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THE METABOLIC SIGNIFICANCE OF THYROXINE-BINDING GLOBULIN

1969; Oxford University Press; Volume: 61; Issue: 1 Linguagem: Inglês

10.1530/acta.0.0610137

1479-683X

T ARNOLD BAYLEY, H P Higgins, VAS V. ROW, William James, Roberto Vidal,

Ion channel regulation and function

ABSTRACT Low thyroxine-binding globulin (TBG) capacity was found in seven members of a family in four generations. The effect on peripheral metabolism, as measured by the basal metabolic rate (BMR), of single 1000 μg intravenous doses of sodium L-thyroxine (T 4 ) and sodium L-triiodothyronine (T 3 ) was studied. In TBG deficient patients and those loaded with diphenylhydantoin (DPH) so that the PBI was depressed to low levels, T 4 produced an effect on the BMR within 2–5 days similar in rapidity of onset and magnitude to that produced by T 3 in all subjects. In normal controls or patients on maintenance DPH therapy, T 4 produced little or no effect on the BMR within 8 days. The calorigenic studies were compared mainly in the TBG deficient patient with the acute (20–50 min) disappearance from plasma as well as with the chronic fate of the 131 I-labelled hormones. The acute and chronic disappearances of T 4 were more rapid in the TBG deficient patients whereas the acute and chronic disappearances of T 3 were similar to that of subjects with normal TBG. These observations support the hypothesis that in normal humans TBG acts as a rate-regulating factor in the peripheral metabolism of acutely administered T 4 by limiting the access of T 4 to the tissues, thereby slowing its action on the cell. Therefore, the difference in peripheral metabolic effect of T 4 and T 3 would appear to be related to the presence of TBG in human plasma.