Adp-Induced Shape Change in Platelets from Normal and Diabetic Subjects

In the absence of Ca⁺⁺, adenosine diphosphate (ADP) induces alterations in light transmittance (LT) of platelet rich plasma (PRP). An initial decrease of LT, representing the platelet shape change (PSC), is followed by a slower self-stabilizing i ncrease, which can be evaluated as % of LT.

Methodological studies showed that the optical recording of PSC was mainly influenced by the concentrations of EDTA (used as chelating agent) and ADP in the test slstem. Under standardized conditions (PRP incubated at room temperature with EDTA 7.6 mM, ADP 5ug/ml) the measurement of PSC is a reproducible and simple test.

The tracings of 19 controls were compared to those of 32 patients with diabetic retinopathy. Significant differences (p < 0.005) were found in 15 proliferative retinopathics (17.25 ± 1.07 SEM) and 6 maculopathics (17.99% ± 1.48), when compared to 11 mild retinopathics (13.96 % ± 1.48) and the controls (13.11% ± 0.73). Conventional aggregometry studies revealed a lower threshold ADP concentration to produce complete aggregation in platelets from diabetics. The response to high concentrations of ADP, to collagen, or ristocetin was identical in the two groups.

The preliminary data presented support the anticipated role of platelets in the development of diabetic microangiopathy, and indicate that the test described is a useful addition to studies of platelet function.