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Query: UMLS:C0003129 (Anoxia)
 551 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Experiments were designed to determine the role of the endothelial cells and the metabolism of arachidonic acid in anoxic contractions of isolated canine basilar arteries. Rings, with and without endothelium, of these arteries were suspended for isometric tension recording; anoxia was induced by switching the mixture gassing the organ chamber from 95% O2-5% CO2 to 95% N2-5% CO2. In rings with endothelium, anoxia evoked increases in tension under basal conditions and during contractions to 5-hydroxytryptamine, uridine triphosphate, prostaglandin F2 alpha, and high K+. Under control conditions, these anoxic contractions were not prevented by alpha-adrenergic and serotonergic antagonists, by apyrase, or by inhibitors of cyclooxygenase. Anoxia prevented endothelium-dependent relaxations evoked by vasopressin and thrombin. In rings without endothelium, anoxia caused increases in tension during contractions evoked by various agonists, and in unstimulated preparations after inhibition of cyclooxygenase. Anoxic contractions were abolished by calcium entry blockers. These observations suggest that anoxic contractions of isolated canine basilar artery can be explained by the release of endothelium-derived contracting factor(s) and the accelerated entry of calcium in the smooth muscle cells, which possibly results from a diversion of arachidonic acid from the cyclooxygenase to the lipoxygenase pathway.
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PMID:Anoxic contractions in isolated canine cerebral arteries: contribution of endothelium-derived factors, metabolites of arachidonic acid, and calcium entry. 243 36

Plants lack specialised organs and circulatory systems, and oxygen can fall to low concentrations in metabolically active, dense or bulky tissues. In animals that tolerate hypoxia or anoxia, low oxygen triggers an adaptive inhibition of respiration and metabolic activity. Growing potato tubers were used to investigate whether an analogous response exists in plants. Oxygen concentrations fall below 5% in the centre of growing potato tubers. This is accompanied by a decrease of the adenylate energy status, and alterations of metabolites that are indicative of a decreased rate of glycolysis. The response to low oxygen was investigated in more detail by incubating tissue discs from growing tubers for 2 hours at a range of oxygen concentrations. When oxygen was decreased in the range between 21% and 4% there was a partial inhibition of sucrose breakdown, glycolysis and respiration. The energy status of the adenine, guanine and uridine nucleotides decreased, but pyrophosphate levels remained high. The inhibition of sucrose breakdown and glycolysis was accompanied by a small increase of sucrose, fructose, glycerate-3-phosphate, phosphenolpyruvate, and pyruvate, a decrease of the acetyl-coenzymeA:coenzymeA ratio, and a small increase of isocitrate and 2-oxoglutarate. These results indicate that carbon fluxes are inhibited at several sites, but the primary site of action of low oxygen is probably in mitochondrial electron transport. Decreasing the oxygen concentration from 21% to 4% also resulted in a partial inhibition of sucrose uptake, a strong inhibition of amino acid synthesis, a decrease of the levels of cofactors including the adenine, guanine and uridine nucleotides and coenzymeA, and attenuated the wounding-induced increase of respiration and invertase and phenylalanine lyase activity in tissue discs. Starch synthesis was maintained at high rates in low oxygen. Anoxia led to a diametrically opposed response, in which glycolysis rose 2-fold to support fermentation, starch synthesis was strongly inhibited, and the level of lactate and the lactate:pyruvate ratio and the triose-phosphate:glycerate-3-phosphate ratio increased dramatically. It is concluded that low oxygen triggers (i) a partial inhibition of respiration leading to a decrease of the cellular energy status and (ii) a parallel inhibition of a wide range of energy-consuming metabolic processes. These results have general implications for understanding the regulation of glycolysis, starch synthesis and other biosynthetic pathways in plants, and reveal a potential role for pyrophosphate in conserving energy and decreasing oxygen consumption.
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PMID:Metabolic activity decreases as an adaptive response to low internal oxygen in growing potato tubers. 1103 Apr 30