Abstract: Objective To explore the effect and related molecular mechanisms of retinoid X receptor（RXR）agonist bexarotene（Bex）on myocardial hypertrophy and cardiac function in spontaneously hypertensive rats（SHR）.Methods A total of 24four-week-old SHR were randomized into 3groups and treated with 30mg/kg Bex（SHR+Bex30）,100mg/kg Bex（SHR+Bex100）and vehicle（SHR）once a day for 12 weeks,respectively,while 8agematched Wistar-Kyoto（WKY）rats were served as control group. Echocardiography was performed to detect cardiac structure and function parameters. Blood pressure was measured with BP98 Atail cuff system. Body mass,heart mass and left ventricle mass（LVM）were monitored. Angiotensin（Ang）Ⅱ level was determined by radio immunoassay. Picrosirius staining was performed to determine myocardial epicardial collagen volume. RXRαprotein level was measured with immunoblotting. Results Compared with WKY rats,blood pressure of SHR was significantly increasedSHR vs WKY:systolic blood pressure:（191.8±3.1）vs（120.5±5.0）mm Hg,P＜0.05;diastolic blood pressure（132.7±5.5）vs（89.6±3.2）mm Hg,P＜0.05. Blood pressures between SHR,SHR+Bex30and SHR+Bex100group were not significantly different. LVM,left ventricular mass index（LVMI）,thickness of left ventricular posterior wall（LVPWT）and interventricular septal thickness（IVST）of SHR were greatly increased compared to those of WKY rats（all P＜0.05）. Compared with WKY,echocardiographic analysis showed that isovolumic relaxation time（IVRT）was significantly increased in SHR,while Ea,Aa and Ea/Aa were decreased. Compared to SHR group,LVM （0.78±0.02）,（0.67±0.01）vs（0.90±0.04）g,LVMI（2.66±0.06）,（2.28±0.03）vs（2.95±0.10）g/kg,LVPWT,IVST in SHR+Bex30and SHR+Bex100groups were significantly decreased（all P＜0.05）. Meanwhile,Ea,Aa and Ea/Aa increased and IVRT decreased in SHR+Bex100group. Compared with WKY,the level of AngⅡ in plasma（79.19±6.25）vs（48.62±1.91）ng/Land heart tissue（85.10±3.48）vs（69.94±4.01）ng/Lof SHR was significantly increased（P＜0.05）. Bex showed no effect on Ang Ⅱ. Myocardial epicardial collagen volume fraction（CVF）of heart tissue was significantly higher in SHR than in WKY （13.2±1.8）% vs（4.1±0.7）%,P＜0.05,but CVF was decreased by Bex treatment(SHR+Bex30vs SHR:（8.1±0.8）% vs（13.2±1.8）%;SHR+Bex100vs SHR:（5.8±0.8）% vs（13.2±1.8）%,P＜0.05. Compared to WKY,RXRαexpression in SHR was significantly dereased,which could be increased by Bex（P＜0.05）. Conclusion RXRαagonists Bex can reduce left ventricular hypertrophy of SHR by regulating collagen content. High dose of Bex can even improve cardiac diastolic function. These effects of Bex are not depended on blood pressure control.