Alzheimer's Dementia and Binding to Alpha₂ Adrenoreceptors in Platelets

Seventy‐five patients with probable Alzheimer's disease were screened for binding of alpha₂ receptors (A₂R) to their platelet membranes; the results were compared with 51 age‐ and sex‐matched controls. Receptor binding assays were performed using [³H] Yohimbine as the radioligand. The results showed a higher binding capacity in the demented population as compared to the control group (2.18 ± 0.15 fmol/mg protein, as compared to 1.73 ± 0.13, P < 0.03). This increased binding to platelets in the demented patients was more prominent in demented females: 34% higher binding as compared with female controls (2.06 ± 0.5 vs 1.54 ± 0.04). The difference between demented and normal males was less (2.34 ± 0.05 vs 1.88 ± 0.05). The results indicate an involvement of the A₂R system, either primarily or secondarily, in the disease process. Since there is an overlap between results from the patients with Alzheimer's disease and the normal subjects, A₂R may serve as only a supportive marker for Alzheimer's disease.