title: Antiplatelet effect of amlodipine: a possible mechanism through a nitric oxide-mediated process.
abstract: The effect of amlodipine, a novel calcium channel blocker of the dihydropyridine type, on rabbit platelet aggregation, and the possible antiaggregatory mechanisms of amlodipine, especially on the nitric oxide (NO) guanosine 3',5'-cyclic monophosphate (cyclic GMP)-mediated pathway, were investigated. Other effects of amlodipine on thromboxane B2 (TXB2) formation in platelets also were examined. Amlodipine concentration-dependently inhibited rabbit platelet aggregation induced by collagen (10 microg/mL) or thrombin (0.1 U/mL) with an IC50 range of 32-69 microM. Along with this inhibition, our results also demonstrated that in the presence of L-arginine (100 IM), amlodipine (50 microM) increased nitric oxide synthetase (NOS) activity (from the resting activity of 2.05+/-0.36 to 7.11+/-0.95 pmol/mg protein/min) and NO release (by 80%), accompanied by an elevation of the cyclic GMP level (from the resting platelet level of 1.27+/-0.12 to 6.21+/-0.55 pmol/10(9) platelets) induced by collagen (10 microg/mL). However, the antiaggregatory effect of amlodipine (50 microM) could be attenuated significantly by oxyhemoglobin (5 microM), a NO scavenger, or N(G)-nitro-L-arginine methyl ester (100 microM), a specific NOS inhibitor. In addition, the TXB2 production in platelets induced by collagen or thrombin was concentration-dependently inhibited by amlodipine. Therefore, we propose that the antiaggregatory mechanisms of amlodipine might be mediated, in part, by a NO-cyclic GMP process accompanied by the inhibition of TXB2 formation in platelets.
authors.affiliation: Graduate Institute of Medical Sciences, Taipei, Taiwan, Republic of China. tcchou@ms5.hinet.net
authors.forename: T C
authors.initials: TC
authors.lastname: Chou
authors.forename: C Y
authors.initials: CY
authors.lastname: Li
authors.forename: M H
authors.initials: MH
authors.lastname: Yen
authors.forename: Y A
authors.initials: YA
authors.lastname: Ding
mesh_terms: D017311:Amlodipine / Q000494:pharmacology*; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008706:Methemoglobin / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009566:Nitrates / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011817:Rabbits; D013929:Thromboxane B2 / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D009566:Nitrates; D010975:Platelet Aggregation Inhibitors; D017311:Amlodipine; D009569:Nitric Oxide; D013929:Thromboxane B2; D008706:Methemoglobin; D000242:Cyclic AMP; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester