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In order to estimate the relative magnitude of the two alternative pathways of monodeiodination of thyroxine (T4) in adult humans, the metabolic clearance rates (MCR) and production rates (PR) of 3,3',5'-triiodothyronine (reverse-T3,rT3) and of 3,5,3'-triiodothyronine (T3) were determined in six euthyroid control subjects (C) and in five hypothyroid patients (H) receiving L-T4 as replacement therapy (0.15-0.3 mg/day). MCR was computed by a non-compartmental method of analysis from the plasma disappearance of 125I rT3 and 131I T3 during 72 h following simultaneous injection of tracers. PR was calculated from MCR and the serum concentration of rT3 and T3, respectively, determined by radioimmunoassay. In the H subjects, rT3 MCR averaged 97.1 +/- 12.8 (SD) 1/day and rT3 PR, 34.3 +/- 12.8 microng/day; T3 MCR was 28.7 +/- 6.1 1/day and T3 PR, 20.3 +/- 6.6 microng/day (all corrected to 70 kg body weight). These results were not significantly different from those in the control group; rT3 MCR 104 +/- 24 1/day, rT3 PR 33.0 +/- 9.2 microng/day; T3 MCR 24.0 +/- 5.9, T3 PR 24.2 +/- 4.1. The proportionof total triiodothyronine (rT3 averaged 62% in H patients and was similar (57%) in the C group. The results obtained in the H subjects indicate that the production of rT3 is a major route of T4 metabolism, equal to or exceeding that of T3. From the close agreement between the mean values for rT3 PR in the C and H groups it is concluded that most, if not all of the rT3 produced in normal humans is derived by extrathyroidal conversion from T4.
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
January 1982,
Methods in enzymology,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
January 1984,
Revista paulista de medicina,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
August 1977,
Endocrinology,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
July 1986,
Zentralblatt fur Veterinarmedizin. Reihe A,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
July 1980,
Acta endocrinologica,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
September 1977,
Clinica chimica acta; international journal of clinical chemistry,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
March 2007,
Endocrinology,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
January 1985,
Comparative biochemistry and physiology. A, Comparative physiology,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
January 1986,
Brazilian journal of medical and biological research = Revista brasileira de pesquisas medicas e biologicas,
L Gavin, and
J Castle, and
F McMahon, and
P Martin, and
M Hammond, and
R R Cavalieri
April 1979,
Mechanisms of ageing and development,
