Determinants of hypofiltration during acute renal allograft rejection

This study sought to determine the extent to which GFR is decreased during acute renal allograft rejection in human subjects and to determine the mechanism of the decrease in GFR. Eight patients with biopsy-proven acute rejection were compared with 18 recipients of optimally functioning renal allografts. GFR and renal plasma flow (RPF) were measured as the clearance of inulin and para-aminohippuric acid, respectively. Arterial BP was determined, blood was sampled, and plasma oncotic pressure (pi(A)) was measured. Glomeruli obtained by biopsy during rejection were subjected to morphometric analysis, for determination of K(f). Control morphometric values for healthy glomeruli were provided by 10 living donors from whom biopsies were obtained at the time of organ donation. The subjects in the acute rejection group exhibited a significantly reduced GFR of 17 +/- 4 ml/min per 1.73 m(2), compared with 72 +/- 4 ml/min per 1.73 m(2) for control subjects (P < 0.001). With the use of a sensitivity analysis to take into account the unknown para-aminohippuric acid extraction ratio, the RPF rate was calculated to have likely been significantly decreased, by 45 to 70%, in the acute rejection group. Neither the plasma oncotic pressure nor the mean arterial pressure differed between the two groups. Morphometric analysis revealed no difference in the single-nephron K(f) values for the acute rejection group, compared with the control group. These results indicate that acute renal allograft rejection causes a profound decrease in GFR, which is attributable to a decrease in RPF alone or in combination with a decrease in the glomerular transcapillary hydraulic pressure gradient (DeltaP).