http://science.sciencemag.org/content/sci/184/4132/19.full.pdf

Modulation of Inflammation and Immunity by Cyclic AMP

Platelet function was studied in 17 patients with Type II hyperlipoproteinemia. As compared with 26 normal subjects, platelets from patients with the Type II syndrome aggregated in response to 1/25 the mean concentration of epinephrine, one third the concentration of collagen, and one third the concentration of ADP. Total nucleotide release was increased from four to six fold with all aggregating agents. However, release of platelet factors 3 and 4, platelet adhesiveness and clot retraction were all normal in patients with Type II hyperlipoproteinemia. In contrast, platelets from 11 patients with Type IV hyperlipoproteinemia showed normal sensitivity to ADP and collagen, normal nucleotide release and normal release of 14C serotonin. The data suggest that heightened platelet function is associated with the thrombotic complications and accelerated atherogenesis of Type II hyperlipoproteinemia. (N Engl J Med 290:434–438, 1974)

Platelet function in hyperlipoproteinemia.

1. The involvement of intracellular 3′:5′-cyclic AMP in the inhibition of platelet aggregation by prostaglandin E1, isoprenaline and adenosine has been examined by a radiochemical technique. Platelet-rich plasma was incubated with radioactive adenine to incorporate 14C radioactivity into platelet nucleotides. Pairs of identically treated samples were taken, one for the photometric measurement of platelet aggregation induced by ADP, the other for estimation of the radioactivity of 3′:5′-cyclic AMP. 2. Theophylline, papaverine, dipyridamole and 2,6-bis-(diethanolamino)-4-piperidinopyrimido[5,4d]pyrimidine (compound RA233) were found to inhibit 3′:5′-cyclic AMP phosphodiesterase from platelets. At concentrations of 3′:5′-cyclic AMP greater than 50μm the most active inhibitor was dipyridamole; at 3′:5′-cyclic AMP concentrations less than 19μm, papaverine and compound RA233 were more active than dipyridamole. 3. In the presence of compound RA233 (50μm), the effectiveness of prostaglandin E1 as an inhibitor of platelet aggregation was increased tenfold. Compound RA233 also increased the stimulation by prostaglandin E1 of the incorporation of radioactivity into 3′:5′-cyclic AMP. 4. Compound RA233 (50μm) increased the effectiveness of both adenosine and 2-chloroadenosine as inhibitors of aggregation by 70–100-fold, and in the presence of compound RA233 both adenosine and 2-chloroadenosine stimulated the incorporation of radioactivity into 3′:5′-cyclic AMP; the extent of the stimulation was proportional to the logarithm of the nucleoside concentration. 5. Compound RA233 (100–500μm) inhibited platelet aggregation by itself and caused small increases in the radioactivity of 3′:5′-cyclic AMP. Partial positive correlations were found between the radioactivity of 3′:5′-cyclic AMP in platelets measured at the time of addition of the aggregating agent (ADP) and the extent to which the aggregation was inhibited. 6. The results are interpreted as indicating that adenosine, 2-chloroadenosine, isoprenaline, prostaglandin E1 and drugs that inhibit platelet 3′:5′-cyclic AMP phosphodiesterase all inhibit aggregation by a common mechanism involving intracellular 3′:5′-cyclic AMP.

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The influence on platelet aggregation of drugs that affect the accumulation of adenosine 3':5'-cyclic monophosphate in platelets.

The effect of parathyroid hormone on the concentration of adenosine 3',5'-monophosphate in skeletal tissue in vitro.

We have studied cyclic adenosine 3′,5′-monophosphate (cyclic AMP) concentrations in human peripheral blood lymphocytes after stimulation with phytohemagglutinin (PHA), isoproterenol, prostaglandins, and aminophylline. Purified lymphocytes were obtained by nylon fiber chromatography, and low speed centrifugation to remove platelets. Cyclic AMP levels were determined by a highly sensitive radioimmunoassay. At concentrations of 0.1-1.0 mmoles/liter isoproterenol and aminophylline produced moderate increases in cyclic AMP concentrations, whereas prostaglandins produced marked elevations. High concentrations of PHA produced 25-300% increases in cyclic AMP levels, alterations being demonstrated within 1-2 min. The early changes in cyclic AMP concentration appear to precede previously reported metabolic changes in PHA-stimulated cells. After 6 hr cyclic AMP levels in PHA-stimulated cells had usually fallen to the levels of control cells. After 24 hr the level in PHA-stimulated cells was characteristically below that of the control cells.

Adenyl cyclase, the enzyme which converts ATP to cyclic AMP, was measured in lymphocyte homogenates. Adenyl cyclase activity was rapidly stimulated by fluoride, isoproterenol, prostaglandins, and PHA. Since adenyl cyclase is characteristically localized in external cell membranes, our results are consistent with an initial action of PHA at this level.

/pdf/cyclic-adenosine-3-5-monophosphate-in-human-lymphocytes-1z73q39xul.pdf

Sidney M. Wolfe

Papers

Adenyl cyclase activity in human platelets.

Inhibition of platelet energy production and release reaction by PGE1, theophylline and cAMP.

Oxygen consumption of human blood platelets. I. Effect of thrombin.

Oxygen consumption of human blood platelets. II. Effect of inhibitors on thrombin-induced oxygen burst

Platelet phosphorylase activity in the presence of activators and inhibitors of aggregation