| Objectives:To observe the influence of different iodine intake on TSH cell in pituitary of 20-day pregnant Wistar rats,and then to study mechanism of the effect of iodine deficiency and iodine excess on pituitary-thyroid axis in pregnant rats.Methods:Female wistar rats,one month after stopping lactation,were divided into five groups randomly:severe low iodine group(L1),medium low iodine group(L2), light low iodine group(L3),normal iodine group(NI),high iodine group(HI). Every group were raised 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(L1),50(L2),133.3 (L3),300(NI) 9966.7μg/L(HI)in the water.According to the intake of the 20g diet and 30 ml water everyday,the rats' iodine intake of the whole day were estimated as follows:1.25I(L1),2.5I(L2),5I(L3),10I(NI),300μg/d(HI).The male rats were bred the same condition as the female rats which belong to normal iodine group.After three months,the female and male rats were mated by 2:1. When the pregnant rats were 20 days,the thyroid hormone was observed.The thyroid gland and pituitary were weighted.After paraffin imbedding,thyrotrophic cell were HE staining,Mallory staining,immunohistochemical staining.The relative weights of pituitary,volume density(Vv),numerical density(N_A) and the number of the strong positive TSH cells were measured.Results:1.The absolute thyroid weight and relative thyroid weigh of every low iodine rats were increased with the aggravating of iodine deficiency.Compared with normal group,group L1 and group L2 were more obvious(p＜0.05).The changes in absolute thyroid weight and relative thyroid weights in group H were insignificant(P＞0.05). 2.Compared with normal group,the absolute pituitary weight in low iodine group was increased,and the absolute pituitary weight in high iodine group was decreased(P＞0.05).The relative pituitary weight in every low iodine groups and high iodine group were insignificant(P＞0.05).3.Observation under light microscope:The TSH cells were concentrated on the center of anterior pituitary,and the reaction degree was different.The stronger reaction was dark brown,the weak reaction was light brown.The grains of low iodine groups were located in lateral plane.4.Compared with normal group,the more severe iodine deficiency,the higher the numerical density and volume density were,and the group L1 and group L2 were more significant(P＜0.05),especially,the increase in L1 is more dramatic (P＜0.01);The group HI and L3 was insignificant(P＞0.05).5.With the aggravating of iodine deficiency,the strong masculine cells in low iodine groups were decreased,and the group L1 was more significant(P＜0.01). Compared with normal group,the high iodine group was insignificant(P＞0.05).Conclusions:1.The levels of thyroid hormone in long and severe deficiency of iodine were decreased significantly in pregnant rats.2.Neither iodine defect nor iodine excess had any influence on pituitary weight.3.The volume density and numerical density on area were raised with the decreasing dosage of groups of low iodine.And with Severity of iodine defect, the TSH cells were mainly weakly positive cells.When in high iodine,the cells were in depot state and mainly were strongly positive cells.4.The influence on pregnant rats from low iodine were more significant than from high iodine.It indicated that when iodine offering was not enough,the thyroid was accommodated of itself firstly.And this would keep the thyroid's normal function,when the thyroid cannot keep the normal hormones by itself, the hypothalamus-anterior pituitary-anterior pituitary would promote as the second mechanism.And the TSH cells were in compensatory high externalization.The TSH cells synthesize and deliver large of TSH,and TSH would stimulate the thyroid hyperplasy,then formed goiter lastly.And when 30 times high iodine intake,the function of thyroid and the morph of pituitary had no significant changes.
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