title: Adenosine increases human platelet levels of cGMP through nitric oxide: possible role in its antiaggregating effect.
abstract: Adenosine is an endogenous antiaggregating substance that influences the platelet responses through specific A-type receptors that activate adenylate cyclase increasing the levels of 3',5'-cyclic adenosine monophosphate (cAMP). In this study, we investigated whether adenosine can also influence the levels of 3',5'-cyclic guanosine monophosphate (cGMP) and decrease the aggregating response of human platelets to adenosine-5-diphosphate (ADP) through this nucleotide. In platelet samples from healthy volunteers, we evaluated the effect of adenosine on ADP-induced aggregation and cyclic nucleotide synthesis. Some experiments were repeated in the presence of dipyridamole (inhibitor of adenosine uptake and phosphodiesterase activity), N(G)-monomethyl-L-arginine (L-NMMA, nitric synthase inhibitor), ionomycin (calcium ionophore), and ambroxol (2-amino-3,5-dibromo-N-[trans-4-hydroxycyclohexyl]benzylamine, inhibitor of nitric oxide (NO)-dependent activation of guanylate cyclase). Adenosine decreased the response to ADP in a concentration-dependent way (analysis of variance, ANOVA: P<.0001): cAMP levels increased from 30.0 +/- 2.0 (control) to 46.0 +/- 3.0 pmol/10(9) platelets (in the presence of 15 mumol/l adenosine) and cGMP levels increased from 5.6 +/- 1.0 (control) to 10.9 +/- 2.0 pmol/10(9) platelets (in the presence of 15 mumol/l adenosine). Also, nucleotide levels measured at the end of aggregation were higher in platelet samples exposed to adenosine than in controls. Dipyridamole at 40 mumol/l slightly increased adenosine's effects on both nucleotides. L-NMMA blunted the effect of adenosine on cGMP both in unstimulated samples and in aggregated platelets without any effect on cAMP synthesis. Platelet exposure to L-NMMA and ambroxol partially prevented adenosine's effect on ADP-induced aggregation. In conclusion, adenosine, which enhances intraplatelet cAMP levels, was determined to also cause an increase in cGMP concentrations through a mechanism that involves NO synthesis. This effect plays a direct role in the adenosine-induced antiaggregation.
authors.affiliation: Diabetes Unit, Department of Clinical and Biological Sciences, University of Turin, Azienda Ospedaliera S. Luigi, I-10043 Orbassano, Turin, Italy. giovanni.anfossi@unito.it
authors.forename: Giovanni
authors.initials: G
authors.lastname: Anfossi
authors.forename: Isabella
authors.initials: I
authors.lastname: Russo
authors.forename: Paola
authors.initials: P
authors.lastname: Massucco
authors.forename: Luigi
authors.initials: L
authors.lastname: Mattiello
authors.forename: Franco
authors.initials: F
authors.lastname: Cavalot
authors.forename: Alessandra
authors.initials: A
authors.lastname: Balbo
authors.forename: Mariella
authors.initials: M
authors.lastname: Trovati
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D000244:Adenosine Diphosphate / Q000037:antagonists & inhibitors / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D006152:Cyclic GMP / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004336:Drug Antagonism; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D006801:Humans; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology
chemical_list: D010975:Platelet Aggregation Inhibitors; D009569:Nitric Oxide; D000244:Adenosine Diphosphate; D006162:Guanylate Cyclase; D006152:Cyclic GMP; D000241:Adenosine