Doctor of Philosophy (PhD)
Department of Biomedical Science - Faculty of Health & Behavioural Sciences
Zeyl, Annerieke, Temperature effects on human leptin physiology: possible implications for the regulation of body composition, PhD thesis, Department of Biomedical Science, University of Wollongong, 2006. http://ro.uow.edu.au/theses/502
In this study evidence has been sought for physiologically-significant, direct, local effects of reduced subcutaneous adipose tissue temperature on leptin as a possible mechanism for body composition regulation in response to environmental temperature. Twelve healthy males participated in 15 repeated cold-water immersions (study 1), human subcutaneous adipose tissue fragments (n=7) were incubated at 27�, 32� and 37�C (study 2) and fourteen healthy subjects underwent two cold-water immersions with and without the beta-adrenergic antagonist propranolol (study 3). The first series of in vivo immersions were conducted over 15 days (60-90 min at 18�C). Acute cold exposure suppressed plasma leptin concentration (25 min: -14%, 60 min: -22%, P≤ssthan0.05), whilst repeated cold-water immersion was associated with an increase of plasma leptin concentration relative to test day 1 (+19% day 8, +13% day 15, overall P≤ss than0.05). Leptin secretion in vitro decreased 3.7-fold as the incubation temperature decreased from 37� to 27�C (P≤ssthan0.05). In a compartmental model of leptin turnover in vivo, the measured (local) temperature effect on leptin secretion in vitro was more than able to account for the observed cold-induced decrease in leptin concentration in vivo. In the second series, of cold-water immersions beta-adrenergic blockade by propranolol, which almost completely abolished cold induced release of non-esterified fatty acids (P≤ssthan0.05), did not prevent the cold-induced decrease in plasma leptin concentrations (P&greaterthan0.05). This latter result suggests that the sympathetic nervous system may be less important in cold-induced regulation of plasma leptin concentration than previously assumed. The presented studies provide several lines of evidence for a role of leptin in energy balance regulation in response to environmental temperature. It is concluded that that local and direct effects of reduced subcutaneous adipose tissue temperature may be a more important contributor to the acute effects observed in vivo, than the sympathetically-mediated suppression of leptin secretion.
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