Identification of brown fat and mechanisms for energy balance in
the marsupial sminthopsis crassicaudata.
Hope, Perdita J., Diana Pyle, Christopher B. Daniels, Ian Chapman,
Michael Horowitz, John E. Morley, Paul Trayhurn, Jaliya Kumaratilake,
Gary Wittert.
Department of Medicine, University of Adelaide, Adelaide, Aust.
5000, Department of Physiology, University of Adelaide, Adelaide,
Aust. 5000, Department of Anatomy, University of Adelaide, Adelaide,
Aust. 5000, Division of Biochemical Sciences, Rowett Research
Institute, Aberdeen, UK. AB21 95B, Division of Geriatrics, St Louis
University, St Louis, MO, USA. 63104
APStracts 4:0101R, 1997.
The presence of brown adipose tissue (BAT) in marsupials is
controversial because attempts to identify mitochondrial uncoupling
protein (UCP) have been unsuccessful. Sminthopsis crassicaudata is a
small nocturnal marsupial with an interscapular pad of adipose.
Electronmicroscopy revealed this tissue to have characteristics
typical of BAT. Guanosine di-phosphate binding and UCP detection by
immunoblot confirmed BAT. Expression of UCP was increased by cold
exposure. When placed from 28 to 15 oC, body temperature (Tb)
decreased by 1.7 oC within 30 minutes and a further 1.0 oC by 90
minutes (P<0.001), before stabilising at these lower levels.
When returned to 28 oC, Tb increased within 30 minutes
(P<0.001), and returned to basal by 120 minutes. When
maintained at 15 oC with ad libitum food for 12 days, Tb
(P<0.05), tail width (P<0.04), and oxygen consumption
(P<0.01) all decreased. The respiratory quotient increased
(P<0.001), indicating a change from fat to carbohydrate
utilisation. Food intake was unchanged, and body weight increased on
day 1 (P<0.01), before returning to baseline on day 3,
remaining stable thereafter. These data suggest that although BAT is
present in the marsupial S. crassicaudata, it may not be necessary
for thermogenesis, at least in the short term. S. crassicaudata
utilises a plasticity in Tb, and a change in substrate utilisation in
order to maintain energy balance and body composition without the
need for an increase in metabolic rate or food consumption and
without the need for torpor.
Received 2 December 1996; accepted in final form 10 February
1997.
APS Manuscript Number R729-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 5 March 1997