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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Experiments were carried out to test the hypothesis whether adenosine produced by ATP catabolism during ischemia can be trapped with L-homocysteine and be re-utilized during reperfusion. During intraatrial infusion of L-homocysteine (100 mg/kg/h), the ischemic accumulation of adenine nucleosides and oxypurines in dog myocardium was found to be less than 50% of that during control ischemia. A high proportion of adenosine was recovered as S-adenosyl-L-homocysteine. On reperfusion, S-adenosyl-L-homocysteine. On reperfusion, S-adenosyl-L-homocysteine tissue content remained high. After 3 hours of reperfusion approximately 50% of the accumulated S-adenosyl-L-homocysteine were still found in the tissue. Infusion of L-homocysteine did not cause an accumulation of S-adenosyl-L-homocysteine in the nonischemic myocardial tissue. L-homocysteine treatment caused a further depletion of ATP during reperfusion after 30 minutes of ischemia, which can be interpreted as a toxic effect. We conclude that L-homocysteine is indeed able to trap adenosine produced by ATP breakdown, but the reaction is not readily reversible and is therefore not useful for quick restoration of postischemic ATP levels.
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PMID:Intracellular trapping of adenosine during myocardial ischemia by L-homocysteine. 375 92

The coronary vasodilator adenosine can be formed in the heart by breakdown of AMP or S-adenosylhomocysteine (SAdoHcy). The purpose of this study was to get insight into the relative importance of these routes of adenosine formation in both the normoxic and the ischemic heart. A novel HPLC method was used to determine myocardial adenosine and SAdoHcy. Accumulation of SAdoHcy was induced in isolated rat hearts by perfusion with L-homocysteine thiolactone or L-homocysteine. The release of adenosine, inosine, hypoxanthine, xanthine and uric acid was determined. Additional in vitro experiments were performed to determine the kinetic parameters of S-adenosylhomocysteine hydrolase. During normoxia the thiolactone caused a concentration-dependent increase in SAdoHcy. At 2000 microM of the thiolactone an SAdoHcy accumulation of 0.49 nmol/min per g wet weight was found during normoxia. L-Homocysteine (200 microM) caused an increase of 0.37 and 4.17 nmol SAdoHcy/min per g wet weight during normoxia and ischemia, respectively. The adenosine concentration in ischemic hearts was significantly lower when homocysteine was infused (6.2 vs. 11.5 nmol/g; P less than 0.05). Purine release was increased 4-fold during ischemia. The Km for hydrolysis of SAdoHcy was about 12 microM. At in vitro conditions favoring near-maximal SAdoHcy synthesis (72 microM adenosine, 1.8 mM homocysteine), the synthesis rate in homogenates was 10 nmol/min per g wet weight. From the combined in vitro and perfusion studies, we conclude that S-adenosylhomocysteine hydrolase can contribute significantly to adenosine production in normoxic rat heart, but not during ischemia.
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PMID:Myocardial S-adenosylhomocysteine hydrolase is important for adenosine production during normoxia. 400 94

Homocystinuria, only partially responsive to pyridoxine, was first diagnosed at the age of 14 years in a boy with high myopia, spherophakia and subluxated lenses, when surgical removal of a dislocated lens became necessary. 2 years previously a fracture of the left tibia, treated conservatively, had been followed by ischemia of the leg necessitating amputation. Postoperatively, deep vein thrombosis had developed in the right leg. Plasma homocysteine was lowered to undetectable levels by treatment with betaine in addition to pyridoxine, folic acid and reduction of protein intake. During the two years on treatment no further thromboembolic complications have occurred.
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PMID:[Vascular and ocular complications in a child with homocystinuria]. 661 Sep 36

To investigate the relationship between flow and energy metabolism during coronary underperfusion, regional myocardial ATP content, cytosolic adenosine concentrations, and blood flow were measured during segmental coronary artery occlusion (complete ligation, n = 10) and demand ischemia (catecholamines plus atrial pacing with subtotal stenosis, n = 6) in halothane anesthetized open-chest dogs. During coronary occlusion or demand ischemia, L-homocysteine thiolactone was infused for 20 min, after which left ventricular tissue was rapidly frozen and analyzed for regional blood flow (microspheres) and content of ATP and S-adenosylhomocysteine (SAH), an index of cytosolic adenosine. In nonischemic regions, ATP and SAH contents in both groups were the same as in unstimulated control animals with intact coronary circulation (n = 7), indicating that adrenergic stimulation during unrestricted flow had no effect on ATP or cytosolic adenosine. In the ischemic regions of both groups, there were decreases in regional flow, ATP content, and systolic wall thickening, and increases in SAH content. To compare the indexes of energy metabolism in tissue regions receiving equal blood flow, tissue samples were grouped into intervals of equal blood flow (ml.min-1.g-1). At every level of flow, ATP content in demand ischemia was 25-39% higher than in coronary occlusion. Estimates of cytosolic adenosine concentrations (using a mathematical model) in the lowest flow interval averaged 5 microM in demand ischemia, approximately twice as high as in coronary occlusion. It is concluded that in tissue regions receiving equal blood flow, ATP was better maintained and cytosolic adenosine was higher in demand ischemia than in coronary occlusion. The differences in ATP content and cytosolic adenosine were not due to different blood flows but rather to more favorable energy metabolism in demand ischemia.
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PMID:Comparison of myocardial ATP, blood flow, and cytosolic adenosine in demand ischemia and coronary occlusion. 757 23

