Advertisement

Evidence for Dual Peripheral 5’Deiodinases (5’D) Regulating Circulating T3 Levels in Man

  • Ananda Nimalasuriya
  • Steven Lin
  • Jonathan LoPresti
  • Alan O. Marcus
  • Carole A. Spencer
  • John T. Nicoloff

Abstract

The majority of circulating T3 in euthyroid man appears to be derived from conversion of T4 to T3 via 5’deiodinase (5’D) systems located in peripheral tissues. Recently, we have reported that a progressive reduction in the efficiency of T4 to T3 conversion occurs when circulating T4 levels rise from subnormal to supraphysiological concentrations (1,2). As shown in Fig. 1 (left panel), the greatest change in conversion efficiency of T4 to T3 is seen over the span of T4 values ranging between 0 and 5 µg/dl in eu-TBG-emic subjects. These data were obtained in 254 patients who had been placed on varying doses of chronic T4 therapy. Some of the T3 values in patients with identical serum T4 levels have been averaged in order to obtain a better overview of the mean pattern of the T3 response in the study population. In separate T4 tracer kinetic studies, we have found that a 50% conversion efficiency of T4 to T3 occurs at low serum T4 values which progressively drops to less than 15% at T4 levels in excess of 20 µg/dl (3).It is of interest that no apparent alteration in the efficiency of T4 to rT3 was detected over this same range of serum T4 values (2).

Keywords

Supraphysiological Concentration Apparent Alteration Southern California School Hanes Plot Half Maximal Velocity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Nicoloff JT, Lum SMC, Spencer CA, et al. Hormone and Metab Res Suppl #14, 74, 1984.Google Scholar
  2. 2.
    Lum SMC, Nicoloff JT, Spencer CA, et al. J Clin Invest 73: 570, 1984.PubMedCrossRefGoogle Scholar
  3. 3.
    Morris RR, Lum SM, Kaptein EK, et al. Clin Res 31: 274, 1983.Google Scholar
  4. 4.
    Braverman LE, Vargenakis A, Downs P, et al. J Clin Invest 52: 1010, 1973.PubMedCrossRefGoogle Scholar
  5. 5.
    Shimizu TC, Pittman JB, Chambers JB, et al. In Thyroid Research, Excerpta Med Int Congr Ser: 263, 1975.Google Scholar
  6. 6.
    Inada M, Kasagi K, Kurata S, et al. J Clin Invest 55: 1337, 1975.PubMedCrossRefGoogle Scholar
  7. 7.
    Rendell M and Salmon D. Clin Endocr 22: 693, 1985.PubMedCrossRefGoogle Scholar
  8. 8.
    Nicoloff JT and Dowling JT. J Clin Invest 47: 2000, 1968.Google Scholar
  9. 9.
    Cornish-Bowden A. Fundamentals of Enzyme Kinetics, Butterworths, London, 1979.Google Scholar
  10. 10.
    Larsen RR, Silva JE, and Kaplan ML. Endocr Rev V 2 (1): 87, 1981.PubMedCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1986

Authors and Affiliations

  • Ananda Nimalasuriya
    • 1
  • Steven Lin
    • 1
  • Jonathan LoPresti
    • 1
  • Alan O. Marcus
    • 1
  • Carole A. Spencer
    • 1
  • John T. Nicoloff
    • 1
  1. 1.Department of Medicine, University of Southern CaliforniaSchool of Medicine and the Los Angeles County/USC Medical CenterLos AngelesUSA

Personalised recommendations