DOCA‐induced salt appetite in old Brown‐Norway rats

Abstract

Old rats, like the elderly, have diminished drinking responses to most stimuli. In addition, old rats are nearly devoid of renin‐dependent salt appetite. In the present work, we investigated mineralocorticoid‐induced salt appetite in old rats. Young (4 mo), middle‐aged (12 mo) and old (30 mo) male Brown‐Norway rats with ad libitum access to water, 0.3 M NaCl and sodium deficient diet received DOCA (5 mg/kg/day, sc) for six days. In response to DOCA, old rats drank as much saline solution as young rats on an absolute basis (~ 25 ml/day), and about a third as much as middle‐aged rats (~75 ml/day). After adjusting intakes for body weight, the salt appetite responses by age were middle‐aged > young > old rats. In addition, old rats preferred saline less than the other groups as indicated by their significantly reduced saline preference ratios (saline/total fluid intake) compared to young and middle‐aged rats. This is the first demonstration of a significant salt appetite in old animals. We hypothesize that the reduced capacity of old rats to excrete water and sodium loads reduces sodium intake in response to DOCA compared to young and middle‐aged rats. This work was supported by AG‐025465 to RLT and HL‐14388 and DK‐066086 to AKJ.