Thyroid's secretory capacity

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Thyroid's secretory capacity (GT, also referred to as thyroid's incretory capacity, maximum thyroid hormone output or, if calculated from levels of thyroid hormones, as SPINA-GT) is the maximum stimulated amount of thyroxine that the thyroid can produce in a given time-unit (e.g. one second).[1]

How to determine GT[edit]

Experimentally, GT can be determined by stimulating the thyroid with high a thyrotropin concentration and measuring its output in terms of T4 production.

In vivo, GT can also be estimated from equilibrium levels of TSH and T4 or free T4. In this case it is calculated with

\hat G_T  = {{\beta _T (D_T  + [TSH])(1 + K_{41} [TBG] + K_{42} [TBPA])[FT_4 ]} \over {\alpha _T [TSH]}}

or

\hat G_T  = {{\beta _T (D_T  + [TSH])[TT_4 ]} \over {\alpha _T [TSH]}}

\hat G_T : Theoretical (apparent) secretory capacity (SPINA-GT)
\alpha _T: Dilution factor for T4 (reciprocal of apparent volume of distribution, 0.1 l−1)
\beta _T: Clearance exponent for T4 (1.1e-6 sec−1)
K41: Dissociation constant T4-TBG (2e10 l/mol)
K42: Dissociation constant T4-TBPA (2e8 l/mol)
DT: EC50 for TSH (2.75 mU/l)[1][2]

Reference Range[edit]

Lower limit Upper limit Unit
1.41[1] 8.67[1] pmol/s

The equations and their parameters are calibrated for adult humans with a body mass of 70 kg and a plasma volume of ca. 2.5 l.[1]

Clinical significance[edit]

GT is elevated in hyperthyroidism and reduced in hypothyroidism[3][4] and it has been observed to correlate with thyroid volume.[1] In longitudinal evaluation GT shows lower intraindividual variation than TSH, FT4 or FT3.[5] Correlation of SPINA-GT with creatinine clearance suggested a negative influence of uremic toxins on thyroid biology.[6] In the initial phase of major non-thyroidal illness SPINA-GT may be temporarily elevated.[7]

See also[edit]

External links[edit]

References[edit]

  1. ^ a b c d e f Dietrich, J. W. (2002). Der Hypophysen-Schilddrüsen-Regelkreis. Berlin, Germany: Logos-Verlag Berlin. ISBN 978-3-89722-850-4. OCLC 50451543. 3897228505 
  2. ^ Dietrich JW, Stachon A, Antic B, Klein HH, Hering S. The AQUA-FONTIS study: protocol of a multidisciplinary, cross-sectional and prospective longitudinal study for developing standardized diagnostics and classification of non-thyroidal illness syndrome. BMC Endocr Disord. 2008 Oct 13;8:13. PMID 18851740.
  3. ^ Dietrich, J., M. Fischer, J. Jauch, E. Pantke, R. Gärtner und C. R. Pickardt (1999). "SPINA-THYR: A Novel Systems Theoretic Approach to Determine the Secretion Capacity of the Thyroid Gland." European Journal of Internal Medicine 10, Suppl. 1 (5/1999): S34.
  4. ^ Dietrich JW. [Thyroid storm]. Med Klin Intensivmed Notfmed. 2012 Sep;107(6):448-53. Epub 2012 Aug 11. German. PMID 22878518
  5. ^ Dietrich JW, Landgrafe, G, Fotiadou, EH. TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis Journal of Thyroid Research, vol. 2012, Article ID 351864, 29 pages, 2012. doi:10.1155/2012/351864. PMID 23365787
  6. ^ Rosolowska-Huszcz D, Kozlowska L, Rydzewski A. Influence of low protein diet on nonthyroidal illness syndrome in chronic renal failure. Endocrine. 2005 Aug;27(3):283-8. PMID 16230785.
  7. ^ Liu S, Ren J, Zhao Y, Han G, Hong Z, Yan D, Chen J, Gu G, Wang G, Wang X, Fan C, Li J (2013). "Nonthyroidal Illness Syndrome: ist it Far Away From Crohn's Disease?". J Clin Gastroenterol. 47 (2): 153–9. doi:10.1097/MCG.0b013e318254ea8a. PMID 22874844.