Anxiety symptoms bias memory assessment in older adults.

BACKGROUND: Older adults with anxiety and/or depression experience additional memory dysfunction beyond that of the normal aging process. However, few studies have examined test bias in memory assessments due to anxiety and/or depressive symptoms. The current study investigated the influence of self-reported symptoms of anxiety and depression on the measurement equivalence of memory tests in older adults. METHOD: This is a secondary analysis of the Advanced Cognitive Training for Independent and Vital Elderly dataset, a randomized controlled trial of community-dwelling older adults. Baseline data were included in this study (n = 2802). Multiple indicators multiple causes modeling was employed to assess for measurement equivalence, differential item functioning (DIF), in memory tests. RESULTS: The DIF was present for anxiety symptoms but not for depressive symptoms, such that higher anxiety placed older adults at a disadvantage on measures of memory performance. Analysis of DIF impact showed that compared with participants scoring in the bottom quartile of anxious symptoms, participants in the upper quartile exhibited memory performance scores that were 0.26 standard deviation lower. CONCLUSION: Anxious but not depressive symptoms introduce test bias into the measurement of memory in older adults. This indicates that memory models for research and clinical purposes should account for the direct relationship between anxiety symptoms and memory tests in addition to the true relationship between anxiety symptoms and memory construct. These findings support routine assessments of anxiety symptoms among older adults in settings in which cognitive testing is being conducted. Copyright © 2016 John Wiley & Sons, Ltd.

Phylogeography of microbial phototrophs in the dry valleys of the high Himalayas and Antarctica.

High-elevation valleys in dry areas of the Himalayas are among the most extreme, yet least explored environments on Earth. These barren, rocky valleys are subjected to year-round temperature fluctuations across the freezing point and very low availability of water and nutrients, causing previous workers to hypothesize that no photoautotrophic life (primary producers) exists in these locations. However, there has been no work using modern biogeochemical or culture-independent molecular methods to test the hypothesis that photoautotrophs are absent from high Himalayan soil systems. Here, we show that although microbial biomass levels are as low as those of the Dry Valleys of Antarctica, there are abundant microbial photoautotrophs, displaying unexpected phylogenetic diversity, in barren soils from just below the permanent ice line of the central Himalayas. Furthermore, we discovered that one of the dominant algal clades from the high Himalayas also contains the dominant algae in culture-independent surveys of both soil and ice samples from the Dry Valleys of Antarctica, revealing an unexpected link between these environmentally similar but geographically very distant systems. Phylogenetic and biogeographic analyses demonstrated that although this algal clade is globally distributed to other high-altitude and high-latitude soils, it shows significant genetic isolation by geographical distance patterns, indicating local adaptation and perhaps speciation in each region. Our results are the first to demonstrate the remarkable similarities of microbial life of arid soils of Antarctica and the high Himalayas. Our findings are a starting point for future comparative studies of the dry valleys of the Himalayas and Antarctica that will yield new insights into the cold and dry limits to life on Earth.

Assessment of lake sensitivity to acidic deposition in national parks of the Rocky Mountains.

The sensitivity of high-elevation lakes to acidic deposition was evaluated in five national parks of the Rocky Mountains based on statistical relations between lake acid-neutralizing capacity concentrations and basin characteristics. Acid-neutralizing capacity (ANC) of 151 lakes sampled during synoptic surveys and basin-characteristic information derived from geographic information system (GIS) data sets were used to calibrate the statistical models. The explanatory basin variables that were considered included topographic parameters, bedrock type, and vegetation type. A logistic regression model was developed, and modeling results were cross-validated through lake sampling during fall 2004 at 58 lakes. The model was applied to lake basins greater than 1 ha in area in Glacier National Park (n = 244 lakes), Grand Teton National Park (n = 106 lakes), Great Sand Dunes National Park and Preserve (n = 11 lakes), Rocky Mountain National Park (n = 114 lakes), and Yellowstone National Park (n = 294 lakes). Lakes that had a high probability of having an ANC concentration <100 microeq/L, and therefore sensitive to acidic deposition, are located in basins with elevations >3000 m, with <30% of the catchment having northeast aspect and with >80% of the catchment bedrock having low buffering capacity. The modeling results indicate that the most sensitive lakes are located in Rocky Mountain National Park and Grand Teton National Park. This technique for evaluating the lake sensitivity to acidic deposition is useful for designing long-term monitoring plans and is potentially transferable to other remote mountain areas of the United States and the world.

