Fig. 1.

Plots of physiological responses and verbal ratings to the infusion of hypertonic saline followed by drinking in young and older groups. (A) Osmolality increased throughout the infusion in both groups and remained elevated thereafter. (B) Levels of vasopressin showed significant increases throughout the infusion in the young group and did not change in the older group. Drinking was associated with a marked decrease in vasopressin levels in the young group, whereas the older group showed a small, nonsignificant downward trend. (C) Old and young groups experienced similar increases in thirst in association with the infusion and reported decreased levels of thirst after drinking. *, P < 0.05