甲状腺功能低下大鼠中枢5-HT对TSH分泌的影响

Effects of central 5-HT on TSH secretion in hypothyroid rats

目的 探讨甲状腺功能低下 (甲低 )大鼠中枢 5 -羟色胺 (5 - HT)系统的代谢变化与机制 ,以及 5 - HT对促甲状腺激素 (TSH)分泌的调节作用。方法 用 0 .5 % Na Cl O4诱导实验大鼠甲低功 ,采用荧光分析方法测定大鼠脑组织 5 - HT、5 - HIAA含量及 MAO活性 ,放免法测定血清 T3、T4及 TSH含量。结果 甲低组大鼠血清 T3、T4含量明显下降 ,而血清 TSH含量及脑组织中 5 - HIAA、5 - HIAA/5 - HT比值、MAO活性显著升高 ,且 5 - HIAA、5 - HIAA/5 - HT比值与 MAO活性的变化呈正相关 ,r值分别为 0 .5 9、0 .5 7,P <0 .0 1。5 - HIAA、5 - HIAA/5 - HT比值与 TSH的变化也呈正相关 ,r值分别为 0 .6 9、0 .6 4,P <0 .0 1。而 5 - HIAA与血清 T3、T4则呈负相关 ,r值分别为 - 0 .74、- 0 .6 8,P <0 .0 1。结论 甲低大鼠中枢 5 - HT代谢活跃 ,其机制主要是通过调节 MAO活性而实现 ;中枢 5 - HT对 TSH的分泌有促进作用 ,在甲状腺激素对 TSH的负反馈调节中 ,5 - HT可能是中间环节之一。

Objective To study the metabolic changes of 5-HT in brain of hypothyroid rats and to observe the effects of 5-HT on TSH secretion.Methods The experimental hypothyroid rats were induced with 0.5% NaClO_4 in their drinking water.Concentrations of 5-HT,5-HIAA and monoamine oxidase (MAO) activity were measured by fluorspectrometry.Serum T_3,T_4 and TSH were measured by RIA.Results Concentration of serum T_3,T_4 decreased obviously in hypothyroid rats,whereas concentration of serum TSH and 5-HIAA content and MAO activity in brain increased significantly.Cocentration of 5-HIAA and ratio 5-HIAA to 5-HT were directly related to MAO activity (r=0.59,0.57,P<0.01).There was also a positive correlation between serum TSH and 5-HIAA content and ratio 5-HIAA to 5-HT (r=0.69,0.64,P<0.01).But a negative correlation between 5-HIAA and serum T_3,T_4 could be observed (r=-0.74,-0.68,P<0.01).Conclusions The metabolism of central 5-HT is active in hypothyroid rats and thyroid hormone has effects on the metabolism of 5-HT by regulating MAO activity.The secretion of TSH is stimulated by 5-HT neuronal activity and 5-HT may be a mediate factor in the negative feedback effect of thyroid hormone on TSH.