Compensatory renal growth in the mouse. I. Allometric approach to the effect of age.

Allometry, defined as the relationship between the growth rates of organs to the weight of the whole body (38), was used to study the effect of age on the degree of compensatory renal growth (CRG) in the mouse. The normal growth of the kidneys relative to body weight (BW) was determined in animals between 5 to 50 days of age. In one group, nephrectomy and sham operations were performed at 5, 15, and 35 days of age. The remaining ("renoprival") kidney was removed 15 days postnephrectomy. In a second group, nephrectomy was performed on 5-day-old animals, the renoprival kidney being removed after 30 or 45 days. Regression equations were calculated by least-squares after logarithmic transformation and different groups were compared by analysis of covariance. The regression equation for the control kidney was kidney weight (KW) = 0.0093 BW0.86 (r = 0.96). The regression for renoprival kidneys in females was KW = 0.0142 BW0.83 (R = 0.96) after 15 days and, in comparison, was not significantly different from 30 to 45 days. The interval between control and renoprival regressions was equivalent to a difference of congruent to 43% KW. In male mice, the regression for renoprival kidneys after 15 days was KW = 0.0103 BM0.96 (r = 0.98) and was not significantly different from 30 to 45 days. This study suggests that in young mice the time required for complete CRG may be a maximum of 15 days and that the amount of CRG does not depend on the age at operation. After CRG, a new equilibrium is reached which is thereafter maintained up to a minimum of 50 days of age.