EFFECTS OF INTERSCAPULAR BROWN ADIPOSE-TISSUE DENERVATION ON BODY-WEIGHT AND ENERGY-METABOLISM IN OVARIECTOMIZED AND ESTRADIOL-TREATED RATS

Ovariectomy-induced increases and estradiol-induced decreases in body wt cannot be fully accounted for by changes in energy intake and appear to reflect alterations in thermogenesis. Because changes in energy expenditure have been linked to altered sympathetic nervous system (SNS) activity in brown adipose tissue (BAT), the role of estradiol in thermogenesis and body wt, as mediated by the SNS innervation of interscapular BAT (IBAT), was examined. The IBAT of ovariectomized rats was bilaterally or unilaterally surgically denervated. The chow-fed, bilaterally denervated group gained more weight than the unilaterally denervated or sham-operated group, an effect that was exaggerated by sucrose feeding. Food intake did not differ among the groups within each dietary condition. Estradiol benzoate (EB) injections decreased body wt in all groups. Bilateral, and to a lesser extent, unilateral IBAT denervation blocked the EB-induced increase in thermogenesis. Treatment with EB increased IBAT wet wt regardless of surgical treatment. Because IBAT denervation markedly decreased lipoprotein lipase activity and fatty acid synthesis/uptake, the estradiol-induced increase in denervated IBAT wet wt is most likely due to decreased lipolysis produced by the surgical sympathectomy. These results are discussed in terms of the role of the SNS and IBAT in the mediation of estradiol-induced changes in body wt and energy metabolism.