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Introduction: Peritubular renal microcirculation has not been directly visualized in acute ureteral obstruction. Therefore, we used epiilluminescence intravital microscopy and an animal model for the assessment of microvascular perfusion. Materials and methods: In group 1 (n=5) the left kidney of Wistar rats was exteriorized and placed on a heatable stage for microcirculatory analysis. FITC-dextran was injected for plasma staining. Microcirculatory stability of the model was assessed by a repeated intravital microscopy at baseline, 60, and 120 minutes. In detail, the functional peritubular vessel density (FVD, total vessel length per area in cm/cm2), the red blood cell velocities and diameters in/of arterioles and peritubular capillaries and the perfusion index were measured. In group 2 (n=7) the left ureter was obstructed after baseline microscopy. In a third group (n=6) the influence of the antidiuretic and vasoconstrictive peptide gastrin releasing peptide on peritubular microcirculation of the obstructed kidney was measured. Results: Repeated intravital microscopy did not induce major microcirculatory disturbances in group 1. Acute ureteral obstruction significantly decreased the index of peritubular perfusion. Moreover, FVD was found decreased at 120 minutes after a small rise at 60 minutes. Whereas blood cell velocities were not changed, arteriolar diameters were decreased after 120 minutes. GRP infusion lowered intrapelvic pressures at 60 and at 120 minutes. The transient increase of FVD (group 2) was not observed. The calculated peritubular flow remained nearly constant compared to a decrease in group 2. Histological assessment did not reveal any microscopy induced renal damage nor any differences between the groups. Conclusions: (1) The model is stable for a time period of at least 120 minutes and allows for the direct visualization of the renal peritubular vessels. (2) Peritubular microcirculation shows a significant deterioration during ureteral obstruction. (3) Infusion of GRP may be beneficial for the microcirculation of the acutely obstructed kidney. [ABSTRACT FROM AUTHOR]