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Am J Physiol Regul Integr Comp Physiol 269: R357-R364, 1995;
0363-6119/95 $5.00
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AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 2 357-R364, Copyright © 1995 by American Physiological Society

ARTICLES

Cold-induced alterations in uncoupling protein and its mRNA are seasonally dependent in ground squirrels

S. E. Nizielski, C. J. Billington and A. S. Levine
Neuroendocrine Research Laboratory, Veterans Affairs Medical Center, Minneapolis 55417, USA.

We were interested in determining whether season affects the ability of cold exposure to increase brown adipose tissue (BAT) thermogenic function in 13-lined ground squirrels after acute and chronic cold (4 degrees C) exposure. Tissues were collected from animals in April and September after cold exposure for 12, 24, or 48 h. Animals chronically exposed to the cold (10 days) were killed in early May and mid-August. We found that mitochondrial uncoupling protein (UCP) concentrations varied seasonally, with concentrations in control animals (at 23 degrees C) higher in late summer (mid-August and September) than in the spring (April and early May). Cold exposure in late summer did not induce further increases in UCP concentrations. In contrast, when animals were cold exposed in the spring, UCP concentrations and total UCP increased. Surprisingly, 10 days at 4 degrees C did not cause a greater increase in UCP concentrations than did 24 h at 4 degrees C. Chronic cold exposure increased the UCP mRNA-to-beta-actin mRNA ratio 48% in May, whereas a fivefold increase occurred in August. GDP binding was increased after 12 h at 4 degrees C in April; in contrast, animals attempted to hibernate when placed in the cold in September, and no increase in GDP binding was observed. Chronic cold exposure caused GDP binding to increase at both times. These results indicate that mitochondrial UCP concentrations are seasonally regulated in the 13-lined ground squirrel.


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B. B. Boyer, B. M. Barnes, B. B. Lowell, and D. Grujic
Differential regulation of uncoupling protein gene homologues in multiple tissues of hibernating ground squirrels
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 1998; 275(4): R1232 - R1238.
[Abstract] [Full Text] [PDF]


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