GPR3 activates adenylate cyclase in the absence of ligand. GPR3 is expressed in mammalian oocytes where it maintains meiotic arrest and is thought to be a communication link between oocytes and the surrounding somatic tissue. It has been proposed that sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) are GPR3 ligands, however this result was not confirmed in a β-arrestin recruitment assay.