Effects of glucocorticoids on adenyl cyclase and phosphodiesterase activity in fat cell homogenates and the accumulation of cyclic AMP in intact fat cells

The effects of adrenalectomy and cortisone replacement in rats on the activities of adenyl cyclase and phosphodiesterase in homogenates of isolated fat cells and on the accumulation of cyclic 3′,5′-AMP in intact cells were studied. 1. Adrenalectomy caused a decrease in the activity of norepinephrine- and fluoride-stimulated adenyl cyclase in homogenates of isolated fat cells. This decrease was not significantly reversed by pretreatment of the animals with cortisone in vivo. 2. Adrenalectomy caused an increase in the activity of phosphodiesterase. This increase was not reversed by pretreatment of the animals with cortisone for 4 h in vivo but was reversed after 18 h. Incubation of cells from adrenalectomized animals with cortisone in vitro caused no change in phosphodiesterase activity. 3. The incorporation of prelabelled nucleotides into cyclic 3′,5′-AMP was significantly reduced in intact cells from adrenalectomized rats. Pretreatment of the animals with cortisone in vivo for 4 h completely restored the ability of the cells to accumulate radiolabelled cyclic 3′,5′-AMP upon stimulation by norepinephrine.