3-Iodothyronamine (T ₁AM): A new chapter of thyroid hormone endocrinology?

3-Iodothyronamine (T ₁AM) is an endogenous thyroid hormone derivative with distinct biological effects that are largely opposite those of thyroid hormone. Administration of T ₁AM to rodents results in rapid and profound reduction in body temperature, heart rate, and metabolism. The structural similarities between thyroxine, T ₁AM, and monoamine neurotransmitters suggest an intriguing role for T ₁AM as both a neuromodulator and a hormone-like molecule that may constitute a part of thyroid hormone action. Several recent studies into its molecular mechanisms of action have shown that T ₁AM can target extracellular receptors such as the trace amine-associated receptors and the α _2A adrenergic receptor, modulate the membrane transport of neurotransmitters, and serve as a substrate of specific membrane transport cellular uptake machinery. This review discusses recent T ₁AM studies, focusing on both the observed in vivo effects of T ₁AM administration and its actions at the molecular level.