Orexin A human, rat, mouse, a 33 amino acid excitatory neuropeptide, orchestrates diverse central and peripheral processes. Orexin A human, rat, mouse has been used to study its effect on the functioning of porcine pancreatic islets. It has also been used as an orexin receptor 1 (OX1R) agonist to study the effect of orexin systems in the effect of etonogestrel on respiratory response to prolonged metabolic acidosis.