The widespread neuropeptide vasoactive intestinal peptide (VIP) has two receptors VPAC1 and VPAC2. The vasoactive intestinal polypeptide receptor VPAC1 is Gs-coupled GPCRs expressed in the lung, prostate, peripheral blood leukocytes, liver, brain, small intestine colon, heart, spleen, placenta, kidney, thymus, and testis.