[Why do we grow old? Theories on age and death].
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Age Factors↗
Biomedical subjects
K Ytrehus
Publications and source records attributed to K Ytrehus.
Blockade of the KATP-channel by glibenclamide aggravates ischemic injury, and counteracts ischemic preconditioning.
Blocking of the KATP-channel with glibenclamide has been shown to abolish the infarct-reducing effect of ischemic preconditioning in dog and swine. In the rabbit the results have been divergent purportedly related to anaesthesia. The aim of this study was to investigate the importance of the KATP-channel in a rabbit model where anaesthesia was not a confounding factor. Isolated rabbit hearts perfused with a Krebs-Henseleit bicarbonate buffer were subjected to 30 min regional ischemia by ligating a coronary artery, followed by 120 min reperfusion. The preconditioning protocol was 5 min global ischemia and 10 min reperfusion. Glibenclamide (100 microM) was added to the perfusion solution before the preconditioning ischemia and stopped after 5 min regional ischemia. Infarcts were measured with tetrazolium staining and risk zones with fluorescent microspheres. The main results expressed as percent infarction of the risk zone +/- SEM for the different groups are as follows: control (n = 12) 26.8 +/- 3.2, ischemic preconditioning (IP) (n = 9) 7.3 +/- 1.5, (p < 0.05 vs. control), control + glibenclamide (n = 9) 46.9 +/- 7.3 (p < 0.05 vs. control), IP + glibenclamide (n = 10) 38.3 +/- 6.9 (p < 0.05 vs. IP). These results show that glibenclamide treatment aggravates ischemia. Also, under the influence of glibenclamide ischemic preconditioning was no longer effective in reducing infarct size in the isolated perfused rabbit heart.
Animals↗
Ultrastructural changes in the myocardial myocytic mitochondria: crucial step in the development of oxygen radical-induced damage in isolated rat hearts?
The present study focuses on the sequential development of myocardial ultrastructural changes produced by oxygen radicals. Isolated rat hearts were perfused with oxygen radicals, generated by hypoxanthine and xanthine oxidase, for 5 and 10 min followed by a 35-min recovery period. The frequency of, and the association between, ultrastructural changes were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph sarcolemmal, myocytic mitochondrial and myofilamental alterations were observed and graded as slight, moderate or severe. The myocytic nucleus and the endothelial cells were scored as normal or altered. Five min group: Among the cellular organelles examined, the myocytic mitochondria showed the highest frequency of alteration (in 15.3% of the micrographs). Among the grades of myocytic mitochondrial ultrastructural changes, slight alterations predominated (12.5%). Slight myocytic mitochondrial alterations were not significantly associated with the occurrence of ultrastructural changes of other cellular organelles. Endothelial ultrastructural alterations were sparse (1.5%). Ten min group: The frequency of altered organelles was greater when compared to the 5 min group. The myocytic mitochondria were still the most frequently altered component (61.7%), and myocytic mitochondrial ultrastructural alterations of all grades were strongly associated with the occurrence of other myocytic ultrastructural changes. In conclusion, the present study showed that myocytic mitochondrial changes predominated after both 5 and 10 min of oxygen radical exposure followed by recovery. In the 5 min group slight myocytic mitochondrial changes appeared independent of other myocardial changes, but in the 10 min group, however, myocytic mitochondrial changes were strongly associated with other myocardial ultrastructural changes. These results indicate that myocytic mitochondria are especially vulnerable to oxygen radicals, and further that myocytic mitochondrial ultrastructural changes may be a crucial step in the development of oxygen radical-induced myocardial damage.
Animals↗
Reduced infarct size in the rabbit heart in vivo by ethylisopropyl-amiloride. A role for Na+/H+ exchange.
