[Long-term effect of iodine deficiency on growth and food utilization rate in second filial generation rats]

Objective: To study the effect of iodine deficiency on body weight, food consumption, and food utilization rate of second filial generation Wistar rats. Methods: According to the food pattern of a high-iodine deficient population, two types of low-iodine food have been produced using the main crops grown in this area (iodine levels of 50 and 20 μg/kg, respectively). Wistar rats were randomly divided into three groups, normal iodine group (NI group), low-iodine group one (LI group) and low-iodine group two (LII group), using the random number table method and fed diets containing 300, 50, and 20 μg/kg of iodine, respectively. Parental generation rats were fed until they reached reproductive age; first filial generation rats were allocated to the same diet as their mothers. After 3 months of feeding, first filial generation rats gave birth to second filial generation rats; second filial generation rats were allocated to the same diet as their mothers. After feeding for 90, 180, and 270 days, rats were sacrificed. One-way analysis of variance was used to analyze body weight, food intake, and food utilization rate data collected during the time of feeding and blood iodine hormone level, which was determined after sacrifice. Results: The LI and LII groups generally demonstrated decreased activity, slow reaction, and growth retardation compared with the NI group. After 270 days, the urine iodine levels of the LI and LII groups were 1.7 and 0.2 μg/L, respectively, which were significantly lower than the NI group (255.2 μg/L) (P<0.001). Additionally, the weight of female rats in the LI and LII groups were (288.1±10.5) and (275.7±2.7) g, respectively, which was significantly lower than that of the NI group ((311.0±2.3) g) (P<0.001). The weight of male rats were (446.0±4.6) and (451.8±19.1) g, respectively, which were significantly lower than that of the NI group ((517.2±7.8) g) (P<0.001). In the LI and LII groups, food intake of female and male rats after 270 days were (465.0±27.7), (658.4±28.6) and (423.0±13.2), (548.0±18.8) g, respectively, which were significantly lower than that of the NI group ((499.5±21.8), (760.8±33.0) g) (P<0.001). Moreover, the food utilization rate of female rats in the LI and LII groups was (8.7±0.4)% and (6.0±0.58)%, which was lower than that of the NI group ((11.7±3.5)%) (P<0.001); similarly, male rats showed rates of (8.9±1.5)% and (6.9±1.31)%, respectively, which were lower than that of the NI group ((13.7±3.0)%) (P<0.001). After 270 days, the level of T3 in the LI and LII groups were (0.45±0.10) and (0.34±0.15) ng/ml, respectively, which was significantly lower than that of the NI group ((0.91±0.49) ng/ml) (P<0.01). Moreover, the level of T4 were (69.02±27.87) , (53.18±13.53) ng/ml in LI and LII groups, respectively, which was lower than that of the NI group ((76.69±29.42) ng/ml) (P<0.05). Conclusion: This study indicated that iodine deficiency induced by a long-term low-iodine diet can cause changes in weight, food intake, and food utilization rate among second filial iodine deficiency rats. More importantly, the iodine content in low-iodine food impacts these parameters.