Separation of Iodothyronines from Iodinated Metabolites in Serum from Reverse T₃ Tracer Kinetic Studies in Man and Dog:

Summary

Iodothyronine separation from free iodide and iodoalbumin in serial serum samples obtained from 7 human and 5 dog studies following intravenous injection of radiolabeled reverse triiodothyronine (reverse T₃) was compared using acidified ammonium acetate/tetrahydrofuran (THF) elution from C-18 SEP-PAK cartridges or ethyl acetate/butanol (EAB) extraction. Both methods excluded > 98% free iodide and > 99% iodoalbumin from the iodothyronine fraction. Recovery of labeled reverse T₃ was higher for the THF/SEP-PAK (79.4 ± 4.1%) than for the EAB method (43.2 ± 6.1%, P < 0.001), and intra-assay coefficients of variation were lower (2.1 ± 0.6% and 4.4 ± 2.0%, respectively, P < 0.001); HPLC analysis of iodothyronine fractions revealed a single peak co-migrating with injected tracer. The THF/SEP-PAK technique allowed use of larger serum samples at later time points. Serum disappearance curves derived from these two methods were highly correlated in all cases (r = 0.998, P < 0.001), as were fits of data to sums of exponentials and calculated serum kinetic parameters.

Key-Words

Iodothyronines - Reverse T₃ Kinetics - Canine - Human