Effect Of L-T₄ And VitE Treatment On Cognitive Function In Hypothyroidism Rats

Objective:To investigate the effect of L-T4 , VitE and L-T4 /VitE combining treatment on cognitive behavior and oxidative stress level in the serum and hippocampus tissue of adult rat with hypothyroidism and to further explore the mechanism of cognitive impair.Methods:50 male SD rats were randomly divided into five groups:Group I, the normal control (control group); Group II, The hypothyroidism group (PTU group); Group III, L- T4 treatment group (PTU+ T4 group); Group IV, VitE treatment group (VitE + PTU group); GroupV,L- L-T4 /VitE combining treatment group (PTU+VitE+ T4 group). the normal control drink tap water,hypothyroidism was achieved by administering0.05% 6-n-propyl-2-thiouracil (PTU) in their drinking water, After Twenty eight days, PTU+VitE+ T4 group and PTU+ T4 group rats were supplemented with2μg/100g body weight of L- T4 orally for four weeks in respective groups at 8am every day .and at 6pm every day, Both VitE + PTU group and PTU+VitE+ T4 group intragastric administration 20mg/100g body weight of vitamin E orally for four weeks in respective groups. In during days ,excepting control group,all other groups were administered 0.05% 6-n-propyl-2-thiouracil (PTU) in their drinking water. After 8 weeks ,the learning and memory abilities of rat were evaluated by Morris Water Maze (MWM).The contents of malondialdehyde (MDA) and the activities of superoxide dismutase (SOD)) in the serum and hippocampus were measured using thiobarbituric acid, xanthine–xanthine oxidase methods, respectively.Data analysis:one-way ANOVA,ANOVA of repeated measurement Data, Analysis of variance of factorial design.Result:Compared with control group rats ,Serum T3 and T₄ levels decreased significantly(P<0.001) , the level of TSH was obviously increased(P<0.001) in PTU group and VitE + PTU group, where as no significant difference was noticed in PTU+VitE+ T₄ group and PTU+ T₄ group(P>0.05). Morris Water Maze test:In the navigation test,The escape latency were longer in the hypothyroidism group(P<0.01), there was no significant difference in the VitE + PTU group, PTU+VitE+ T₄ group and PTU+ T₄ group(P>0.05).In the probe test score, there was no significant difference among groups(P>0.05).the MDA level was increased and the SOD activity was decreased in the serum(P<0.001) and hippocampus(p<0.001) of the hypothyroidism group.The SOD activity was increased and the MDA level was decreased in the the PTU+ T₄ group,PTU+VitE group and PTU+VitE+ T₄ group(P<0.05), moreover there was obviously significant difference of score compared with PTU group(P<0.01).Conclusion:Results show that VitE , L- T₄ and L-T₄ /VitE combining treatment can improve hypothyroidism rats cognitive function ,probably through depleting free radical production and increase activities of antioxidatant.