showed a direct effect on liver extracellular GSH content in anesthetized rats. However, DEM treatment did not affect the relative release of GSH following global liver ischemia.