Nonshivering Thermogenesis in a Marsupial (the Tasmanian Bettong Bettongia gaimardi) Is Not Attributable to Brown Adipose Tissue

Abstract

The Tasmanian bettong (Bettongia gaimardi, a marsupial) is a rat-kangaroo that increases nonshivering thermogenesis (NST) in response to norepinephrine (NE). This study attempted to assess whether brown adipose tissue (BAT), a specialized thermogenic effector, is involved in NST in the bettong. Regulatory NST, indicated by resting oxygen consumption (Vo2) of the whole body, was measured under conscious conditions at 20 degrees C with various stimuli: cold (4 degrees -5 degrees C) or warm (25 degrees C) acclimation, NE injection, and the beta3-adrenoceptor agonist (BRL) 37344. In line with the functional studies in vivo, the presence of BAT was evaluated by examining the expression of the uncoupling protein 1 (UCP1) with both rat cDNA and oligonucleotide probes. Both NE and BRL 37344 significantly stimulated NST in the bettong. After cold acclimation of the animals (at 4 degrees -5 degrees C for 2 wk), the resting Vo2 was increased by 15% and the thermogenic effect of NE was enhanced; warm-acclimated animals showed a slightly depressed response. However, no expression of UCP1 was detected in bettongs either before or after cold exposure (2 wk). These data suggest that the observed NST in the marsupial bettong is not attributable to BAT.

Cost of transport is increased after cold exposure inMonodelphis domestica: training for inefficiency

“…Thus long-term cold exposure has been reported to result in increased muscle oxidative capacity in numerous species (Block, 1994), including Monodelphis domestica . Shivering is the first mechanism invoked in response to cold exposure, but there is growing evidence for the role of non-shivering thermogenesis in skeletal muscle of placental mammals (Dubois-Ferriere and Chinet, 1981), birds (Duchamp and Barre, 1993) and marsupial mammals (Rose et al, 1999). Although these two mechanisms for heat production differ in that the contractile elements are not engaged in non-shivering thermogenesis, both consist of metabolic energy consumption in the absence of mechanical work.…”

Roles of Norepinephrine, Free Fatty Acids, Thyroid Status, and Skeletal Muscle Uncoupling Protein 3 Expression in Sympathomimetic-Induced Thermogenesis

“…First, in the hyperthyroid state, UCP1-dependent thermogenesis is blunted as a result of suppression of adrenergic signaling in brown adipocytes (Golozoubova et al, 2004), but isolated SKM mitochondria from hyperthyroid rats show enhanced FFA-induced uncoupling (Brand et al, 1992). In addition, SKM is the primary contributor to thermogenesis and oxygen consumption induced by NE in animals (Rose et al, 1999), and humans (Astrup et al, 1985), and a 35-fold increase in plasma NE precedes MDMA-induced hyperthermia (Sprague et al, 2005). Interestingly, combined antagonism of ␣ 1 -and ␤ 3 -AR, which are expressed in SKM (Martin et al, 1990;Sillence et al, 1993), prevents and reverses hyperthermia induced by MDMA (Sprague et al, 2005).…”

“…The prototype UCP1 mediates FT in brown adipose tissue (BAT), an organ specialized for heat production in hibernating mammals and rodents (Lin and Klingenberg, 1980). However, because of the absence of BAT in humans, skeletal muscle (SKM) plays a much larger and more significant role in the thermogenic response to sympathetic nervous system (SNS) stimulation (Astrup et al, 1989;Ye et al, 1996;Rose et al, 1999). This FT is thought to be mediated by norepinephrine (NE)-induced activation of a TH-regulated homolog of UCP1 (UCP3), found primarily in SKM (Gong et al, 1997;Lombardi et al, 2002).…”

Developmental phenotypic plasticity in a marsupial

“…In marsupials however the role of BAT is controversial. Although some studies have shown that BAT in marsupials is absent or non-functional (Nicol et al, 1997;Rose et al, 1999), others have shown that BAT is present in some marsupials (e.g. Hope et al, 1997).…”