Dietary protein restriction ameliorates the decrease in GFR and renal plasma flow that occurs 24 hours after the onset of bilateral ureteral obstruction (BUO). The vasoactive hormones, prostaglandins (PGs) and thromboxane (Tx), have a role in the changes in renal function described above. Thus, we evaluated the effect of dietary protein restriction on the production of PGE2, 6-keto PGE(1α) and TxB2 and on the activities of cyclooxygenase and phospholipases A2 and C in glomeruli isolated from sham-operated control (SOC) and BUO rats fed a low (6% casein) or a normal protein (23% casein) diet for approximately four weeks. A normal protein diet compared to a low protein diet significantly increased the glomerular production of PGE2, 6-keto PGF(1α) and TxB2 in SOC rats. Glomeruli of rats with BUO fed a normal protein diet had further increased production of eicosanoids when compared to glomeruli of SOC rats ingesting the same diet. The production rates of eicosanoids correlated well with the activity of cyclooxygenase in the two groups of rats. On the other hand, a low protein diet completely abolished the increase in glomerular eicosanoid production seen in rats with BUO. The synthetic levels of eicosanoids were comparable in low protein-fed SOC and BUO rats, indicating normalization of glomerular eicosanoid production in BUO rats fed a low protein diet. Moreover, there were no significant differences in the activities of cyclooxygenase and phospholipases A2 and C between the SOC and BUO rats. We demonstrated previously that increases in the activities of cyclooxygenase and phospholipase A2 have a key role in glomerular eicosanoid production in rats with BUO. Thus, our results indicate that dietary protein restriction prevents the increase in production of eicosanoids by glomeruli due to inactivation of phospholipase A2 and cyclooxygenase in the setting of BUO of 24 hours duration. The protective effect of dietary protein restriction on renal function in rats with BUO may be due in part to normalization of the glomerular production of eicosanoids, particularly TxA2.