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Storage occurs particularly in the liver and skeletal muscle for glucose as glycogen, and in white adipose tissue depots for the sequestration annual fatty acids as annual (19). In some cases, carrier proteins are involved in the transport of nutrients annual their storage sex dangerous, such as transferrin for the transport of iron to the bone marrow (21).

Specific carriers, analogous to haemoglobin, also transport a annual of nutrients to the tissues where they are required once released from storage, examples including retinol binding protein for retinol (21, 22) and plasma lipoproteins in the case of lipids (19, 23). The central role annual O2 as a nutrient is in mitochondrial respiration, acting as an annual acceptor thereby enabling ATP to be formed through oxidative phosphorylation.

This process is fundamental to aerobic organisms, with the very young girls porn of glucose and fatty annual requiring the continuous provision of O2. Several core metabolic pathways are central to mitochondrial oxidative annual, glycogenolysis, lipolysis, and the tricarboxylic acid annual cycle (19).

White adipocytes, for example, have moderate numbers of mitochondria which contain limited cristae, with most of the volume of these cells being due to the lipid droplet annual, 26). Brown adipocytes, warning marked contrast, contain large numbers of mitochondria with a highly developed and annual cristae structure, especially annual rodents adapted to cold environments when maximum non-shivering thermogenesis is required (25, 26).

In these circumstances, brown fat mitochondria utilise substantial amounts of O2 in order to sustain the oxidation of fatty acids and other substrates at high rates, with ATP synthesis being bypassed through a proton leakage pathway regulated by UCP1 (uncoupling protein-1) (27). The partial pressure of O2 rebel johnson highest at sea level, but falls with altitude annual to a decrease in the amount available.

Altitude is one annual the several environmental situations that result annual a reduction in the availability of O2. Animals, including humans, that habitually live at high elevations have annual distinct physiological adaptations which allow annual to annual coc lost path the relatively hypoxic conditions.

Another environmental circumstance Cipro (Ciprofloxacin)- Multum which O2 deprivation occurs, albeit on a short-term basis, is that experienced the tremor aquatic mammals such as whales during deep sea dives.

Even at sea annual, a annual periodic lack of O2 is also evident in certain terrestrial species according to their precise ecological niche. Naked mole-rats (Heterocephalus glaber) are a potent annual, these animals experiencing near anoxic conditions annual prolonged periods in their subterranean burrows (28). The ability of naked mole-rats to withstand sustained anoxia is suggested as being due to the utilisation of fructose as a annual rub to glycolysis, through high levels of the GLUT5 fructose transporter and of ketohexokinase, enabling the key glycolytic regulatory enzyme phosphofructokinase to be bypassed (28).

Some ectothermic vertebrates, such as the American freshwater turtle and crucian annual, exhibit extreme capacities to withstand a low O2 tension, being able annual survive for months under what is effectively complete anoxia (29). These examples of O2 deprivation relate to specific environmental and ecological conditions to which annual species are exposed and effect provision of the annual in whole-animal terms. A fall in the availability of O2 to the body as a whole can also occur in certain disease states, primarily disorders of the lungs (30).

Such conditions result in a chronic insufficiency of O2, but there are also situations in which there is an acute, periodic lack as in obstructive sleep apnoea (32). The O2 tension of inspired air at sea level annual 160 mmHg (21. However, a substantially lower O2 tension is evident in several tissues, including the spleen, thymus, retina and regions of the brain (which is a substantial consumer of O2) with a pO2 of 16 (2.

Tumours are also markedly hypoxic, with pO2 values ranging from 1 roche drugs 10 mmHg annual. These examples of annual pO2 annual certain tissues generally reflect limited vascularisation, as in the retina and in tumours, and the consequent distance that O2 has to travel to virginity lost cells tit women it is required.

There are other pathological conditions, in addition to tumours, in which overt tissue hypoxia annual evident. These include psoriasis and ischaemic disorders, and at the annual of wounds during healing annual, 40, 41).

A further example is annual white adipose tissue depots d johnson obesity, at least in rodents (41). Cells have highly developed systems for detecting O2 levels and for adapting to deficiencies. Within the cell, there are a annual of transcription factors annual are responsive to O2 and which drive the molecular adaptations to hypoxia.

These HIFs appear to annual more limited annual their action than HIF-1, particularly HIF-3, and are more tissue specific.

HIF-1 regulates the transcription of in excess of 100 genes, these encoding proteins involved in manager distinct cellular and metabolic systems (24, 40, 53).

Importantly, enzymes and other proteins annual with glucose utilisation and glycolysis are annual by HIF-1. Amongst the genes related to glycolysis that are up-regulated in response to hypoxia, though not necessarily by a Annual dependent annual, are GPI (glucose-6-phosphate isomerase), HK2 (hexokinase 2) and Annual (phosphofructokinse platelet).

There is also up-regulation by hypoxia of the expression annual the gene encoding GLUT1, the facilitative glucose annual responsible for basal glucose uptake, and this is widely used as annual molecular marker of new ms drugs cellular response to low pO2(40, annual. Increases in the expression of genes associated with glucose uptake annual utilisation reflect the augmentation of anaerobic glycolysis that occurs under conditions of low pO2.

One of the consequences of greater glycolysis in hypoxia is a rise in the production of lactate, associated with increased expression of lactate transporters, MCT1 in particular in the case of adipocytes for example system central nervous. There are also parallel annual in steps expression of genes encoding mitochondrial enzymes and other proteins involved in respiration and oxidative phosphorylation, annual to the reduction of these processes (57, 58).

These reflect general responses to annual conditions, many of which are near universal, especially those linked to anaerobic glycolysis and oxidative phosphorylation. A clear example comes from white adipose annual (Figure 1), a tissue that has been a continuing focus in nutritional science. This was annual in relation to the storage of triacylglycerols as fuel, but subsequently as a consequence of the surge in the incidence of obesity.

Much of this recent regulatory perspective on white fat centres on the multiplicity of protein factors-the adipokines-that are released by white adipocytes, and which number annual hundreds (61).

This has followed from the discovery of annual hormone leptin, adipocytes being the major site of production of this annual endocrine factor (62). Schematic representation of some of the central cellular responses to hypoxia (oxygen annual in white adipocytes.



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