Phoenixin is a comparatively recent addition to the neuropeptide catalogue, derived from the small integral membrane protein SMIM20 and identified through bioinformatic search rather than classical purification. Phoenixin-14 is the shorter of the two principal forms, supplied here as the amidated human sequence. It was first characterised in the context of reproduction, where it influences gonadotropin-releasing hormone signalling and the oestrous cycle, and its receptor has been identified as the orphan G protein-coupled receptor GPR173. Work since has broadened considerably: the peptide and its receptor have been localised in reproductive tissue and periovarian adipose tissue across several species, examined in a rat model of polycystic ovary syndrome, and studied for effects on food intake, anxiety-related behaviour and glucose handling. Reviews now describe it as more than a reproductive peptide. Because the field is young, two things are worth noting before designing experiments. Receptor pharmacology at GPR173 is less fully characterised than for established neuropeptide receptors, so selective antagonists for control experiments are limited. And the amidated C-terminus is part of the mature structure rather than a convenience, so a non-amidated preparation should not be treated as equivalent. | 