This report describes a 33-year-old female patient who presented with severe neurological symptoms and signs during postpartum relapse of Crohn's ileocolitis. The cause of the neurological deficit was extensive major vessel thrombosis resulting in spinal cord ischemia. Etiologic factors involved in this exceptional thrombotic state are discussed with emphasis on the relationship between low levels of folic acid, homocysteine metabolism, and coagulation.
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PMID:Severe thrombotic complications in a postpartum patient with active Crohn's disease resulting in ischemic spinal cord injury. 778 67

The purpose of this study was to determine the effects of homocysteine, which consumes intracellular adenosine via formation of S-adenosylhomocysteine, on interstitial fluid (ISF) adenosine and cerebral blood flow (CBF) before, during, and after cerebral ischemia. Microdialysis probes, used to measure local CBF (H2 clearance) and to sample ISF, were implanted bilaterally into the caudate nucleus of halothane-anesthetized rats (n = 8). L-Homocysteine thiolactone was administered locally via one of the probes. Animals were exposed to 20 min of ischemia, induced by bilateral carotid occlusion plus hemorrhage to an arterial blood pressure of 50 mm Hg, followed by 60 min of reperfusion. Before ischemia, CBF and dialysate adenosine were decreased with homocysteine. During ischemia and early reperfusion, dialysate purine metabolites increased on both sides of the brain; however, the ischemia-induced increase in adenosine was attenuated on the side of local homocysteine. CBF was lower on the side of homocysteine throughout reperfusion. These data demonstrate that homocysteine (a) decreases basal ISF adenosine and CBF, (b) attenuates the increase in dialysate adenosine during ischemia, and (c) reduces hyperemia during early reperfusion.
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PMID:Attenuation of ischemia-induced extracellular adenosine accumulation by homocysteine. 843 12

We describe a 39-year-old woman with an 8-month history of abdominal pain, diarrhea, and weight loss. Clinical and laboratory evaluation indicated the presence of a malabsorption syndrome. Endoscopy revealed multiple gastric ulcerations and an abnormal "picture" of the duodenal mucosa. At duodenal biopsy, necrosis confined to the distal parts of the enteric villi and a polymorphonuclear leukocyte response were found. Further evaluation revealed intestinal ischemia as a result of mesenteric atherosclerosis. After a revascularization procedure was performed, the symptoms disappeared. The macroscopic and microscopic picture of the bowel normalized. In our search for risk factors of atherosclerosis, we found a substantially increased basal plasma homocysteine concentration. This case suggests that hyperhomocysteinemia may have a causal role in the development of symptomatic, premature atherosclerosis of the mesenteric circulation.
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PMID:Malabsorption syndrome associated with ulceration of the stomach and small bowel caused by chronic intestinal ischemia in a patient with hyperhomocysteinemia. 917 39

Dynamic changes in the reduction-oxidation (redox) state of the tissue lead to the pathophysiological condition. Reduced homocysteine causes dysfunctions in endothelium. The proliferation of smooth muscle cells may lead to occlusive vascular disease, ischemia, and heart failure, but whether fibrosis and hypertension are a consequence of smooth muscle proliferation is unclear. Redox changes during hyper-homocyst(e)inemia may be one of the causes of premature atherosclerotic heart disease. To examine the effect of homocystine on human vascular smooth muscle cells (HVSMC), we isolated HVSMC from idiopathic dilated cardiomyopathic hearts. Coronaries in these hearts were apparently normal. HVSMC numbers in culture were measured by hemocytometer in the presence and absence of homocystine. Results show that homocystine induced cellular proliferation. This proliferation was reversed by the addition of the antioxidant N-acetylcysteine (NAC). Homocystine induces collagen expression in a dose- and time-dependent manner, as measured by Northern blot (mRNA) analysis. The 50% inhibitory concentration of 5 microM for collagen was estimated. The induction of collagen was reversed by the addition of NAC and reduced glutathione. To localize the receptor for homocystine on HVSMC, we synthesized fluorescamine-labeled homocystine conjugate. Incubation of labeled homocystine with HVSMC demonstrated membrane and cytosol localization of homocystine binding. The receptor-ligand binding was disrupted by NAC. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis fluorography, we observed a 40- to 25-kDa homocystine redox receptor in HVSMC. Our results suggested that the redox homocysteine induces HVSMC proliferation by binding to the redox receptor and may exacerbate atherosclerotic lesion formation by inducing collagen expression.
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PMID:Homocysteine redox receptor and regulation of extracellular matrix components in vascular cells. 948 29

