Effects of high iodine given during pregnancy and lactation period of maternal rats and their offspring on thyroid function, memory / 中华地方病学杂志

ABSTRACT

Objective:The aim of this study was to investigate the alteration of thyroid function, learning and memory induced by high iodine exposure of both maternal rats during pregnancy and lactation period and their offspring and the possible mechanisms.Methods:Wistar rats(6 - 8 weeks old, 220 - 240 g), after one week of adaptation, female rats were mated with male rats (1 ∶ 1). Pregnant rats were divided into normal iodine intake group (NI), 10 times high iodine intake group (10 HI) and 100 times high iodine intake group (100 HI), iodine uptake was 7.5, 75.0, 750.0 μg/d through drinking water and feed, 8 pregnant rats in each group. Their offspring were continuously exposed to different doses of iodine until 180 d after weaning; learning and memory ability was assessed by Morris water maze. Blood sample was taken from the common carotid artery of the offspring and serum was separated. Serum free triiodothyronine (FT 3), free thyroxine (FT 4), and thyroid stimulating hormone (TSH) levels were measured by enzyme linked immunosorbent assay (ELISA). Total RNA was extracted from the hippocampus of the brain and the mRNA expressions of 10-11 translocation methylcytosine dioxygenase (TET 1, TET 2 and TET 3) were detected by Real-time qPCR. The co-localized expressions of thyroid hormone receptor beta 1 (TRβ1) and TET 3 in brain tissue were detected by immunofluorescence staining. Results:Compared with NI group [(4.95 ± 0.53), (12.62 ± 1.81) pmol/L, (7.70 ± 1.04) mU/L], in 10 HI and 100 HI groups, the levels of serum FT 3 and FT 4 [(4.60 ± 0.49), (4.62 ± 0.54), (11.67 ± 1.54), (10.85 ± 1.56) pmol/L] were significantly decreased ( P < 0.05), and serum TSH levels [(9.62 ± 0.93), (9.77 ± 1.28) mU/L] were significantly increased ( P < 0.05). Compared with NI group, the average escape latency of 10 HI and 100 HI groups in the first five days was significantly increased ( P < 0.05), and the space exploration experiment in the sixth day showed that the number of crossing platforms was significantly decreased ( P < 0.05); the mRNA expressions of TET 3 in the hippocampus of the brain were significantly decreased in 10 HI and 100 HI groups ( P < 0.05). Immunofluorescence staining showed that TRβ1 and TET 3 were co-localized in the cerebrovascular intima, choroid plexus and neurons in rats' brain in the 100 HI group. Conclusions:Under the condition of high iodine intake during pregnancy and lactation of the maternal rats, and continued exposure to their offspring until 180 d after weaning, the decreased ability of spatial learning and memory may be related to the alteration of thyroid hormone and the interaction of TET 3 with TRβ1 in the brain.