Na,K-ATPase in skeletal muscle: two populations of beta-spectrin control localization in the sarcolemma but not partitioning between the sarcolemma and the transverse tubules.

We used immunological approaches to study the factors controlling the distribution of the Na,K-ATPase in fast twitch skeletal muscle of the rat. Both alpha subunits of the Na,K-ATPase colocalize with beta-spectrin and ankyrin 3 in costameres, structures at the sarcolemma that lie over Z and M-lines and in longitudinal strands. In immunoprecipitates, the alpha1 and alpha2 subunits of the Na,K-ATPase as well as ankyrin 3 associate with beta-spectrin/alpha- fodrin heteromers and with a pool of beta-spectrin at the sarcolemma that does not contain alpha-fodrin. Myofibers of mutant mice lacking beta-spectrin (ja/ja) have a more uniform distribution of both the alpha1 and alpha2 subunits of the Na,K-ATPase in the sarcolemma, supporting the idea that the rectilinear sarcomeric pattern assumed by the Na,K-ATPase in wild-type muscle requires beta-spectrin. The Na,K-ATPase and beta-spectrin are distributed normally in muscle fibers of the nb/nb mouse, which lacks ankyrin 1, suggesting that this isoform of ankyrin is not necessary to link the Na,K-ATPase to the spectrin-based membrane skeleton. In immunofluorescence and subcellular fractionation experiments, the alpha2 but not the alpha1 subunit of the Na,K-ATPase is present in transverse (t-) tubules. The alpha1 subunit of the pump is not detected in increased amounts in the t-tubules of muscle from the ja/ja mouse, however. Our results suggest that the spectrin-based membrane skeleton, including ankyrin 3, concentrates both isoforms of the Na,K-ATPase in costameres, but that it does not play a significant role in restricting the entry of the alpha1 subunit into the t-tubules.

Class I areas at risk: event-based nitrogen deposition to a high-elevation, western site.

Between June 1, 2000 and September 30, 2000, 32 precipitation events were sampled near Telluride, CO at an elevation of 3200 m. The wet deposition site was operated following protocols of the Atmospheric Integrated Research Monitoring Network (AIRMoN), a network of the National Atmospheric Deposition Network (NADP). Inorganic nitrogen deposition at the Telluride site of 1.41 kg ha(-1) during the study period was 25 to 50% higher than nearby NADP sites. In turn, nitrogen deposition at these NADP sites was similar to high-elevation sites in and near the Colorado Front Range that have been shown to be impacted by atmospheric deposition of inorganic nitrogen in wetfall. Power plant emissions are a likely source of a major portion of this elevated inorganic nitrogen in wetfall to the San Juan Mountains. Principal component analysis (PCA) shows that solutes formed by gases that are emitted from power plants were clustered tightly together, including nitrate, ammonium, sulfate, and chloride. Trajectory analysis, including both backward and forward trajectories, shows that the air masses that contributed to the precipitation events with high amounts of nitrogen deposition at the Telluride site passed directly over or near power plants. Our results suggest that Class I Wilderness Areas in and near the San Juan Mountains are at risk to ecosystem impairment at present rates of atmospheric deposition of inorganic nitrogen in wetfall. Deployment of proposed power plants to this area will likely increase the risk of degradation of resource values in nearby Class I areas. While these data were collected over a short time span, they indicate that establishment of an official AIRMoN site in the southwestern U.S. may be warranted.

Seasonal changes in the character and nitrogen content of dissolved organic matter in an alpine/subalpine headwater catchment.

