Effects Of Iodine Excess On Rat Femur Articular Cartilage And Growth Plate

Objective 1.To evaluate the excessive iodine intake effect on rat thyroid structure and funcitons.2.To evaluate the iodine excess effect on rat growth.3.To explore the influence of iodine excess and thyroid function on ferum articular cartilage and epiphyseal growth plate,providing theoretical basis for high iodine prevention and cure.Methods Wistar rats,weaning one month,were randomly divided into five groups according to their sex and body weight,that is normal iodine group(NI),five fold high iodine group(5HI),ten fold high iodine group(10HI),fifty fold high iodine group(50HI)and one hunred fold high iodine group(100HI),40 rats per group.5 groups iodine intake is 6.15?g/d,30.75?g/d,61.5?g/d,307.5?g/d and 615?g/d,respectively.Urine iodine,body weight,body length and the femur length of rat were regularly measured.At 6 months,12 months femoral artery taking rat blood and serum was segregated.Chemiluminescence was used to detect the levels of free triiodothyronine(FT3),free thyroxine(FT4),sensitive thyroid stimulating hormone(sTSH);Radioimmunoassay was used to detect the levels of triiodothyronine(T3)and thyroxine(T4)in rat serum.Execute rat,stripping the femoral,HE staining to observe pathological changes of epiphyseal growth plate and articular cartilage;Real-time polymerase chain reaction(RT-PCR)were used to detect the mRNA expression of type ? collagen,type X collagen,fibroblast growth factor receptor 1(FGFR1),matrix metalloproteinase-13(MMP-13)mRNA expression of rat femur articular cartilage chondrocytes.Results 1.Urine iodine level in HI group multiplied increased compared with NI group(P<0.05).2.At 6 months,serum sTSH levels in male rat show a rising trend in HI group,but no statistical difference(P>0.05);At 12 months,each HI group serum sTSH level rised,but FT4 level reduced in male rat(P<0.05).3.Compared to NI group,in HI group the rat thyroid appeared polymorphic changes.Growth plate appear abnormal in HI group,showing the proliferating cells number reduced,hypertrophic cell zone increase and chondral calcification obstacles.Compared with NI group,in HI group,articular cartilage show disorder arrange of chondrocytes and tidal line breaked and became indistinct.4.At 6 months,although body weight changes,body length changes and femur length in HI group has a decreasing trend,but no statistical difference(P>0.05);At 12 month,femur length of male rats show a downward trend,and in 10HI group appear statistical difference(P<0.05)5.Rat BMD between groups have no significant statistical difference(P>0.05)at 6 months;But at 12 months,BMD decreased in male rat in 5H1 and 10HI group(P<0.05).6.At 6 months,in each HI group,growth plate thickness decrease in male rats compared with NI group(P<0.05),but in female rats,only in 100HI group there is a statistical difference in growth plate thickness compared with NI group;At 12 months,growth plate thickness decrease in 50HI,100HI group in male rats and in 100HI group in female rats compared with NI group(P<0.05);Correlation analysis showed that growth plate thickness is negatively correlation with total daily iodine intake and serum sTSH level,the correlation coefficient is 0.721 and 0.343 respectively(P<0.001).7.In high iodine group,Collagen ? and MMP-13 mRNA expression of chondrocytes is increased than NI group(P<0.05),and FGFR1mRNA expression show an increasing trend,but only in 5HI group,FGFR1mRNA expression appear statistical difference(P<0.05);There is no statistical difference in Collagen ? mRNA expression compared with NI group(P<0.05).Conclusion 1.Excessive iodine intake increases the risk of hypothyroidism.2.The excessive iodine intake can lead to growth plate histomorphology changes and decrease the thickness of the growth plate,leading to growth and metabolic abnormal of long bone.3.Excessive iodine intake increase the risk of arthritis,indicating that iodine nutrition monitoring should be strengthened to avoid excessive iodine.