| Objective: To establish stable and reliable animal model of rabbit ear for hypertrophic scar and to observe the effects of radix astragali on morphology,histology,thickness and hardness of scar and gene expression of TGF-β1and Smad3 in hypertrophic scar of rabbits'ear and to explore the mechanism of radix astragali in treating hypertrophic scar and to supply experimental and theoretical basis for clinical applications of Astragalus.Methods: Twenty four healthy adult Japanese big ear rabbits of either weighing 1.8～2.5 kg were used to establish animal model for hypertrophic scars. The rabbits were taken as experimental animal and randomized into experimental A,B,C group and normal skin,saline,blank control group (A: 1000mg/ml, B: 500mg/ml and C: 250mg/ml concentration of radix astragali treatment groups). Each group contained 4 rabbits. Except for normal skin,four wound surfaces in size of 1cm2 were created down to bare cartilage on the ventral surface of each ear. There were 160 wound surfaces with 1cm gap between each wound. They were treated with radix astragali in different concentrations or saline and blank control 21d after wound, the local injection was 0.2 ml. On postoperative 32th and 43th day thickness and hardness of scar and normal skin were measured with color ultrasound diagnostic unit and especial measurement. The changes of hypertrophic scar and normal skin were observed with HE staining and Masson staining under light microscopy;TGF-β1 mRNA and Smad3 mRNA which is TGF-β1 downstream signal were detected in hypertrophic scar and normal skin samples with RT-PCR, immunohistochemical observe the expression level of TGF-β1and Smad3.Results: (1) wound scab 8~12d after operation, wound epithelization and scab loose shell has begun to drop 16d after operation gradually, all wound epithelization and we can see obvious scar 21d after operation, postoperative 28d the scar reached the peak and gradually fade into the period 43d after operation. (2) HE, Masson staining showed that astragalus dermis thinning, a small number of fibroblasts and collagen fibers arranged rules, no collagen nodule or nodules of collagen is not obvious in the experimental groups; while dermal layer of thick, fibroblast density, collagen fibers were arranged into a spiral-like disorder or to form a collagen nodules in the saline groups and blank control groups; small bundles of collagen arranged in the rules in negative control group. (3)Compared with the saline group and blank control group, thickness and hardness of scar in all radix astragali-treated groups decreased(P<0.05), immunohistochemistry showed that the expression levels of TGF-β1 and Smad3 in all radix astragali -treated groups significantly reduced compared with those in saline group and blank control group, RT-PCR results showed that the expression levels of TGF-β1 and Smad3 in radix astragali -treated groups decreased compared with saline group and blank control group(P<0.05); There were significant differences between the 32d and 43d radix astragali-treated groups (P<0.05), but there were no significant differences between the 32d and 43d control groups (P>0.05).Conclusions: (1) Retaining cartilage, removing of full-thickness skin and perichondrium in rabbit ear, can extend access to a greater proliferative phase of scar to form a stabilizing effect on the hypertrophic scars, in favor of dynamic observation of the effect of drug treatment scar; (2) After wound epithelization, local injection of astragalus could inhibit the proliferation of scar tissue and one of its mechanisms is to inhibit the expression level of TGF-β1 and its downstream signal Smad3; (3)The inhibiting effect was in a concentration dose dependent manner.
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