Sulfhydryl analogues of adenosine diphosphate: chemical synthesis and activity as platelet-aggregating agents

Platelet aggregation is inhibited by long chain acyl-CoA

Oleoyl coenzyme A and other acyl-CoA derivatives inhibited ADP or thrombin-induced aggregation of platelets. Arachidonic acid-induced aggregation was also inhibited, but not the slower aggregation caused by 1-oleoyl-2-acetylglycerol or tetradecanoyl-phorbol-13-acetate. Coenzyme A and free fatty acids had little or no effect, and transfer of labeled oleate from oleoyl Co-A to other lipid classes was not detected. Because acyl Co-A compounds have recently been shown to modulate protein kinase C activity, acyl Co-A may provide a useful tool for investigating activation sequences in platelets and other membranes.

Interaction of human blood platelets with the 2',3'-dialdehyde and 2',3'-dialcohol derivatives of adenosine 5'-diphosphate and adenosine 5'-triphosphate

1. The 2',3'-dialdehyde derivative of ADP (oADP) at concentrations approaching the millimolar range induces human blood platelets to undergo the transition from discoid to globular morphology (the 'shape change') but is incapable of inducing aggregation. 2. When incubated with platelets for 1 min before addition of the agonist, oADP acts as a competitive inhibitor of shape change and aggregation induced by ADP. Under these conditions secretion and hence aggregation induced by low concentrations of collagen; and secretion and hence secondary aggregation induced by adrenaline, thrombin and vasopressin are also inhibited by this analogue. In addition, oADP stimulates the rate of primary aggregation induced by adrenaline and causes partial inhibition of primary aggregation induced by thrombin or vasopressin. When longer preincubation times are employed the extent of inhibition with respect to all agonists, except for high concentrations of collagen, is increased and the competitive character of the inhibition with respect to ADP is no longer apparent. 3. Incubation of human platelets with the 2',3'-dialdehyde derivative of ATP (oATP) causes effects similar to those described for oADP except that the analogue neither induces platelet shape change, nor stimulates the rate of primary aggregation induced by adrenaline. In addition oATP fails to cause significant inhibition of platelet shape change induced by serotonin. The extent and character of inhibition caused by addition of oATP is not a function of the time of incubation. 4. The 2',3'-dialcohol derivatives of ADP and ATP and orATP) effect the aggregation properties of human blood platelets in a manner generally resembling those observed for the 2',3'-dialdehyde analogues. However, orADP is only weakly effective in causing platelet shape change and stimulating the rate of primary aggregation induced by adrenaline and does not inhibit secretion induced by adrenaline, collagen, thrombin and vasopressin. The extent of inhibition by orADP increases only slightly with increased time of incubation. 5. The data suggest that oADP acts as a partial agonist, and oATP as an antagonist, at the platelet ADP receptor, but that platelet membrane stabilisation also results from interaction with these dialdehyde analogues. Such membrane stabilisation does not complicate the interaction of platelets with orADP, which appears to act as a classical antagonist for the ADP receptor.