RT Journal Article SR Electronic T1 Effect of platelet activation on the agglutination of platelets by von Willebrand factor. JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 271 OP 277 VO 37 IS 2 A1 D C Mills A1 K Hunchak A1 D W Karl A1 E P Kirby YR 1990 UL http://molpharm.aspetjournals.org/content/37/2/271.abstract AB Agglutination of human platelets by bovine von Willebrand factor (vWF) or by human vWF in the presence of ristocetin is inhibited by ADP and by several other platelet agonists but not by epinephrine. Vincristine, which causes a shape change by disrupting microtubules, neither inhibited agglutination nor blocked the effect of ADP. The action of ADP was blocked by ATP, by p-fluorosulfonylbenzoyladenosine, and by the thiol-reactive regents cytochalasin A and p-chloromercuribenzenesulfonate. In contrast to its effects on vWF, ADP enhanced agglutination induced by wheat germ lectin. ADP caused a small decrease in the number and affinity of binding sites for vWF on platelets, too small to explain the inhibition of agglutination. The ability of ADP and other agonists to inhibit agglutination appears to be related neither to inhibition of adenylate cyclase nor to the loss of their discoid shape but rather to the membrane changes that accompany the shape change.