An approach to the self regulatory mechanism of substance P actions: II. Biological activity of new synthetic peptide analogs related both to enkephalin and substance P.

Analogs of substance P in which the N-terminal part of native peptide was replaced by an enkephalin active fragment have been synthesized. We found this peptide to be as active as substance P on the GPI test. The analogs were completely inactive on GPI opiate test; the opiate activity was observed on MVD and RVD tests. Surprisingly, we found that SP-activity was reduced by naloxone.