Antidiuretic activities of substance P and its analogs.

Substance P (SP) and analogs, including 5 nucleoside (ARA or HRA)-peptides, were examined for antidiuretic activity in ethanolized rats. The activity was potent in the analogs embodying the C-terminal hexapeptide, weak in the nucleoside-pentapeptide, and negligible in the nucleoside-tetrapeptide. In addition, the activity was increased by acylation of the hexapeptide. The antidiuretic potencies were also compared with the hypotensive potencies.