Abstract: Objective:To investigate the influence of soy isoflavones on gene expression of myocardial sarcoplasmic reticulum calcium regulatory proteins in diabetic rats.Methods:Forty male Sprague-Dawley rats were randomly divided into four groups:normal control (NC) group,diabetic control (DC) group,soy isoflavones treatment (ST) group and nilestriol treatment (NT) group.All the groups were given streptozotocin (STZ) 55 mg/kg intraperitoneal injection (IP) except NC group.After 6 weeks,soy isoflavones 120 ml·kg^-1·d^-1 was given to ST group,nilestrioli 0.2 mg/kg to NT group twice a week,and the same CMC-Na was given to NC and DC groups.The volumes to all groups were 2 ml·kg^-1·d^-1.The drugs were all intragastrically administered using stomach tubes.The left ventricular systolic pressure (LVSP),left ventricular end diastole pressure (LVEDP) and Mean,±dp/dtmax of the rats were recorded at the end of the 12th week.The gene expressions of calcium regulatory proteins were detected by RTPCR.Results:Compared with NC group,the LVSP,LVEDP and Mean,±dp/dtmax of DC group were significantly lower (P<0.01),but those in ST and NT groups were markedly higher than DC group (P<0.01).LVEDP was increased in DC group while it was significantly decreased in ST and NT groups (P<0.01).The mRNA level of sarcoplasmic reticulum Ca²⁺-ATPase (SERCA),ryanodine receptor type 2 (RyR₂) and 1,4,5-triphosphate inositor type 2 (IP₃R₂) in DC group were sharply decreased compared with that in NC group,but the mRNA level of phospholamban (PLB) was increased (P<0.01).The mRNA's expression of SERCA,RyR₂,IP₃R₂ in ST and NT groups were significantly increased compared with that in DC group,but that of PLB was decreased (P<0.01).Conclusions:Soy isoflavones treatment could improve the heart function of the diabetic rats,which is possibly owing to its up-regulation of the levels of SERCA,RyR₂,IP₃R₂ mRNAs and down-regulation of PLB mRNA.