A new analogue of substance P with antagonistic properties in renal and pulmonary arteries.

The effects of a new analogue of substance P (SP-A) and its interaction with substance P (SP) were studied in vitro isolated preparations from rabbit renal arteries and rat renal and pulmonary arteries. SP-A in did not affect the resting tone and the contractions of the rabbit renal arteries, evoked by field electrical stimulation (FES) but dose-dependently (10(-10)M - 5 X 10(-8)M) antagonized the inhibitory effects of SP on the FES-provoked contractions, the antagonism being of a non-competitive type. In the rat renal arteries SP had two different effects--depression of the FES-evoked contractions, and increase of the resting tone. SP-A did not exert per se effects on the tone and on the electrically-provoked contractions in these arteries. SP-A non-competitively antagonized both actions of SP in the same vessels. In rat pulmonary arteries SP increased the resting tone, whereas SP-A did not affect the resting tone and the FES-induced contractions. SP-A non-competitively antagonized the tone-increasing action of SP. The new analogue of SP may be useful in studying the mechanism of action of SP and its role in physiological and pathological reactions.