Adipose Tissue Hypoxia, A Conceptual Alometric View

Abstract

Hypoxia is a condition in which there is an insuffi ciency of oxygen for normal cell operation. It is directly related to diminished oxygen supply, usually because of restricted/insuffi cient blood circulation or defective oxygen transport and release. However, in absolute terms, cells in a small size animal may experience hypoxia with an oxygen supply comparable to that of normalcy in larger animals. The question is, essentially, the alometrically-related metabolic rate which translates into the actual individual cell metabolism. Cells in large animals consume less oxygen in vivo than their smaller animal counterparts, but this is not translated into hypoxia in the former. The critical point is not the absolute oxygen supply but the relationship of this to the incorporation of substrates to oxidize. It is the alteration of the ratio between oxidizable substrates and oxygen availability, the factor eliciting the ravages of hypoxia. The normal function of the circulatory system maintains a balanced supply of both terms of the equation; however, substrate oversupply, such as that experienced by adipose tissue in the metabolic syndrome may break the equilibrium, eliciting hypoxia and acidosis, which may derive into infl ammation and further cell and tissue damage.Keywords: Hypoxia; Acidosis; Adipose tissue; Infl ammation; Metabolic syndrome Hipoxia, A Relative TermHypoxia is a transient situation in which a given mass of tissue cells does not receive enough oxygen from the blood vessels, i.e. the arterial (assuming a normal oxygen content) blood fl ow, in ml/kg tissue, is not high enough to supply suffi cient oxygen (and nutrients), as well as to eliminate excess acidity, carbon dioxide and other excreta [1]. However, the amplitude of margin for most cells in this sense is considerable (except perhaps for neurons). Current theories explaining the effect of size on metabolic rate are based, precisely in higher values for blood fl ow across tissues in small versus large animals, with cell structures, vascularization, etc. being intrinsically the same. The relationship of metabolic rate as the 0.75 power of body weight [2] shows that the difference in metabolic rate of a 0.25 kg rat and a 70 kg man is about 1:68. Since the ratio of masses is 1:280, the average rat cell is irrigated roughly fourfold than a human cell. Surprisingly, this large difference does not mean customarily that most human cell had to be hypoxic; but a drop in 75% of oxygen supplied to a rat (i.e. lowering its cells' oxygen supply to human levels) makes them markedly hypoxic and die. The cell structures and oxygen supply may be the same, but there are wide different metabolic consequences derived from organization and, especially, size: size matters. This effect is observed only in vivo, with the cells integrated in a functioning body. Human and rat cells kept in primary tissue cultures do not show signifi cant differences in their consumption of oxygen and substrates; however, if we scale these data to the situation in vivo, the sum of a ...

Evidences of Basal Lactate Production in the Main White Adipose Tissue Sites of Rats. Effects of Sex and a Cafeteria Diet

“…The data on the expression of genes involved in lipogenesis from glucose show clearly that cafeteria diet had a marked overall influence; the entry of glucose into WAT cells was probably limited, as shown by lower Glut4 and Hk2 expressions. This decrease may be part of the tissue mechanism of defence against a sustained excess of energy supply and the generalized insulin resistance [ 63 ] that makes WAT the ultimate destination for excess circulating glucose [ 49 , 64 ]. The relative lack of changes in the expression of pyruvate dehydrogenase kinases suggest that the oxidation of pyruvate to acetyl-CoA was practically unaffected by diet, i.e.…”