We are studying the chemical quality of dissolved organic nitrogen (DON) in a high-elevation watershed in the Colorado Front Range. Samples were collected over the 2000 snowmelt runoff season at two sites across an alpine/subalpine ecotone to understand how the transition between the lightly vegetated alpine and forested reaches of the catchment influences the chemical character of DON. Samples were analyzed approximately weekly for dissolved organic material (DOM) content and chemical character. A subset of samples was analyzed for the elemental content of fulvic and hydrophilic acids. Concentrations of DON at both sites were highest in the spring at the initiation of snowmelt, decreased during snowmelt, and increased again during the late summer and fall. In contrast, concentrations of dissolved organic carbon (DOC) peaked on the ascending limb of the hydrograph and declined to seasonal minima on the descending limb of the hydrograph. The ratio of DOC:DON showed a seasonal shift at both sites with high values (40 to 55) during peak runoff in early summer and lower values (15 to 25) during low flows late in the runoff season. These results indicate that there was a seasonal change in the relative N content of DOM at both sites. Chemical fractionation of DOC showed that there were temporal and longitudinal changes in the chemical character of DOC. At the alpine site, the fulvic acid content of DOC decreased from 57% in June to 35% in September. The change in fulvic acid was less pronounced at the forested site, from 66% in June to 54% in September. Elemental analysis of fulvic and hydrophilic acids indicated that hydrophilic acids were N rich compared to fulvic acids. Additionally, fulvic and hydrophilic acids isolated at the alpine site had a lower C:N ratio than those isolated at the forested site. Similarly, the C:N ratio of organic acids at both sites was lower in September than in June during peak runoff. These differences appear to be a result of changes in both DOM precursor material and hydrologic flowpaths. Using C:N ratios of fulvic and hydrophilic acids, we estimate that nonhumic material carried between 54 to 73% of the organic N in surface water at the alpine site and 44 to 58% of the organic N in surface water at the subalpine site.

Power frequency magnetic field exposure and gap junctional communication in Clone 9 cells.

Exposure to a power-frequency magnetic field has been reported to produce a statistically significant inhibition of gap junctional communication (GJC) in Clone 9 cells that have been pre-stressed by treatment with low concentrations of chloral hydrate (CH) [C.F. Blackman, J.P. Blanchard, S.G. Benane, D.E. House, J.A. Elder, Double blind test of magnetic field effects on neurite outgrowth, Bioelectromagnetics, 19 (1998) 204-209]. This observation might provide mechanistic insight into the possible role of electromagnetic fields (EMFs) in the carcinogenic process, since cancer cells frequently show decreased or absent GJC, and tumor promoting chemicals have been observed to inhibit GJC. Magnetic field exposure conditions were 45 Hz, 23.8 microT rms + parallel DC 36.6 microT, for 30 min of exposure. The responses of Clone 9 cells to the GJC-inhibiting effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate and the chemical CH were evaluated and compared to reported results [S.G. Benane, C.F. Blackman, D.E. House, Effects of perchloroethylene and its metabolites on intercellular communication in Clone 9 rat liver cells, J. Toxicol. Environ. Health, 48 (1996) 427-437]. Before magnetic field exposure, cells were exposed for 24 h to either 3 (nine experiments) or 5 mM (11 experiments) CH to produce GJC of 67% or 50%, respectively, relative to unexposed controls. GJC was assessed microscopically using the scrape-loading technique and a blinded protocol. No statistically significant effect was observed due to magnetic field exposure with either CH concentration.

Cellular communication in clone 9 cells exposed to magnetic fields.

Magnetic-field exposure (45 Hz B(a.c.) over a flux density range of 7.7 to 49.9 microT r.m.s. with parallel B(d.c.) of 36.6 microT) has been reported by Blackman and coworkers to inhibit gap junction intercellular communication in Clone 9 cells treated with chloral hydrate for 24 h prior to field exposure in accord with predictions of the ion parametric resonance model. The study reported here is an attempt to reproduce this effect. Baseline experiments showed that growth in culture and state of confluence at time of addition of chloral hydrate were comparable in both laboratories. PMA inhibited cell-cell communication in a dose-dependent manner, similar to the results of Blackman and coworkers, whereas cells in the present study were somewhat more sensitive to chloral hydrate than reported by Blackman and coworkers. A total of 38 exposure experiments were undertaken using a 45 Hz magnetic field with a flux density of 23.8 microT r.m.s., in parallel with a 36.6-microT static magnetic field for 40 to 45 min, after pretreatment with 2.5 mM chloral hydrate for 24 h. In 14 unblinded experiments, a small but statistically significant effect of magnetic-field exposure was observed, but due to the subjective nature of the assay, it was deemed essential to carry out blinded experiments. The remaining 24 experiments were blinded. In 15 blinded experiments, cells purchased from the American Type Culture Collection and grown only in this laboratory were used, while in 9 experiments, the cells had originally been grown in Blackman's laboratory and were subsequently sent to this laboratory. There was no statistically significant effect of magnetic-field exposure on gap junction intercellular communication in these blinded experiments using either cell line.

Membrane skeleton of innervated and denervated fast- and slow-twitch muscle.

