Effects of iodine and iron comitant deficiency on thyroid function of rat

Objective To explore the effect of iodine and iron comitant deficiency on thyroid function of rat,and to provide new clues and ideas for prevention and control of iodine deficiency disorders in iron deficiency areas.Methods Using 2 × 2 factorial analysis method,sixty male healthy SPF/VAF level weaning SD rats were randomly divided into normal group (N),iodine deficiency group (ID),iron deficiency group (FD) and iodine and iron comitant deficiency group(IFD) by body mass,and 15 rats in each group.Diet was controlled to meet the iodine and iron intake requirement in each group.Rats of all groups drank deionized water.After 6 weeks feeding,body mass and thyroid gland mass were measured,and the relative mass of thyroid gland was calculated.Rat urine samples were collected,(NH4)2S2O8 digesting,As3+-Ce4+ catalyzing spectrophotometry was used to verify urine iodine.Blood was taken from femoral artery,and serum was obtained by centrifugation.The following tests were carried out:biochemical assay of hemoglobin,serum iron,and total iron binding capacity; chemiluminescence detection of total triiodothyronine (TT3),total thyroxine (TT4),free triiodothyronine (FT3),free thyroxine (FT4) and thyroid stimulating hormone(TSH).Results Compared with N group [(341.0 ± 24.2)g],rats in FD and IFD groups [(307.0 ± 17.6),(294.5 ± 29.5)g] had less body mass(all P ＜ 0.01) ; and compared with N group[(17.6 ± 3.7)mg,(5.2 ± 1.1)mg/100 g body mass] those in ID and IFD groups had larger absolute[(31.8 ± 3.8),(22.9 ± 3.4)mg] and relative thyroid mass[(9.4 ± 1.6),(7.8 ± 1.1)mg/100 g body mass,all P ＜ 0.01].Medians of urinary iodine in ID and IFD groups(31.5,22.5 μg/L) were lower than that in FD and N groups(167.6,163.8 μg/L,all P ＜0.01).Rats in IFD and FD groups had lower hemoglobin[(69.2 ± 7.4),(62.2 ± 8.1)g/L] and serum iron[(4.9 ±1.4),(5.2 ± 0.8)μmol/L] and higher total iron binding capacity[(176.3 ± 4.4),(186.4 ± 13.7)μmol/L]than N group[(161.1 ± 9.4)g/L,(27.3 ± 6.5)μmol/L,(99.1 ± 9.0)μmol/L,all P ＜ 0.01].In FD,ID and IFD groups,their serum hormones TT4[(47.42 ± 6.58),(35.27 ± 6.97),(30.07 ± 4.75)nmol/L] and FT4[(27.60 ±2.32),(21.67 ± 2.79),(19.45 ± 1.97)pmol/L] were lower than N group[(68.97 ± 9.95)nmol/L,(34.01 ±3.28)pmol/L,all P ＜ 0.01)],but compared with N group[(1.23 ± 0.13)nmol/L,(5.89 ± 0.62)pmol/L],TT3 and FT3 decreased in IFD[(0.95 ± 0.13)nmol/L,(5.18 ± 0.54)pmol/L] and FD groups[(0.90 ± 0.14)nmol/L,(4.81 ±0.41)pmol/L,all P ＜ 0.01],while increased in ID group [(1.46 ± 0.14)nmol/L,(7.28 ± 0.79) pmol/L,all P ＜0.01].Compared with N group [(1.97 ± 0.83)mU/L],TSH of the rats in ID [(6.39 ± 4.41)mU/L] and IFD [(3.12 ± 1.52)mU/L] groups rose obviously,especially in ID group (P ＜ 0.01 or 0.05).Factorial analysis showed iodine and iron have reciprocal actions to TT3,TT4,FT3,FT4 and TSH(P ＜ 0.01 or 0.05).Conclusions Both iron deficiency and iodine deficiency can lead to hypothyroidism,and they present reciprocal action.The combined supplement of iodine and iron will possibly improve the prevention effect to iodine deficiency disorders in the iron deficiency area. Key words: Iodine and iron comitant deficiency; Thyroid function; Rats