N ephrotoxic nephritis (NTN) is characterized by a marked increase in glomerular eicosanoid synthesis, which appears to play an important role in the pathophysiology of this disease model. In this study, we investigated the biochemical and cellular basis of this metabolic change. By examining the enzymatic conversion of exogenous substrates by intact glomeruli, we found that cyclooxygenase, TX synthase, and 5-lipoxygenase activities increased 4-, 8-, and 100-fold, respectively, in acute NTN. PGH2-PGE2 isomerase and leukotriene A4 hydrolase activities did not change. The cellular basis of these changes was examined using dissociated glomerular cells in vitro and by depleting platelets in vivo. Dissociated glomerular cells from nephritic glomeruli (largely mesangial cells and leukocytes) exhibited an enhanced arachidonate metabolism similar to intact nephritic glomeruli. Depletion of neutrophils (PMNs) from these cell preparations by 90% commensurately decreased 5-lipoxygenase and cyclooxygenase activity but had little effect on TX synthase activity. The recovered PMN fraction, however, did exhibit TX synthase activity. Immunocytochemical analysis of dissociated cells using an antiplatelet antibody demonstrated the presence of platelets, both adherent to cells and noncell associated. Depletion of platelets in vivo using this antibody substantially attenuated the increase in glomerular eicosanoid synthesis that accompanied NTN. Platelet depletion also decreased the influx of PMNs into the glomerulus by 50%. These data show that PMNs and platelets colocalize to the glomerulus in acute NTN and are coordinately essential to the increase in glomerular arachidonate metabolism.