Compensatory and Obligatory Renal Growth in Babies and Adults1

On the basis of previous studies in rats, and clinical observations in human renal transplantation and in patients with a renal duplication anomaly, we have postulated two distinct types of renal growth. Compensatory growth is caused by a nephron deficit, while obligatory growth is part of the normal process of growing into adulthood. The former is reversible, and the latter is not. A definitive test of this hypothesis required the transplantation of extra kidneys into baby rats and comparison of their growth with that of normal litter-mate controls. This showed that there is little if any retardation of obligatory renal growth in spite of the presence of an excess of kidneys in the baby.