Objective To investigate the effect of ovariectomy and estrogen on secretion function and number of pancreatic islet beta cell in low-dose streptozotocin-induced diabetic rats. Methods Thirty female SD rats were randomly divided into five groups: normal control(NC) group, streptozotocin(STZ) group, ovariectomized(OVX) group, OVX + STZ(OS) group and OVX+STZ+estradiol(OSE) group. OVX, OS and OSE groups underwent ovariectomy, while NC and STZ groups underwent just sham operation. After surgery, OSE group was treated subcutaneously with estradiol 0.2 mg/kg twice weekly. At the end of 3 weeks, STZ, OS and OSE groups were induced by a single intraperitoneal injection of 40 mg/kg STZ. Then eight days later, plasma glucose and insulin levels were tested. The insulin protein, the average beta cell area and the relative beta cell mass were tested by streptavidin peroxidase conjugation method (SP). The quantification of beta cell apoptosis was performed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL). The expressions of proliferating cell nuclear antigen(PCNA) protein, Bax and Bcl-2 were tested. Results With the administration of low-dose STZ, the plasma glucose was significantly higher and the insulin secretion curve after glucose loading, △I30/△G30 and modified beta cell function index(MBCI) were lower in OVX group than in other groups(all P<0.05). At the same time, the insulin protein, the relative beta cell mass and the beta cell area were dramatically decreased(all P<0.05). The beta cell apoptotic index was increased (t = 2.957, P< 0.05), the expression ratio of Bcl-2/Bax was decreased (0.41±0.03 vs. 0.76±0.05, P<0.05). Estrogen replacement therapy could obviously inhibit these changes. Compared with OS group, glucose disturbances and insulin secretion were improved dramatically in OSE group(all P<0.05); the insulin content, the relative beta cell mass and the average beta cell area were all enhanced (all P<0.05); the beta cell apoptotic rate was decreased(t =2.482, P<0.05), and the expression tatio of Bcl-2/Bax was increased (0.71±0.05 vs. 0.41±0.03, P<0.05). Conclusions The ovx rats are significantly more susceptible to low-dose STZ toxicity than in control rats. Under the effect of STZ, the ability of insulin secretion of beta cell is obviously decreased, while apoptosis is increased, which induces a higher glucose level and a lower insulin secretion. Administration of estrogen may protect OVX rats from the metabolic disturbances.%目的 观察大鼠在去卵巢和雌激素替代治疗状态下,经小剂量链脲佐菌素(STZ)干预后胰岛β细胞数量和功能的变化. 方法 30只雌性SD大鼠随机分为5组,正常对照组、STZ组、去卵巢组、去卵巢+STZ组和雌激素组.正常对照组和STZ组行假手术,其余均行去卵巢手术.术后雌激素组给予雌激素治疗,3周后STZ组、去卵巢+STZ组、雌激素组给予STZ(40 mg/kg)干预,检测各组大鼠血糖、血胰岛素水平,平均β细胞面积和相对β细胞数量,β细胞凋亡数量,β细胞内的促凋亡基因Bax、抗凋亡基因Bcl-2及增殖细胞核抗原(PCNA)蛋白表达水平. 结果 在STZ作用下,去卵巢大鼠口服葡萄糖耐量(OGTT)各时点血糖均较未去卵巢大鼠明显升高(P<0.05),且各时点胰岛素分泌水平均减少(P<0.05);胰岛素生成指数(△I30/△G30)及修正的β细胞胰岛素分泌指数MBCI下降,β细胞内胰岛素蛋白表达水平、相对β细胞数量和平均β细胞面积均明显下降(P<0.05),Bcl-2/Bax比值下降(0.41±0.03对0.76±0.05,P<0.05),β细胞的凋亡指数升高(t=2.957,P<0.05).去卵巢后给予雌激素替代治疗则对上述变化有明显的改善作用,OGTT各时点血糖水平显著下降(P<0.05),β细胞内胰岛素蛋白表达水平及血胰岛素水平的升高,Bcl-2/Bax比值上升(0.71±0.05对0.41±0.03),β细胞的凋亡指数下降(t=2.782,P<0.05). 结论 去卵巢大鼠对外来刺激明显易感,小剂量STZ即导致胰岛β细胞的凋亡增加,数量减少,胰岛素分泌水平的下降,血糖明显升高.补充雌激素能够对抗去卵巢带来的对胰岛β细胞的不利影响,改善β细胞的凋亡,具有保护作用.
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