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-adrenergic
responses of isolated F344 rat brown adipocytes in vitro
1 Section of Neurobiology,
We previously reported greater age-related
attenuation of cold-induced thermoregulation and brown adipose tissue
thermogenic capacity in male vs. female F344 rats. With onset of the
rapid weight loss that occurs near the end of the lifespan, this
age-related attenuation becomes severe. We refer to this
"end-of-life" physiological state of older rats as senescence.
Here, we measured oxygen consumption of isolated brown adipocytes and
found no age (6 vs. 12 vs. 26 mo) or gender effects on maximal
norepinephrine (NE)- or CL-316,243 (
3-adrenergic agonist)-induced
responses. In contrast, brown adipocytes from 22- to 26-mo-old
senescent rats (males and females) consumed 51-60% less oxygen
during maximal stimulation with NE and CL-316,243 than did cells from
26-mo-old presenescent rats. This attenuation was associated with lower
(65-72%) uncoupling protein 1 concentrations but no alterations
in NE-induced cAMP levels or lipolysis. Our data indicate that
senescence, but not chronological age, significantly impacts
NE-/
3-mediated thermogenesis of
isolated brown adipocytes and that this effect involves altered mitochondrial rather than altered membrane or cytosol events.
oxygen consumption; lipolysis; adenosine 3',5'-cyclic monophosphate; uncoupling protein 1; CL-316,243; norepinephrine; weight loss
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