We used confocal microscopy and immunoblotting to study membrane skeletal proteins of fast-twitch (extensor digitorum longus) and slow-twitch (soleus) muscles of the adult rat. In the extensor digitorum longus (EDL), beta-spectrin concentrates in costameres, whereas dystrophin is enriched at costameres but is also present in intercostameric regions. In the soleus, beta-spectrin and dystrophin underlie much of the sarcolemma, and intercostameric regions are difficult to detect. The EDL sarcolemma reorganizes following denervation to resemble soleus sarcolemma, but denervation does not significantly affect the latter. Consistent with these observations, soleus contains similar amounts of dystrophin but more beta-spectrin than EDL. Denervation increases beta-spectrin levels only in the EDL and dystrophin levels in both muscles. Denervation does not affect beta-fodrin, a beta-spectrin homolog expressed in embryonic myofibers. Thus, neuromuscular activity controls sarcolemmal organization and the levels of beta-spectrin and dystrophin, but not postnatal downregulation of beta-fodrin. The differences in organization of the sarcolemma may underlie the differential susceptibility of fast and slow myofibers to dystrophinopathies.

Differential distribution of dystrophin and beta-spectrin at the sarcolemma of fast twitch skeletal muscle fibers.

We used double label immunofluorescence and confocal microscopy to examine the organization of beta-spectrin and dystrophin at the sarcolemma of fast twitch myofibers in the Extensor Digitorum Longus (EDL) of the rat. Both beta-spectrin and dystrophin are concentrated in costameres, a rectilinear sarcolemmal array composed of longitudinal strands and transverse elements overlying Z and M lines. In contrast, intercostameric regions, lying between these linear structures, contain significant levels of dystrophin but little detectable beta-spectrin. The dystrophin-associated proteins, syntrophin and beta-dystroglycan, are also concentrated at costameres but, like dystrophin, are present in intercostameric regions as well. Dystrophin is present at costameres and intercostameric regions in fast twitch muscles of the mouse but is absent from all regions of the sarcolemma in the mdx mouse, which lacks dystrophin. Areas of the sarcolemma near myonuclei also contain dystrophin without beta-spectrin, consistent with the idea that the distribution of dystrophin at the sarcolemma is not dependent on beta-spectrin. We conclude that dystrophin is present under all areas of the sarcolemma. The increased fragility of the sarcolemma in patients with Duchennes muscular dystrophy may be explained in part by the absence of dystrophin not only from costameres, but also from intercostameric regions.

Extensive but coordinated reorganization of the membrane skeleton in myofibers of dystrophic (mdx) mice.

We used immunofluorescence techniques and confocal imaging to study the organization of the membrane skeleton of skeletal muscle fibers of mdx mice, which lack dystrophin. beta-Spectrin is normally found at the sarcolemma in costameres, a rectilinear array of longitudinal strands and elements overlying Z and M lines. However, in the skeletal muscle of mdx mice, beta-spectrin tends to be absent from the sarcolemma over M lines and the longitudinal strands may be disrupted or missing. Other proteins of the membrane and associated cytoskeleton, including syntrophin, beta-dystroglycan, vinculin, and Na,K-ATPase are also concentrated in costameres, in control myofibers, and mdx muscle. They also distribute into the same altered sarcolemmal arrays that contain beta-spectrin. Utrophin, which is expressed in mdx muscle, also codistributes with beta-spectrin at the mutant sarcolemma. By contrast, the distribution of structural and intracellular membrane proteins, including alpha-actinin, the Ca-ATPase and dihydropyridine receptors, is not affected, even at sites close to the sarcolemma. Our results suggest that in myofibers of the mdx mouse, the membrane- associated cytoskeleton, but not the nearby myoplasm, undergoes widespread coordinated changes in organization. These changes may contribute to the fragility of the sarcolemma of dystrophic muscle.

Cloricromene reduces myocardial infarct size in rabbits when administered during the early reperfusion period.

Cloricromene is a coumarin derivative without anticoagulant activities that has recently been found to decrease myocardial infarct size after an ischemic-reperfusion injury. This study seeks to determine when the cardioprotective action of cloricromene is exerted in an in vivo rabbit model of ischemic-reperfusion injury. Forty-nine rabbits subjected to 30 min of coronary occlusion and 120 min of reperfusion were randomized into five groups: VEH (n = 11) received saline vehicle; IR (n = 9) received an infusion of cloricromene starting at the onset of ischemia at 8 micrograms.kg-1.min-1; R(-5)(n = 9) and R(+30)(n = 9) received an infusion of cloricromene at 8 micrograms.kg-1.min-1 starting 5 min before reperfusion and 30 min after reperfusion, respectively; and RB(-5)(n = 11) received 300 micrograms/kg bolus of cloricromene 5 min before reperfusion followed by an infusion of 8 micrograms.kg-1.min-1. All infusions were continued until the end of the reperfusion period. Myocardial infarct size was significantly reduced in groups IR, R(-5), and RB(-5). We conclude that cloricromene's effective time of action occurs prior to the first 30 min of the reperfusion period.

