Epinephrine-induced reversal of aspirin effects on platelet deformability

Influence of Adrenergic Receptor Blockade on Aspirin-induced Inhibition of Platelet Function

Studies from our laboratory have demonstrated that epinephrine via alpha(2)-adrenoreceptor modulation can restore the sensitivity of aspirin-treated platelets to the action of agonists independent of secretion of granule contents or synthesis of prostanoids. The present study has evaluated the effects of full strength aspirin (take on alternate days) and low dose aspirin (taken daily) and sought to determine whether agents which antagonise alpha or beta adrenergic receptors can prevent the corrective influence of epinephrine on aspirin-treated platelets. Adult volunteers were given 325 mg aspirin every other day or 80 mg aspirin daily. After confirming the inhibitory effect of aspirin, these individuals were given yohimbine (5 mg), atenolol (100 mg), verapamil (160 mg) or ethanol (white wine 8 oz). Two hours later, blood was drawn for platelet studies. Cells exposed to aspirin did not aggregate when stirred with arachidonate (0.45 mM) or epinephrine (5 M) alone. Addition of epinephrine to aspirin treated platelets restored the sensitivity to the action of arachidonate and resulted in irreversible aggregation. Ethanol and verapamil at the concentrations tested did not potentiate the action of aspirin. Ingestion of yohimbine, an alpha(2)-adrenergic antagonist, or atenolol, a beta blocker, prevented the corrective influence of epinephrine on aspirin-treated refractory platelets. Results suggest that alpha and beta blockers may serve a useful role in reinforcing the antithrombotic influence of aspirin in vivo.

Aspirin, prostaglandin E1 and Quin-2 AM-induced platelet dysfunction: restoration of function by noradrenalin

Studies from our laboratory have demonstrated that adrenalin can restore the function of drug-induced refractory platelets to the action of physiological agonists via a novel mechanism (membrane modulation). In various disease states and clinical conditions the circulating levels of noradrenalin (NA) increase several fold more than adrenalin. Therefore, in this study the influence of NA on three well characterized platelet refractory models has been evaluated. Aspirin-exposed platelets were obtained for these studies from blood of donors who had taken one baby aspirin (80 mgs) per day for four consecutive days. Prostaglandin-exposed platelets were obtained by disaggregating ADP-induced aggregates through addition of prostaglandin E1 (1 microM). Finally, low calcium platelets were obtained by buffering cytosolic free calcium with a calcium specific cell permeant fluorophore, Quin-2 AM (60 microM). Drug-exposed platelets did not aggregate irreversibly when stirred with arachidonate (0.45 mM) or NA 5 microM). However, when treated with NA first, drug-treated platelets regained their sensitivity to the action of arachidonate and aggregated irreversibly. The ability of NA to restore the sensitivity of drug-induced refractory platelets was effectively blocked by yohimbine (10 microM), an alpha 2 adrenoceptor antagonist. Results of these studies suggest that NA, similar to the action of adrenalin, can activate membrane modulation and restore the sensitivity of platelets to the action of physiological agonists under a variety of experimental conditions.