Vasoactive intestinal peptide (VIP) and peptide having N-terminal histidine and C-terminal isoleucine amide (PHI) stimulate adenylate cyclase activity in human heart membranes.

The presence of receptors, recognized by Vasoactive Intestinal Peptide (VIP) and Peptide having N-terminal Histidine and C-terminal Isoleucine amide (PHI), was documented in membranes from human right auricle and left ventricular cardiac muscle by the ability of these peptides to stimulate adenylate cyclase. The capacity of VIP and PHI to activate the enzyme was comparable, in auricle as well as ventricle membranes, the affinity of the system being moderately higher for VIP than for PHI. In auricles, dose-effect curves appeared compatible with the coexistence of high-affinity and low-affinity VIP receptors. PHI could not, however, discriminate these subclasses of VIP receptors.