Pharmacological characterization of VIP receptors in human lung membranes.

The ability of VIP, PHI, secretin, helodermin, and seven N-terminally D-amino monosubstituted VIP and PHI analogs to occupy (125I)iodo-VIP labeled receptors and to activate adenylate cyclase was tested on human lung membranes purified by the method of Schachter et al. Best fitted Kd, Kact and % of max. values suggested the coexistence, in near equal proportions, of two classes of VIP-preferring binding sites coupled to adenylate cyclase that showed similar decreasing affinity for: VIP greater than (D-Ala4)-VIP greater than (D-Asp3)-VIP = (D-Ser2)-VIP greater than (D-His1)-VIP greater than PHI greater than (D-Phe2)-VIP greater than (D-Phe4)-VIP. (D-Arg2)-VIP was a non-selective agonist. A third receptor type, coupled to adenylate cyclase and showing high affinity for secretin and helodermin but not for VIP, was also detected.