Effect Of High Blood Pressure Variability On The Antiplatelet Action Of Aspirin

PurposeThis study was designed to investigate effect of high blood press variability on theantiplatelet action of aspirin (Asp).MethodThe experiment was divided into two parts: in vivo and in vitro.1. In vivo: The Sprague-Dawley(SD) rats with sinoaortic denervation (SAD) or sham(Sham),were randomly divided into8groups: Sham group, SAD group, Sham+low doseAsp group (5mg/kg), SAD+low dose Asp group(5mg/kg), Sham+middle dose Asp group(15mg/kg), SAD+middle dose Asp group(15mg/kg), Sham+high dose Asp group,(45mg/kg)，SAD+high dose Asp group(45mg/kg), n=6. Four weeks after the operation, in freelymoving state, blood pressure (BP), BPV and baroreflex sensitivity (BRS) of rats were mo-nitored in freely moving state. Animals were orally administered Asp or solvent daily for7consecutive days. Then they were sacrificed and blood was taken by cardiac puncturefor measurement of platelet aggregation. The perfusion chamber was used to detectplatelet adhesion to collagen at the high (1200s-1) and low (300s-1) shear rate. Expressionof P-selection, platelet micro-aggregation, reactive oxygen species(ROS), nitric oxide(NO)and calcium(Ca2+) mean fluorescence intensity were determined with flow cytometry assay.TXB2was measured with RIA and platelet cyclo-oxygenase (COX) activity was detectedwhile induced by AA.2. In vitro: Heparined blood from SD rats were randomly divided into8groups:normal fluctuating group, fluctuating group, normal fluctuating+low concentration Asp (10μg/ml) group, fluctuation+low concentration Asp(10μg/ml) group, normal fluctuating+Asp(30μg/ml) middle concentration group, fluctuations+middle concentration Asp (30μg/ml) g-roup, normal fluctuating high concentration Asp(100μg/ml) group, fluctuating+high co-ncentration Asp(100μg/ml) group,n=5.After incubation with Asp or solvent at37℃for15min, blood was put into the pressure fluctuation model for5min. Platelet micro-aggregate- ion, adhesion to collagen, ROS, NO and Ca2+were detected with the above methods.Results1. In vivo experimental results1.1The hemodynamics and BRS changes of SAD rats There was no significantdifference in SBP, DBP and MBP between Sham and SAD group. But compared with Sha-m group, SBPV, DBPV and MBPV were significantly increased and BRS decreased in SAD group.1.2The influence of high blood pressure variability on the antiplatelet action ofAsp①Compared with the corresponding Sham group, in SAD (Asp0,5,15mg/kg)group, platelet aggregation rate, platelet adhesion rate, the rate of positive expression ofP-selection, plasma TXB2content and COX activity were significantly increased;②compared with Sham+Asp(45mg/kg) group, in SAD+Asp (45mg/kg)group, platelet aggre-gation rate, adhesion rate, platelet surface of P-selection expression rate, TXB2content,COX activity in plasma did not change significantly;③compared with the SAD+Asp (0mg/kg) group, the above index in SAD+Asp(45mg/kg)group significantly decreased.1.3The change of platelet COX activity and levels of ROS, NO, Ca2+①Compared with the corresponding Sham group, in SAD (Asp0,5,15mg/kg) group, plat-elet COX activity and the mean fluorescence intensity(MFI) of platelet ROS and Ca2+sign-ifycantly decreased, and MFI of NO significantly increased.②Compared with the Sham+Asp (45mg/kg) group, in SAD+ASP(45mg/kg) group, platelet COX activity, the MFI ofCa2+, ROS and NO did not change significantly;③compared with the SAD+Asp (0mg/kg)group, in SAD+Asp (45mg/kg) group, platelet COX activity, MFI of ROS and Ca2+weresignificantly reduced, the MFI of NO were significantly elevated.2. In vitro experimental results2.1The pressure and the pressure fluctuation Compared with normal fluctuatinggroup, SBP, DBP and MBP in fluctuations group did not change significantly. But SBPV,DBPV and MBPV were significantly elevated.2.2The influence of high pressure variability on the antiplatelet action of Asp①Compared with the corresponding normal fluctuation group, in fluctuation group(Asp0,10,30μg/ml), P-selection expression rate on platelet surface, platelet micro-aggregationand adhesion rate increased significantly;②Compared with the normal fluctuation+Asp(100μg/ml) group, in fluctuation+Asp (100μg/ml)group, P-selection expression rate on pla-telet surface, platelet micro-aggregation and adhesion rate did not change significantly.;③ Compared with the fluctuation+Asp (0μg/ml) group, in the fluctuation+Asp (100μg/ml)group, P-selection expression rate on platelet surface, platelet micro-aggregation and adhe-sion rate increased significantly significantly decreased.2.3The change of MFI of platelet ROS, NO, Ca2+①Compared with the cor-responding non fluctuation group, in fluctuation group (Asp0,10,30μg/ml),the MFI of pl-atelet Ca2+and ROS significantly increased, the MFI of platelet NO were significantly red-uced;②compared with the normal fluctuation+Asp (100μg/ml) group, in the fluctuation+Asp (100μg/ml) group, the MFI of platelet Ca2+、ROS and NO did not change significantly;③compared with the fluctuation+Asp(0μg/ml) group, in the fluctuation+Asp (100μg/ml)group, the MFI of platelet Ca2+and ROS significantly decreased, and the MFI of plateletNO significantly increased.ConclusionHigh blood pressure variability might reduce the antiplatelet effect of aspirin, Themechanism might be related to inhibitation of COX activity and signal changes ofoxidative stress,NO and Ca2+in platelet. Increasing the dose of aspirin could counteractthe effect of high blood pressure fluctuation on platelet activation.