Small, membrane-bound, alternatively spliced forms of ankyrin 1 associated with the sarcoplasmic reticulum of mammalian skeletal muscle.

We have recently found that the erythroid ankyrin gene, Ank1, expresses isoforms in mouse skeletal muscle, several of which share COOH-terminal sequence with previously known Ank1 isoforms but have a novel, highly hydrophobic 72-amino acid segment at their NH2 termini. Here, through the use of domain-specific peptide antibodies, we report the presence of the small ankyrins in rat and rabbit skeletal muscle and demonstrate their selective association with the sarcoplasmic reticulum. In frozen sections of rat skeletal muscle, antibodies to the spectrin-binding domain (anti-p65) react only with a 210-kD Ank1 and label the sarcolemma and nuclei, while antibodies to the COOH terminus of the small ankyrin (anti-p6) react with peptides of 20 to 26 kD on immunoblots and decorate the myoplasm in a reticular pattern. Mice homozygous for the normoblastosis mutation (gene symbol nb) are deficient in the 210-kD ankyrin but contain normal levels of the small ankyrins in the myoplasm. In nb/nb skeletal muscle, anti-p65 label is absent from the sarcolemma, whereas anti-p6 label shows the same distribution as in control skeletal muscle. In normal skeletal muscle of the rat, anti-p6 decorates Z lines, as defined by antidesmin distribution, and is also present at M lines where it surrounds the thick myosin filaments. Immunoblots of the proteins isolated with rabbit sarcoplasmic reticulum indicate that the small ankyrins are highly enriched in this fraction. When expressed in transfected HEK 293 cells, the small ankyrins are distributed in a reticular pattern resembling the ER if the NH2-terminal hydrophobic domain is present, but they are uniformly distributed in the cytosol if this domain is absent. These results suggest that the small ankyrins are integral membrane proteins of the sarcoplasmic reticulum. We propose that, unlike the 210-kD form of Ank1, previously localized to the sarcolemma and believed to be a part of the supporting cytoskeleton, the small Ank1 isoforms may stabilize the sarcoplasmic reticulum by linking it to the contractile apparatus.

Intravascular adenosine at reperfusion reduces infarct size and neutrophil adherence.

BACKGROUND: Adenosine has been shown to reduce infarct size predominantly during reperfusion by adenosine A2-receptor-mediated processes. This cardioprotection may involve inhibition of events in the vascular compartment, such as adherence-independent and adherence-dependent actions of neutrophils. This study tested the hypothesis that adenosine exerts its cardioprotection during reperfusion by targeting effectors in the vascular compartment. METHODS: Polyadenylic acid (molecular weight, 230,000 daltons) was used as an intravascularly confined adenosine mimetic. In anesthetized New Zealand white rabbits, the left coronary artery was occluded for 30 minutes and reperfused for 120 minutes. RESULTS: Polyadenylic acid (1 mg/kg bolus, 0.5 mg kg-1 h-1) given 5 minutes before reperfusion significantly (p < 0.05) reduced infarct size compared with vehicle (23% +/- 2% versus 37% +/- 2% area at risk). The A1-antagonist KW-3902 had no effect on this polyadenylic acid-induced protection (17% +/- 3%), whereas the A1-A2 antagonist sulfophenytheophylline blocked this infarct size reduction (41% +/- 2%). In vitro adherence of platelet-activating factor-activated neutrophils to thoracic aortic endothelium was significantly diminished by polyadenylic acid (185 +/- 12 neutrophils/mm2 versus 36 +/- 4 neutrophils/mm2 endothelial surface). Sulfophenytheophylline inhibited this effect (280 +/- 6 neutrophils/mm2), whereas KW-3902 did not (31 +/- 7 neutrophils/mm2). CONCLUSIONS: An intravascular adenosine mimetic agent exerts cardioprotection during reperfusion by targeting receptor-mediated mechanisms in the intravascular compartment, possibly involving inhibition of neutrophil-related processes.

Adenosine A2-receptor activation inhibits neutrophil-mediated injury to coronary endothelium.

