目的 研究成年期甲状腺功能减退症(简称甲减)大鼠海马突触前膜蛋白syntaxin-1的表达及不同剂量甲状腺素替代治疗的作用,探讨甲减脑损伤可能的分子机制.方法 健康3月龄成年SD雄性大鼠44只,体质量250 ～ 300 g,按体质量随机分为4组:甲减组、常规治疗组、大剂量治疗组和对照组,每组11只.甲减组、常规治疗组和大剂量治疗组每日腹腔注射丙基硫氧嘧啶(PTU) 10 mg/kg;4周后,甲减组继续给予PTU腹腔注射2周,常规治疗组和大剂量治疗组每日分别给予50、200μg/kg左旋甲状腺素腹腔注射2周;对照组每日腹腔注射等量生理盐水.造模结束后,采用放射免疫法检测4组大鼠血清T3、T4水平;采用免疫组化法检测4组大鼠海马syntaxin-1蛋白的表达.结果 与对照组[(0.65±0.05)、(55.20±3.56)nmol/L]比较,甲减组血清T3、T4[(0.34±0.04)、(43.01±2.95)nmol/L]明显降低(P均＜0.05),大剂量治疗组血清T3、T4[(1.11±0.10)、(96.68±6.42)nmol/L]显著升高(P均＜0.05);常规治疗组血清T3、T4[(0.63±0.05)、(55.04±3.77)nmol/L]与对照组比较,差异无统计学意义(P均＞0.05).甲减组大鼠海马CA1、CA3区起始层、放射层、腔隙层和齿状回(DG)分子层、多形层syntaxin-1蛋白表达水平(0.059±0.016、0.064±0.014、0.068±0.016,0.069±0.017、0.072±0.016、0.070±0.011,0.051±0.012、0.072±0.017)显著高于对照组(0.037±0.008、0.045±0.010、0.042±0.009,0.040±0.010、0.053±0.009、0.042±0.009,0.032±0.007、0.047±0.010,P均＜0.05);常规治疗组和大剂量治疗组各层syntaxin-1蛋白表达水平(0.041±0.011、0.046±0.017、0.044±0.014,0.037±0.008、0.051±0.010、0.043±0.010,0.033±0.011、0.045±0.014和0.040±0.010、0.045±0.011、0.043±0.010,0.033±0.009、0.050±0.010、0.041±0.009,0.032±0.009、0.046±0.009)较甲减组降低(P均＜ 0.05),与对照组比较,差异无统计学意义(P均＞0.05).结论 成年期甲减大鼠海马内syntaxin-1蛋白表达增加,常规剂量甲状腺素替代治疗能使其恢复至正常水平.%Objective To observe the expression of syntaxin-1 in hippocampus of adult rats with hypothyroidism and the role of different doses of thyroid hormone replacement therapy,further to explore the molecular mechanism of brain damage.Methods All 44 male adult SD rats were randomly divided into 4 groups according to their body mass(250 - 300 g):hypothyroidism group,routine dosage thyroxine treatment group,high dosage thyroxine treatment group and control group (11 in each group).Hypothyroidism group,routine dosage thyroxine treatment group and high dosage thyroxine treatment group received daily intraperitoneal injection of propylthiouracil (PTU) 10 mg/kg.Hypothyroidism group was given PTU by intraperitoneal injection for two weeks after the previous four week treatment,the routine dosage thyroxine treatment group and the high dosage thyroxine treatment group were given 50,200 μg/kg L-thyroxine daily intraperitoneally for two weeks; the control group received daily intraperitoneal injection of saline.The levels of serum T3,T4 were assayed by radioimmunoassay method,and the level of syntaxin-1 in hippocampus was analyzed by immunohistochemistry.Results In the hypothyroidism group,the levels of serum T3,T4[(0.34 ± 0.04),(43.01 ± 2.95)nmol/L] were significantly lower than those in the control group[(0.65 ± 0.05),(55.20 ± 3.56)nmol/L,all P ＜ 0.05].In the routine dosage of thyroxine treatment group,the levels of serum T3,T4[(0.63 ± 0.05),(55.04 ± 3.77)nmol/L] were not significantly different compared to the control group (all P ＞ 0.05 ).In the high dosage thyroxine thyroid hormone treatment group,the levels of serum T3,T4[(1.11 ± 0.10),(96.68 ± 6.42)nmol/L] were significantly higher than those in the control group(all P ＜ 0.05).The levels of syntaxin-1 protein in the CA1,CA3 and dentate gyrus(DG) of all layer regions of hippocampus (0.059 ± 0.016,0.064 ± 0.014,0.068 ± 0.016,0.069 ± 0.017,0.072 ± 0.016,0.070 ± 0.011,0.051 ± 0.012,0.072 ± 0.017) were significantly higher compared to the control group(0.037 ± 0.008,0.045 ± 0.010,0.042 ±0.009,0.040 ± 0.010,0.053 ± 0.009,0.042 ± 0.009,0.032 ± 0.007,0.047 ± 0.010,all P ＜ 0.05).In the routine dosage and the high dosage thyroxine thyroid hormone treatment group,the level of syntaxin-1 in CA1,CA3and DG regions(0.041 ± 0.011,0.046 ± 0.017,0.044 ± 0.014,0.037 ± 0.008,0.051 ± 0.010,0.043 ± 0.010,0.033 ± 0.011,0.045 ± 0.014 and 0.040 ± 0.010,0.045 ± 0.011,0.043 ± 0.010,0.033 ± 0.009,0.050 ± 0.010,0.041 ± 0.009,0.032 ± 0.009,0.046 ± 0.009)were not significantly different compare to the control group(all P＞0.05).Conclusion The expression of syntaxin-1 in hippocampus of adult-onset hypothyroidism is increased,which can be reversed by routine dosage treatment of thyroxine.
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