| Background and objectivesIt has got sufficient verification within human and animal that Iodine deficiency arousesmorphological and functional changes in thyroid gland. And it's noticed that the trace elementselenium also participates in this process. At present, this mechanism research focuses on theselenium's defense for hyperoxide damage as well as the selenium's influence on thyroxinemetabolism process.Adult primary-generation animal models are used in most of the studies on this aspectbefore. The epidemiological investigation demonstrated that if people had lived in Se/I-deficientareas for generations, the thyroid gland of their young generation sometimes suffers more seriousdamage. At present, the effects of both selenium and iodine deficiency on different developingperiods in young generation have not been report. Basing on the animal model already builtsuccessfully by our laboratory team in the earlier stage, this experiment chose the thyroid glandof the third generation rats with three time points (4 days, 21 days, adult) as research subjects.These thyroid glands had been histological observed, stereology measured andimmunohistochemical detected on PCNA/TTF-1. Try to find effect of selenium deficiency andiodine deficiency on different developing periods in young generation rats from folliclemorphous, cell proliferative and functional condition to approach effect of selenium deficiencyand iodine deficiency on these aspects.MethodsBasing on SD rats model already built successfully in the earlier stage, the thyroid gland ofthe third generation rats with the age of four time points including embryo(F3E), 4 days(F3P4),21 days(F2P21), adult(F3A) were chosen as research subjects. SD rats from each of the timepoint were divided into control group, Se-deficient group (Se-group), I-deficient group(I~- group)and both Se-and I-deficient group(Se~- I~- group), to be studied as following:1. Every group of F3E, F3P4, F3P21 and F3A were hematoxylin-eosin stained and then histological observed under microscope.2. Every group of F3P4, F3P21 and F3A were hematoxylin-eosin stained and then stereologymeasured on average follicle number, average follicular cavities area and average follicularepithelial cells height.3. Every group of F3P4, F3P21 and F3A were immunohistochemistry stained to observeexpression of PCNA in follicular epithelial cells.4. Every group of F3P4, F3P21 and F3A were immunohistochemistry stained to observeexpression of TTF-1 in follicular epithelial cells.Results1. Results of histological observation: In the F3A, F3P21 and F3P4, the Se~- group comparedwith the control group thyroid gland structure are similar. In addition, in the F3A Se~- groupthe part thyroid follicle have necrosis fibrosis change. The I~-group and the Se~-I~-group thyroidgland structure change are similar, small follicle proliferation change, small follicular cavity,even have not the cavity, in follicular cavitys the colloid are scarce. The epithelial cells offollicles are cube or high columnar. F3E thyroid gland compared with the other each agepresents obvious immature condition, the cells is crowded, the typical follicles are few.2. Results of stereology measure:①Average follicle number: in the F3A, the Se~-group and thecontrol group does not have the difference (P＞0.05). The I~-group and the Se~-I~-group folliclenumber are more than the control group and the Se~-group (P＜0.01). In the F3P21, theSe~-group and the control group does not have the difference (P＞0.05). The I~-group and theSe~-I~-group follicle number is more than the control group and the Se~-group (P＜0.01). In theF3P4, the Se~-group, the I~-group and the control group do not have the difference (P＞0.05),the Se~-I~-group follicle number is more than other each group (P＜0.05).②Average follicularcavities area: in the F3A, the Se~-group and the control group does not have the difference(P＞0.05), the I~-group and the Se~-I~-group follicular cavity area reduces obviously (P＜0.01), inwhich the Se~-I~-group follicular cavity area reduces the most obviously. In the F3P21, theSe~-group and the control group as well as the I~-group and the Se~-I~-group do not have thedifference (P＞0.05), the I~-group and the Se~-I~-group follicular cavity area are obviously smaller than the control group and the Se~- group (P＜0.01). In the F3P4, between the Se~-groupand the Se~-I~-group has the difference (P＜0.05), between other each group does not have thedifference (P＞0.05). I~-group and the Se~-I~-group follicular cavity area is the smallest.③Average follicular epithelial cells height: in the F3A, the Se~-group and the control groupdoes not have the difference (P＞0.05). The I~-group and the Se~-I~-group cells increase highly, inwhich the Se~-I~- group follicle epithelial cell is highest. In the F3P21, Each experimentalgroups have the remarkable difference with the control group (P＜0.01). In which theSegroup cells are the lowest and the Se~-I~-group cells are highest. In the F3P4, the Se~-groupand the control group as well as the I~-group and the Se~-I~-group do not have the difference(P＞0.05), the I~-group and the Se~-I~-group cells are obviously increase highly than the controlgroup, in which Se-I- group cells are the highest.3. Results of PCNA expression: In each age group, PCNA expression in the rat thyroid follicleepithelial cells from the control group to the Se~-I~-group strengthens gradually. The controlgroup and the Se~-group expression most for negative or weak masculine, the I~-group and theSe~-I~-group expression obvious enhancement (concentrates in +++～++++). Strong masculineexpression percentage of four groups increases gradually. In the F3: Control group 0％,Se~-group 6.3％, I~-group 28.6％, Se~-I~-group 50％. In the F3P21: Control group 0％, Se~-group0％, I~-group 16.7％, Se~-I~-group 21.4％. In the F3P4: Control group 0％, Se~-group 0％,I~-group 42.9％, Se~-I~-group 33.3％.4. Results of TTF-1 expression: TTF-1 expression in the F3A control group concentratescompletely in the negative or the weak masculine, in the Segroup, the I~-group and theSe~-I~-group obvious enhancement (concentrates in +++～++++). Strong masculineexpression(++++) percentage of four group respectively is: Control group 0％, Segroup 23.5％, I~-group 12.5％, Se~-I~-group 53.8％. In the F3P21, four group's expression intensitiesconcentrate in (+++～++++). Strong masculine expression(++++) percentage of four grouprespectively is: Control group 61.5％, Se~-group 55.6％, I~-group 90％, Se~-I~-group 85.3％. Ineach group of F3P4, TTF-1 expression does not have difference and no strong masculineexpression.Conclusion 1. Pure selenium deficiency can cause thyroid gland morphous and structure changing in thethird generation rats from different developing periods, make the follicles quantity increase,volume reduced and the epithelial cells proliferate. But its effect degree is weaker than pureiodine deficiency. And selenium deficiency has superimposition effect in the iodinedeficiency foundation. There are different effect degrees of selenium deficiency on differentdeveloping period. It is gradually obvious along with the ontogenesis.2. Selenium deficiency and iodine deficiency can both make the third generation rats' thyroidfollicle cell PCNA expression strengthen. Selenium deficiency's effect degree is weaker thaniodine deficiency's, and has superimposition effect on the iodine deficiency foundation. Thisfortified effect of selenium deficiency in F3P4 is not remarkable, obvious in F3P21 and keepto adult. The effect is gradually obvious along with the ontogenesis.3. Selenium deficiency and iodine deficiency can make the third generation rat thyroid folliclecell TTF-1 expression strengthen. Selenium deficiency effect degree is weaker than iodinedeficiency, and has superimposition effect on the iodine deficiency foundation. Seleniumdeficiency strengthens the TTF-1 expression is not display in F3P4, however, obviously inF3P21 and F3A display. The effect is gradually obvious along with the ontogenesis. |
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