Adenosine (ADO) attenuates polymorphonuclear neutrophil (PMN)-mediated damage, partly by inhibiting superoxide anion (O2-.) generation and PMN adherence to the coronary artery endothelium. This study tests the hypothesis that the antineutrophil effects of ADO are mediated by A2-receptor activation. Isolated canine PMN were activated by 100 nM platelet-activating factor (PAF). Compared with untreated activated PMN (100%), ADO attenuated O2-. production (46 +/- 9% of activated PMN), which was mimicked by the A2 agonist CGS-21680 (50 +/- 6% of activated PMN), unaltered by A1-selective antagonism with KW-3902 in the presence of ADO (40 +/- 7%), but blocked by combined A1-A2 blockade with 8-p-sulfophenyl theophylline (8-SPT, 94 +/- 14%). ADO reduced adherence of fluorescent PMN to endothelial surfaces of isolated canine coronary artery segments from 174 +/- 12 to 29 +/- 9/mm2 (P < 0.01), which was unaltered by A1 antagonism (35 +/- 7/mm2) but was reversed by 8-SPT (150 +/- 11/mm2). CGS-21680 inhibited adherence (48 +/- 8/mm2), comparable to that of ADO. Canine coronary artery rings were incubated with activated PMN to induce injury to the endothelium. The concentration of drug required to elicit 50% of maximal relaxation (-log M) derived from dose-relaxation responses to acetylcholine in PMN-damaged rings was significantly (P < 0.05) less in ADO-treated (6.88 +/- 0.08) and CGS-21680-treated (7.12 +/- 0.09) rings than untreated rings (6.54 +/- 0.10). This protection with ADO was reversed by inclusion of 8-SPT (6.49 +/- 0.12) but not KW-3902 (6.96 +/- 0.07). We conclude that ADO reduces PMN-induced coronary endothelial injury by A2-receptor-mediated inhibition of O2-. generation and adherence.

Supplemental L-arginine during cardioplegic arrest and reperfusion avoids regional postischemic injury.

Unenhanced hypothermic cardioplegia does not prevent postischemic endothelial and contractile dysfunction in hearts subjected to antecedent regional or global ischemia. This study tested the hypothesis that supplementing blood cardioplegic solution and reperfusion with the nitric oxide precursor L-arginine would preserve endothelial function, reduce infarct size, and reverse postcardioplegia regional contractile dysfunction by the L-arginine-nitric oxide pathway. In 23 anesthetized dogs, the left anterior descending coronary artery was ligated for 90 minutes, after which total bypass was established for surgical "revascularization." In 10 dogs, unsupplemented multidose hypothermic blood cardioplegic solution was administered for a total of 60 minutes of cardioplegic arrest. In eight dogs, L-arginine was given intravenously (4 mg/kg per minute) and in blood cardioplegic solution (10 mmol) during arrest. In five dogs, the nitric oxide synthesis blocker N omega-nitro-L-arginine (1 mmol) was used to block the L-arginine-nitric oxide pathway during cardioplegia and reperfusion. Infarct size (triphenyltetrazolium chloride) as percent of the area at risk was significantly reduced by L-arginine compared with blood cardioplegic solution (28.2% +/- 4.1% versus 40.5% +/- 3.5%) and was reversed by N omega-nitro-L-arginine to 68.9% +/- 3.0% (p < 0.05). Postischemic regional segmental work in millimeters of mercury per millimeter (sonomicrometry) was significantly better with L-arginine (92 +/- 15) versus blood cardioplegic solution (28 +/- 3) and N omega-nitro-L-arginine (26 +/- 6). Segmental diastolic stiffness was significantly lower with L-arginine (0.46 +/- 0.06) compared with blood cardioplegic solution (1.10 +/- 0.11) and was significantly greater with N omega-nitro-L-arginine (2.70 +/- 0.43). In ischemic-reperfused left anterior descending coronary arterial vascular rings, maximum relaxation responses to acetylcholine, the stimulator of endothelial nitric oxide, was depressed in the blood cardioplegic solution group (77% +/- 4%) and was significantly reversed by L-arginine (92% +/- 3%). Smooth muscle function was unaffected in all groups. We conclude that cardioplegic solution supplemented with L-arginine reduces infarct size, preserves postischemic systolic and diastolic regional function, and prevents arterial endothelial dysfunction via the L-arginine-nitric oxide pathway.

