In this study, we tested the hypothesis that the plasma arginine vasop
ressin (AVP) response to osmotic stimulation induced by hypertonic sal
ine infusion is blunted in the early and middle stages of Alzheimer di
sease (AD). Because animal data support stimulatory cholinergic mediat
ion of AVP osmoregulation at a brain level, the AVP response in AD mig
ht provide clinically useful information about the status of brain cho
linergic systems. Seventeen AD outpatients and eight normal older subj
ects underwent both a 90-min hypertonic saline infusion and a 90-min c
ontrol (normal saline) infusion. Substantial increases in plasma osmol
ality during hypertonic saline infusion were accompanied by substantia
l and linear increases in plasma AVP in both groups. However, there we
re no significant differences in AVP responses between AD and normal o
lder subjects. These results do not support the utility of plasma AVP
response to hypertonic saline in the assessment of brain cholinergic s
tatus in AD.