Potently contracts gastrointestinal (GI) smooth muscle. Induces proliferation, migration and fenestration (the formation of membrane discontinuities) in capillary endothelial cells derived from endocrine glands. Has little or no effect on a variety of other endothelial and non-endothelial cell types. Induces proliferation and differentiation, but not migration, of enteric neural crest cells. Directly influences neuroblastoma progression by promoting the proliferation and migration of neuroblastoma cells. Positively regulates PTGS2 expression and prostaglandin synthesis. May play a role in placentation. May play a role in normal and pathological testis angiogenesis. {ECO:0000269|PubMed:11259612, ECO:0000269|PubMed:11528470, ECO:0000269|PubMed:15292351, ECO:0000269|PubMed:17289879, ECO:0000269|PubMed:18339712}. This is the function of PROK1 (prokineticin 1, Ensembl gene identifier ENSG00000143125).