Endogenous nitric oxide (NO) protects against ischaemia-reperfusion injury in the rabbit.

OBJECTIVES: Recent studies suggest that nitric oxide (NO) is deleterious in models of shock and hypoxia-reoxygenation However, the role of endogenous NO in ischaemia-reperfusion injury in vivo remains controversial. We tested the hypothesis that blockade of endogenous NO produced during myocardial ischaemia-reperfusion or during reperfusion alone in vivo increases infarct size after coronary occlusion in the rabbit, and conversely, supplementation with L-arginine would reduce infarct size. METHODS: Ketamine-xylazine anaesthetised New Zealand white rabbits were subjected to left coronary artery occlusion for 30 min and reperfusion for 120 min. The rabbits were divided into five groups: (1) saline (VEH); (2) L-nitro arginine (L-NA), a NO-synthase inhibitor, was infused intravenously (15 mg/kg bolus followed by 7.5 mg/kg h-1) before coronary occlusion to block NO synthase activity during ischaemia and reperfusion (IR); (3) L-NA was administered during reperfusion only (R) at the same dose as in the IR group; (4) D-arginine (D-ARG) (25 mg/kg bolus followed by 4 mg/kg min-1), the non-metabolised enantiomer of L-arginine was infused intravenously during reperfusion only; (5) L-arginine (L-ARG) (25 mg/kg bolus followed by 4 mg/kg min-1), the physiological precursor of NO, was infused intravenously during reperfusion only. RESULTS: L-NA infusion in the IR and R groups caused an increase in mean arterial pressure and a decrease in heart rate; however, no significant change in pressure rate product (PRP) occurred immediately after drug infusion. PRP did not change significantly during the experiment across groups except at the end of reperfusion. The area at risk was comparable in all groups, averaging 29(1)%. The infarct size (triphenyltetrazolium chloride) expressed as a percent of area at risk was 27(2)% for the untreated vehicle group. In contrast, L-NA significantly (P < 0.05) increased infarct size in the IR group, 51(2)%; this augmented infarct size persisted when NO synthase activity was blocked during reperfusion only in the R group, 50(2)%. There was no significant (P < 0.05) difference in infarct size between the IR and the R groups. D-ARG-treated group showed a comparable increase in infarct size 48(2)% versus the IR and R groups. However, supplementation of NO with L-arginine (L-ARG) showed no reduction in infarct size, 24(3)%, over vehicle group (VEH). CONCLUSIONS: We conclude that (1) blockade of NO synthase activity with L-NA increases infarct size, (2) this effect was expressed primarily during reperfusion, (3) D-arginine mimicked the infarct augmentation of L-NA, while (4) L-arginine supplementation did not reduce infarct size. These data imply that endogenous NO production exerts a tonic cardioprotective effect on myocardial infarct following coronary reperfusion.

Acadesine reduces myocardial infarct size by an adenosine mediated mechanism.

OBJECTIVE: The aim was to test the hypotheses that acadesine (1) augments endogenous interstitial fluid (ISF) adenosine during ischaemia, and (2) reduces infarct size by adenosine receptor mediated mechanisms. METHODS: To test these hypotheses, the left coronary artery of anaesthetised rabbits (n = 33) was occluded for 30 min and reperfused for 120 min. Acadesine (1 mg.kg-1.min-1 for 5 min, then 0.2 mg.kg-1.min-1) was infused intravenously beginning 30 min before coronary occlusion and ending 30 min after reperfusion. The area at risk was comparable in all groups, averaging 34.7 (SEM 2.2%) of the left ventricle. In separate studies (n = 22), estimates of ISF adenosine and adenosine metabolites were obtained by cardiac microdialysis. Although dialysate adenosine levels increased significantly in the area at risk during ischaemia in the untreated group [from 0.044(0.008) to 0.339(0.146) microM], acadesine did not significantly augment dialysate adenosine levels before or during ischaemia [preischaemia = 0.094(0.032) microM; ischaemia = 0.542(0.262) microM]. In addition, there was no significant difference in dialysate adenosine concentrations during the first 10 min of reperfusion, after which adenosine levels returned to baseline levels. A 2.5-fold large dose failed to increase interstitial fluid adenosine. However, the adenosine receptor blocker 8-p-sulphophenyltheophylline (SPT) in the presence of acadesine increased ISF adenosine fourfold. Acadesine significantly (P < 0.05) reduced infarct size [n = 8, 19.7(2.9)% of risk area] compared with the untreated group [n = 8, 29.4(1.3)%]. This infarct size reduction with acadesine was antagonised by SPT given during ischaemia-reperfusion [n = 8, 46.2(3.0)%] or only during reperfusion [n = 9, 42.7(2.6)%. CONCLUSIONS: Acadesine reduces infarct size by an adenosine mediated mechanism, but this cardioprotective action is not associated with significantly augmented interstitial fluid adenosine levels.

