甲状腺素联合多奈哌齐对成年期甲状腺功能减退症大鼠额叶乙酰胆碱、munc-18的影响

Effect of thyroxine and donepezil on acetylcholine content and munc-18expression in the frontal cortex of rats with adult-onset hypothyroidism

目的观察甲状腺素联合多奈哌齐对成年期甲状腺功能减退症(简称甲减)大鼠额叶内乙酰胆碱含量以及munc-18表达的影响,探讨甲减脑额叶损伤及恢复的可能分子机制。方法采用给予含0.05%丙基硫氧嘧啶的饮用水6周建立大鼠甲减模型。自第5周起,给予多奈哌齐、甲状腺素或甲状腺素联合多奈哌齐治疗2周,采用放射免疫法检测血清甲状腺激素水平,碱性羟胺比色法测定额叶内乙酰胆碱含量,免疫组化法检测额叶内munc-18的分布与表达。结果甲减组、多奈哌齐治疗组大鼠血清三碘甲状腺原氨酸(T3)、四碘甲状腺原氨酸(T4)水平显著减低、促甲状腺激素(TSH)水平明显增加(P<0.01),甲状腺素治疗组、联合治疗组T3、T4、TSH水平与正常对照组相比差异无统计学意义;甲减组大鼠额叶内乙酰胆碱含量下降(P<0.05),多奈哌齐治疗组、甲状腺素治疗组、联合治疗组乙酰胆碱含量均恢复至正常水平,其中联合治疗组有进一步恢复趋势;甲减组、多奈哌齐治疗组大鼠munc-18在额叶内Ⅱ、Ⅲ、Ⅳ、Ⅴ层表达下降(P<0.05)。其中,以Ⅲ/Ⅴ层下降最为显著(P<0.01),甲状腺素治疗组munc-18表达仍下降(P<0.05),联合治疗组额叶内munc-18表达正常。结论多奈哌齐可以改善甲状腺功能减退引起的额叶内乙酰胆碱含量改变;甲状腺素联合多奈哌齐治疗有利于成年期甲状腺功能减退造成的额叶内胆碱含量改变和突触蛋白损伤的恢复。

Objective To investgate the thyroxine and donepezil on acetylcholine concentration and munc-18 expression in the frontal lobe of adult-onset hypothyroid rats and clarify the possible molecular mechanism of frontal lobe lesions of hypothyroidism. Methods The models of hypothyroidism were established by induction with adding propylthiouracil drinking water for 6 weeks,and since the fifth week, the hypothyroid rats received a two-week treat-ment of levothyrocine （L-T4）, donepezil or a combination of both drugs. The levels of serum triiodothyronine（T3）,tetraiodothyronine（T4）,thyroid-stimulating hormone（TSH） were measured by radioimmunoassay kits, acetylcho-line concentration in frontal lobe was determined by alkaline hydroxylamine colorimetry and the expression and dis-tribution of munc-18 in frontal cortex were evaluated by immunohistochemistry. Results In the hypothyroid rats,the levels of serum T3 and T4 decreased with the increase of TSH （ P〈0. 01 ） , the content of acetylcholine in frontal lobe was significantly decreased（P〈0. 05）,and the expression of munc-18 was at significantly lower levels in theⅡ,Ⅲ,Ⅳ,Ⅴ layers of frontal cortex （P〈0. 05）. In addition, donepezil treatment reversed the content of acetyl-choline to normal values. L-T4 monotherapy normalized the level of serum thyroid hormone and acetylcholine con-tent while the expression of munc-18 was not. Munc-18 was normalized completely by co-administration of L-T4 and donepezil. Conclusion The alteration of acetylcholine content and expression of munc-18 in the frontal lobe of a-dult-onset hypothyroidism can be better ameliorated by co-administration of L-T4 and donepezil.