Endocrine Abstracts

Introduction: So far, only two representatives of thyronamines, namely 3-iodothyronamine (3-T₁AM) and the iodine–free thyronamine (T₀AM), have been detected in vivo. While intensive research is done on the (patho-) physiological function of 3-T₁AM, the physiological role of T₀AM is poorly studied. Conflicting data have been reported for the acute cardiac effects of T₀AM. This project therefore determined whether a repeated administration of T₀AM affects cardiovascular function, metabolism or thermoregulation.

Methods: C57BL/6J male mice were injected with a pharmacological dose of T₀AM (5 mg/kg/day, 7 days, i.p.). The mice were killed 24 h after the last injection, and organs were collected for subsequent gene expression analysis.

Results: Daily administration of T₀AM did not alter body weight, food or water intake, heart rate, blood pressure, brown adipose tissue thermogenesis or body temperature compared to sham-injected controls. There was no significant difference in hepatic glycogen content or mRNA expression of genes involved in cardiac, blood pressure or metabolic control between the treatment groups. While the thyroid hormone (TH) responsive genes Spot14 and selenoprotein S were significantly up-regulated in liver after T₀AM treatment, hepatic deiodinase 1 (Dio1) was unaffected, which is in line with unaltered levels of serum total T₄ and T₃ concentrations. No significant effects were observed on hepatic or renal trace element concentrations like Se, Cu, and Zn.

Conclusions: Our data demonstrate that T₀AM displays only minor cardiovascular, metabolic and thermoregulatory activity in mice upon repeated administration. T₀AM does not interfere with TH metabolism, and does not affect Dio1 as a most sensitive hepatic TH-target genes or TH serum levels. Hence, T₀AM may not constitute a physiologically active TH metabolite.