Increased platelet aggregation due to chilling to 20 degrees C is not related to increased sensitivity to agonists.
BACKGROUND
Previous studies suggested that chilled platelets have a greater sensitivity to agonists than do platelets aggregated at 37 degrees C.


METHODS
Washed platelets were aggregated at 20 or 37 degrees C with ADP (0-20 microM), arachidonic acid (0-200 microM), or the thromboxane mimetic U46619 (0-9 nM).


RESULTS
Chilling caused a significant (p < or = 0.05) increase in spontaneous platelet aggregation (> 27% at 20 degrees C vs < 5% at 37 degrees C) and spontaneous dense granule release (> 0.01 nM of ATP at 20 degrees C vs. 0 nM of ATP at 37 degrees C), ADP and U46619 caused a significantly greater aggregation response and dense granule release at 20 degrees C, although there was no change in agonist sensitivity of platelets (effective dose of agonist necessary to induce 50% aggregation [ED50]: 1.00 +/- 0.35 microM ADP at 20 degrees C and 1.63 +/- 0.47 microM ADP at 37 degrees C; 8.26 +/- 3.65 pM U46619 at 20 degrees C and 18.97 +/- 4.82 pM U46619 at 37 degrees C). Platelets aggregated with arachidonic acid showed a significant decrease in aggregation and agonist sensitivity at 20 degrees C (ED50 118.7 +/- 44.4 microM) from those at 37 degrees C (ED50 25.6 +/- 7.2 microM), possibly as a result of the reduced enzymatic activity of cyclooxygenase and thromboxane synthase at the lower temperature.


CONCLUSIONS
The data suggested that washed platelets chilled to 20 degrees C and aggregated are not more sensitive to agonists than are 37 degrees C controls, but rather that chilled platelets undergo greater spontaneous aggregation.
Hansen
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TN
CryoLife, Inc., Marietta, Georgia, USA.
Brockbank
K G
KG
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000244:Adenosine Diphosphate / Q000494:pharmacology; D000704:Analysis of Variance; D016718:Arachidonic Acid / Q000494:pharmacology; D001792:Blood Platelets / Q000737:chemistry; D003080:Cold Temperature; D006801:Humans; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D013929:Thromboxane B2 / Q000097:blood; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D011450:Prostaglandin Endoperoxides, Synthetic; D014662:Vasoconstrictor Agents; D016718:Arachidonic Acid; D013929:Thromboxane B2; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid