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SummaryMature human milk samples from young healthy women on an equilibrated diet contained a mean of 81 ng/ml total iodine. Iodide represented a mean of 77% of the total iodine. Of the 22 ng/ml organic iodine, there was about 1 ng thyroxine and triiodothyronine and,,after pepsin hydrolysis, up to 40% of organic iodine in monoiodotyrosine form. By electrophoresis, after incubation with radioactive thyroid hormone, we found an absence of binding on thyroxine-binding globulin, but thyroxine and triiodothyronine were bound to albumin with a maximal capacity 50 times higher than in human serum. All these differences did not favor transport of iodinated compounds from maternal serum to milk. In conclusion, milk iodide was taken up by newborn thyroid to make thyroid hormones. Abbreviations T4, thyroxine T3, triiodothyronineFor the past 10 years, thyroid congenital screening has brought a new approach to the neonatal thyroid function, and thyroxine appeared as the most important feature. These considerations have been certainly related to the interest recently developed by breast milk studies. Sack et a/. (19) had found a significant amount of thyroxine in human milk. These last 2 years, using two different sensitive methods, Mallol et a/. (10) and Moller et a/. (13) found that the thyroxine supplied by breast milk was inadequate for normal neonatal development.Recently. we have noticed a very low content of thyroid hormones in human breast milk and determined its total iodine level (4). This study presents the chemical form of the iodine and the proteins contained in the human milk with the aim of comparing milk to serum. MATERIALS AND METHODSPooled and individual mature breast milks were obtained from the Lactarium of the lnstitut de Pukriculture of Paris for the neonates in the Hbpital des Enfants-Malades. The mothers were young, healthy, living in and around the city, and had an equilibrated diet. Some samples of commercial cow milks were used for comparison.Fresh milk samples were used immediately or kept frozen at -18°C. For total iodine determination, the catalytic effect of iodine on the reduction of ceric ions by arsenious acid is used in a Technicon Autoanalyzer. The automatic micromethod was applicable in the range of 0.5 to 6 ng/O.l-ml sample. Milk was free of substance interfering with the reaction; the recovery of a stable amount of iodine added to the milk was complete. Iodide was determined either after 24-h dialysis against water and/or after shaking with an anion exchange resin (Bio-Rad AG 1-X2 type). Radioimmunoassays used were: T4 (6), T3 (18), both with curve sensitivity of 20 to 600 pglassay, and thyroxine-binding globulin with a commercial kit (Behringwerke, Marburg, Germany). Radioactive T4 and Tg used for radioimmunoassays and for the different incubations had high specific activity (>I200 pCi/pg, Amersham, UK). Peroxidase was determined according to Fragu and Nataf (5). Protein determinations were performed after trichloracetic acid precipitation, albumin after ammonium sulfate separation by t...

The thyroid tissues of 17 infants who died between 3 hours and 46 days after birth were studied by histological and biochemical techniques. The morphological aspect and the iodine content of these tissues are not related to the gestational age of the neonates, but they are related to the survival time. There are dramatic events early after birth: desquamation of the epithelium and absence of colloid, low iodine content of tissue extract (less than 1 mu g 127I per mg of protein) and low percentage of thryoglobulin (less than 10%). 24 hours after birth, the vesicles fill with colloid and the epithelium is cuboidal; the iodine content of the protein increases (between 1 and 2 mu g 127I per mg protein) as well as the thyroglobulin percentate (around 20%). One week after birth, there is a maximum of colloid and flat epithelium; the iodine content of the protein extract is much higher (more than 2 mu g 127I per mg protein) as is thyroglobulin percentage (up to 40%). Our studies of thyroid tissues of neonates suggest that a leakage of colloid, iodine and thyroglobulin takes place in the perinatal period, this phenomenon being followed by their rapid repletion.

The iodine and protein concentrations, the iodoamino acids content of thyroglobulin (TG) were determined in 17 thyroid tissues from human neonates who died from 3 hours to 47 days after birth. Total iodine concentration of neonate tissues increased with life duration. TG concentration was related to the survival duration of the neonates. Increase of the iodine content was associated to the increase of the TG content: mean value was 0.16 mug 127I/100 mug TG in neonates who died within the first 20 hours after birth, 0.25 mug in neonates who survived 26 to 72 hours and 0.43 mug in neonates living more than 10 days. Expressed as iodine content to total iodine ratio, iodoamino acid percentages were not related to the tissue. When the iodoamino acids were expressed in residues per molecule of TG, iodtyrosines, thyroxine and triiodothyronine increased with duration of survival. These variations in iodine content and concentration of thyroglobulin could be related to acute hormonal changes in serum observed in early neonatal period.

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A biochemical study of the thyroid tissue in pigs at various stages of development was undertaken. The iodine and protein concentrations, and the iodoamino acid content of thyroglobulin (TG) were determined. Expressed as μg ¹²⁷I/100 mg wet tissue, the mean iodine content of pig fetus is 66.4, 89.2 in the piglet and 168 in the adult pig. TG accounts for 95% of total proteins; its content increases with age. Mean iodine content of TG is 0.70 μg ¹²⁷I/100 μg in the fetus, 0.78 in the piglet and 0.97 in the adult pig. The average number of molecules of thyroxine residues is 1.6 in the fetus, 2.2 in the piglet and 3.5 in the adult. Average triiodothyronine residues are lower around birth than in the adult. At all stages of development, synthesis of thyroxine is less effective in the pig than in the human, relative to the iodine content of TG. In contrast to the human, iodinated compounds are not found at a very low level near birth, but TG and iodine content regularly increase.