Treatment with dexamethasone increases glomerular prostaglandin synthesis in rats

To determine whether chronic glucocorticoid excess influences the metabolism of arachidonic acid to prostaglandins (PGs) in the renal cortex, the authors investigated the effects of dexamethasone treatment (2.5 mg/kg/week) on the metabolism of arachidonic acid by renal cortex homogenates and microsomes and by isolated glomeruli, and on the release of immunoreactive prostanoids from isolated glomeruli incubated for 30 min in buffered salt solution at 37 degrees C. Glomeruli from dexamethasone-treated rats released, during basal incubation conditions, about twice (P less than .01) as much PGE2 and PGF2 alpha as did glomeruli from vehicle-treated rats. During incubation with arachidonic acid (33 microM) or calcium ionophore, A23187 (2.0 micrograms/ml), the release of PGE2 and PGF2 alpha from glomeruli of rats receiving dexamethasone also exceeded (P less than .01) the release from glomeruli of control rats. The rate of conversion of [1-14C]arachidonic acid to PGE2 and PGF2 alpha and to less polar metabolites having the chromatographic mobility of 5-hydroxyeicosatetraenoic acid and 12-hydroxyeicosatetraenoic acid, by isolated glomeruli and by renal cortex homogenates and microsomes from dexamethasone-treated rats, was higher (P less than .01) than the conversion by glomeruli and renal cortex homogenates and microsomes from control rats. The metabolism of arachidonic acid to the nonpolar metabolite(s) was not inhibited by indomethacin (10 microM), suggesting that it is not catalyzed by cyclooxygenase. The authors conclude that chronic dexamethasone treatment increases the release of glomerular PGE2 and PGF2 alpha and the metabolic transformation of arachidonic acid by glomeruli and by renal cortex homogenates and microsomes via both cyclooxygenase and noncyclooxygenase pathways.