It is well known that non-steroidal anti-inflammatory drugs (NSAIDs) are nephrotoxic and indomethacin has been shown to reduce medullary blood flow (MBF) by up to 20 % [1]. Since NSAIDs inhibit cyclooxygenase enzymes, the NSAID-evoked reduction in MBF is thought to be due to inhibition of cyclooxygenases and the subsequent reduction of vasodilatory prostaglandin E2 (PGE2) synthesis. Here we use a live kidney slice model to investigate (i) the role of contractile pericyte cells in the indomethacin-induced reduction in MBF and (ii) to localise the cyclooxygenase (COX) enzymes and E-prostanoid 2 and 4 (EP 2, EP 4) receptors in the medulla. Kidney slices (200 µm thick) containing intact medulla were obtained from adult (~300 g) male Sprague-Dawley rats and maintained in physiological saline solution (PSS), bubbled with 95% O2/5% CO2. Real-time images of vasa recta were recorded using video imaging techniques and vasa recta diameter at pericyte and non-pericyte sites was measured off-line. Immunohistochemistry techniques were used to localise COX enzymes and EP 2 and 4 receptors in the medulla of fixed kidney slices.It has previously been demonstrated that PGE2 dilates isolated perfused descending vasa recta (DVR) capillaries [2]. Application of PGE2 (10 µM) to live kidney slices evoked a significantly greater vasodilation of vasa recta at pericyte sites (8.60±1.58%) than at non-pericyte sites (1.00±0.83%) (P<0.01). PGE2 (10 µM and 50 µM) significantly attenuated the pericyte-mediated vasoconstriction evoked by ET-1 (10 nM, P<0.001) and Ang-II (10 nM, P<0.001) respectively. We also investigated the ability of a range of NSAIDs (indomethacin, SC-560 meloxicam and celecoxib) to regulate vasa recta diameter and measured a significant reduction in vasa recta diameter specifically at pericyte sites (P<0.001) in respone to all compounds tested. Indomethacin significantly attenuated the pericyte-mediated vasodilation of vasa recta evoked by PGE2 (P<0.001), bradykinin (P<0.01) and the NO donor S-Nitroso-N-Acetyl-D,L-Penicillamine (SNAP) (P<0.001). In addition to functional studies an enzyme immune assay (EIA) kit was used to monitor PGE2 concentration in our experimental perfusate and was used to determine whether indomethacin treatment inhibited production of PGE2 specifically. COX enzymes were localised to the apical membrane of medullary tubular structures and EP 2 and 4 receptors were localised with medullary vasa recta. All data are expressed as mean±s.e.m., n=≥5 animals. Collectively data presented here indicate that i) PGE2 is key in attenuating vasa recta diameter via its action at contractile pericytes and ii) NSAID-evoked constriction of vasa recta occurs at pericyte sites and is likely to be due to a reduction in PGE2. Hence, pericytes are likely to be key in NSAID-evoked reduction in MBF and the ensuing reduced kidney function.