Persistence of increased platelet cyclic AMP induced by prostaglandin E1 after removal of the hormone.

Prostaglandin E1 (PGE1) covalently linked to omega-NH2-hexyl-agarose (PGE1-hexyl-agarose) stimulates the activity of human platelet adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] 3-fold over control level at 60 sec when stirred at 1200 rpm at 37 degrees C. The time course exhibited a lag phase of 20 sec, a rapid increase to a maximum plateau between 60 and 80 sec, and a more gradual decrease to basal level at about 120 sec. During this entire period of incubation PGE1-hexyl-agarose could be easily separated; therefore it bound only transiently to the platelet. No prostaglandin(s) were found to be released into plasma. The stimulation of adenylate cyclase activity by the insolubilized hormone was dependent on the rate of collision as influenced by the speed of stirring. Removal of the insoluble PGE1 before the end of the lag period (10 sec) prevented the increase of adenylate cyclase. In contrast, separation of PGE1-hexyl-agarose from platelets by filtration after the lag period (at 30 or 40 sec) allowed the stimulation of the enzymatic activity to continue to completion in the absence of the hormone. The results suggest that PGE1 initiates molecular events leading to an increase of adenylate cyclase that do not require its continued presence for maintenance of the stimulated state.