Effect of thyroxine treatment on expression of hippocampus syntaxin-1 in rats with hypothyroidism / 中国地方病学杂志

ABSTRACT

ObjectiveTo 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.MethodsAll 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.ResultsIn 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).ConclusionThe expression of syntaxin-1 in hippocampus of adult-onset hypothyroidism is increased,which can be reversed by routine dosage treatment of thyroxine.