Pericytes reside at regular intervals on vasa recta capillaries and are known to regulate in situ vasa recta diameter following exposure to vasoactive agents including the co-transmitters noradrenaline (NA) and ATP [1,2]. The aim of this study was to (i) co-localise vasa recta pericytes with sympathetic nerves in the renal medulla of fixed kidney tissue slices, (ii) to demonstrate that tyramine-stimulated release of endogenous NA can similarly evoke pericyte-mediated regulation of in situ vasa recta diameter in live kidney slices and iii) to investigate whether the constriction evoked by the co-transmitters ATP and NA was additive. Kidney slices (200µm) were obtained from adult male Sprague Dawley rats, following cervical dislocation and maintained in oxygenated physiological saline solution (PSS). For live imaging experiments, slices were secured in an open bath chamber on the stage of an upright microscope and continually superfused with oxygenated PSS. Video-imaging techniques were used to capture pericyte-mediated changes in vasa recta diameter following exposure to Tyramine (1µM) plus and minus the co-transmitter ATP (100µM). Pericytes and sympathetic nerves were labelled in fixed kidney slices using anti-NG2 and anti-TH antibodies (respectively), and the appropriate fluorescently-conjugated secondary antibodies. Fluorescence images of sympathetic nerves and pericytes in both the inner and outer medulla were taken with a Zeiss LSM 510 confocal microscope and the distance between sympathetic nerves and the nearest pericyte measured. Bath application of tyramine (1µM) alone evoked an 11.9±2.9% constriction of vasa recta capillaries at pericyte sites, which was significantly greater than at non-pericyte sites (3.0±0.6%,P<0.05,n=7). Co-application of tyramine and ATP caused a significantly greater constriction of vasa recta at pericytes sites (26.5±4.6%) than at non-pericte sites (1.7±0.5%,P<0.05,n=5), an additional 55% decrease in vessel diameter compared with tyramine alone (P<0.05). Sympathetic nerves were identified in both the inner and outer medulla of fixed kidney slices. Mean distance between sympathetic nerves and the nearest pericyte in the outer medulla (1.6±0.4 µm) is significantly reduced compared to the inner medulla (4.8±1.1 µm,P<0.05,n=19). Here we demonstrate tyramine-stimulated release of endogenous NA causes pericyte-mediated constriction of in situ vasa recta. The effect on pericyte-mediated constriction of vasa recta was additive when kidney slices were exposed to ATP with tyramine. Given the identification of sympathetic nerves in close proximity to vasa recta pericytes we hypothesize that sympathetic nerves are an endogenous source of the co-transmitters NA and ATP and that local release of these vasoactive agents is one of the mechanisms involved in regulation of vasa recta blood flow.