Summary
The ADP-induced platelet adhesiveness has been investigated under experimental various
conditions by the in vitro method of Hellem. The platelet, adhesiveness was found
to be proportional to the logarithm of the ADP concentrations between 0.025—0.2 μg/ml
in citrated and heparinized plasma. The effect of ADP on platelets decreased with
increasing concentrations of citrate. In contrast, increasing amounts of heparin did
not alter the platelet adhesiveness significantly, except when extremely high concentrations
were used. Variations in the temperature highly influenced the result of the estimations
when suboptimal concentrations of ADP were used. The reason for this probably inactivation
of ADP by plasma enzymes, which have an optimal activity at about 37° C. This may
explain why estimation at 20° C gives higher values of the platelet adhesiveness than
at 37° C. If too high concentrations of ADP are used, this effect is not detectable.
This may be the reason why O’Brien (1962) did not find any inactivating property of
platelet poor plasma. Washing of platelets in buffered saline leads to a marked release
of ADP, indicating that washed platelets are damaged. Repeated resuspension of platelets
even in their own plasma gives release of ADP. When studying the mechanism of the
ADP-induced reaction all the above variations must be taken into account.
