Angiotensin II and fluid ingestion in old rats.

Fluid ingestion was studied in Fischer 344/Brown Norway F1 rats aged 3, 12, 20, and 24 months of age. There was an age-related decrease in fluid ingestion when fluid intake was measured over 24 h. After water deprivation, 24- and 20-month-old rats drank less than 3- and 12-month-old rats. Twelve, 20-, and 24-month-old rats had less fluid intake associated with food deprivation than did 3-month-old rats. Three month old rats drank more fluid after angiotensin II than did 12-, 20-, and 24-month-old rats when expressed as fluid intake per kg body weight. These studies confirm that the rat is a reasonable model to study age-related hypodipsia.