LTI Models for 3-Iodothyronamine Time Dynamics: A Multiscale View

3-Iodothyronamine (Tι AM) is a novel relative of thyroid hormone that plays a role in critical body regulatory processes such as glucose metabolism, thermal regulation, and heart beating. This paper was aimed at characterizing time dynamics of T
₁
AM and its catabolite 3-iodothyroacetic acid (TA
₁
) in different biological scales with linear time-invariant models. Culture medium samples coming from culture of H9c2 murine cells and perfusion liquid samples from perfused rat heart were collected after the injection of a T
₁
AM bolus. T
₁
AM and TA
₁
concentrations in the samples were assayed with high-performance liquid chromatography coupled to tandem mass spectrometry. Kinetic constants relative to T
₁
AM transport and conversion were estimated with weighted least-squares method. We found that these constants can be related with an allometric power law depending on mass, with a negative exponent of -0.27 ± 0.19, implying that the velocity of conversion and internalization of Ti AM decreases with increasing of system mass.