CHANGES IN THE COUNTERCURRENT SYSTEM IN THE RENAL PAPILLA - DIURESIS INCREASES PH AND HCO3- GRADIENTS BETWEEN COLLECTING DUCT AND VASA-RECTA

This study was designed to elucidate the acid-base balance local to th e collecting duct urine (CD) and vasa recta blood (VR) in the rat rena l papilla in diuresis. The pH changes were measured in both a furosemi de-induced and a volume-load-induced diuresis, whereas the PCO2 (i.e., CO2 tension) and HCO3- concentration were measured only in a furosemi de-induced diuresis. In an antidiuresis, the pH of the VR was more aci dic than that of the systemic arterial blood (Delta pH = 0.44-0.73). A dditionally, the pH of the ascending VR was significantly lower than t hat of the descending VR (Delta pH = 0.14-0.16). In diuresis, the pH o f the CID decreased (Delta pH = 0.81-0.97), while the pH of the descen ding and the ascending VR increased; however the increase was only sig nificant in the ascending VR (Delta pH = 0.23-0.30). Consequently, the significant difference in the pH gradient between the descending and the ascending VR was eliminated. The PCO2 values in the CD and the asc ending VR were not different from those in antidiuresis, while the HCO 3- concentration in the CD and the ascending VR, respectively, decreas ed and increased significantly. Thus, in diuresis, the decrease in the pH of the CD and the increase in the pH of the ascending VR result, r espectively, from the decrease and the increase in the HCO3- concentra tion, with no changes in the PCO2 values.