EFFECT OF GLUCOCORTICOIDS ON MITOCHONDRIAL OXIDATIVE ENZYME AND NA-K-ATPASE ACTIVITIES IN THE RAT PROXIMAL TUBULE AND THICK ASCENDING LIMB OF HENLE

The activities of three mitochondrial oxidative enzymes (citrate synth ase, 3-ketoacid-CoA transferase, beta-hydroxyacyl-CoA dehydrogenase) a nd Na-K-ATPase were microassayed in isolated segments of the rat proxi mal convoluted tubule (PCT) and medullary thick ascending limb of the loop of Henle (mTAL). The effects of adrenalectomy (ADX) and ADX plus exogenous glucocorticoids were analyzed. The hormonal replacement was daily injections of dexamethasone (10 mug/100 g body weight/24 h) for 5 days. ADX lowered the activity of all oxidative enzymes studies in t he mTAL, but not in the PCT and led to a decrease in Na-K-ATPase in bo th nephron segments. Dexamethasone restored the normal level of oxidat ive enzymes and Na-K-ATPase in the mTAL and of Na-K-ATPase in the PCT We conclude that the activities of citrate synthase, 3-ketoacid-CoA tr ansferase and beta-hydroxyacyl-CoA dehydrogenase and of Na-K-ATPase ar e coordinately regulated in the mTAL and that glucocorticoids are esse ntial for the long-term regulation of these enzyme activities in this nephron segment. In contrast, the activities of mitochondrial oxidativ e enzymes are not influenced by glucocorticoids in the PCT. This study presents the first evidence for a cell-specific regulation by glucoco rticoids of oxidative metabolism in the nephron of adult rat kidney.