434 SEPARATION AND RADIOIMMUNOASSAY OF TRIIODOTHYRONINE (T3) IN HUMAN BREAST MILK

Abstract

The purpose of this study was to identify and quantitate T3 in human breast milk (HBM), and to elucidate the relationship of this radioimmunoassayable material with organified 125I in Na125 I-injected rats. The presence of thyroid hormone, and particularly T3, in HBM has been poorly documented, and inconsistency in sample preparation and methods of quantitation have resulted in ambivalent data. Since thyroid hormones are routinely administered per-orally as corrective therapy for hypothyroidism, the presence of T3 in milk has obvious implications for thyroid regulation in the suckling newborn, as the infant will consume ∼ 800 ml/day by 4-6 wks. of age if exclusively breast-fed. Aliquots of either HBM or rat breast milk (RBM) were extracted with acidic ethanol (H+EtOH) after overnight digestion with pancreatin. Samples were eluted from an LH-20 column (Pharmacia) using an ethyl-acetate based solvent mixture. Iodotyrosine and-thyronine standards were run, both in their native form, and after extraction. While the bulk of absorbance (HBM)and organified 125 I (RBM) appears in the monoiodotyrosine (MIT) region of elution profiles, an absorbance peak in HBM in the region of the H+EtOH-extracted T3 standard was observed which corresponds to a radiolabelled peak in RBM. T3-RIA of this region revealed 625 ng/dl in HBM, equivalent to a dose of 5.0 μg/day (800 ml. day consumption in a 1 mo. old infant). We conclude from these data that HBM contains sufficient T3 to be of therapeutic value in amelioration of hypothyroidism in infants.