Room temperature ADP induced first stage hyperaggregation of human blood platelets: a previously undescribed phenomenon and its relationship to spontaneous cold induced platelet aggregation.

ADP induced human platelet aggregation was shown to be accentuated when tested at 20-30 degrees C as increased sensitivity and as a greater change of optical density although second stage aggregation and the release reaction did not occur. This previously undescribed phenomenon is defined as room temperature ADP induced first stage hyperaggregation. Aggregation, which occurs under the above mentioned conditions with a quantity of ADP insufficient to maintain the aggregation (usually less than 1.5 micron), is reversible when the temperature is raised to 37 degrees C. After rewarming to these temperatures, second stage aggregation appeared in the presence of larger quantities of ADP (usually more than 2 microns) and could be blocked by aspirin. The absence of the release reaction was demonstrated with a lumi-aggregometer. Spontaneous cold induced platelet aggregation seen after chilling platelets to 0-4 degrees C is shown to be a distinct phenomenon.