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There are two known receptors for the vasoactive intestinal peptide termed VPAC1 and VPAC2. These receptors bind both VIP and pituitary adenylate cyclase-activating polypeptide to some degree. Both receptors are members of the 7 transmembrane G protein-coupled receptor family.
VPAC1 is distributed widely in the CNS, liver, lung, intestine and T-lymphocytes.
VPAC2 is found in the CNS, pancreas, skeletal muscle, heart, kidney, adipose tissue, testis, and stomach.
Vasoactive intestinal peptide and pituitary adenylate cyclase-activating peptide receptors are activated by the endogenous peptides VIP, PACAP-38, PACAP-27, peptide histidine isoleucineamide , peptide histidine methionineamide and peptide histidine valine. “PACAP type II receptors” display comparable affinity for PACAP and VIP, whereas PACAP-27 and PACAP-38 are >100 fold more potent than VIP as agonists of most isoforms of the PAC1 receptor.