Dynamic interaction of prostaglandin and norepinephrine in the formation of adenosine 3′,5′-monophosphate in human and rabbit platelets

Abstract

Various factors governing dynamic changes in the intracellular level of adenosine 3′,5′-monophosphate (cyclic AMP) in response to hormonal stimulation have been studied in human and rabbit platelets. Cyclic AMP formation was measured by prelabeling the ATP in the cells with [ 3H]adenine; platelets were incubated with [ 3H]adenine which was taken up by the cells and converted to [ 3H]ATP which served as a substrate for adenyl cyclase. In intact platelets, prostaglandin E 1 caused a rapid increase in the levels of cyclic AMP, reaching a peak within seconds. This effect of prostaglandin E 1 was observed in the absence of the phosphodiesterase inhibitor, theophylline; in the presence of theophylline (2·10 −3M), the peak accumulation of cyclic AMP was doubled. The platelet adenyl cyclase system was temperature dependent. As the temperature was lowered, the peak level of cyclic AMP obtained on incubation with prostaglandin E 1 was reduced. It is possible that temperature may influence both the binding of prostaglandin E 1 to the receptor as well as the enzyme systems involved in the synthesis and degradation of cyclic AMP. Norepinephrine not only inhibited the stimulant effect of prostaglandin E 1 on cyclic AMP formation, but also caused a rapid, dose-dependent decrease in cyclic AMP levels that had been elevated by prior incubation of the platelets with prostaglandin E 1. The norepinephrine-induced decline in cyclic AMP levels was reduced but not prevented by theophylline. These data suggest that norepinephrine may lower cyclic AMP levels by inhibiting cyclic AMP formation and by activation of the degradative enzyme, cyclic AMP phosphodiesterase. Changes in cyclic [ 3H]AMP levels induced by prostaglandin E 1 were compared with the changes in the endogenous cyclic AMP in the same cells and were found to be similar.