title: Effect of lactational intensity on extrathyroidal 5'-deiodinase activity in rats.
abstract: Concentrations of thyroxine and triiodothyronine in serum and 5'-monodeiodination activity in liver and kidney were studied in lactating Sprague-Dawley rats with different litter sizes. Litter sizes were adjusted at birth to 0 (postpartum nonlactating group), 4, 8, 12, and 16 pups per lactating rat. Serum and tissue samples were collected from lactating rats and pups on d 12 of lactation and from 6 nulliparous females. Nulliparous and postpartum nonlactating rats did not differ in serum thyroxine, triiodothyronine concentrations, or in 5'-deiodinase activity in liver and kidney. As litter size increased, maternal serum thyroxine, triiodothyronine concentrations, and 5'-deiodinase activity in liver and kidney decreased. Growth rate of pups was inversely correlated with litter size and positively correlated with concentration of serum thyroxine and liver 5'-deiodinase in mothers. In pups, serum triiodothyronine concentrations decreased as litter size increased, but serum thyroxine concentrations were not affected. Results suggest a relationship between the hypothyroid status of lactating rats and suckling intensity. The thyroid status of the dam may influence thyroid status and growth of offspring.
authors.affiliation: Milk Secretion and Mastitis Laboratory, USDA, ARS, Livestock and Poultry Sciences Institute, Beltsville, Maryland 20705.
authors.forename: S
authors.initials: S
authors.lastname: Kahl
authors.forename: J
authors.initials: J
authors.lastname: Bitman
authors.forename: A V
authors.initials: AV
authors.lastname: Capuco
authors.forename: J E
authors.initials: JE
authors.lastname: Keys
mesh_terms: D000818:Animals; D000833:Animals, Suckling / Q000254:growth & development; D005260:Female; D007453:Iodide Peroxidase / Q000032:analysis*; D007668:Kidney / Q000201:enzymology*; D007774:Lactation / Q000502:physiology*; D008098:Litter Size; D008099:Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D015430:Weight Gain
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D007453:Iodide Peroxidase; D013974:Thyroxine