Effect of dexamethasone on cyclo-oxygenase activity in reno-medullary cells in culture

The steroid-induced inhibition of prostaglandin secretion has been shown to be mediated through the interaction of the steroid with specific receptors and to require RNA and protein synthesis. At present the nature of the protein(s) involved is unknown although several suggestions have been made for the role of phospholipase A2. It has also been postulated that the early action of steroid is a stimulation of cyclo-oxygenase activity leading only secondarily to an inhibition of arachidonate supply. In this paper, we have therefore investigated the effect of dexamethasone on cyclo-oxygenase activity in cultures of rat reno-medullary interstitial cells. Pretreatment of the cells with the anti-inflammatory steroid dexamethasone induces a moderate increase in cyclo-oxygenase activity but this elevation does not appear sufficient to account for the inhibitory action of dexamethasone on PG secretion.