Structure-activity relationship of dermorphin on gastric secretion.

The amphibian skin heptapeptide dermorphin (DM) administered intracerebroventricularly to rats significantly reduces gastric secretion. Dermorphin and 19 DM homologs and analogs were tested for their effect on gastric volume, pH, H+ ion concentration, and gastric acid output. DM, DM N-terminal pentapeptide and tetrapeptide amides, [D-Met2]DM, [Sar4]DM, [Trp5]DM, [Phe5]DM, [Gly7]DM, [Ser(Bzl)7]DM, and deamidated-DM significantly (P less than 0.01) reduced gastric acid output 2 h after injection. These data provide evidence for the following conclusions on the effect of DM on gastric secretion: ability to inhibit gastric secretion depends on the presence of the D-isomer of Ala at position 2, since [L-Ala2]DM is inactive; the shortest sequence with significant bioactivity is DM N-terminal tetrapeptide amide; the single replacement of amino acid residues in DM elicits a wide range of activities, varying from full biological activity of [Gly7]DM to those analogs with a complete lack of activity, such as [Pro4]DM and [Gly6]DM; and 4) coupling of protective groups to amino and hydroxyl groups of DM results in a significant loss of activity.