Orexins are endogeneous peptides that activate Orexin Receptor type 1 and type 2, two closely related G-protein coupled receptors. Orexins-A and -B are hypothalamic peptides derived from a precursor called preproorexin and affect the stimulation of food intake. They act on G protein receptors named orexin receptor-1 (OX1R) and orexin receptor-2 (OX2R), respectively.timulation of these receptors by orexins causes an increase in intracellular calcium levels in hypothalamic cells in vitro. In vivo, orexins control feeding and may also be involved in modulating sleep-wake cycles and other hypothalamic functions.Synonyms: HCRTR1, Hypocretin receptor type 1, Ox1r