Brown adipose tissue thermogenesis

Himms-Hagen, J. (1990). Brown adipose tissue thermogenesis interdisciplinary studies. FASEB J. 4 2890-2898. 

Himms-Hagen, J. 1989. Brown adipose tissue thermogenesis and obesity. Prog, lipid Res. 28 67-115. 

J. Himms-Hagen,Brown Adipose Tissue Thermogenesis and Obesity, Progress in Lipid Research, 1989, 28, 2, 67-115. 

Brown adipose tissue is the site of nonshivering thermogenesis. It is found in hibernating and newborn animals and is present in small quantity in humans. Thermogenesis results from the presence of an uncouphng protein, thermogenin, in the inner mitochondrial membrane. 

The major types of adipose tissue are (1) white adipose tissue, which manufactures, stores, and releases lipid and (2) brown adipose tissue, which dissipates energy via uncoupled mitochondrial respiration. Obesity research includes evaluation of the activity of adrenergic receptors and their effect on adipose tissue with respect to energy storage and expenditure or thermogenesis. 

Khat produces sympathomimetic effects, increasing heart rate and blood pressure. When khat is chewed, the increases are gradual, maximizing at about 2 hours and lasting for 4 hours. However, tolerance develops to blood pressure and heart rate effects in habitual users. Mydriasis and increases in respiration also occur. Cathinone induces thermogenesis in brown adipose tissue, which is mediated by jS-adrenergic receptors (Tariq et al. 1989). 

The hypothesis that is formulated on the basis of these properties is as follows. The signal for increased thermogenesis, when the body temperature falls, is an increase in the level of catecholamines, probably the local concentration of noradrenaline, which will be increased via stimulation of sympathetic nervous system. The catecholamine increases the activity of triacylglycerol lipase within the brown adipose tissue, by a similar mechanism to that which occurs in white adipose tissue (Chapter 7), i.e. by an... 

Brown adipose tissue is most prevalent in neonatal mammals, but it is now thought to persist in many adult forms as well, including adult humans (for review, see Ricquier and Bouillaud, 2000). Small mammals such as rodents rely heavily on BAT thermogenesis as adults. The high surface-to-volume ratios of small mammals appear to favor the persistence of this mode of heat generation throughout life. 

Within the last decade we have obtained a tentative concept of the molecular basis for this mammalian mitochondrial thermogenesis, and we know that in contrast to the thermogenic plant mitochondria, substrate oxidation in brown adipose tissue mitochondria is basically energy conserving, with proton extrusion occurring [5], with respiratory control, and with an ability, in principle, to capture the chemical energy in the form of ATP. 

The utility of these drugs in man as hypoglycaemic agents remains to be established, since the brown adipose tissue which plays an important role in rodent thermogenesis may not be of paramount importance in man. Selectivity across the receptor subtypes is also likely to be essential for success. 

Quite a few studies have been published examining potential relationships between indices of obesity or type n diabetes and the Arg64 /i3AR polymorphism (74). The basis for such studies is the expression of the /i3AR in brown adipose tissue, where receptor activation increases thermogenesis, and in white adipose tissue,... 

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