In:
American Journal of Physiology-Endocrinology and Metabolism, American Physiological Society, Vol. 279, No. 2 ( 2000-08-01), p. E314-E322
Abstract:
To study the thermal response of interscapular brown fat (IBF) to norepinephrine (NE), urethan-anesthetized rats (1.2 g/kg ip) maintained at 28–30°C received a constant venous infusion of NE (0–2 × 10 4 pmol/min) over a period of 60 min. IBF temperatures (T IBF ) were recorded with a small thermistor fixed under the IBF pad. Data were plotted against time and expressed as maximal variation (Δ t°C). Saline-injected rats showed a decrease in T IBF of ∼0.6°C. NE infusion increased T IBF by a maximum of ∼3.0°C at a dose of 10 4 pmol · min −1 · 100 g body wt −1 . Surgically thyroidectomized (Tx) rats kept on 0.05% methimazole showed a flat response to NE. Treatment with thyroxine (T 4 , 0.8 μg · 100 g −1 · day −1 ) for 2–15 days normalized mitochondrial UCP1 (Western blotting) and IBF thermal response to NE, whereas iopanoic acid (5 mg · 100 g body wt −1 · day −1 ) blocked the effects of T 4 . Treatment with 3,5,3′-triiodothyronine (T 3 , 0.6 μg · 100 g body wt −1 · day −1 ) for up to 15 days did not normalize UCP1 levels. However, these animals showed a normal IBF thermal response to NE. Cold exposure for 5 days or feeding a cafeteria diet for 20 days increased UCP1 levels by ∼3.5-fold. Nevertheless, the IBF thermal response was only greater than that of controls when maximal doses of NE (2 × 10 4 pmol/min and higher) were used. Conclusions: 1) hypothyroidism is associated with a blunted IBF thermal response to NE; 2) two- to fourfold changes in mitochondrial UCP1 concentration are not necessarily translated into heat production during NE infusion.
Type of Medium:
Online Resource
ISSN:
0193-1849
,
1522-1555
DOI:
10.1152/ajpendo.2000.279.2.E314
Language:
English
Publisher:
American Physiological Society
Publication Date:
2000
detail.hit.zdb_id:
1477331-4
SSG:
12
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