DETERMINATION OF THYROXINE IN THE HAIR OF NEWBORNS BY RADIOIMMUNOASSAY WITH HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC CONFIRMATION

Hair analysis is often used in forensic toxicology to study, retrospec tively, chronic exposure of individuals to drugs, and consequently new born hair may become an ideal sample to study intrauterine exposure to xenobiotics as well as to endogenous compounds. As a tool to investig ate a supposed maternal thyroxine (T-4) supply to the congenital hypot hyroid fetus, we devised to use the analysis of T-4 extracted from new born hair. In the present paper, the analytical method based on T, ext raction from hair followed by a radioimmunoassay is described. To veri fy the nature of the T-4-like immunoreactive material present in newbo rn hair, it was further studied by HPLC fractionation with radioimmuno assay of the eluted fractions. On the basis of a clear correspondence between retention times of T-4 standard and T-4-immunoreactive compoun d extracted from hair, we assigned this immunoreactive material to T-4 . Then,we determined T-4 hair concentrations in 19 control newborns at birth and 12 congenital hypothyroid infants at 22 days of life. Value s obtained from hypothyroid infants (31.47+/-8.8 pg/mg(hair) mean+/-S. D.) were not-significantly lower than those obtained from healthy newb orns at birth (36.10 +/- 13.2 pg/mg(hair)). Such results are in agreem ent with the hypothesis of a maternal supply of thyroxine to the fetus through placental crossing. (C) 1998 Elsevier Science B.V. All rights reserved.