G protein coupled receptors (GPCRs, or GPRs) contain 7 transmembrane domains and transduce extracellular signals through heterotrimeric G proteins. GPCR GPR18 is a member of this family and has been reported to be expressed at high levels in testis and spleen and at lower levels in other tissues associated with endocrine and immunologic/hematologic functions. It is thought to be a receptor for N arachidonyl glycine. It may contribute to regulation of the immune system.