Impaired Effects Of Short-term Withdrawal Of Thyroxine On Aorta Intima With Rabbits After Near-total Thyroidectomy And¹³¹I Therapy:the Benefit Of Atorvastatin

Objective:1Establish of rabbit models with short-term hypothyroidism by near totalresection and¹³¹I ablation.2Observe the morphology changing in short-term withdrawal of thyroxineand analysis expression of eNOS, ET-1in the impaired aortic intima.3Observe the protective effect of atorvastatin on impaired aortic intimaduring hypothyroidism.Method:1The study included60rabbits（30males and30females）, with a medianage of9.2weeks （8-10months） and a mean weight of1.7kg （1.5-2.0kg）. Theexperimental animals were fed in the animal house of the Hebei GeneralHospital, given the standard diet, drinking tap-water, indoor temperature15-25℃, humidity50%-60%,12h light/12h dark cycle. According to sex, age andweight all rabbits were randomly divided into three groups:（1） Shamthyroidectomy （group ST: no thyroid glsnds resection）;（2） Near-totalthyroidectomy （group NT: Resect all of the unilateral thyroid and90%of thecontralateral）;（3） Near-total thyroidectomy and medicine intervention （groupNT+A: Resect all of the unilateral thyroid and90%of the contralateral andfollowing with Atorvastatin treatment）. All rabbits were anesthetized by10%hydrated chloral（2mL/Kg）. Group NT+A：Start to give atorvastatin calciumsuspension by gavage in three days after surgery, with a daily dose of5mL/Kg（atorvastatin calcium7.5mg/Kg）. The others were given distilled water. Allrabbits were weighed once every3days. In order to remove the residualthyroid the rabbits were injected¹³¹I in both group NT and group NT+A ontwenty-two days after the surgery. 2Disposing time points:（1） At the point P1（the day before the surgery）,point P2(the three weeks after surgery, the day before the¹³¹I ablation), pointP3(the five weeks after surgery, the second weeks after¹³¹I ablation)respectively. Serum samples from the ear middle arteries were collected andcentrifuged on3000rev/min about10minutes, and then placed in therefrigerator at-70℃.（2） At the point P2and point P3¹³¹I （0.1mCi） was giveninto intraperitoneal injection on all rabbits. After24h the thyroid scintigraphywas following.（3） In order to remove the residual thyroid function¹³¹I（1.0mCi/Kg） was given to both group NT and group NT+A by ear vein afterthe twenty-two days of the surgery （The day after the P2）.（4） Ascending aortaof all rabbits were removed at the point of36days after surgery （The day afterthe P3） by killing them.3Serum total cholesterol （TC）, triglyceride （TG）, high-density lipoproteincholesterol （HDL-C）, low-density lipoprotein cholesterol （LDL-C）, thyroidstimulating hormone （TSH）, free three triiodothyronine （FT3）, free thyroxine（FT4）, endothelin-1（ET-1） were measrued by using the enzyme-linkedimmunosorbent assay （ELISA）. Serum nitric oxide （NO） were measrued byusing the nitrate reductase assay. Morphological changes in arterial intimawere observed by H.E. staining. Endothelial nitric oxide synthase （eNOS） andET-1expression were observed by immunohistochemical technique （ICH）.4All data were analysed by the statistical software SPSS13.0. Statisticalsignificance was assumed with P＜0.05.Results:1All rabbits of each group survived until the end point of the experimentwithout the accidental death.2Morphological changes of the aortic intima:（1） ascending aortic intima inGroup ST had normal morphology.（2） group NT: fatty streak-liking changeson aortic intima were fond in7of20cases at five weeks after surgery, andfibrous plaque change was fond in one rabbit. The remaining12rabbits hadnormal morphological changes.（3） group NT+A: fatty streak-liking changeswere fond in3of20rabbits at five weeks after surgery, while the other18 rabbits hadnormal morphological changes.3Comparison of serum results in each groups3.1Comparison of TSH, FT3, FT4levels in each groups3.1.1TSH level:（1） Time factor, grouping factors and the packetinteractions of the time factor and the grouping factors were statisticallysignificant （F values ranged between80.778～750.247；P＜0.001）.