Inhibition of Na+/H+ exchange with amiloride analogues has been shown to offer functional protection during ischemia and reperfusion and reduce infarct size in isolated rat hearts and intact pigs. The aim of the present study was to examine if pre- or postischemic treatment with ethylisopropylamiloride (EIPA), a selective Na+/H+ exchange inhibitor, could reduce infarct size in an in situ rabbit model of regional ischemia and reperfusion. Anesthetized, open-chest rabbits were subjected to 30 min of regional ischemia and 180 min of reperfusion. The risk zone was determined by fluorescent particles, and infarct size was determined by TTC staining. Preischemic treatment with EIPA (0.65 mg/kg) significantly reduced infarct size from 45.8 +/- 3.5% of the risk zone in the control group to 10.6 +/- 3.1% (p < 0.01). EIPA-treatment during the first part of the reperfusion period did not reduce infarct size compared to controls (41.9 +/- 3.5%). We conclude that EIPA, when administered prior to ischemia, reduces infarct size in the rabbit heart of in situ, a protection most likely due to inhibition of Na+/H+ exchange.
Amiloride↗
Ibuprofen abolishes the increase in leucocyte chemiluminescence observed during ischemic myocardial failure, but fails to improve hemodynamic function.
The aim of the study was to evaluate 1) whether the ability of leucocytes to produce oxygen radicals was increased by ischemia and 2) if ibuprofen pretreatment could influence leucocyte oxygen radical production, hemodynamic function, and myocardial oxygen consumption during acute ischemic myocardial failure. We studied two groups of anesthetized dogs (control and ibuprofen-treated), both subjected to coronary embolization with polystyrene microspheres (diameter 50 microns). The embolization procedure was ended when left-ventricular end-diastolic pressure in both groups exceeded 20 mm Hg. Before and after induction of ischemia leucocytes were isolated and stimulated with opsonized zymosan, and oxygen radical production was measured using the luminol-dependent chemiluminescence technique. Significant increase occurred in oxygen radical production (from 10.9 +/- 2.2 to 16.3 +/- 2.3 x 10(5) counts x 10(6) cells-1 x 60 min-1) 90 min after failure in the control group, whereas in ibuprofen-pretreated dogs oxygen radical production was unchanged. Hemodynamic registrations and myocardial oxygen consumption 90 min after failure were, however, not significantly different in control dogs and dogs pretreated with ibuprofen. Thus, in the present study, within the first 90 min of acute ischemic failure, a decrease in the ability of leucocytes to produce oxygen radicals was not related to significant changes in myocardial function.
Animals↗
Mitochondrial calcium in hearts subjected to lipid peroxidation with contracture development.
In the present study we have investigated isolated rat hearts perfused with oxygen radicals generated by xanthine oxidase and hypoxanthine. The influence of verapamil (1 mg.1(-1] pretreatment on oxygen radical-induced contracture development and decrease in contractility was examined. In addition, we have measured mitochondrial calcium and magnesium levels in control hearts and hearts perfused with oxygen radicals with and without addition of superoxide dismutase (SOD) and catalase. The presence of oxygen radical-induced lipid peroxidation was confirmed by the increased level of conjugated diens in lipid extracts from oxygen radical-perfused hearts. Verapamil prevented contracture development in hearts perfused with oxygen radicals. Diastolic pressure measured with a left ventricle balloon was at the end of the experiments. 18 +/- 3 mm Hg (mean +/- SEM) with verapamil and 66 +/- 9 mm Hg without (p less than 0.001). Perfusion with oxygen radicals resulted in a reduction in mitochondrial calcium from 14.63 +/- 0.93 to 8.26 +/- 0.61 nmol.mg-1 (p less than 0.001) which was partly reversed by superoxide dismutase and catalase. Mitochondrial magnesium levels were unchanged in all groups.
Animals↗
Estimates of free-radical production in rat and swine hearts: method and application of measuring malondialdehyde levels in fresh and frozen myocardium.
Toxic peroxides result when oxygen radicals react with various peroxidic precursors in tissue or blood. A colorimetric method based on reactions of malondialdehyde (MDA), a key intermediate in the formation of peroxides, has been described in fresh tissues. The present report adapts this assay to measure MDA levels in frozen heart muscle from rats and swine. Mean tissue values of MDA ranged from 154-353 nmol/g (n = 13) in fresh rat hearts perfused by the Langendorff technique. Values in frozen samples were 228 +/- 14 nmol MDA/g (n = 22). When mechanical function was increased in isolated working rat hearts, tissue MDA levels decreased by -25 delta % (P less than 0.025). In working swine hearts, increasing perfusate levels of unsaturated fatty acids caused a 42% increase in tissue MDA levels, P less than 0.001. Suppressing fatty acid oxidation with either oxfenicine or low flow ischemia caused no significant shifts in peroxide contents. Thus, the thiobarbituric acid method for MDA measurements is well adapted to analyzing frozen myocardium, and MDA levels appear sensitive to alterations in mechanical function and the presence of excess fatty acids.
