Effects of glucocorticoid hormones on lipid-synthetic enzymes from different adipose tissue regions and from liver

Abstract

The regional diversity of adipose tissue is dramatically accentuated in states of glucocorticoid excess, in which certain fat depots expand, while others contract. We have studied the molecular basis of this redistribution by determining the activity of fatty acid synthetase and enzymes catalyzing di- and tri-acylglycerol synthesis, in subcellular fractions from four adipose depots of rats injected with dexamethasone and from interscapular and epididymal adipocyte precursors after addition of either dexamethasone or corticosterone to confluent monolayers in secondary culture. Subcellular fractions from cervical and interscapular adipose tissue, as well as from cultured interscapular precursors, revealed a general increase in specific enzyme activity. The opposite trend was observed for retroperitoneal and epididymal fat tissue, as well as cultured epididymal precursors. Fatty acid synthetase and cytosolic phosphatidate phosphohydrolase appeared to be most responsive. The findings in culture indicate that the regional effects of glucocorticoids are partly independent of other circulating or neural factors. Injections of dexamethasone led to significantly enhanced specific activity of all the lipid-synthetic enzymes assayed in subcellular fractions from liver. Differences in hormonal influences between liver and certain fat tissue regions represent tissue specificity. In addition, the diverse effects of glucocorticoids on various adipose tissue depots indicate regional or "intratissue" specificity.