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AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 3 347-R355, Copyright © 1983 by American Physiological Society
ARTICLES |
B. E. Levin, J. Triscari and A. C. Sullivan
Sprague-Dawley rats developed diet-induced obesity (DIO) after 3 mo on a high-fat, high-sucrose diet (DIO diet), with associated increases in total body and interscapular brown adipose tissue (IBAT) lipid content. After 7 days on the DIO diet, rats had increased levels of tyrosine hydroxylase (TH; 34%), norepinephrine (NE; 34%), and NE turnover (94%; estimated by alpha-methyl-p-tyrosine inhibition of TH) in their IBAT compared with chow-fed controls. After 3 mo on the DIO diet, NE levels and/or turnover were reduced by 27-50% in aortas, hearts, and pancreata in obese rats. While IBAT NE turnover was normal, TH inhibition failed to increase the lipid content of IBAT in obese rats as it did in controls, suggesting a postsynaptic defect in basal NE-stimulated lipolysis in this thermogenically active tissue. When obese rats were switched from the DIO diet to rat chow for 3 days, NE levels remained depressed in their hearts (25%) and aortas (14%) but were increased by 36-45% in IBAT, pancreata, and white adipose tissue. NE turnover rates and/or constants were increased by 37-110% in hearts, aortas, pancreata, and IBAT of these obese rats while there were increased IBAT TH (20%) and dopamine-beta-hydroxylase (87%) activities compared with chow-fed controls. Therefore, sympathetic activity varied markedly as a function of both dietary composition and relative body weight during the development of DIO.
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