Suppression by dexamethasone of isoproterenol-mediated changes in fatty acyl-CoA desaturase activity of Tetrahymena microsomes.

Preincubation of Tetrahymena pyriformis cells with dexamethasone inhibited the microsomal fatty acyl-CoA desaturase activities of isoproterenol-induced modulation; that is, an increase in delta 9-desaturase activity accompanied by a decrease in delta 12-desaturase activity. Although isoproterenol caused an increase in delta 9-terminal component activity with decreased delta 12-terminal component activity, dexamethasone reduced these isoproterenol-mediated activity changes. In cells treated with dexamethasone prior to isoproterenol administration, stimulation of cyclic AMP accumulation by isoproterenol was inhibited. These results suggest that dexamethasone may repress isoproterenol modulation of the activity of terminal components (cyanide-sensitive factor) in the fatty acyl-CoA desaturase system by reducing the cyclic AMP level.