Agonist effects of [D-Pro2,D-Phe7,D-Trp9]substance P--evidence for different receptors

[D-Pro2,D-Phe7,D-Trp9]substance P contracted guinea-pig ileum (GPI) indirectly, probably via substance P (SP) receptors on postganglionic parasympathetic neurones. It also depolarised rat superior cervical ganglion cells and contracted the rabbit external jugular vein, suggesting an agonist action on SP receptors in these tissues. In contrast, it had weak antagonist activity on smooth muscle SP receptors in GPI. This suggests that the receptor in GPI smooth muscle may differ from those in the other tissues.