Animals↗
Ultrastructural alterations during the critical phase of reperfusion: a stereological study in buffer-perfused isolated rat hearts.
The present study focuses on myocardial ultrastructural alterations during the early phase of reperfusion. Isolated buffer-perfused rat hearts were exposed to standard perfusion (control group,n = 10); 60 min of global ischemia (n = 10); 60 min of global ischemia followed by 2 min of reperfusion (n = 10); or 60 min of global ischemia followed by 10 min of reperfusion (n = 10). The hearts were perfusion-fixed for electron microscopy, and ultrastructural evaluation was performed using stereological technique in order to obtain an estimate of the volume fraction and absolute volume of different tissue components. EFFECT OF ISCHEMIA: Neither the ventricular nor the myocytic volume differed significantly from the respective control values. Both the myocytic mitochondrial volume (135+/-8 vs control 89+/-6 microl) and the volume of myocytic clear space (35+/-6 vs control 10+/-2 microl) were significantly increased. The capillary volume (22+/-4 vs control 58+/-6 microl) and the volume of the capillary lumen (15+/-3 vs control 48+/-5 microl) were significantly decreased. The volume of the capillary wall, however, was not altered after exposure to ischemia (7+/-3 vs control 10+/-1 microl). ADDITIVE EFFECT OF ISCHEMIA AND REPERFUSION: Both the ventricular volume (755+/-28 vs control 600+/-32 microl) and the myocytic volume (396+/-24 vs control 287+/-16 microl) were significantly increased after 10 min of reperfusion. EFFECT OF REPERFUSION: The ischemic-induced myocytic mitochondrial swelling and increase of clear space were not reinforced during reperfusion. Furthermore, the volume of the capillary lumen and the capillary wall did not alter significantly in the groups exposed to reperfusion compared to the ischemic hearts. In conclusion, stereological evaluation did not reveal significant aggravation of ischemic-induced myocardial injury during the early phase of reperfusion.
Actin Cytoskeleton↗
The initial phase of myocardial reperfusion is not associated with aggravation of ischemic-induced ultrastructural alterations in isolated rat hearts exposed to prolonged global ischemia.
The present study focuses on the qualitative and sequential development of myocardial ultrastructural changes during the first 10 min of reperfusion in isolated rat hearts exposed to 60 min of global ischemia. The frequency of and the association between ultrastructural changes were examined by semiquantitative morphometry using the micrograph as unit. In each micrograph the subcellular components of the myocytes (sarcolemma, mitochondria, myofilaments and nucleus) and the endothelial cells were evaluated and graded as slightly, moderately, or severely altered. Ischemia alone induced moderate to severe ultrastructural alterations. The myocytes revealed sarcolemmal disattachment or rupture. The myocytic mitochondria had a clear matrix with abundant broken cristae and amorphous matrix densities. The myofilamental pattern was irregular or even disrupted, and most nuclei had reduced density and showed margination of chromatin. The endothelium showed vacuolization, rupture of the plasma membrane, and extracellular accumulation of cellular debris. During the first 2 min of reperfusion severe ultrastructural alterations were partly reversed. After 10 min of reperfusion both the frequency and grade of myocardial ultrastructural alternations were similar to that observed after ischemia. Cristal adhesions occurred predominately during reperfusion and were associated with moderately and severely altered myocytic mitochondrial alterations. In conclusion, the results showed that ischemic-induced ultrastructural alterations were transiently improved upon reperfusion. With exception of the development of cristal adhesions, the acute phase of reperfusion was not associated with additional ultrastructural changes in isolated buffer-perfused rat hearts exposed to prolonged ischemia.
Animals↗
Ultrastructure of reperfused skeletal muscle: the effect of oxygen radical scavenger enzymes.
