| Objective (1) To investigate the effect of the dosage of streptozotocin (STZ) and the level of blood glucose (BG) on the incidence and the survival rate of diabetic rats.(2) To observe myocardial injury on different stages and BG levels of diabetic rats.(3) To study the cardioprotection of soy isoflavones (SI) from myocardial injury and its mechanism in diabetic rats.Methods (1) Seventy-five SD rats were randomly divided into five groups:norrnal control group (NC), four experimental groups (A, B, C, D). Rats of A, B, C, D were given STZ 50, 55, 60, 65 mg-kg-1 intraperitneally (ip) except NC group rats. The same citric acid buffer was given in NC group. The incidence and the survival rate of diabetic rats were compared with each other. Other ninty SD rats were used to establish STZ-DM, and dibetic rats were divided into 3 groups by BG: E 16.7~21 .emmol-L-1, F 21.7~26.6 mmol-L-1, G >26.7mmol-L-1. After 4 weeks, the incidence and the survival rate of diabetic rats were compared with each other.(2) Sixty-four SD rats were randomly divided into two groups: normal control group (NC), three experimental groups (DM). Rats were given STZ 55mg-kg-1 ip except NC group rats. The same citric acid buffer was given in NC group. NC and DM group were all divided into four groups. After 2w, 4w, 6w, 8w, the heart function and LDH, CK, SOD activities and MDA, NO contents in myocardial homogenate were measured. Other forty SD rats were randomly divided into two groups: normal control group (NC), experimental groups (DM). Rats were given STZ 55mg-kg-1 ip except NC group rats, and dibetic rats were divided into 3 groups by BG: DM1 16.7~21.6 mmol-L-1, DM221.7~26.6 mmol-L"1, DM3 26.7 mmol-L"1. After 4 weeks, the heart function and LDH, CK, SOD activities and MDA, NO contents were measured.(3) Forty-eight SD rats were randomly divided into six groups: normal control group (NC), diabetic control group (DC), three SI treatment groups (L-SI, M-SI, H-SI) and nilestrioli treatment group (NT). Rats were given STZ 55mg-kg"1 ip except NC group rats. After 6 weeks, SI 30, 60, 120 mg-kg-1-d-1 were given in L-SI, M-SI, H-SI groups, nilestriol 0.2 mg-kg^-wk"1 was given in NT group, and the same CMC-Na was given in NC and DC groups. The volumes in all groups were 2ml-kg"1-d"1. The drugs were all oral administered using a stomach tube. 1) The level of body weight (BW) and blood glucose (BG) in rats were measured. Peak, LVSP, LVDP, Mean, +dp/dtmax, -dp/dtmax, Vpm and t-dp/dt of rats were recorded, observed and analyzed. 2) LDH, CK, SOD, NOS, Na+-K+-ATPase, Ca2+-ATPase activities and MDA, NO contents in myocardial homogenate or serum were measured. 3) The pathological changes in the heart cells were observed.Results (1) The survival rate of STZ SSmg-kg"1 was significantly highest and it was decreased with the level of BG (PO.01).(2) Compared with NC group, LVEDP and -dp/dtmax in 4w were significantly lower (PO.05, PO.01), MDA content in 4w were significantly higher (PO.01). All the items except CK in 6w and all in 8w had significant difference (PO.05, P<0.01). Compared with NC group, all the items of 3 DM groups had significant difference (PO.05, PO.01). Compared with DM1 group, LVEDP, -dp/dtmax, t-dp/dt, CK, SOD, MDA of DM2 and all but LDH of DM3 had significant difference (P<0.05, PO.01). Compared with DM2 group, LVSP, LVEDP, +dp/dt, SOD of DM3 had significant difference (PO.05, PO.01).(3) 1) Compared with NC group, the level of BW in DC group was significantly lower (PO.01), but those of M-SI, H-SI group were markedly higher than those of DCgroup (P<0.05, P<0.01). But levels of BG in every group had no significant difference. 2) Compared with NC group, LVSP> LVDP> Meam +dp,dtmax, -dp,dtmax, Vpm and t-dp,dt of DC group were significantly lower(P<0.05, .P<0.01), but those of SI groups were markedly higher than those of DC group( P<0.01). 3) LDH, CK, SOD, NO, NOS, Na+-K+-ATPase, Ca2+-ATPase activities were significantly lower in DC group than those in NC group. Compared with DC group, LDH, CK, SOD, NO, NOS, Na+-K+-ATPase, Ca2+-ATPas...
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