Effects of chronic treatments upon the brown adipose tissue of rats. II. Comparison between the effects of catecholamine injections and cold adaptation.

The role of noradrenaline in the trophic response of brown adipose tissue (BAT) to chronic and cold exposure was studied in young adult rats treated chronically with catecholamines. 2 In young rats, it was difficult to induce a BAT development with this type of treatment. After injection of a beta-agonist (isopropylnoradrenaline) directly upon BAT, a slight hypertrophy of the tissue was observed accompanied by a decrease of its relative protein content. 3 In adult rats, catecholamines were able to induce a growth of BAT and increases of the DNA and protein contents which were as great as in the BAT of cold-exposed rats. 4 Catecholamine treatments did not reproduce the effects of cold exposure on the phospholipids of BAT in either young or adult rats. 5 In the BAT of rats receiving chronically thyroxine and catecholamines, no synergy was observed. Moreover, a chronic treatment by thyroxine induced a slight increase of the DNA content of BAT in rats bred at room temperature, but prevented the marked DNA increase observed in cold-exposed animals.