（2） Eachgroup pairwise comparisons on the three points of time: the difference of TSHlevel was not statistically significant at each time point in group ST （P＞0.05）;The TSH level was increased gradually and statistically significant after thesurgery in group NT and group NT+A （P＜0.01）.3.1.2FT3, FT4levels:（1） the difference of FT3, FT4level was notstatistically significant at each time point in group ST （P＞0.05）;（2） comparedto before the surgery, FT3, FT4levels in group NT and group NT+A wereobvious reduced at three weeks after surgery, although this difference wasstatistically significant （P<0.01）;（3） FT3and FT4in group NT and groupNT+A could not be detected after five weeks surgery.3.2Comparison of lipid levels in each groups3.2.1Time factor, grouping factors and the interaction fo time factor and thegrouping factor:（1） TG, TC, LDL-C: time factor, grouping factors and theinteractions of the time factor and the grouping factor were statisticallysignificant （F values ranged between3.998～23.687；P＜0.05）.（2） HDL-C:time factor, grouping factors and the interaciong of the time factor and thegrouping factor were not statistically significant,（P＞0.05）.3.2.2comparisons on each group pairwise on the three points of time:（1）group ST: the difference of TG, TC, HDL-C, LDL-C levels were notstatistically significant at each time point （P＞0.05）;②group NT: the leves ofTG, TC, LDL-C were increased gradually with the extension of time aftersurgery, and statistically significant at each time point （P＜0.05）; comparedwith before the surgery, HDL-C level at five weeks after surgery wassignificantly declined （P<0.05）.（3） group NT+A: compared with before thesurgery, TG level at both three weeks and five weeks after the surgery were significantly increased （P<0.05）; LDL-C level at three weeks after the surgerywere significantly increased then before the surgery （P＜0.05）.There were not statistically difference significant among the others ofresults （P>0.05）.3.3Comparison of NO、ET-1levels in each groups3.3.1Time factor, grouping factors and the packet interactions werestatistically significant （F values ranged between5.452～133.765；P＜0.01）.3.3.2Each group pairwise comparisons on the three time points:（1） groupST: the NO levels on both three weeks and five weeks after the surgery hadsignificant increased （P＜0.05） when compaired with the before the surgery;the ET-1levels in five weeks after the surgery had significantly increasedwhen compared with the before the surgery and the three weeks after thesurgery （P＜0.05）.（2） group NT: The NO level was gradually declined withthe surgery points, and statistically significant at each time point （P＜0.01）;the ET-1levels in both three weeks and five weeks after the surgery weresignificantly increased the before the surgery （P＜0.01）.（3） group NT: thedifference of NO, ET-1levels were not statistically significant at each timepoint （P＞0.05）.There were not statistically difference significant among the others ofresults （P>0.05）.4Comparison of the results of immunohistochemical detection indicators4.1the results of eNOS, ET-1expression: eNOS expression was mainly seenin the group ST and group NT+A, group NT only a few or no expression;ET-1expression was mainly seen in the group NT and group NT+A, the groupST only a few or no expression.4.2eNOS, ET-1statistical results4.2.1Test for several independent: The differences of NO, ET-1amountthree groups were significantly difference （H=10.198,13.572; P＜0.01）.4.2.2Two-Independent samples test: compared with the group ST, eNOS ingroup NT were significantly reduced （Z=-3.087, P<0.01）, and ET-1weresignificantly increased （Z=-3.722, P<0.01）. The others of Results compared, the difference was not statistically significant （P>0.05）.5Thyroid static imaging: Compared with the ST group, thyroidscintigraphy had significantly reduced on three weeks after the surgery ingroup NT and group NT+A; There were no thyroid static imaging on thefive weeks after the surgery.This is due to the decline of the rate of theresidual thyroid iodine uptake.Conclusion:1A hypothyroidism model of rabbit was established by near-totalthyroidectomy plus¹³¹I ablative therapy.2Hypothyroidism can cause the harm fo the arterial intimal by the changesof the levels foTG, TC, LDL-C.3Atorvastatin can produce the aortic intima injury.