THROMBOXANE RECEPTOR STIMULATION INHIBITS ADENYLATE-CYCLASE AND REDUCES CYCLIC AMP-MEDIATED INHIBITION OF ADP-EVOKED RESPONSES IN FURA-2-LOADED HUMAN PLATELETS

Stimulation of human platelets with the thromboxane A2 analogue, U46619, after treatment with prostaglandin E1 or forskolin, reduced the inhibition of ADP-evoked Mn2+ influx and the release of Ca2+ from intracellular stores. U46619 decreased the elevated concentration of 3',5'-cyclic AMP in platelets that were pretreated with prostaglandin E1. These results suggest that occupation of prostaglandin H-2/thromboxane A2 receptors, like those for other agonists, inhibits adenylate cyclase activity, which can contribute to the promotion of platelet activation.