EFFECT OF UNILATERAL SURGICAL DENERVATION OF BROWN ADIPOSE-TISSUE ON UNCOUPLING PROTEIN MESSENGER-RNA LEVEL AND CYTOCHROME-C-OXIDASE ACTIVITY IN THE DJUNGARIAN HAMSTER

The bilateral lobe of interscapular brown adipose tissue of the Djunga rian hamster was unilaterally denervated in order to study the role of the sympathetic innervation for maintenance and cold-induced increase of non-shivering thermogenesis. Denervation decreased the noradrenali ne content of brown adipose tissue to less than 9% of the intact contr alateral pad. This low noradrenaline level was maintained for 1-14 day s after denervation. First, to study the role of the sympathetic inner vation of brown adipose tissue in the maintenance of the high thermoge nic capacity characteristic of the cold acclimated state, brown adipos e tissue was denervated in hamsters either kept at thermoneutrality or acclimated to 5-degrees-C ambient temperature for 4 weeks. Cold-accli mated hamsters had elevated levels of uncoupling protein messenger rib onucleic acid (8.1-fold) and cytochrom-c oxidase-activity (3-fold). De nervation of brown adipose tissue decreased uncoupling protein-messeng er ribonucleic acid level and cytochrom-c-oxidase-activity as compared to the intact pad in thermoneutral and in cold-acclimated hamsters. H owever, in cold-acclimated hamsters uncoupling protein-messenger ribon ucleic acid level and cytochrom-c-oxidase-activity in denervated brown adipose tissue both were maintained on an elevated 6-fold higher leve l as compared to thermoneutral controls. Second, to study the role of the sympathetic innervation of brown adipose tissue in the cold-induce d increase in thermogenic capacity, hamsters were denervated prior to cold acclimation and responses were measured after 3 and 14 days of co ld exposure. Uncoupling protein-messenger ribonucleic acid level and c ytochrom-c-oxidase-activity of intact brown adipose tissue increased a fter 14 days cold acclimation. Denervation did not completely prevent a cold-induced 1.5-fold increase of cytochrom-c-oxidase-activity and a 3.2-fold increase of the uncoupling protein-messenger ribonucleic aci d level in denervated brown adipose tissue after 14 days of cold accli mation. In conclusion, high levels of uncoupling protein-messenger rib onucleic acid and cytochrom-c-oxidase activity in brown adipose tissue of cold-acclimated hamsters can partially be maintained without intac t sympathetic innervation, suggesting a considerable contribution of t rophic factors not requiring sympathetic innervation for maintenance. The cold-induced increase of cytochrom-c-oxidase activity and expressi on of uncoupling protein-messenger ribonucleic acid largely depends up on sympathetic innervation of brown adipose tissue.