GT

Definition

G_T, also referred to as SPINA-GT, is an abbreviation for "gain of thyroid". It is a mathematical symbol for calculated secretory capacity of the thyroid gland. Calculation of G_T is part of a structure-parameter inference approach, a method that is used e.g. in experimental thyroid research. The equations are derived from a mathematical model of thyrotropic feedback control.

Calculation

${\hat {G}}_{T}={{\beta _{T}(D_{T}+[TSH])(1+K_{41}[TBG]+K_{42}[TBPA])[FT_{4}]} \over {\alpha _{T}[TSH]}}$

${\hat {G}}_{T}={{\beta _{T}(D_{T}+[TSH])[TT_{4}]} \over {\alpha _{T}[TSH]}}$

$\alpha_T$: 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)
D_T: EC₅₀ for TSH (2.75 mU/l)

Reference range

1.41 - 8.67 pmol/sec (in adult humans)

see also: G_D, SPINA

Web Links

• SPINA Reference
• SPINA-Thyr (Software for calculating GT)

References

1. 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.
2. Dietrich, J. W. (2002). Der Hypophysen-Schilddrüsen-Regelkreis. Entwicklung und klinische Anwendung eines nichtlinearen Modells. Berlin, Logos-Verlag.
3. Rosolowska-Huszcz D, Kozlowska L, Rydzewski A (2005). Influence of low protein diet on nonthyroidal illness syndrome in chronic renal failure. Endocrine. 27(3):283-8
4. Dietrich, J. W., A. Stachon, B. Antic, H. H. Klein, and S. Hering (2008). "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 Endocrine Disorders 8 (13). PMID 18851740.