Morphine-Potentiated Platelet Aggregation in in vitro and Platelet Plug Formation in in vivo Experiments

Abstract

The detailed mechanisms underlying morphine-signaling pathways in platelets remain obscure. Therefore, we systematically examined the influence of morphine on washed human platelets. In this study, washed human platelet suspensions were used for in vitro studies. Furthermore, platelet thrombus formation induced by irradiation of mesenteric venules with filtered light in mice pretreated with fluorescein sodium was used for an in vivo thrombotic study. Morphine concentration dependently (0.6, 1, and 5 µM) potentiated platelet aggregation and the ATP release reaction stimulated by agonists (i.e., collagen and U46619) in washed human platelets. Yohimbine (0.1 µM), a specific α₂-adrenoceptor antagonist, markedly abolished the potentiation of morphine in platelet aggregation stimulated by agonists. Morphine also potentiated phosphoinositide breakdown and intracellular Ca²⁺ mobilization in human platelets stimulated by collagen (1 µg/ml). Moreover, morphine (0.6–5 µM) markedly inhibited prostaglandin E₁ (10 µM)-induced cyclic AMP formation in human platelets, while yohimbine (0.1 µM) significantly reversed the inhibition of cyclic AMP by morphine (0.6 and 1 µM) in this study. The thrombin-evoked increase in pH_i was markedly potentiated in the presence of morphine (1 and 5 µM). Morphine (2 and 5 mg/g) significantly shortened the time require to induce platelet plug formation in mesenteric venules. We concluded that morphine may exert its potentiation in platelet aggregation by binding to α₂-adrenoceptors in human platelets, with a resulting inhibition of adenylate cyclase, thereby reducing intracellular cyclic AMP formation followed by increased activation of phospholipase C and the Na⁺/H⁺ exchanger. This leads to increased intracellular Ca²⁺ mobilization, and finally potentiation of platelet aggregation and of the ATP release reaction.

Preconditioning ischemia attenuates molecular indices of platelet activation‐aggregation

“…Epinephrine is not a plausible option, as it is well recognized to potentiate (not attenuate) platelet aggregation [8,40,41]. With regard to opioids, there is no consensus on their effect on platelet reactivity or, indeed, whether opioid receptors are present on platelets [42–44]. Moreover, while both NO and PGI 2 inhibit platelet aggregation, temporal issues argue against their contribution as trigger(s) for the prolonged (3 h) improvement in arterial patency seen with PC ischemia: the antiplatelet effects of NO and PGI 2 are transient and rapidly reversed [12,45–49].…”

Antiplatelet Activities of Anthrax Lethal Toxin Are Associated with Suppressed p42/44 and p38 Mitogen‐Activated Protein Kinase Pathways in the Platelets

“…Washed platelets were prepared as described elsewhere [27,[31][32][33][34], and agonist-induced platelet aggregation was measured using a platelet aggregometer (Chrono-Log) [27,[31][32][33][34]. Platelet counts were determined using an automated hematology analyzer (KX-21; Sysmex).…”

Calcium oscillation and phosphatidylinositol 3-kinase positively regulate integrin αIIbβ3-mediated outside-in signaling

“…Human platelets were obtained from healthy donors who were not taking any medication and were prepared as previously described [10,[35][36][37][38]. Rabbit platelets were collected from the forearm vein of New Zealand white rabbits.…”