The Relationship Between Central Thyroid Function And Transport Protein OATP1C1,MCT8 MRNA And Cognitive Ability Between Rats With VCI And NTIS

Objective:Vascular dementia(VD) is one of the major types of senile dementia.Recently, vascular cognitive impairment(VCI) has been paid more and more attention by researchers and VD is one of the types of VCI.Abnormal TH levels in serum were found in patients with VD in clinical investigation and were correlated to the degree of dementia,which was ever considered to be belong to nonthyroidal illness syndrome(NTIS) by most researchers,i.e.no thyroid dysfunction.But protophase work done by our colleagues showed that rats with merely chronic cerebral ischemia showed central thyroid dysfunction and cognitive impairment.But when the rats suffered from chronic cerebral ischemia were supplied exogenous thyroxin in the begin of experiment,their water maze results were normal,which suggested that study and memory impairment of rats with chronic cerebral ischemia were associated with thyroid dysfunction in brain.In this study,we made chronic cerebral ischemia impairment mode(VCI group)and chronic hepatic fibrosis mode(NTIS group).Morris water-maze palace test was used to test the rat's ability to study and memory. Concentrations of T₃,T₄,FT₃,FT₄,rT₃,TSH,TRH in blood serum and T₃,T₄,rT₃ in brain tissue were detected using radioimmunoassay(RIA),levels of OATP1C1mRNA and MCT8mRNA in brain tissue were detected using fluorescent quantitation PCR in the end of experiment.The aim of our study are to explore TH metabolic process in brain of the rats with chronic cerebral ischemia,to disclose whether the abnormal metabolism of TH in brain is concomitant phenomenon of NTIS or independent pathogenesis in VCI and to give a new therapy way of VCI.Method:1.26 SPF Sprague-Dawley(SD) male or female rats were randomly divided into 3 groups:control group(n=9);chronic cerebral ischemia result in VCI group(VCI)(n=7),permanently bilateral common carotid artery ligation was performed for 5 weeks;Chronic hepatic fibrosis result in NTIS group(NTIS)(n=10), carbon tetrachloride 0.025ml(1:6,diluted by corn oil),intraperitoneal injection,three times/one week,for eight weeks.2.Morris water-maze palace test was used to test the rat's ability to study and memory at the end of experiment,including positioning navigation test and space exploration test.3.Liver of Rats in NTIS group were excised and fixed by 10%formaldehyde for geometry morphologic measuring by hematoxylin and eosin(HE)staining.4.Concentrations of T₃,T₄,FT₃,FT₄,rT₃,TSH,TRH in blood serum and T₃,T₄,rT₃ in brain tissue were detected using radioimmunoassay(RIA).5.Transcription level of OATP1C1 and MCT8 in brain tissue were detected using fluorescent quantitation PCR.6.All the numerical data have been statistically analyzed by SPSS11.5 for windows statistical package.Measurement data was said in(mean±standard deviation),independent samples comparison use single-factor analysis of variance(one-way ANOVA),further multiple comparison use LSD;The positioning navigation test use Repeated measurement of the multi-factor analysis of variance.P＜0.05 was regarded as statistical significance.Result:1.Liver pathological changes of rats in NTIS group HE staining,200 times normal light microscope NTIS group rats at liver.The structure of hepatic Iobules still existed,the swollen liver cells arranged in strip. Bile deposited in some hepatic cells cytoplasm.Chronic inflammation cells infiltrate in Portal(area),accompanied with fibroplasia.Part of the fibre tissues stretchinged into the hepatic Iobule,which may lead the hepatic Iobule to separate into Nodules,namely the formation of fake hepatic Iobule.2.Determination of memoryTest result of the study and memory of the rats by Morris water maze,and found that the learning and memory capacity of the VCI group rats was significant lower than that of the NTIS group and the control group rats.In the positioning navigation test,the escape latent period of the VCI group was longer than that of the NTIS group and the control group(P＜0.026,P＜0.013);The escape latent period had no significance between the NTIS group and the control group(P＞0.585).There was significance among four daytimes.(F=9.518,P=0.000).In the space exploration test,the navigating time spent in the quadrant where the platform once situated in 120 seconds of the VCI group was shorter than that of the NTIS group and the control group(P＜0.016,P＜0.047).But,there was no significance between the NTIS group and the control group(P＞0.756).3.Serum TH concentrationThe concentrations of T₄,FT₃,FT₄ in blood serum of the NTIS group were decreased when compared with the control group(P＜0.008,P＜0.000,P＜0.000); the concentration of T₃ of the NTIS group was lower than that of the control group(P＜0.04).The concentrations of T₃,T₄,FT₃ of the VCI group were decreased when compared with the control group(P＜0.001,P＜0.006,P＜0.009);the concentration of FT₄ in the VCI group was also lower than that of the control group(P＜0.016).The concentrations of TSH,rT₃ in blood serum had no significance among the three group(P＞0.618,P＞0.434).The concentration of TRH in the VCI group and the NTIS group was higher than that of the control group(P＜0.014,P＜0.023).4.TH concentration in brain tissue The concentrations of T₃,T₄,rT₃ in brain tissue of the VCI group were decreased when compared with the control group(P＜0.042,P＜0.049,P＜0.049);The concentrations of T₃,T₄,rT₃ in brain tissue of the VCI group were lower than those of the NTIS group(P＜0.008,P＜0.012,P＜0.008).There was no significance of concentration of T₃,T₄,rT₃ in brain tissue between the NTIS group and the control group(P＞0.453,P＞0.526,P＞0.420).5.TH transporter transcription level in brain tissue1.OATP1C1mRNA:OATP1C1mRNA was increased in the NTIS group when compared with the VCI group and the control group(P＜0.030,P＜0.008),While there was no significance between the VCI group and the control group(P＞0.710).2.MCT8mRNA:MCT8mRNA was higher in the NTIS group and the VCI group than that of the control group(P＜0.014,P＜0.047);There was no significance between the NTIS group and the VCI group(P＞0.738).Conclusion1.Rats with chronic cerebral ischemia cognitive impairment or chronic hepatic fibrosis both had NTIS phenomenon.2.The hypothalamus-pituitary-thyroid axis functional disorder may be one of NTIS pathogenesies.3.TH concentration(T₃,T₄,rT₃) in brain tissue of rats with chronic cerebral ischemia were decreased and their cognitive ability were impaired,which is considered to be relevant with hypothyroidism in brain.4.TH concentration(T₃,T₄,rT₃)in brain tissue of rats with chronic hepatic fibrosis were normal,and their cognitive ability were also normal.5.Compensated increase of TH transport protein OATP1C1,MCT8 in brain tissue of rats with chronic hepatic fibrosis is a crucial factor in the relative stabilization of TH concentration in their brain.6.Impairment of TH transport protein,especially OATP1C1 in brain tissue of rats with chronic cerebral ischemia,is one of the important causes in inducing low TH concentration in their brain. 7.Though both rats with chronic cerebral ischemia cognitive impairment and rats with chronic hepatic fibrosis had typical NTIS phenomenon,the level of TH and its transporters OATP1C1mRNA and MCT8mRNA in their brain had significant differences.Rats with chronic cerebral ischemia showed central thyroid hypofunction, which possibly induced "brain hypothyroidism".