Low-protein diet changes thyroid function in lactating rats

Lactating rats were fed with free access to an 8% protein-restricted diet ( PR); the control group was fed a 23% protein diet (C), An energy-restricted (pair-fed) group was given the same food as the animals in the control gro up, but the amounts of food consumed by both PF and PR were about the same. The body weight and serum albumin concentration of PR and PF darns were si gnificantly (P < 0.05) lower than that of the controls. The PR group had a significant increase in serum-free triiodothyronine (FT,) concentration, 24 -hr mammary gland and milk radioiodine (I-131) uptake (67%, 278%, and 200%, respectively) as compared with the controls. On the other hand, those anim als had a significantly lower serum-free thyroxine (FT,) concentration and 2- and 24-hr thyroid I-131 uptake (67%, 64%, and 74%, respectively). Protei n malnutrition during lactation did not alter thyroid or liver 5'-deiodinas e activity significantly. However, PF darns had a significantly lower (25%) thyroid 5'-deiodinase activity. These data suggest that protein-restricted lactating dams had an adaptive change in the thyroid function, which could be important to increase the transference of iodine or triiodothyronine th rough the milk to their pups and prevent sequelae of neonatal hypothyroidis m.