The aim of the present study was (1) to examine changes in ultrastructure and subcellular volume fractions in reperfused skeletal muscle and (2) to examine the effect of pre- plus postischaemic treatment with oxygen radical scavenger enzymes. Experiments were performed in 8 pentobarbital anesthetized dogs. The gracilis muscle was denervated and vascularly isolated on both lower limbs, except for the main artery and vein. A catheter was advanced through the distal end of the femoral artery for supply of superoxide dismutase (SOD) and catalase (each enzyme 12,000 U/10 min prior to ischaemia and 36,000 U/30 min at reperfusion) through the muscle artery to the muscle on one side. A catheter in the muscle vein secured the collection of venous blood to avoid a supply of SOD and catalase to the other muscle. Ischaemia was induced on both sides by clamping the branch of the femoral artery supplying the muscle for 4 h, and the muscle was thereafter reperfused for 1 h. Ultrastructural examination (morphometric by point counting and semiquantification) of the reperfused tissue revealed mitochondrial damage, margination of nuclear chromatin, lipid droplets, filamental disruption, as well as oedema in both endothelial and myofibrillar cells. In addition some influence of treatment with SOD and catalase could be seen, mainly in reduction of the number of micrographs with cellular oedema and especially oedema in endothelial cells.
Animals↗
Reversible ultrastructural alterations in the myocytic mitochondria of isolated rat hearts induced by oxygen radicals.
The present study focuses on reversible mitochondrial ultrastructural alterations in myocardial myocytes that correspond or accompany reversible metabolic depression observed after oxygen radical exposure. The myocytic mitochondrial membranes and matrix of isolated Langendorff-perfused rat hearts were examined by semiquantitative morphometry using the electron micrograph as unit. The hearts were exposed to either standard perfusion (group A), 10 min of oxygen radicals together with superoxide dismutase and catalase followed by 35 min of recovery (group B), 10 min of oxygen radicals alone (group C), or 10 min of oxygen radicals followed by 35 min of recovery (group D). Mitochondrial ultrastructural alterations were detected in only a few micrographs in groups A and B. The frequency of micrographs with mitochondrial ultrastructural alterations was 69% in group C and 62% in group D. In the group exposed to 10 min of oxygen radicals without recovery (group C) condensed pentalaminar membranous profiles arranged in parallel, interpreted to be closely adhering cristae, were detected in the intracristal compartment of myocytic mitochondria in 50% of the micrographs. The cristal adhesions were associated with other mitochondrial ultrastructural changes. Cristal adhesions were not present in group A or B, and were rarely found in the group exposed to 10 min of oxygen radicals followed by 35 min of recovery (group D). Thus, the cristal adhesions appear to be reversible alterations caused by exposure to oxygen radicals.
Animals↗
Melatonin prevents cardioprotection induced by a multi-cycle ischaemic preconditioning protocol in the isolated perfused rat heart.
The powerful cardioprotective actions of melatonin, the chief secretory product of the pineal gland, have been attributed largely to its free radical-scavenging properties. Free radicals play an important role in the triggering action of ischaemic preconditioning, the phenomenon whereby exposure of the heart to one or more short episodes of ischaemia leads to protection against a subsequent long period of ischaemia. The aim of this study was, therefore, to establish whether melatonin, in view of its free radical-scavenging ability, would affect the beneficial actions of preconditioning. Isolated, perfused, working hearts were subjected to 1 x 5 minute or 3 x 5 min ischaemic preconditioning protocols, in the presence or absence of melatonin (50 microM), followed by 20 minutes global ischaemia and 30 minutes reperfusion. Use was also made of sodium nitroprusside (100 microM), a nitric oxide (NO) donor and preconditioning mimetic. Using functional recovery as the endpoint, melatonin abolished the cardioprotective effects of a multi-cycle (3 x 5 min) preconditioning protocol, while having no effect on a one-cycle (1 x 5 min) protocol or SNP (1 x 5 or 3 x 5 min) preconditioning. The results suggest that free radicals play an important role in the cardioprotection induced by a multi-cycle ischaemic preconditioning protocol and that this process could be attenuated by a potent scavenger such as melatonin.
Animals↗