TABLE 1.

Thyroid Hormone^a Elimination Rates, Generation Rates, Baseline Values, and Slope Parameters Used for the Rat and Human Thyroid Feedback PD Model

Model	Parameter	Value	Units	Source
	T4 Elimination	9.63E-04	1/min	Modified from Silva et al. (1984) b
	T3 Elimination	9.17E-03	1/min	Modified from Silva et al. (1984) b
	T4 Generation	4.04E-03	ug/dl/min	Modified from Ekerot et al. (2013) d
Rat	T3 Generation	1.70E-06c	ug/dl/min	Modified from Ekerot et al. (2013) d
	TSH Generation	1.22E-04	ug/dl/min	Modified from Ekerot et al. (2013) d
	T4 Base Line	4.2	ug/dl	Huffman and Hedge (1986)
	T3 Base Line	95.0	ng/dl	Huffman and Hedge (1986)
	TSH Base Line	5.0	ng/ml	Choksi et al. (2003)
	fr	0.215c	unitless	Silva et al. (1984)
	T4 Elimination	7.78E-05	1/min	Nicoloff et al. (1972)
	T3 Elimination	4.72E-04	1/min	Nicoloff et al. (1972)
	T4 Generation	7.50E-03	nM/min	Modified from Ekerot et al. (2013) d
Human	T3 Generation	7.78E-06c	nM/min	Modified from Ekerot et al. (2013) d
	TSH Generation	3.14E-05	nM/min	Modified from Ekerot et al. (2013) d
	T4 Base Line	96.5	nmol/l	Ridgway et al. (1974)
	T3 Base Line	3.2	nmol/l	Ridgway et al. (1974)
	TSH Base Line	0.129	nmol/l	Odell et al. (1967) e
	fr	0.20c	unitless	McGuire and Hays (1981)
	TSH Elimination	2.43E-04	1/min	Ekerot et al. (2013)
For all models	SF1	2.53	unitless	Ekerot et al. (2013)
	SF2	1.90	unitless	Ekerot et al. (2013)
	SF3	0.11	unitless	Ekerot et al. (2013)

^aT₄, thyroxine, T₃, triiodothyronine, and TSH, thyroid stimulating hormone.

^bExtrapolated using the results of radiolabelled iodine tracer studies (Oppenheimer et al., 1972).

^cThe 35% reduction in the fractional conversion of T₄ to T₃ caused by 6-propylthiouracil (21.5–14.0% in rats and 20–13% in humans) resulted in a T₃ generation rate of 3.06E-04 in rats and 5.33E-04 in humans. The value provided in the table represents generation of T₃ without this reduced fractional conversion and was used for all chemicals other than 6-propythiouracil.

^dGeneration rates were derived from differential equations used to describe changes in time of TSH, T₄, and T₃ (Equations 3, 6, and 9 of Ekerot et al., 2013). Rather than examining changes in thyroid hormone concentrations, it was assumed that in absence of a chemical dose each respective hormone could be assigned its baseline concentration to simulate steady state.

^eAssuming 1.5 U/mg and a molecular weight of 14 000 for the active alpha subunit of the TSH hormone, with a baseline concentration of 2.7 uU/ml for eurythyroid individuals (Odell et al. 1967).