Single nephron study of intrarenal urea handling in experimental pyelonephritis

Micropuncture experiments were carried out in 20 rats with bilat. experimental chronic pyelonephritis. Inulin and urea concentrations were estimated in the late proximal, early distal and latte distal nephron segment. Proximal urea reabsorption did not differ from that in control animals. Fractional amount of filtered urea in the early distal segment was significantly lower in the pyelonephritic rats, urea reabsorption in the distal tubule approcimated zero. The data indicate that intrarenal urea recirculation is abolished by the experimental lesion, thus determining maximal urine urea concentration. It is suggested that the concentrating defect of experimental pyelonephritis is not only a result of an adaptational increase in individual nephron GFR; an additional intrinsic lesion seems to be present, located in the renal medulla.