Alzheimer's dementia and binding to alpha 2 adrenoreceptors in platelets.

Seventy-five patients with probable Alzheimer's disease were screened for binding of alpha 2 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 less than 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.