AGE-RELATED DECLINE IN THIRST AND SODIUM APPETITE IN RATS RELATED TO KININASE-II INHIBITION

Water intake was examined in young (3-5 months) and old (20-24 months) rats following peripheral administration of either angiotensin (Ang) II or captopril + bradykinin (BK). Relative to body weight, intake aft er Ang II showed no age-related difference, while that after captopril + BK was markedly reduced in the old rats. In other rats that were no t allowed to drink after captopril + BK, the induction of Fos-like imm unoreactivity (IR) was much lower in the subfornical organ, supraoptic and median preoptic nuclei of old rats compared with their young coun terparts. Intake of 0.15 M NaCl during chronic dietary administration of enalapril was robust in young rats but was much reduced in old rats , as was their plasma renin activity. Thus, reduced thirst and sodium appetite are found in conjunction with kininase II (angiotensin-conver ting enzyme) inhibitors in aging rats, possibly because they fail to g enerate the high levels of circulating renin seen in young rats under these conditions.