Increase of T3 secreted through the milk in protein restricted lactating rats

Lactating rats were fed an 8% protein-restricted diet (PR), a 23% protein diet (C), and an energy-restricted pair-fed to PR group (PF). Thyroxine (T-3) and triiodothyronine (T-3) concentrations were analyzed in milk and in the serum of mothers and pups on different days of lactation. Serum T-3 was always higher (p < 0.01) in PR mothers, while T-4 was lower (p < 0.05) on days 4 and 21. PR group showed higher T-3 (p < 0.001) on days 4, 8, and 12, while PF showed higher T-3 in milk (p < 0.05) on days 12 and 16, In PR pups serum T-3 was higher (p < 0.05), while T-3 was lower on day 4 and both were lower (p < 0.05) on day 12. In PF pups T-4 was lower (p < 0.01) on day 21, and T-4 was lower (p < 0.01) on day 12. These data suggest a higher transfer of T-3 for the PR pups that could be important for their nervous system development. (C) 2001 Elsevier Science Inc. All rights reserved.