Transfer of iodine through the milk in protein-restricted lactating rats

Iodine supply is important to avoid neonatal hypothyroidism. This study eva luated whether protein restriction during lactation affects iodine transfer to the pups through the milk. We studied lactating rats fed an 8% protein- restricted diet (PR), a control 23% protein diet (C), and an energy-restric ted diet group (ER). On days 4, 12 and 21, mothers were separated from thei r pups for 4 h, injected with I-131 IP, and put together with their pups. T he animals were killed 2 h later. PR pups had a significant decrease in iod ine uptake in the gastric content and duodenal mucosa on the 4th day. On th e contrary, at 12 and 21 days radioiodine was increased in the gastric cont ent and in the duodenal mucosa. ER pups had an increase in iodine uptake in the gastric content and in the duodenal mucosa only at the end of lactatio n. The thyroid iodine uptake in PR pups was significantly decreased on the 4th day and significantly increased on the 21st day compared to control. Wh en injected IP with an equivalent amount of I-131. the PR pups had a decrea se in thyroid iodine uptake on the 4th and 12th day, while ER pups had no s ignificant changes. So, these data suggest that protein restriction during lactation was associated with lower iodine secretion into the milk in the b eginning of lactation. However, at the end of lactation, an adaptation proc ess seems to occur leading to a higher transfer of iodine through the milk that compensates the impairment of thyroid iodine uptake in these pups. (C) 2001 Elsevier Science Inc. All rights reserved.