Abstract
Aspirin decreases epinephrine-induced platelet aggregation and release reaction. Activation by epinephrine is mediated through interaction with alpha2-adrenoceptors on platelet membrane. We evaluated specific binding of alpha2-antagonist 3H-yohimbine to determine the maximal number of binding sites (Bmax) and the dissociation constant (KD) of alpha2-receptors. Platelet alpha2-receptor Bmax and KD were quantitated in four normal subjects before and 24 hours after aspirin 650 mg ingestion. In these subjects, Bmax increased from 166±40 to 281±30 fmol/mg protein (P<0.05) and KD, from 2.95±0.52 to 5.91±0.92 nM (P<0,05). To determine if these effects were direct, isolated human platelet membranes were studied before and after in vitro incubation with aspirin (90μg/ml) for 30 minutes. In three experiments, alpha2-adrenoceptor Bmax increased significantly (P<0.05) from 135±34 to 236±42 fmol/mg protein, KD also increased from 2.52±0.42 to 9.42±1.12 nM (P<0.05).
These studies indicate that aspirin causes an increase in the number of alpha2-adrenoceptors on platelets, and increase in KD, representing a decrease in affinity. Decreased affinity may be a mechanism for diminished responsiveness of platelets to epinephrine after aspirin.
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Mehta, P., Mehta, J. 925 EFFECT OF ASPIRIN ON ALPHA2-RECEPTORS ON HUMAN PLATELETS. Pediatr Res 19, 265 (1985). https://doi.org/10.1203/00006450-198504000-00955
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DOI: https://doi.org/10.1203/00006450-198504000-00955
