Introducing drugs – 1

All comments here are all theoretical and based on a complicated mathematical model.
Proceeding from page 10 in the supplementary material for:
Hoermann R, Pekker MJ, Midgley JEM, Larisch R and Dietrich JW (2022)
Principles of Endocrine Regulation: Reconciling Tensions Between Robustness in Performance and Adaptation to Change.
Front. Endocrinol. 13:825107. doi: 10.3389/fendo.2022.825107 – I look at the two equations for sys1 and multiple systems.

The two parameters k43, k42, drug4 and drug3 are set to zero in the multiple systems equation. Making the result of the two equations the same. This equals fig. 4a in the article.

In sys. 9 k43 is changed to 1. (k43 increases the FT3 production rate // the FT3 production rate constant of peripheral organs account for non-thyroidal peripheral FT3 production (by adding the term k43*[FT4]) which physiologically depends on FT4, but not on TSH). See fig. 4b in the article.

Changing k42 to one increases FT3 further. (The TSH feedforward on FT3 is switched on (k42 = 1)). The other hormones decreases. The TSH FT4 values follow each other closely. See fig. 4c in the article.

Now a drug is introduced (drug3=0.5) in the equation which gives the following result:

See fig. 4d in the article and the comments.

In the next plot drug3=0.5 (LT3) is replaced by drug4=0.8 (LT4) in the equation, which affects the TSH and FT4 values:

The distance between FT4 and TSH is increased. In the earlier plots, FT4 and TSH were almost in the same line with no spread.

Next, I will reproduce fig. 4 from the article as a test of the R-script:

The FT4 production rate parameter k32, is the proportionality constant positive feedforward of TSH onto FT4 (downstream, activating)