Uptake of serotonin into platelets of senile dementia of the Alzheimer type patients.

[3H]-serotonin uptake in platelets was studied in 26 patients with senile dementia of the Alzheimer type (SDAT), 29 age-matched normal elderly persons, and 21 young subjects. The results showed a significantly lower uptake of serotonin into platelets of SDAT patients than in those of elderly controls (p < .02). Uptake of serotonin into platelets of elderly normal subjects was significantly lower than in the young (p < .01). These differences were due to reduced Vmax, whereas Km was unchanged. Isolated plasma from SDAT patients did not affect the uptake of serotonin into platelets of elderly controls, and vice versa, i.e., plasma obtained from elderly controls did not affect serotonin uptake in SDAT patients. The results indicate that serotonin uptake into platelets is reduced in normal aging, and more so in SDAT. Moreover, the reduced uptake in SDAT is not caused by a plasma factor in SDAT patients. No correlation was found between serotonin uptake and degree of cognitive impairment in SDAT patients.