May function as an output molecule from the suprachiasmatic nucleus (SCN) that transmits behavioral circadian rhythm. May also function locally within the SCN to synchronize output. Potently contracts gastrointestinal (GI) smooth muscle (By similarity). Expressed at high levels in testis and at lower levels in brain, lung, ovary, spleen, thymus and uterus. Activated by CLOCK and BMAL1 heterodimers and light; inhibited by period genes (PER1, PER2 and PER3) and cryptochrome genes (CRY1 and CRY2). Belongs to the AVIT (prokineticin) family.