The influence of the recipient upon renal function after isogeneic kidney transplantation in the rat

Little attention has been paid to the changes in renal function that occur after kidney transplantation when donor and recipient differ markedly in size. We studied this phenomenon after isogeneic kidney transplantation in rats of varying body weight (BW). Renal functional parameters, such as the glomerular filtration rate (GFR), the effective renal plasma flow (ERPF), and the plasma levels of creatinine (Pcr) and urea (Pur) were determined at regular intervals following transplantation. In the initial experimental series, juvenile (BW approximately 150 g) and adult (BW approximately 300 g) rats were used. Four groups of transplant recipients were studied. These consisted of 2 groups of adult recipients of juvenile or adult donor kidneys, and 2 groups of juvenile recipients of juvenile or adult donor kidneys. These 4 groups were compared with adult and juvenile control rats, as well as with unilaterally nephrectomized (NX) rats. A comparison between the 2 groups of juvenile recipients revealed no significant difference in the GFR, ERPF, Pcr, or Pur levels after the transplantation of adult or juvenile donor kidneys. Nor were any significant differences found when comparing the functional parameters of the 2 groups of adult recipients after transplantation of adult or juvenile donor kidneys. The transplanted kidneys generally functioned at a level amounting to 80-90% of the GFR and 90-100% of the ERPF of NX rats of comparable BW. These observations are a clear indication of functional adaptation after kidney transplantation. The compensatory functional response is augmented--in case of a young donor kidney transplanted into an adult recipient, or attenuated--in case of an adult donor kidney transplanted into a juvenile recipient. In an additional experiment, kidneys were transplanted from very young rats (BW approximately 50 g) to adult recipients. It appeared that as early as two weeks after transplantation, renal function had reached adult kidney levels, as observed in the first experimental series. In conclusion, after isogeneic kidney transplantation in rats, the transplanted kidney generally adapts rapidly to the size of the recipient and functions like an inherent part of the recipient's body.