RESUMO
Objective:To observe the urinary iodine content (UIC), breast milk iodine content (BMIC) and milk iodine excretion of lactating rats under different iodine nutrition levels, and to explore the iodine metabolism of the lactating rats under different iodine nutrition levels.Methods:Forty female Wistar rats with body weight ranging from 70 to 120 g were divided into low iodine (LI) group, normal iodine (NI) group, hight iodineⅠ (HIⅠ) group and hight iodine Ⅱ (HIⅡ) group according to body weight by random number table method, with 10 rats in each group. The rats were fed low-iodine diet, and the iodine ion concentration of drinking water in each group was 0, 325, 18 700 and 37 450 μg/L. Twenty male rats were fed according to the feed method of NI group. After 8 weeks of intervention, the male and female rats were caged and mated in a ratio of 1 ∶ 2. Milk and 24 h urine were collected on the 7th, 14th and 21st days of lactation (L7, L14 and L21), and the amount of food and drinking water consumed were recorded. The 24 h milk excretion was calculated by acute lactation test. UIC and BMIC were determined by inductively coupled plasma mass spectrometry (ICP-MS).Results:The 24 h total iodine intake of lactating rats in LI, NI, HIⅠ and HIⅡ groups were (1.84 ± 0.51), (30.51 ± 6.79), (765.95 ± 317.41) and (1 654.26 ± 560.55) μg/d, respectively. The difference between groups was statistically significant ( P < 0.001). At L7, L14 and L21, there were statistically significant differences in UIC, BMIC and milk iodine excretion at the same lactation stages among different groups ( P < 0.001). In HIⅡ group, the difference of BMIC and milk iodine excretion at different lactation stages (L7, L14, and L21) were significantly signrficant ( P < 0.05). The 24 h milk iodine excretion of LI, NI, HIⅠ and HIⅡ groups was (1.23 ± 0.85), (11.88 ± 5.23), (207.09 ± 114.51), (493.67 ± 242.47) μg, respectively. The proportion of 24 h milk iodine excretion to 24 h total iodine intake was 66.85%, 38.94%, 27.04% and 29.84%, respectively. Conclusions:About 39% of dietary iodine is supplied to offspring through milk when iodine nutrition is normal. The iodine excretion ratio of milk is increased or decreased with low and high iodine levels. These results indicate that lactating rats with different iodine nutrition levels can regulate the ratio of iodine excretion in milk through their own compensatory effect to reduce the influence of iodine deficiency and iodine excess on their offspring.