EFFECTS OF AGE AT THE TIME OF UNILATERAL NEPHRECTOMY AND DIETARY-PROTEIN ON LONG-TERM RENAL-FUNCTION IN RATS

Glomerular filtration rate (GFR) and urinary protein excretion (UpV) w ere studied in male rats with a uninephrectomy at 3 (UNX-3) or 15 week s of age (UNX-15) and fed a low (12%, LP), normal (24%, NP) or high (3 6%, HP) protein diet. Measurements were made every 12 weeks throughout the entire life-span. The UNX rats were compared with sham-operated ( 2K) rats of the same age and on the same diets. At 12 weeks after surg ery, the GFR of UNX rats, corrected for differences in body weight, ag e and protein intake (GFRcor), ranged between 73% and 77% of that of 2 K rats. On the HP and NP diet, UpV was higher in UNX-3 than in UNX- 1 5 rats. On the LP diet, UpV was equally low in both groups. Long-term follow-up indicated that the GFR of UNX rats on the HP diet started to decline first, followed by those on an NP diet, while those on an LP diet had the longest period of stable GFR. For UNX rats, the time to r each a GFRcor of 50% was used as an indicator of the length of renal s urvival. Analysis of variance of the renal survival times indicated a highly significant interaction between the protein diet and age at the time of UNX. On the HP diet, UNX-3 rats have a shorter renal survival time than UNX-15, while on the LP diet UNX-3 rats have a longer renal survival time. This indicates that the long-term outcome of UNX at yo ung age depends on the protein intake. Simultaneous stimulation of ren al growth by HP intake and compensatory growth, during the period of n ormal kidney growth, results in early damage of the remaining kidney.