Adenosine in blood cardioplegia prevents postischemic dysfunction in ischemically injured hearts.

Adenosine (ADO) is an endogenous cardioprotective autacoid that exerts receptor-mediated cardioprotection from ischemic-reperfusion injury. This study tested the hypothesis that blood cardioplegia (BCP) supplemented with ADO reduces postischemic left ventricular dysfunction in ischemically injured hearts. Twenty-one anesthetized dogs on total bypass were subjected to 30 minutes of normothermic global ischemia. Cold (4 degrees C) potassium BCP was then delivered every 20 minutes for 60 minutes of cardioplegic arrest. In 7 dogs, unsupplemented BCP was used; in 7 dogs, BCP was supplemented with 400 mumol/L ADO; and, in 7 dogs, ADO receptors were blocked with 8-p-sulfophenyltheophylline (30 mg/kg) given with 400 mumol/L ADO in BCP. Preischemic and postischemic left ventricular systolic function was assessed by the slope and volume axis intercept of the end-systolic pressure-volume (impedance catheter) relationship (ESPVR). In unsupplemented BCP, the postischemic slope of the ESPVR was significantly depressed by 42% versus the preischemic value (from 6.8 +/- 1.2 mm Hg/mL to 3.9 +/- 0.4 mm Hg/mL; p < 0.05 versus the preischemic value). In contrast, BCP supplemented with ADO was found to restore the postischemic ESPVR slope to preischemic levels (7.7 +/- 1.0 mm Hg/mL versus 7.4 +/- 1.2 mm Hg/mL, respectively). This cardioprotection was reversed by 8-p-sulfophenyltheophylline (9.9 +/- 1.5 mm Hg/mL versus 4.5 +/- 0.7 mm Hg/mL; p < 0.05 versus the preischemic value). Postischemic plasma creatinine kinase activity was elevated equally in all groups over the baseline values. We conclude that ADO in BCP attenuates postcardioplegia dysfunction in severely injured hearts through the operation of receptor-mediated mechanisms.

Pentostatin-augmented interstitial adenosine prevents postcardioplegia injury in damaged hearts.

This study tests the hypothesis that the adenosine deaminase inhibitor pentostatin (2-deoxycoformycin), when given before ischemia or during infusions of blood cardioplegia, augments interstitial adenosine levels and prevents postcardioplegia dysfunction in hearts with antecedent ischemia. Twenty-one anesthetized dogs were placed on cardiopulmonary bypass, and the hearts were made globally ischemic for 30 minutes. Dogs received blood cardioplegia with no pentostatin (BCP group, n = 6), pretreatment pentostatin (0.2 mg/kg) infused 5 minutes before global ischemia (PS-PTx group, n = 7), or pentostatin included only in the blood cardioplegia without pretreatment (PS-BCP group, n = 8). Microdialysate myocardial adenosine levels (an index of interstitial fluid levels) increased only modestly in the BCP group (from 0.55 +/- 0.13 microM to 2.64 +/- 0.50 microM) and the PS-BCP group (from 0.55 +/- 0.18 microM to 1.08 +/- 0.48 microM) during normothermic ischemia, but interstitial adenosine levels were not augmented further during cardioplegic arrest in either group. In contrast, the adenosine level in the PS-PTx group was significantly (p < 0.05) augmented during global ischemia (from 0.50 +/- 0.13 microM to 63.16 +/- 28.08 microM) and cardioplegia infusion (to 15.26 microM +/- 5.61 microM). Relative to baseline, postischemic left ventricular performance (end-systolic pressure-volume relation) was depressed in both the BCP (from 5.5 +/- 1.2 mm Hg/mL to 3.8 +/- 0.4 mm Hg/mL) and PS-BCP groups (from 7.1 +/- 0.9 mm Hg/mL to 3.8 +/- 0.7 mm Hg/mL). In contrast, PS-PTx restored postischemic performance (from 6.2 +/- 0.5 mm Hg/mL to 7.5 +/- 0.9 mm Hg/mL).(ABSTRACT TRUNCATED AT 250 WORDS)