| Objectives:To study the effect of different dosage of Potassium iodine(KI) on morphological changes of thymus in pregnant rats.Methods:Female Wistar rats,1 month after stopping lactation,were divided randomly into 5 groups by giving various concentrations of KI:the lowest iodine(L1),the lower iodine(L2),low iodine(L3),normal iodine(N),high iodine(H).All groups were fed with the diet derived from endemic goiter area containing iodine concentration is less than 50μg/kg,and drank different iodine concentration tap water which containing iodine of 8,50,133.3,300,9966.7μg/L in order.According to intake of the 20g diet and 30ml water everyday,the iodine intake of the whole day of the five groups are estimated as follows:1.25μg/d(L1),2.5μg/d(L2),5μg/d(L3),10μg/d(N),300μg/d(H).After three months,the rats mated with male rats fed with normal-iodine diet.At the 16th day of pregnancy,the pregnant rats were killed,and the thymus were excised and weighed,stained with HE and immunohistochemistry, light microscopic study.and we focused on the thymus weight and thymus index,the thyroid hormones level in serum,the thymus volume density ratio of cortex/medulla, the description of histological section in light microscope,the volume density(Vv)and numerical density on area(NA)of thymus CK19~+ thymus epithelial cells decreased.Results:1.Compared with normal group,thymus index were decreased in all experimental groups(L1,L2,L3,H),but only the decreases in L1 and L2 have a statistical significance(P<0.05 ).2.The degree of athyroxinosis became larger with the aggravating of iodine deficiency.Compared with normal group,T4 both in the L1 and L2 had decreased dramatically(P<0.05).the decrease of T3 has no statistical significance.3.Compared with normal group,the thymus volume density ratio of cortex/medulla decreased in L1 and L2(P<0.05),especially,the decrease in L1 is more dramatic.There is no significant change in L3 and H.4.Stained with HE,in L1 and L2 thymus shrank,thymus envelope and thymus septula thickened,thymus cortex became thinning,medulla expanded relatively by light microscopic observation.At the same time,local hyperplasia of thymus epithelial cells was seen in L1.There is no obvious changes in H.5.Compared with normal group,Volume density(Vv)and numerical density on area(NA)of thymus CKI9~+ epithelial cells also decreased significantly in L1 and L2(P<0.05),especially,the decrease in L1 is more dramatic;The decrease in H has no statistical significance.Conclusions:1.Long time of large deficiency of KI results in decreased thyroid hormone level in serum of pregnant rats.The decrease became larger with the aggravating of iodine deficiency.2.Long time of large deficiency of KI results in thymus degenerate,which can be testified from changes as follows:the thymus weight and thymus index decreased, the thymus volume density ratio of cortex/medulla reduced,thymus cortex epithelial cells occurred local hyperplasia,the volume density(Vv) and numerical density on area(NA)of thymus CK19~+ thymus epithelial cells decreased.The degeneration became more serious with the aggravating of reduction of thyroid hormone level in serum of pregnant rats.3.The influence of iodine deficiency is more dramatic than overdose of iodide to pregnant rats.Iodine intake within 30HI has no dramatic effect on the function of thyroid gland or the histologic structure of thymus.4.In a word,long time of abnormal intake of KI,especially iodide deficiency, results in decreased thyroid hormone level in serum of pregnant rats,thereafter thymus microenviroment is destroyed and thymus is degenerated.In life,it has little possibility to overdose iodine more than 30HI for a long time.These findings above demonstrated that iodine in appropriate dosage is safe and effective for pregnant women.Being the result of animal experiment,the conclusion can not be applied to pregnant women simply. |
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