Reduced water intake but normal response to acute water deprivation in elderly rhesus monkeys.

The ability to compensate for acute water deprivation was studied in young adult (YA, 7-9 years), middle aged (MA, 13-17 years), and older adult (OA, 20-36 years) rhesus monkeys of both sexes (N = 6/group). Water intake and urine volume were measured during three 7-day trials: 3 days of baseline measurement, 1 day of deprivation and 3 days of compensation. OA drank less during baseline (380 +/- 63 mL/day) than MA (679 +/- 92 mL/day, p < 0.05) or YA (750 +/- 128 mL/day, p < 0.01). All groups drank more following deprivation than at baseline and the OA drank significantly less than the younger groups (both p < 0.01), but the increase above baseline did not differ among groups when expressed as a cumulative percentage of baseline (89% for OA; 77% for MA; 83% for YA). Urine volume of all groups decreased by similar percentages on the day of deprivation (56% overall) and this reduction represented a similar proportion (58% overall) of baseline water intake. Urine concentration increased significantly during deprivation (p < 0.05) and returned to baseline values during compensation with no differences among age groups. OA water balance appears to have been maintained at lower levels of intake and excretion. In conclusion, responses to acute hydrational challenges in the elderly should be interpreted in the context of customary fluid intake.