EVALUATION OF METHODS INDICATING HIGHER SUSCEPTIBILITY OF IMMATURE RATS TO RENAL ISCHEMIA

After 45-min bilateral warm renal ischemia lethality amounted to 45 % and 82 % in 55- and 20-day-old rats, respectively (n = 176). Lethality rates were not significantly different after 20-min unilateral ischem ia followed by contralateral nephrectomy after 24 hours (34 vs. 48 % i n young vs. adult rats; n = 168). The latter experimental approach was used to characterize age dependent differences in the susceptibility to ischemia. The degree of postischemic renal damage was the highest a t the 1st and 2nd days after ischemia; at this time, lethality rates w ere similar in young and adult rats. However, urea concentration in se rum was significantly more enhanced in young animals whereas that of c reatinine was increased to the same extent in both age groups. The inc rease in protein excretion into urine was similar in young and adult r ats, too. Furthermore, urine flow rates and GFR were significantly dim inished after ischemia, independent of age. However, excretion of Naand K+ was distinctly more depressed in immature individuals. Finally, the glutathione content in kidney tissue of both age groups was reduc ed and lipid peroxidation was significantly higher after ligation of t he renal arteries. The relative changes were similar in both age group s although the glutathione content was significantly lower in 20-day-o ld control rats. 4-5 days after ischemia, most parameters returned to baseline values. In 55-day-old rats, 45-min ischemia has more severe c onsequences on renal function compared to 20-min ischemia. Obviously l ethality after ischemia is caused by various mechanisms and the pathog enetic importance of a single event can not explain the higher lethali ty in young rats after 45-min bilateral renal ischemia.