Cyclic 3′,5′-adenosine monophosphate in human blood platelets

Abstract

The relation of cyclic 3′,5′-adenosine monophosphate to platelet function has been studied by investigating the influence of this compound and of its N⁶-2′-0-dibutyryl derivative on platelet aggregation and other aspects of platelet behavior after demonstration of adenyl cyclase activity in disrupted platelets. Dibutyryl cyclic AMP inhibited platelet aggregation induced by ADP, epinephrine, collagen, and thrombin. Cyclic AMP was also inhibitory but was less effective. The platelet “release reaction” was also inhibited; specifically, there was inhibition of the induction of platelet factor 3 activity and of the release of labeled 5-hydroxytryptamine. Platelet swelling produced by ADP was not inhibited. The action of dibutyryl cyclic AMP did not result from contamination with 5′-AMP, nor was it attributable to production of 5′-AMP by plasma enzymes. Dibutyryl cyclic AMP was degraded to 2′-O-monobutyryl cyclic AMP and to cyclic AMP in plasma, but plasma exhibited no cyclic nucleotide phosphodiesterase activity, and the production of 5′-AMP did not occur. The in vitro effects of dibutyryl cyclic AMP were associated with uptake of the compound by platelets. Adenyl cyclase activity of platelet homogenates was demonstrated with production of 9.27 × 10^-11 (±2.62 × 10^-11) mole cyclic AMP per min per 10¹⁰ platelets. The activity was increased by NaF and by prostaglandin PGE₁ and was decreased by epinephrine. The effect of epinephrine was blocked by phentolamine but not by propanolol. Adenyl cyclase activity was also inhibited by collagen, 5-hydroxytryptamine, and thrombin. ADP, dibutyryl cyclic AMP, and cyclic AMP did not alter adenyl cyclase activity. These observations are consistent with the hypothesis that platelet aggregation is favored by a decrease in platelet cyclic AMP and inhibited by an increase in cyclic AMP.