The purpose of this study was to determine the roles of cytosolic and ecto 5'-nucleotidase in myocardial ischemia-induced increases in interstitial fluid (ISF) adenosine. Pentobarbital anesthetized, open chest pigs were instrumented with two microdialysis fibers in the distally perfused bed of the left anterior descending (LAD) coronary artery to estimate ISF metabolites. Fibers in control hearts were perfused with standard Krebs buffer. In two additional groups, after collecting one dialysate sample with normal Krebs, fibers were perfused with buffer supplemented with either L-homocysteine thiolactone (5 mM) or the ecto 5'-nucleotidase inhibitor alpha, beta-methylene adenosine 5'-diphosphate (AOPCP, 5 mM). Hearts were then submitted to 60 minutes LAD occlusion and two hours reperfusion. Dialysate nucleosides and AMP were measured by high performance liquid chromatography. The local delivery of homocysteine did not alter preischemic dialysate adenosine concentration (0.30 +/- 0.04 microM) compared to pre-homocysteine infusion (0.39 +/- 0.04 microM) or control hearts (0.36 +/- 0.04 microM), but AOPCP significantly decreased preischemic dialysate adenosine levels (from 0.36 +/- 0.02 to 0.14 +/- 0.03 microM). During LAD occlusion both homocysteine and AOPCP reduced dialysate levels by approximately 50%. At 30 minutes ischemia dialysate adenosine concentrations were 19.47 +/- 2.72, 11.41 +/- 2.44, and 7.93 +/- 1.01 microM in control, homocysteine, and AOPCP hearts, respectively. AOPCP significantly increased dialysate AMP levels; at 60 minutes ischemia AMP levels were 6.22 +/- 2.97 microM in control hearts and 38.60 +/- 5.69 microM in AOPCP treated hearts. These results suggest that both cytosolic and ecto 5'-nucleotidase contribute to ischemia-induced increases in ISF adenosine in porcine myocardium.
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PMID:Evidence that cytosolic and ecto 5'-nucleotidases contribute equally to increased interstitial adenosine concentration during porcine myocardial ischemia. 1042 38

Hyperhomocysteinemia (HH) is an independent risk factor for atherosclerosis, including peripheral arterial occlusive disease (PAOD). Because angiogenesis and collateral vessel formation are important self-salvage mechanisms for ischemic PAOD, we examined whether HH modulates angiogenesis in vivo in a rat model of hindlimb ischemia. Rats were divided into 3 groups: the control group was given tap water, the HH group was given water containing L-methionine (1 g x kg(-1) x d(-1)), and the HH+L-arg group was given water containing methionine (1 g x kg(-1) x d(-1)) and l-arginine (2.25 vol%). At day 14 of the dietary modifications, the left femoral artery and vein were excised, and the extent of angiogenesis and collateral vessels in the ischemic limb were examined for 4 weeks. Plasma homocysteine levels significantly increased (P:<0.001), and plasma and tissue contents of nitrite+nitrate as well as tissue cGMP levels significantly decreased in the HH group compared with the control group (P:<0.01). Laser Doppler blood flowmetry (LDBF) revealed a significant decrease in the ischemic/normal limb LDBF ratio in the HH group at days 7, 14, 21, and 28 (P:<0.01 versus control). Angiography revealed a significant decrease in the angiographic score in the HH group at day 14 (P:<0.001 versus control). Immunohistochemistry of ischemic tissue sections showed a significant reduction in the capillary density in the HH group (P:<0. 001 versus control). Oral l-arginine supplementation in rats with HH (HH+L-arg) restored the decreased plasma and tissue nitrite+nitrate and cGMP contents (P:<0.05) as well as angiogenesis, as assessed by LDBF (P:<0.05 versus HH), angiographic score (P:<0.01 versus HH), and capillary density (P:<0.001 versus HH). In summary, HH impaired ischemia-induced angiogenesis and collateral vessel formation in a rat model of hindlimb ischemia in vivo. The mechanism of the HH-induced impairment of angiogenesis might be mediated in part by a reduced bioactivity of endogenous NO in the HH state.
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PMID:Hyperhomocysteinemia impairs angiogenesis in response to hindlimb ischemia. 1111 56


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