Sites and cellular mechanisms of human adrenergic thermogenesis - a review [Review]

摘要

Nonshivering thermogenesis (NST) is considered to be an important physiological mechanism, which contributes to the maintenance of the heat balance in cold exposed mammals. Numerous studies confirmed the role of noradrenaline released from the sympathetic nervous system and the significance of #beta#_3-adrenergic cell membrane receptors and mitochondrial uncoupling proteins in mediation of NST in rodents. Furthermore, the literature documents sample evidence that NST can be potentiated in cold adapted mammals that increased their survival limits considerably. It has been shown that NST plays a significant role mainly in small mammals. In species bigger than about 10kg its physiological significance appears to be questionable and in humans a role in the maintenance of heat balance is still to be precisely established (Jansky, 1995). It has also been suggested that NST plays a role in the maintenance of heat balance even under thermoneutral conditions. Defective heat production mechanisms may lower energy expenditure during diet-induced thermogenesis and, consequently, may be one of the reasons of obesity. Evidence exists that in obese subjects a reduced response to adrenomimetics (Jung et al., 1979; Vybiral et al., 2000a, b), mutation of the fi3-adrenoceptor gene (Yoshida and Sakane, 1999) and uncoupling protein polymorphism (Walder et al., 1998) are found. In consequence, studies on NST in humans could be of considerable practical importance and could contribute to explaining various problems of pathophysiology of thermoregulation. The purpose of this review is to discuss the evidence that thermoregulatory NST also functions in humans and that the cellular mechanisms of human NST differ from those found in small mammals. It is also possible that metabolic rate (MR) can be regulated by physiological processes at the organ level as well as by biochemical mechanisms (Kolar and Jansky, 1984a, b; Clark et al., 1994, 1995), new approaches to the problem appear to be desirable.