Substance P antagonists active in vitro and in vivo.

[Pro4, Trp7,9]SP-(4-11) and a newly developed compound, [Pro4, Trp7,9,10]SP-(4-11) were shown to be potent antagonists of substance P (SP). They inhibited the hypotensive effect of SP in the anesthetised rats, the vasodilator effect in the rabbit perfused heart and the relaxation induced by SP in dog carotid arteries contracted with noradrenaline. Stimulatory actions of SP in the guinea pig ileum and the guinea pig trachea were also inhibited by the two antagonists, which were shown to be specific for substance P and related peptides in all the pharmacological preparations utilised in the present study.