Effect of Temperature on Lipoprotein Lipase and Lipogenic Enzyme Activities in Brown Adipose Tissue of Hypophysectomized Rats

 

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Summary

It has been shown that the same modifications on the composition of brown adipose tissue (BAT) which are normally induced following cold stimulation are also observed in hypophysectomized rats acclimated either at 28° C or 15° C. To test the possibility of BAT stimulation in hypophysectomized rats, we have determined some enzymatic activities known to modulate the energy supply to that organ. Seven week old Long-Evans rats were hypophysectomized. Three weeks later, they were exposed to either 28° C or 15° C ambient temperature for five or six weeks. Hypophysectomized rats were compared to age matched or weight matched controls. Total lipoprotein lipase activity (LPL) (triglyceride uptake) was enhanced in BAT of 28° C hypophysectomized rats compared to controls. Cold acclimation led to a large increased activity. Total LPL activity was comparable in BAT of hypophysectomized and control rats. Total malic enzyme and glucose-6-phosphate dehydrogenase activities (in situ lipogenesis) were doubled in BAT of 28° C hypophysectomized compared to controls. A large enhancement was observed in BAT of either 15° C control or 15° C hypophysectomized rats. Among the studied organs (liver, white adipose tissue, heart, BAT) hypophysectomy promotes the three enzyme activities only in BAT. These variations were discussed with relation to the effect of hypophysectomy on brown adipose tissue at 15° C and 28° C.